JP2016203034A - Wastewater treatment method and terephthalic acid production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wastewater treatment method that, in a waste water treatment process in which a membrane separation treatment is performed while or after subjecting the wastewater to a biological treatment, allows for suppression of transmembrane pressure difference in a membrane module to a low level even when treating a wastewater having high CODand containing heavy metals.SOLUTION: There is provided a method for treating wastewater having CODof 3000 mg/L to 10000 mg/L and a heavy metal concentration of 0.1 wt.ppm to 200 wt.ppm. The method comprises (1) a step of reducing the heavy metal concentration, (2) a membrane separation step of carrying out solid-liquid separation by means of a membrane module while or after performing a biological treatment, and (3) a washing step of washing the membrane module. The washing step comprises a hypochlorite washing step and an acid cleaning step in this order.SELECTED DRAWING: Figure 2

Description

The present invention relates to a wastewater treatment method for treating wastewater containing COD _Cr and containing heavy metals, such as wastewater discharged in a terephthalic acid production process, and a method for producing terephthalic acid. Further, the present invention relates to a method for stably recycling at least a part of wastewater treated water in a terephthalic acid production process and the like and greatly reducing the amount of wastewater discharged into public water areas and the amount of water taken as industrial water.

  The increase in the amount of wastewater accompanying the expansion of the production scale of terephthalic acid is a major factor that increases the production cost of terephthalic acid. From the perspective of global production expansion in the future, reduction of industrial water consumption through resource recycling has become an urgent issue from the viewpoint of global environmental conservation.

  As a method for treating wastewater discharged in the terephthalic acid production process, for example, Patent Document 1 discloses biological treatment of wastewater by aerobic microorganisms in activated sludge in a first aeration tank 1010 as shown in FIG. In the first sedimentation tank 1020, solid-liquid separation into sludge and supernatant liquid, and biological treatment of the supernatant liquid by aerobic microorganisms in the activated sludge in the second aeration tank 1030. A method is disclosed that includes performing and solid-liquid separation into sludge and supernatant in a second settling tank 1040.

However, in this method, when treating wastewater having high COD _Cr , such as wastewater discharged in the terephthalic acid production process, the reduction of COD _{Cr in} the supernatant liquid separated by the second settling tank is insufficient. There are problems that it takes time to separate the solid and liquid in the first and second settling tanks, and that a large area is required for installing the first and second settling tanks.

As a general method for solving these problems, a method of providing a membrane module in a second aeration tank to form a membrane separation activated sludge treatment apparatus and omitting the second sedimentation tank is well known. However, this method, high COD _Cr as waste water discharged in the terephthalic acid production process, and when directly applied to the processing of waste water containing heavy metals used as the catalyst or the like, the following problem arises.

  In the case of solid-liquid separation into sludge and permeated water by the membrane module, organic or inorganic substances are adsorbed on the pores of the filtration membrane or deposited on the surface of the filtration membrane, thereby increasing the transmembrane pressure difference of the membrane module. It is necessary to clean the membrane module during the separation process. However, when the membrane module is washed at a normal frequency, even if the membrane module is washed, the transmembrane differential pressure of the membrane module does not sufficiently decrease. Therefore, the membrane separation process is performed with the transmembrane differential pressure of the membrane module kept low. Therefore, the operation cannot be stably continued for a long time. Moreover, since the wastewater treated by this method has a high concentration of residual metals and residual organic matter in water, it is difficult to reuse it in the terephthalic acid production process.

As a method for removing metals and organic substances in wastewater derived from the production of aromatic carboxylic acids, insoluble metal components such as iron, nickel, and chromium are adsorbed with a strongly acidic cation exchange resin and then catalyzed with a chelate resin. After adsorbing metal cobalt and manganese, a method of removing dissolved organic substances by a reverse osmosis membrane filtration system has been proposed (see Patent Document 2).
According to the method, the treated waste water can be reused in the process for producing aromatic carboxylic acid. However, in this method, the adsorption capacity of the chelate resin to be used decreases early, and the chelate resin reaches the end of its life in a very short period. Not reached.

JP 2005-095754 A Special table 2003-507156

In the wastewater treatment process in which the membrane separation process is performed while performing biological treatment on the wastewater or after performing the biological treatment, the present invention is applicable to the case where wastewater containing COD _Cr and containing heavy metals is treated. Disclosed are a wastewater treatment method and a method for producing terephthalic acid, in which a differential pressure can be kept low.
In addition, the present invention provides a wastewater treatment method and a method for producing terephthalic acid, in which wastewater containing COD _Cr and containing heavy metals is biologically treated and subjected to membrane separation treatment to keep the transmembrane pressure difference of the membrane module low.

Accordingly, the first invention of the present application is as follows.
1. A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10,000 mg / L and a heavy metal concentration of 0.1 to 200 ppm by weight,
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) having a washing step for washing the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The waste water treatment method, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours.
2. A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10,000 mg / L and a heavy metal concentration of 0.1 to 200 ppm by weight,
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) having a washing step for washing the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The waste water treatment method, wherein the acid cleaning step is started when a transmembrane differential pressure of the membrane module becomes 3 kPa to 30 kPa higher than a transmembrane differential pressure after the start of operation.
3. 3. The waste water treatment method according to item 1 or 2, wherein the heavy metal is cobalt and / or manganese.
4). The waste water treatment method according to any one of the preceding items 1 to 3, wherein the waste water is waste water discharged in a terephthalic acid production process.
5. The wastewater treatment method according to any one of items 1 to 4, wherein the acid is citric acid.
6). The waste water treatment method according to any one of the preceding items 1 to 5, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step. .
7). The wastewater treatment method according to any one of items 1 to 6, wherein the hypochlorite aqueous solution contains a surfactant.
8). A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) having a washing step for washing the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The method for producing terephthalic acid, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours.
9. A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) a cleaning step of cleaning the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The method for producing terephthalic acid, characterized in that the acid washing step is started when a transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than a transmembrane pressure difference after starting operation.
10. 10. The method for producing terephthalic acid according to 8 or 9 above, wherein the acid aqueous solution is a citric acid aqueous solution.
11. Any one of the preceding items 8 to 10, wherein COD _Cr in the waste water is 3000 mg / L to 10000 mg / L, and a heavy metal concentration in the waste water is 0.1 to 200 ppm by weight. The manufacturing method of the terephthalic acid as described in a term.
12 The terephthalic acid according to any one of 8 to 11 above, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step. Production method.
13. 13. The method for producing terephthalic acid according to any one of 8 to 12 above, wherein the heavy metal is cobalt and / or manganese.
14 14. The method for producing terephthalic acid according to any one of items 8 to 13 above, wherein the cobalt concentration in the treated waste water is 1/10 or less of the cobalt concentration in the waste water.
15. Any of the preceding items 8 to 14, wherein in the heavy metal concentration reduction step, the heavy metal in the waste water is recovered by bringing the waste water into contact with the chelate resin and recovering the heavy metal in the waste water into the chelate resin. A method for producing terephthalic acid according to Item 1.
16. 16. The method for producing terephthalic acid according to 15 above, wherein the pH of the waste water is 5.1 or more and 5.9 or less.
17. The method for producing terephthalic acid according to 15 or 16 above, wherein a flow rate of the waste water with respect to the chelate resin is 5 m / hr or more and 14 m / hr or less when the waste water is brought into contact with the chelate resin.
18. 18. The method for producing terephthalic acid according to any one of items 15 to 17, wherein the chelate resin has a uniformity coefficient of 1.4 or less.
19. 19. The method for producing terephthalic acid according to any one of 15 to 18 above, wherein a decrease rate of Cu adsorption amount of the chelate resin is 11% / month or less.
20. Any one of the items 15 to 19 above, further comprising a step of regenerating the chelate resin by causing a regenerant to act on the chelate resin from which the heavy metal has been recovered to obtain a regenerated solution containing the heavy metal. The manufacturing method of the terephthalic acid of description.
21. 21. The method for producing terephthalic acid as described in 20 above, wherein the regenerant is hydrogen bromide having a concentration of 7.1 wt% or more and 19 wt% or less.
22. The method for producing terephthalic acid according to any one of the preceding items 8 to 21, further comprising a step of separating the permeated water into membrane concentrated water and membrane permeated water by subjecting the permeated water to reverse osmosis membrane treatment.
23. 23. The method for producing terephthalic acid according to item 22 above, further comprising the step of further performing an adsorbent treatment on at least a part of the membrane permeated water to obtain adsorbed purified water.
24. Item 23. The adsorbent treatment is performed with at least one adsorbent selected from the group consisting of activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, and alkaline earth metal aluminate. A method for producing terephthalic acid according to 1.
25. The terephthalic acid production process comprises
oxidizing p-xylene to crude terephthalic acid;
The method for producing terephthalic acid according to any one of items 8 to 24, further comprising the step of purifying the crude terephthalic acid to form terephthalic acid.
26. 26. The method for producing terephthalic acid according to item 25, wherein the step of purifying the crude terephthalic acid to form terephthalic acid includes a step of hydrogenating the crude terephthalic acid.
27. 26. The method for producing terephthalic acid according to item 25, wherein the step of purifying the crude terephthalic acid to form terephthalic acid includes a step of performing an additional oxidation reaction on the crude terephthalic acid.
28. Any one of the above items 25 to 27, wherein at least a part of the membrane permeated water and / or at least a part of the adsorption purified water are used as cooling water and / or process water in the terephthalic acid production process. The manufacturing method of the terephthalic acid as described in a term.
29. 29. The method for producing terephthalic acid according to any one of items 8 to 28, wherein the aqueous hypochlorite solution contains a surfactant.
30. A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10000 mg / L and a heavy metal concentration of 0.1 mass ppm to 200 mass ppm,
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The waste water treatment method, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours.
31. A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10000 mg / L and a heavy metal concentration of 0.1 mass ppm to 200 mass ppm,
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The wastewater treatment method, wherein the acid cleaning step is started when a transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than a transmembrane pressure difference after the start of operation.
32. 32. The wastewater treatment method according to item 30 or 31, wherein the heavy metal is at least one selected from the group consisting of manganese and cobalt.
33. 33. The wastewater treatment method according to any one of items 30 to 32, wherein the wastewater is wastewater discharged in a terephthalic acid production process.
34. 34. The waste water treatment method according to any one of 30 to 33, wherein the acid is citric acid.
35. 35. The wastewater treatment method according to any one of 30 to 34, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step.
36. 36. The wastewater treatment method according to any one of items 30 to 35, wherein the hypochlorite aqueous solution contains a surfactant.
37. A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The method for producing terephthalic acid, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours.
38. A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The method for producing terephthalic acid, wherein the acid washing step is started when the transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than the transmembrane pressure difference after the start of operation.
39. 39. The method for producing terephthalic acid according to 37 or 38 above, wherein the acid is citric acid.
40. 40. The method for producing terephthalic acid according to any one of 37 to 39 above, wherein COD _{Cr in the} waste water is 3000 mg / L to 10000 mg / L, and the heavy metal concentration is 0.1 mass ppm to 200 mass ppm.
41. The terephthalic acid production process comprises
oxidizing p-xylene into crude terephthalic acid;
41. The method for producing terephthalic acid according to any one of 37 to 40 above, comprising a step of purifying the crude terephthalic acid to obtain terephthalic acid.
42. 42. The method for producing terephthalic acid according to item 41, wherein the step of purifying the crude terephthalic acid includes a step of performing a hydrogenation treatment.
43. 42. The method for producing terephthalic acid according to item 41, wherein the step of purifying the crude terephthalic acid includes a step of performing an additional oxidation reaction.
44. 44. The method for producing terephthalic acid according to any one of items 37 to 43, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step.
45. The wastewater treatment process
45. The method for producing terephthalic acid according to any one of 37 to 44 above, further comprising a step of filtering permeated water that has permeated through the membrane module with a reverse osmosis membrane filtration device.
46. The wastewater treatment process
At least a part of the permeated water is further subjected to an adsorbent treatment to obtain purified purified water;
The method for producing terephthalic acid according to any one of 37 to 45, further comprising: recovering the adsorbed purified water.
47. 47. The terephthalic acid according to item 46, wherein the adsorbent treatment is performed with at least one adsorbent selected from the group consisting of activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, and alkaline earth metal aluminate. Manufacturing method.
48. 48. The method for producing terephthalic acid according to any one of 37 to 47 above, wherein at least a part of the recovered permeated water is used as cooling water and / or process water in the terephthalic acid production process.
49. 48. The method for producing terephthalic acid according to 46 or 47 above, wherein at least a part of the recovered purified purified water is used as cooling water and / or process water in the terephthalic acid production process.
50. 50. The method for producing terephthalic acid according to any one of 37 to 49 above, wherein the hypochlorite aqueous solution contains a surfactant.

According to the wastewater treatment method and the terephthalic acid production method of the first invention of the present application, it is possible to keep the transmembrane pressure difference of the membrane module low even when treating wastewater containing high COD _Cr and containing heavy metals. is there. Therefore, since the membrane separation process can be performed stably, the equipment becomes compact as compared with the conventional biological treatment system. As a result, the construction cost can be reduced and the maintenance can be facilitated. In addition, most of the water and valuables contained in the wastewater can be recovered and reused in the process stably over a long period of time. This makes it possible to greatly reduce the amount of industrial water used, and also improves the recovery rate of valuable materials, which is advantageous in terms of cost.

According to the wastewater treatment method and the terephthalic acid production method according to the second invention of the present application, the transmembrane differential pressure of the membrane module during the biological treatment and membrane separation treatment of wastewater containing high COD _Cr and containing heavy metals. Can be kept low.

FIG. 1 is a schematic configuration diagram relating to an embodiment of reducing the heavy metal concentration of the present invention. FIG. 2 is a schematic configuration diagram showing an aspect of a wastewater treatment system in one embodiment of the wastewater treatment method of the present invention. FIG. 3 is a perspective view showing a partially broken example of the membrane unit. FIG. 4 is a perspective view of the diffuser generating device of the membrane unit. FIG. 5 is a schematic configuration diagram showing another aspect of the wastewater treatment system in one embodiment of the wastewater treatment method of the present invention. FIG. 6 is a perspective view and a partial cross-sectional view showing an example of a reverse osmosis membrane module. FIG. 7 is a schematic configuration diagram showing another aspect of the wastewater treatment system in one embodiment of the wastewater treatment method of the present invention. FIG. 8 is a schematic configuration diagram showing an aspect of a wastewater treatment system in another embodiment of the wastewater treatment method of the present invention. FIG. 9 is a schematic configuration diagram showing another aspect of the wastewater treatment system in another embodiment of the wastewater treatment method of the present invention. FIG. 10 is a diagram illustrating a process flow and a substance flow in the first representative method for producing terephthalic acid. FIG. 11 is a diagram illustrating an embodiment of the first representative method for producing terephthalic acid. FIG. 12 is a diagram for explaining another embodiment of the first representative method for producing terephthalic acid. FIG. 13 is a diagram illustrating a process flow and a substance flow in a second representative method for producing terephthalic acid. FIG. 14 is a diagram for explaining an embodiment of a second representative method for producing terephthalic acid. FIG. 15 is a schematic configuration diagram illustrating an example of a conventional wastewater treatment system. FIG. 16 is a diagram of an experimental flow in Experimental Examples 3-1 to 3-3. FIG. 17 is a graph showing changes over time in the transmembrane pressure difference of the membrane module in Experimental Example 3-1. FIG. 18 is a graph showing changes with time in transmembrane pressure difference of the membrane module in Example 3-2. FIG. 19 is a graph showing changes over time in the transmembrane pressure difference of the membrane module in Comparative Example 3-2. FIG. 20 is a graph showing changes over time in the transmembrane pressure difference of the membrane module in Comparative Example 3-3-1. FIG. 21 is a graph showing changes over time in the transmembrane pressure difference of the membrane module in Comparative Example 3-3-2.

  The following definitions of terms apply throughout this specification and the claims.

“COD _Cr ” means a chemical oxygen consumption value measured using potassium dichromate as an oxidizing agent, as defined in JIS K0102, and is expressed in mg / L.

“BOD ₅ ” means the value of biochemical oxygen consumption for 5 days specified in JIS K0102, and is expressed in mg / L.

“Heavy metal” means a metal element having a density of 4.0 g / cm ³ or more when a single metal is used.

  “Biological treatment” means that organic substances are decomposed by metabolism of microorganisms in activated sludge.

  “To obtain sludge and permeate by performing solid-liquid separation with membrane module while biological treatment of wastewater” means that the membrane module installed inside the aeration tank that performs biological treatment is used in the aeration tank. This means that membrane separation of sludge-containing water is performed.

  "After biological treatment of wastewater, solid-liquid separation is performed by a membrane module to obtain sludge and permeate" means that an aeration tank is used by using a membrane module disposed outside the aeration tank for biological treatment. This means that membrane separation of sludge-containing water supplied from the aeration tank is performed outside.

  “Aerobic biological treatment” means that organic substances are decomposed by aerobic metabolism of aerobic microorganisms in activated sludge.

  “Anaerobic biological treatment” means decomposing organic matter by anaerobic metabolism of anaerobic microorganisms in activated sludge.

  “Solid-liquid separation (treatment)” means separation of sludge-containing water generated by biological treatment of waste water or supernatant liquid into sludge and permeated water not containing sludge.

  “Membrane separation (treatment)” means separation of substances using a selective filtration membrane.

  “Permeated water” means water that has permeated through a filtration membrane in membrane separation treatment.

  “Membrane module” means a device provided with a filtration membrane.

  “Washing the membrane module” means that organic or inorganic substances adsorbed on the pores of the filtration membrane or deposited on the surface of the filtration membrane are removed from the filtration membrane with a chemical solution.

  The “transmembrane pressure difference” means a pressure required to obtain permeated water, and is a pressure difference (absolute value) between the inside and outside of the membrane module separated by the filtration membrane of the membrane module.

  The “transmembrane pressure difference after the start of operation” means the transmembrane pressure difference of the membrane module 1 hour after the start of the solid-liquid separation process by the membrane module.

  The “terephthalic acid production process” means a series of steps for producing terephthalic acid.

  “Wastewater treatment process” means a series of steps for treating wastewater.

  “Adsorbent treatment” means a treatment for purifying water by bringing water into contact with the adsorbent.

  “Adsorption purified water” means water purified by adsorbent treatment.

  The “ion exchange resin” is a concept including a cation exchange resin and an anion exchange resin.

  “Alkaline earth metal” means a Group 2 element broadly and includes not only calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra), but also beryllium (Be) and magnesium (Mg). ).

“Alkaline earth metal aluminate” means a composite oxide of aluminum and an alkaline earth metal, and examples include aluminum calcium oxide (calcium aluminate, Ca (AlO ₂ ) ₂ ).

  The “cooling water in the terephthalic acid manufacturing process” means water (industrial water) used for cooling various devices in the terephthalic acid manufacturing process.

  “Process water in the terephthalic acid production process” means water that comes into contact with a substance (for example, crude terephthalic acid) that can be changed in reaction, purification, etc. in the terephthalic acid production process, and is used as a solvent for dissolving the substance. It is a concept including an embodiment used and an embodiment used as a solvent for washing the substance.

  "Membrane separation activated sludge treatment device" is a treatment device based on the membrane separation activated sludge method, which performs biological treatment of waste water and biological treatment of waste water or after biological treatment of waste water, It means a device that separates solid and liquid into sludge and permeate.

  Unless otherwise specified, the notation “A to B” in the numerical range means “A to B”. In such a notation, when a unit is attached only to the numerical value B, the same unit shall be applied to the numerical value A as well.

About 1st invention of this application <Wastewater treatment method>
The waste water treatment method of the first invention of the present application is a waste water treatment method for treating waste water having COD _Cr of 3000 mg / L to 10000 mg / L and a heavy metal concentration of 0.1 ppm to 200 ppm by weight. The wastewater treatment flow is a flow that first reduces the concentration of heavy metals, then performs a process that combines membrane separation and biological treatment by the membrane separation activated sludge method (hereinafter referred to as membrane separation activated sludge treatment). Osmotic membrane treatment and adsorbent treatment may be further performed.
This will be described in the order of flow.

(Heavy metal concentration reduction step)
In the heavy metal concentration reduction step in the wastewater treatment method of the first invention of the present application, it is important to recover the heavy metal in the wastewater and suppress the heavy metal concentration in the wastewater to a certain concentration or less. The heavy metal concentration in the waste water is 0.1 wt ppm or more and 200 wt ppm or less, preferably 100 wt ppm or less, more preferably 10 wt ppm or less, and the heavy metal concentration of the treated waste water obtained by the heavy metal concentration reduction step is preferably It is 10 weight ppm or less, More preferably, it is 5 weight ppm or less, More preferably, it is 1 weight ppm or less. Moreover, it is preferable that the heavy metal density | concentration of treated waste water is 1/10 or less with respect to the heavy metal density | concentration of waste water, and it is more preferable that it is 1/100 or less.

  The heavy metal is preferably cobalt and / or manganese, and more preferably cobalt. If the heavy metal concentration is not reduced to such a level, complicated washing and regeneration operations can be performed by adsorbing or depositing inorganic substances or organic substances on the pores of the membrane of the membrane module or on the surface of the membrane in the membrane separation step. It needs to be done frequently.

In the heavy metal concentration reduction step in the wastewater treatment method of the first invention of the present application, any method may be adopted as long as the heavy metal in the wastewater is recovered and the heavy metal concentration is reduced. Examples of a method for recovering heavy metal in wastewater and suppressing heavy metal concentration in wastewater include (1) a method in which heavy metal in the wastewater is insolubilized as a carbonate metal salt, and the insoluble carbonate metal salt is recovered from the wastewater. 2) A method of adsorbing heavy metals using an adsorbent such as activated carbon, strongly acidic cation exchange resin, chelate resin, silica, alumina, synthetic zeolite, bentonite, alkaline earth metal aluminate, and the like.
Among the above (2), since the adsorption performance is good, a method of adsorbing a heavy metal using a chelate resin can be given as a preferred example.

  For example, wastewater discharged from the production process of terephthalic acid may contain heavy metals such as cobalt and manganese used as an oxidation reaction catalyst. As a method for reducing such a heavy metal to a certain concentration using a chelate resin, for example, a method using a chelate resin having specific properties disclosed in International Publication No. 2010/008055 can be preferably used.

  The chelate resin selects a specific metal by introducing a chelate-forming group (hereinafter sometimes referred to as “chelate group”) that easily forms a chelate bond with a metal instead of the ion-exchange group in the ion-exchange resin. It is a resin that can be adsorbed on the surface. The chelate group is a group containing elements such as N, S, O, and P as the electron-donating element in combination of two or more of the same kind or different kinds as in the case of general chelating agents. Examples include N—N and O—O types. When these chelate groups are bonded to the three-dimensional polymer substrate, a chelate resin having selectivity for a specific metal corresponding to the chelate group is obtained.

  Although heavy metals can be removed with cation exchange resins, there are many metals in the wastewater that do not need to be removed, such as alkali metals and alkaline earth metals. When these are used, these metal elements that do not need to be removed are simultaneously adsorbed, leading to waste of the regenerant. Therefore, it is preferable to use a chelate resin for removing heavy metals. The chelate group is not particularly limited as long as it is a chelate group having metal selectivity that selectively adsorbs heavy metals. Preferable examples include iminodiacetic acid group, polyamine group, thiourea group, aminophosphonic acid group, polyacrylic acid group, N-methylglucamine group, etc. Among them, iminodiacetic acid group is more preferable.

  The treatment for ionizing the above chelate resin with, for example, sodium ions as a counter cation may be carried out by a fixed bed flow system in which a sodium hydroxide aqueous solution is passed through a packed tower filled with a chelate resin having a hydrogen functional end. preferable. The concentration of the aqueous sodium hydroxide solution used at this time is preferably 0.5 wt% or more and 20 wt% or less, more preferably 1 wt% or more and 10 wt% or less. The linear velocity of the aqueous sodium hydroxide solution when ionized by the fixed bed flow method is preferably 1 m / hr or more and 20 m / hr or less, more preferably 2 m / hr or more and 15 m / hr or less. The ionization method on the fixed bed may be downflow or upflow, but is preferably upflow, and it is preferable to treat the chelate resin under conditions such that it is immersed in an aqueous sodium hydroxide solution for 2 hours or more.

  The ionization temperature is preferably 10 ° C. or higher and 80 ° C. or lower, more preferably a temperature around room temperature (15 ° C. or higher and 40 ° C. or lower). In the first invention of the present application, the ionization operation as described above is not necessarily required when the chelate group of the chelate resin is already completely or partially ionized with an alkali metal such as sodium as described above.

  Examples of the resin substrate to which the chelate group is bonded include crosslinked polystyrene, styrene-divinylbenzene copolymer, and crosslinked polyacrylic acid. Among these, cross-linked polystyrene or styrene-divinylbenzene copolymer is particularly preferable.

  The higher order structure of the substrate constituting the chelate resin is generally classified into a gel type, a porous type, and a high porous type. In the first invention of the present application, any of them may be used. Among them, the porous type or the high porous type is preferable, and the porous type is most preferable.

  The suitable chelate resin used in the first invention of the present application has a uniformity coefficient indicating uniformity of the particle size of the chelate resin of 1.4 or less, more preferably 1.2 or less, and even more preferably 1.1 or less. Especially preferably, it is 1.05 or less. When the uniformity coefficient exceeds the above upper limit, pressure loss in the chelate resin layer occurs when the treated wastewater is adsorbed by the fixed bed flow method using the chelate resin as a stationary phase and when the chelate resin is regenerated. Is likely to occur. Specific examples of suitable chelating resins include, for example, Sybron Chemicals Inc. Lewatit (R) MonoPlus TP 207 commercially available from A LANXESS COMPANY.

  Hereinafter, the treatment for adsorbing heavy metals such as cobalt and manganese in the waste water to the chelate resin and the treatment conditions will be described with reference to FIG.

  The solid line in FIG. 1 shows the flow of wastewater to be treated. Various wastewaters (217 ′, 221 ′ to 223 ′, 225 ′ to 226 ′, 255 ′ to 256 ′, 260 ′ to 262 ′) generated from chemical processes (for example, terephthalic acid production process) are transferred to the pH adjustment tank 101. Collected and mixed to adjust pH. The wastewater whose pH is adjusted is passed through either the treatment tower 102 or 103 filled with the chelate resin. The processing towers 102 and 103 are usually a fixed bed type, and a flow system is adopted for liquid flow. The permeate (treated wastewater) that has passed through either the treatment tower 102 or 103 is sent to the activated sludge treatment step via the treated wastewater tank (storage tank) 104. When one treatment tower 102 reaches the breakthrough region, the drainage liquid is switched to the other treatment tower 103, and the permeate is sent to the treatment wastewater tank 104 in the same manner as described above. The reverse is also true.

  In the pH adjustment tank 101, the pH of the waste water is adjusted. The pH of the waste water passed through the treatment tower 102 or 103 is preferably 5.1 or more, more preferably 5.2 or more, still more preferably 5.3 or more, preferably 5.9 or less, more preferably It is 5.8 or less, more preferably 5.7 or less. When the pH of the wastewater exceeds the above upper limit, a heavy metal compound may be deposited in the wastewater and deposited on the chelate resin surface in the treatment tower 102/103, making it difficult to recover. On the other hand, if the pH of the waste water is less than the lower limit, organic substances such as terephthalic acid and p-toluic acid contained in the waste water may be deposited, and the heavy metal recovery rate may be reduced.

  The temperature of the wastewater passed through the treatment tower 102 or 103 is preferably 51 ° C. or higher, more preferably 53 ° C. or higher, further preferably 55 ° C. or higher, and preferably 59 ° C. or lower, more preferably 57 ° C. or lower. It is. If the temperature of the wastewater is less than the above lower limit, if terephthalic acid is contained in the wastewater, this tends to precipitate, and the heavy metal recovery rate may decrease. On the other hand, when the temperature of the waste water exceeds the upper limit, the chelate resin tends to deteriorate.

  The flow rate of the wastewater passed through the treatment tower 102 or 103 is a linear flow rate, preferably 5 m / hr or more, more preferably 7 m / hr or more, preferably 14 m / hr or less, more preferably 10 m / hr. hr or less. When the flow rate exceeds the above upper limit value, drift (channeling) occurs inside the processing tower 102 or 103, and the efficient adsorption tends to be difficult. On the other hand, if the flow velocity is less than the lower limit, it is necessary to enlarge the processing tower 102/103, which tends to be economically disadvantageous.

  As a method for adsorbing the heavy metal compound, there is a batch method in addition to the continuous method described above for the processing towers 102 and 103, but the continuous method is more general. The recovery of heavy metals in the first invention of the present application is preferably carried out by a continuous fixed bed flow system. Specifically, two or more treatment towers are installed in parallel, and liquid is passed by a simultaneous liquid passing method or a switching method. As the material of the processing tower, FRP (glass fiber reinforced plastic) lined carbon steel or the like is usually used.

  The adsorption rate of cobalt and manganese under the above adsorption conditions is preferably 80% or more, and more preferably 90% or more with respect to the contents of cobalt and manganese on the inflow side of the treatment tower 102/103. . In particular, the cobalt concentration on the treatment tower outflow side is preferably 1/10 or less of the cobalt concentration on the treatment tower inflow side, more preferably 1/100 or less, and more preferably 10 ppm by weight or less. It is preferably 5 ppm by weight or less, more preferably 1 ppm by weight or less.

  After the processing tower 102/103 is switched from one processing tower to the other processing tower, the processing tower that has completed adsorption is washed by circulating water to wash out the adsorbed or deposited metals and organic compounds. The temperature and pressure at this time are preferably the same temperature and pressure as the conditions during the adsorption.

  Desorption / regeneration of the processing tower 102/103 and its conditions will be described. As a regenerant for desorbing the heavy metal adsorbed by the chelate resin, it is preferable to use an aqueous hydrogen bromide solution. As regenerants for the regeneration of chelating resins, sulfuric acid, hydrochloric acid, etc. are common, but in the production process of terephthalic acid, cobalt, manganese and bromine compounds are used as oxidation reaction catalysts, so the production process of terephthalic acid In the case of treating the wastewater generated from the above, it is preferable to use an aqueous hydrogen bromide solution as a regenerant.

  In the first invention of the present application, the concentration of hydrogen bromide water used as the regenerant of the chelate resin is preferably 7.1% by weight or more, more preferably 7.5% by weight or more, and further preferably 8% by weight or more. On the other hand, it is preferably 19% by weight or less, more preferably 15% by weight or less, and further preferably 12% by weight or less. The amount of heavy metal recovered depends on the hydrogen bromide water concentration and there is an optimum concentration. When the concentration of hydrogen bromide water is less than the above lower limit value or exceeds the above upper limit value, efficient recovery of heavy metals may be difficult. The flow rate of hydrogen bromide water to the treatment tower 102/103 is preferably in the range of 1 m / hr to 10 m / hr in terms of linear flow rate. If the liquid flow rate is within this range, there is no effect on the recovery amount.

  The temperature of the hydrogen bromide water during the passage is preferably around normal temperature (15 ° C. or more and 40 ° C. or less). The desorption rate of heavy metal by the hydrogen bromide water treatment is preferably 90% or more, more preferably 95% or more, and the closer to 100%, the more preferable.

  The attachment / detachment / regeneration process will be further described with reference to FIG. Hydrogen bromide water as a regenerant is stored in the regenerant tank 106. The hydrogen bromide water in the regenerant tank 106 is passed through the treatment tower 102 (or 103) after the adsorption operation (broken line in FIG. 1) to desorb heavy metals. Next, the treatment tower 102 (or 103) is washed by passing water, thereby removing the metal remaining on the chelate resin in the treatment tower.

  Thereafter, the aqueous sodium hydroxide solution stored in the caustic soda tank 108 or the caustic soda preparatory tank 109 is passed through the treatment tower 102 (or 103) after the regeneration operation, whereby the chelate resin ionized with sodium or partially The chelate resin ionized with sodium is regenerated. The concentration of the aqueous sodium hydroxide solution used for the ionization treatment is preferably 1% by weight to 10% by weight, more preferably 3% by weight to 7% by weight. The linear flow rate when the aqueous sodium hydroxide solution is passed through the treatment tower 102/103 is preferably 1 m / hr to 20 m / hr, more preferably 2 m / hr to 15 m / hr.

  When the treatment tower 102/103 is a fixed bed, the ionization method is preferably an upflow rather than a downflow, and the ionization treatment is preferably performed in the upflow under the condition that the chelate resin is immersed in an aqueous sodium hydroxide solution for 2 hours or more. The temperature during the ionization treatment is preferably 10 ° C. or higher and 80 ° C. or lower, more preferably around normal temperature (15 ° C. or higher and 40 ° C. or lower). The effluent from the processing tower 102/103 in the desorption / regeneration process is stored in the recovery liquid tank 105.

  When the end point of the desorption operation approaches, the flow path of the effluent is switched, and the effluent is stored in the desorption operation end liquid tank 107. The liquid stored in the desorption operation end liquid tank 107 is used after passing through the chelate resin tower 102 or 103 at the next desorption. The liquid that has flowed out of the treatment tower 102/103 in the washing treatment after the desorption treatment with hydrogen bromide water is stored in the treatment wastewater tank 104 as treatment wastewater, and is subjected to membrane separation activated sludge treatment in the next step.

The adsorption capacity of the chelate resin in the first invention of the present application is preferably such that the Cu adsorption capacity at the start of use is 0.5 mmol / mL or more, using Cu adsorption capacity as an index, and 0.7 mmol / mL. More preferably. The upper limit of the Cu adsorption capacity is not limited, but is usually 2 mmol / mL or less.
Measurement methods such as the preferred uniformity coefficient of the chelate resin and the adsorption capacity of Cu are as described in International Publication No. 2010/008055.

(Biological treatment (membrane separation activated sludge treatment))
The heavy metal in the wastewater is recovered by the heavy metal concentration reduction step, and the treated wastewater whose heavy metal concentration is reduced is subsequently subjected to biological treatment (membrane separation activated sludge treatment).
The biological treatment (membrane separation activated sludge treatment) in the first invention of the present application,
(I) A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of treated wastewater or after biological treatment of treated wastewater;
(Ii) a cleaning step of cleaning the membrane module.

(Membrane separation activated sludge treatment system)
FIG. 2 is a schematic configuration diagram showing an aspect of a membrane separation activated sludge treatment system in the wastewater treatment method of the first invention of the present application. The membrane separation activated sludge treatment system shown in FIG. 2 is a membrane in which treated wastewater that has undergone the heavy metal concentration reduction step is biologically treated by aerobic microorganisms in the activated sludge and simultaneously separated into sludge and permeate by the membrane module 35. A separation activated sludge treatment device 30; a first chemical solution tank 90 for storing a hypochlorite aqueous solution for cleaning the membrane module 35; and a second chemical solution tank 92 for storing an acid aqueous solution for cleaning the membrane module 35; A control unit (not shown) for controlling the supply of the chemical solution from the first chemical solution tank 90 and the second chemical solution tank 92 to the membrane module 35; and the drainage flow path for supplying the treated wastewater to the membrane separation activated sludge treatment device 30 50 ;; a permeate flow path 55 for discharging the permeated water from the membrane separation activated sludge treatment apparatus 30; and an excess sludge flow path 56 for discharging excess sludge from the membrane separation activated sludge treatment apparatus 30. ;; And a liquid medicine flow channel 59 for supplying a chemical liquid from the first chemical solution tank 90 and the second chemical liquid tank 92 to the membrane module 35.

(Membrane separation activated sludge treatment equipment)
The membrane separation activated sludge treatment apparatus 30 includes a tank main body 31 (first aeration tank); a diffuser pipe 32 disposed near the bottom in the tank main body 31 (first aeration tank); A blower 33 to be supplied; an air introduction pipe 34 connecting the diffuser pipe 32 and the blower 33; a membrane module 35 disposed in the tank body 31 (first aeration tank) and above the diffuser pipe 32; A suction pump 36 which is provided in the middle of the passage 55 and performs solid-liquid separation of sludge and permeate by reducing the pressure in the membrane module 35 and sends the permeate to the downstream process; And a backwash pump 37 for sending backwashing chemicals and the like to the membrane module 35.

  As the membrane module 35, a known membrane module provided with a known filtration membrane can be employed. As the type of the filtration membrane, a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) is preferable. Examples of the shape of the filtration membrane include a hollow fiber membrane, a flat membrane, a tubular membrane, and a bag-like membrane. Of these, hollow fiber membranes are preferred because they can be highly integrated when compared on a volume basis.

  Examples of the material of the filtration membrane include organic materials (cellulose, polyolefin, polysulfone, polyvinyl alcohol, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, etc.), metals (stainless steel, etc.), and inorganic materials (ceramics, etc.). . The material of the filtration membrane is appropriately selected according to the properties of the waste water. What is necessary is just to select the hole diameter of a filtration membrane suitably according to the objective of a process. In the membrane separation activated sludge method, the pore size of the filtration membrane is preferably 0.001 to 3 μm. If the pore diameter is less than 0.001 μm, the resistance of the membrane may increase. When the pore diameter exceeds 3 μm, it becomes difficult to completely separate the activated sludge, so that the quality of the permeated water may be deteriorated. The pore size of the filtration membrane is more preferably 0.04 to 1.0 μm, which is the range of the microfiltration membrane.

  In the membrane separation activated sludge treatment apparatus 30, a membrane unit in which the air diffuser 32 and the membrane module 35 are integrated may be used. An example of such a membrane unit is shown in FIGS. The membrane unit shown in FIGS. 3 and 4 includes an air diffuser 60; a membrane module 35 provided on the upper part of the air diffuser 60; and a water collection header 80 provided on the upper part of the membrane module 35. . Hereinafter, the membrane unit will be described with reference to FIGS.

  The air diffuser 60 includes a rectangular casing 61 that is open at the top and bottom; a column 62 that extends downward from the four corners of the casing 61; an outer wall of the casing 61; A connection pipe 63 for supplying air supplied through the casing 61; an air supply header 64 provided along the inner wall of the casing 61 and communicating with the connection pipe 63; an inner wall orthogonal to the air supply header 64 And a plurality of air diffusers 32 connected to 64a.

  The air diffuser 32 discharges air supplied from the blower 33 upward, and is composed of a single tube with a hole or a membrane type one end connected to an air supply header 64 and the other end closed. Yes.

  The membrane module 35 includes a frame 65 extending upward from four corners of the air diffuser 60; a plurality of hollow fiber membrane elements 70 supported by the frame 65 and arranged in parallel; and covers four side surfaces And a casing 66.

  The hollow fiber membrane element 70 has a passage (not shown) formed along the longitudinal direction inside, and has a permeated water outlet 71a formed at one end of the passage and communicating with the passage of the vertical rod 72. A pair of vertical rods 72, 73 that extend upward from both ends of the lower frame 71 and have a passage (not shown) formed along the longitudinal direction therein; and upper ends of the vertical rods 72, 73 An upper frame 74 having a passage (not shown) formed along the longitudinal direction and having a permeate outlet 74a formed at one end of the passage; and connected to the permeate outlet 74a. An L-shaped joint 75 that bends upward; a hollow fiber membrane sheet 76 composed of a number of hollow fiber membranes 76a arranged along the vertical rods 72 and 73 in a direction perpendicular to the water surface; and an upper frame 74 And the end of the hollow fiber membrane 76a is opened in the passage inside the lower frame 71. At state, the upper and lower ends of the hollow fiber membrane 76a, respectively on frame 74, secured in a liquid tight manner to the lower frame 71 comprises a potting material 77 which supports.

  The number of hollow fiber membranes 76 a constituting the hollow fiber membrane sheet 76 is preferably 500 to 3000 per one hollow fiber membrane sheet 76. If the number of the hollow fiber membranes 76a is less than 500, the membrane area of the hollow fiber membranes may be reduced, and the water permeation amount per unit volume may be reduced. When the number of the hollow fiber membranes 76a exceeds 3000, the installation area of the membrane unit becomes too large.

  It is preferable that the hollow fiber membranes 76a have a slack and are arranged in a substantially vertical direction with respect to the water surface. By arranging the hollow fiber membranes 76a in a substantially vertical direction with respect to the water surface, it becomes difficult for solids to accumulate on the surface of the hollow fiber membranes 76a, and the air from the diffuser tube 32 causes the surface of the hollow fiber membranes 76a to be deposited. It is cleaned efficiently. Further, since the hollow fiber membrane 76a has slackness, the air from the air diffuser 32 causes the hollow fiber membrane 76a to swing, and the surface of the hollow fiber membrane 76a is efficiently cleaned.

  The water collection header 80 is provided along the arrangement direction of the hollow fiber membrane elements 70. The water collecting header 80 includes a plurality of water collecting ports 80a formed along the longitudinal direction; one end is connected to the water collecting port 80a, and the other end is connected to the L-shaped joint 75 of the hollow fiber membrane element 70. A bent L-shaped joint 81; and a water suction port 80b provided on the upper surface of the water collecting header 80 and connected to the permeate flow passage 55.

(Reverse osmosis membrane filtration device)
The membrane separation activated sludge treatment system performs reverse osmosis membrane filtration on the permeated water of the membrane separation activated sludge treatment apparatus, thereby separating the purified water that has permeated the reverse osmosis membrane and the concentrated water that has not permeated. You may have further the osmosis membrane filtration apparatus. FIG. 5 is a diagram for explaining a membrane separation activated sludge treatment system in which a reverse osmosis membrane filtration device is added to the membrane separation activated sludge treatment system of FIG. The membrane separation activated sludge treatment system of FIG. 5 includes a reverse osmosis membrane filtration device 40 that filters permeated water that has passed through the membrane module 35 of the membrane separation activated sludge treatment device 30 through a reverse osmosis membrane; A purified water channel 57 for discharging the purified water; and a concentrated water channel 58 for discharging the concentrated water that has not permeated through the reverse osmosis membrane filtration device 40.

  The reverse osmosis membrane filtration device 40 includes one or more reverse osmosis membrane modules. The reverse osmosis membrane module is not particularly limited as long as it has a configuration capable of separating purified water that has passed through the reverse osmosis membrane and concentrated water that does not pass through the reverse osmosis membrane.

  Examples of the reverse osmosis membrane module include a so-called spiral reverse osmosis membrane module in which a cylindrical reverse osmosis membrane element in which a reverse osmosis membrane is wound around a water collection pipe is housed in a cylindrical casing. Examples of the material of the reverse osmosis membrane include polyamide, polysulfone, cellulose acetate, and the like. Among these, a polyamide containing an aromatic polyamide or a crosslinked aromatic polyamide is preferable.

  FIG. 6 is a perspective view and a partial cross-sectional view showing an example of a spiral type reverse osmosis membrane module. The spiral type reverse osmosis membrane module 41 folds the reverse osmosis membrane 42 in a state where a water collection pipe 43 having a plurality of water collection holes 43 a is placed at the center of the reverse osmosis membrane 42. 3 sides of the reverse osmosis membrane 42 overlapped with the liquid-permeable support fiber 44 sandwiched between them, and a double reverse osmosis membrane 42 with a mesh spacer 45 overlapped, and a double pipe centering on the water collecting pipe 43 A reverse osmosis membrane 42 is wound into a columnar shape to form a reverse osmosis membrane element 46, and the reverse osmosis membrane element 46 is accommodated in a cylindrical casing 47.

(Control part)
The control unit controls the interval from the end of the supply of the hypochlorite aqueous solution to the membrane module 35 to the start of the supply of the next aqueous acid solution to the membrane module 35 within 100 hours, and / or the membrane module When the transmembrane pressure difference 35 is 3 kPa to 50 kPa higher than the transmembrane pressure difference before the start of operation, the supply of the acid aqueous solution to the membrane module 35 is started.

  The control unit is roughly configured to include a processing unit and an interface unit, and controls operation start and stop of the backwash pump 37, opening / closing of a valve (not shown) of the chemical liquid channel 59, and the like. The interface unit electrically connects the backwash pump 37, a valve, a pressure gauge (not shown), and the like to the processing unit. The processing unit controls the start and stop of the operation of the backwash pump 37 and the opening / closing of the valve based on the operation schedule input to the processing unit and / or the pressure signal from the pressure gauge.

  Note that the function of the processing unit may be realized by dedicated hardware, and the processing unit is configured to include a storage device (memory) and a central processing unit (CPU) to realize the function of the processing unit. The function of the processing unit may be realized by reading this program into the memory and executing it by the CPU. In addition, an input device, a display device, or the like may be connected to the control unit as a peripheral device. An input device refers to an input device such as a display touch panel, a switch panel, or a keyboard, and a display device refers to a CRT or a liquid crystal display device.

(Processing flow)
In addition to the following step (γ), the treatment flow in the wastewater treatment method of the first invention of the present application includes the following steps (c) and (c) when using the membrane separation activated sludge treatment system having the configuration of FIG. In the case of using e) and (f) and the membrane separation activated sludge treatment system having the configuration shown in FIG. 5, the following steps (c) to (f) are included.
(Γ) The heavy metal concentration reduction step for obtaining the treated waste water whose heavy metal concentration is reduced by collecting the heavy metal in the waste water as described above.
(C) The treated wastewater that has undergone the heavy metal concentration reduction step is solid-liquid separated into sludge and permeate by the membrane module 35 while performing biological treatment with the aerobic microorganisms in the activated sludge in the membrane separation activated sludge treatment apparatus 30. , Membrane separation step.
(D) In the reverse osmosis membrane filtration device 40, reverse osmosis is performed by filtering the permeated water that has passed through the membrane module 35 with a reverse osmosis membrane and separating the purified water that has passed through the reverse osmosis membrane and the concentrated water that has not passed through Membrane filtration step.
(E) A hypochlorite cleaning step of cleaning the membrane module 35 with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module 35 with an aqueous acid solution.

(Drainage)
The wastewater treated in the wastewater treatment method of the first invention of the present application is wastewater having a COD _Cr of 3000 to 10000 mg / L and a heavy metal concentration of 0.1 to 200 ppm by weight. The wastewater goes through step (γ), and the heavy metal in the wastewater is recovered to become treated wastewater with a reduced heavy metal concentration. This treated wastewater is supplied to the membrane separation activated sludge treatment system.

When the COD _{Cr of the} waste water exceeds 10,000 mg / L, the burden of biological treatment in the membrane separation activated sludge treatment apparatus 30 may become too large. When COD _Cr is low, it is not necessary to treat waste water by the waste water treatment method of the first invention of the present application. Therefore, in the first invention of the present application, it is assumed that COD _Cr of waste water is 3000 mg / L or more. To do. The COD _Cr of the waste water is preferably 4000 to 8000 mg / L.

  When the heavy metal compound concentration in the wastewater is 200 ppm by weight or less, the load on the treatment in the heavy metal concentration reduction step (γ) and the load on the membrane module in the acid cleaning step (f) are greatly reduced. If the heavy metal concentration exceeds 200 ppm by weight, the load on the treatment in step (γ) increases, the treatment such as adsorption and regeneration increases, and the load on the membrane module in step (f) may increase significantly. There is sex. The heavy metal concentration in the waste water is preferably 1 to 100 ppm by weight. The heavy metal preferably contains cobalt and / or manganese, and more preferably contains cobalt.

  The wastewater discharged from the terephthalic acid production process usually contains manganese and / or cobalt used as a catalyst. When the wastewater is wastewater discharged from the terephthalic acid production process, it is preferable that the heavy metal concentration in the treated wastewater is particularly less than one-tenth of the heavy metal concentration in the wastewater in step (γ). More preferably, it is 1 or less.

Moreover, it is preferable that the waste water treated in the waste water treatment method of the first invention of the present application has a ratio of COD _Cr to BOD ₅ (COD _Cr / BOD ₅ ) of 3 to 10. If COD _Cr / BOD ₅ is within the above range, decomposition by biological treatment is easy, and the target treated water quality can be obtained even when the volume load is a normal load. When COD _Cr / BOD ₅ exceeds 10, it is difficult to dispose by the wastewater treatment method of the first invention of the present application because decomposition by biological treatment is difficult.

As the wastewater whose COD _Cr and heavy metal concentrations satisfy the above-mentioned ranges, wastewater discharged from the terephthalic acid production process can be exemplified, and the wastewater treatment method of the first invention of this application is the wastewater discharged from the terephthalic acid production process. Suitable for processing. The details of the terephthalic acid production process will be described in relation to a method for producing terephthalic acid described later.

  Of the above steps (γ) and (c) to (f), the heavy metal concentration reduction step (γ) has already been described in detail, and the description thereof will be omitted. In the following, each step of (c) to (f) will be described. This will be described with reference to FIGS. In the following, a mode for treating wastewater discharged from a process for producing an aromatic carboxylic acid such as terephthalic acid will be described as a main example, but the first invention of the present application is not limited to this mode.

(Membrane separation step (c))
The treated wastewater discharged when the aromatic carboxylic acid such as terephthalic acid is produced and passed through the step (γ) is supplied to the membrane separation activated sludge treatment apparatus 30 via the drainage flow path 50 (see FIGS. 2 and 5). ) Before supplying the treated wastewater to the membrane separation activated sludge treatment apparatus 30, coarse suspended solids and earth and sand are removed from the treated wastewater, the pH of the treated wastewater is adjusted, and the treated wastewater is diluted. May be.

  In the membrane separation activated sludge treatment apparatus 30, the blower 33 is operated to introduce air from the air diffusion pipe 32, and oxygen is given to the aerobic microorganisms in the activated sludge to perform biological treatment of the supplied treatment wastewater. This biological treatment decomposes aromatic compounds (aromatic carboxylic acids, etc.) in the treated wastewater into aliphatic carboxylic acids (acetic acid, etc.), and further decomposes aliphatic carboxylic acids (acetic acid, etc.) into carbon dioxide, etc. To do.

Examples of the aromatic compound include terephthalic acid, p-toluic acid, benzoic acid, 4-carboxybenzaldehyde, and salts thereof (alkali metal salt, alkaline earth metal salt, ammonium salt).
Aerobic microorganisms are bacteria etc. which can decompose | disassemble an aromatic compound etc. using oxygen. Examples of such bacteria include Alkaligenes and Rhodococcus.

  3000-15000 mg / L is preferable and, as for MLSS (mixed water floating substance) in the membrane separation activated sludge processing apparatus 30, 5000-10000 mg / L is more preferable. When MLSS is less than 3000 mg / L, there is a possibility that aerobic microorganisms are insufficient and biological treatment of waste water cannot be performed sufficiently. When MLSS exceeds 15000 mg / L, fluidity is deteriorated as the viscosity of the sludge increases, and the cleaning efficiency of the membrane surface is lowered and may be clogged.

The membrane separation activated sludge treatment apparatus 30 is preferably operated so as to maintain the COD _Cr volumetric load at 1 to 3 [COD _Cr -kg / m ³ / day]. If the COD _Cr volumetric load is less than 1 [COD _Cr -kg / m ³ / day], the processing time may be long. When the COD _Cr volumetric load exceeds 3 [COD _Cr -kg / m ³ / day], there is a possibility that biological treatment of waste water cannot be sufficiently performed. The COD _Cr volumetric load can be adjusted to the above range by adjusting the hydraulic residence time (HRT) depending on the COD _Cr of the waste water treated per hour.

  Further, in the membrane separation activated sludge treatment apparatus 30, the mixed water is solid-liquid separated into sludge and permeated water by operating the suction pump 36 to reduce the pressure in the membrane module 35. At this time, by introducing air into the membrane module 35 from the diffuser tube 32, solid-liquid separation can be performed efficiently while cleaning the surface of the hollow fiber membrane 76a (see FIG. 3).

  The separated excess sludge is discharged through the excess sludge channel 56. Further, since the surplus sludge contains aerobic microorganisms, a part of the surplus sludge may be returned to the membrane separation activated sludge treatment apparatus 30 and used again for biological treatment.

The smaller the COD _Cr of the permeated water, the more preferable. Specifically, 80 mg / L or less is preferable. If the COD _{Cr of the} permeated water is 80 mg / L or less, the influence on the environment is sufficiently small.

(Reverse osmosis membrane filtration step (d))
The permeated water from the membrane separation activated sludge treatment apparatus 30 may be discharged to the outside as it is. However, if the wastewater is wastewater from the terephthalic acid manufacturing process, the permeated water contains a trace amount of heavy metal ions such as cobalt and manganese derived from the catalyst, etc. It is preferable not to discharge to the outside. In such a case, the permeate from the membrane separation activated sludge treatment device 30 is transferred to the reverse osmosis membrane filtration device 40 (see FIG. 5) via the permeate flow channel 55, and ions in the permeate are reverse osmosis membrane 42. (See FIG. 6).

  In the spiral reverse osmosis membrane module 41 (see FIG. 6) of the reverse osmosis membrane filtration device 40, the permeated water is introduced into the permeated water inlet 41a formed on one end surface of the columnar reverse osmosis membrane element 46, It flows through the flow path formed by the mesh spacer 45. During this time, a part of the permeated water permeates through the reverse osmosis membrane 42 to become purified water, is led to the water collecting pipe 43 through the flow path formed by the liquid-permeable support fibers 44, and reaches the end of the water collecting pipe 43. It is discharged from the purified water outlet 41b. On the other hand, the permeated water that has not permeated the reverse osmosis membrane 42 becomes concentrated water and is discharged from the concentrated water outlet 41 c formed on the other end face of the reverse osmosis membrane element 46.

  Purified water that has permeated through the reverse osmosis membrane 42 in the reverse osmosis membrane filtration device 40 is transferred to a terephthalic acid production facility or the like via a purified water flow path 57 (see FIG. 5), and reused as cooling water, partial process water, or the like. Is done. The concentrated water that has not permeated through the reverse osmosis membrane 42 in the reverse osmosis membrane filtration device 40 is discharged to the outside through the concentrated water channel 58. The concentrated water may be discharged after sterilizing with chlorine or the like.

(Hypochlorite washing step (e) and acid washing step (f))
When organic substances, inorganic substances, etc. present in the wastewater are adsorbed by the pores of the filtration membrane or deposited on the surface of the filtration membrane, the transmembrane pressure difference of the membrane module 35 (see FIGS. 2 and 5) increases. When the transmembrane pressure difference of the membrane module 35 increases to some extent, the efficiency of solid-liquid separation by the membrane module 35 decreases. Therefore, the hypochlorite washing step (e) or the acid washing step (f) is performed during the membrane separation step (c). In the hypochlorite cleaning step (e), a chemical solution (hypochlorite aqueous solution) is supplied from the first chemical solution tank 90 to the membrane module 35 to clean the membrane module 35. In the acid cleaning step (f), a chemical solution (acid aqueous solution) is supplied from the second chemical solution tank 92 to the membrane module 35 to clean the membrane module 35.

  By performing the hypochlorite washing step (e), the organic matter adsorbed on the pores of the filtration membrane or deposited on the surface of the filtration membrane is decomposed by the hypochlorite aqueous solution, and is removed from the filtration membrane. Can be removed. Examples of hypochlorite include sodium hypochlorite and calcium hypochlorite.

The concentration of hypochlorite in the hypochlorite aqueous solution (chemical solution) used in step (e) is preferably 300 to 10000 mg / L, more preferably 1000 to 5000 mg / L, from the viewpoint of the cleaning effect. Step (e) passing liquid amount of the chemical in the terms of protection of the cleaning effect and filtration membrane is preferably 0.5～10L / filtration membrane 1m ^2, 1.0~4.0L / filtration membrane 1 m ² Gayori preferable. The passage time of the chemical solution in step (e) is preferably 10 to 180 minutes, more preferably 15 to 120 minutes, from the viewpoint of the cleaning effect and time efficiency. In step (e), it is preferable that the membrane module 35 is allowed to stand for a while after the chemical solution is passed, in view of the cleaning effect. The standing time is preferably 120 minutes or less, and more preferably 30 to 120 minutes. When the membrane module 35 is allowed to stand after the passage of the hypochlorite aqueous solution, the hypochlorite cleaning step is completed at the end of the standing time.

  Moreover, it is preferable that surfactant is contained in hypochlorite aqueous solution. Hypochlorous acid is a highly hydrophilic compound, and as it is, it is difficult to permeate oils or low-degradability coloring components such as hydrocarbon compounds and aromatic compounds with low hydrophilicity attached to the membrane, and the water permeability of the membrane It is difficult to remove deposits that lower the temperature. By allowing the surfactant to coexist in the hypochlorite aqueous solution, the permeability of the cleaning agent to the membrane used for filtration is improved, and the membrane deposits are decomposed and emulsified / dispersed. Therefore, it is possible to easily remove the dirt of the filtration membrane used for the treatment of waste water containing oils and coloring components such as hydrocarbon compounds and aromatic compounds.

  The surfactant is more preferably a low-foaming nonionic surfactant from the viewpoints of better cleaning performance of the filter membrane, cost merit, and handleability. Moreover, you may mix 1 or more types of anionic surfactant, a cationic surfactant, and an amphoteric surfactant.

  Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polystyryl phenyl ether, polyoxyethylene-polyoxypropylene glycol, polyoxyethylene-polyoxypropylene alkyl ether, polyvalent Alcohol fatty acid partial ester, polyoxyethylene polyhydric alcohol fatty acid partial ester, polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, polyoxyethylenated castor oil, fatty acid diethanolamide, polyoxyethylene alkylamine, triethanolamine fatty acid partial ester, Examples include trialkylamine oxide.

  Examples of the anionic surfactant include alkyl sulfonic acid, alkyl benzene sulfonic acid, alkyl carboxylic acid, alkyl naphthalene sulfonic acid, α-olefin sulfonic acid, dialkyl sulfosuccinic acid, α-sulfonated fatty acid, N-methyl-N-oleyl taurine, Petroleum sulfonic acid, alkyl sulfuric acid, sulfated oil and fat, polyoxyethylene alkyl ether sulfuric acid, polyoxyethylene styrenated phenyl ether sulfuric acid, alkyl phosphoric acid, polyoxyethylene alkyl ether phosphoric acid, polyoxyethylene alkyl phenyl ether phosphoric acid, naphthalene sulfone Examples include acid formaldehyde condensates and salts thereof.

  Cationic surfactants include primary to tertiary fatty amines, quaternary ammonium, tetraalkylammonium, trialkylbenzylammonium alkylpyridinium, 2-alkyl-1-alkyl-1-hydroxyethylimidazolinium, N, N -Dialkylmorpholinium, polyethylene polyamine fatty acid amide, urea condensate of polyethylene polyamine fatty acid amide, quaternary ammonium of urea condensate of polyethylene polyamine fatty acid amide, and salts thereof.

  Amphoteric surfactants include betaines (N, N-dimethyl-N-alkyl-N-carboxymethylammonium betaine, N, N, N-trialkyl-N-sulfoalkyleneammonium betaine, N, N-dialkyl-N N-bispolyoxyethylene ammonium sulfate betaine, 2-alkyl-1-carboxymethyl-1-hydroxyethylimidazolinium betaine, etc.), aminocarboxylic acids (N, N-dialkylaminoalkylene carboxylate, etc.), etc. Can be mentioned.

The concentration of the surfactant in the aqueous hypochlorite solution is preferably 0.05 to 3.0% by mass, and more preferably 0.3 to 1.5% by mass. If the surfactant concentration is not less than the lower limit, the filtration membrane can be sufficiently washed. However, even if the upper limit is exceeded, the effect of improving the cleaning performance reaches its peak, and the cost only increases.
Further, the ratio of the surfactant when the free chlorine concentration of chloric acid or a salt thereof is set to 1 is preferably 0.3 to 1.5 because higher detergency can be obtained.

  By performing the acid washing step (f), the inorganic substance adsorbed on the pores of the filtration membrane or deposited on the surface of the filtration membrane can be solubilized with the acid aqueous solution and removed from the filtration membrane. Examples of the acid aqueous solution that can be used in step (f) include an organic acid aqueous solution and an inorganic acid, and an organic acid aqueous solution is preferable because it has little influence on activated sludge. Examples of the aqueous organic acid solution that can be used in step (f) include an aqueous citric acid solution and an aqueous oxalic acid solution, and an aqueous citric acid solution is preferred. Examples of inorganic acids that can be used in step (f) include hydrochloric acid, sulfuric acid and the like.

The concentration of the acid in the acid aqueous solution (chemical solution) used in step (f) is preferably 0.5 to 5% by weight and more preferably 1 to 3% by weight from the viewpoint of the cleaning effect. Passing liquid amount of the chemical in step (f) is, in terms of protection of the cleaning effect and filtration membrane is preferably 0.5～10L / filtration membrane 1 m ^2, and more preferably 1～4L / filtration membrane 1 m ^2. The liquid passing time in step (f) is preferably 10 to 180 minutes, more preferably 15 to 120 minutes, from the viewpoint of the cleaning effect and time efficiency. In step (f), from the viewpoint of cleaning effect, it is preferable to leave the membrane module 35 for a while after the chemical solution is passed. The standing time is preferably 180 minutes or less, and more preferably 30 to 120 minutes. In the case where the membrane module 35 is allowed to stand after the acid aqueous solution is passed, the acid cleaning step is completed at the end of the standing time.

  In the wastewater treatment method of the first invention of the present application, as the washing step, first, a hypochlorite washing step (e) is performed, and then an acid washing step (f) is performed so as to satisfy a predetermined condition. Is preferred. By performing each step in this order, it is possible to remove the inorganic occluding substance generated by the hypochlorite cleaning step by the acid cleaning step.

In the wastewater treatment method of the first invention of the present application, step (f) after step (e) is performed so as to satisfy the following condition (A) and / or condition (B).
Condition (a): The interval from the end of step (e) to the start of step (f) is within 100 hours.
Condition (b): Step (f) is started when the transmembrane differential pressure of the membrane module 35 becomes 3 kPa to 50 kPa higher than the transmembrane differential pressure after the start of operation.
Here, the “transmembrane differential pressure after the start of operation” means the transmembrane differential pressure of the membrane module 35 one hour after the start of the solid-liquid separation process by the membrane module 35.

In either case of adopting the conditions (b) and (b), when the solid-liquid separation process by the membrane module 35 is in operation, the solid-liquid separation process by the membrane module 35 in the membrane separation step (c) is temporarily performed. The hypochlorite washing step (e) will be performed after interruption.
When the condition (a) is adopted, the acid washing step (f) is started within 100 hours after the hypochlorite washing step (e) is completed. As the mode, the following modes (P) to (R) can be exemplified.

(P) After the hypochlorite washing step (e) is completed, the acid washing step (f) is performed as it is without restarting the solid-liquid separation process by the membrane module 35.
(Q) A mode in which the solid-liquid separation process by the membrane module 35 is performed within 100 hours from the completion of the hypochlorite washing step (e) to the start of the acid washing step (f).
(R) A mode in which the solid-liquid separation process by the membrane module 35 is suspended within 100 hours from the end of the hypochlorite cleaning step (e) to the start of the acid cleaning step (f).
When the condition (b) is adopted, after the hypochlorite washing step (e) is completed, the transmembrane pressure difference of the membrane module 35 is 3 kPa to 50 kPa higher than the transmembrane pressure difference after the start of operation. When this happens, the acid washing step (f) is started. As the mode, the following modes (S) to (U) can be exemplified.
(S) After the hypochlorite washing step (e) is completed, when the transmembrane differential pressure of the membrane module 35 is within the range of the transmembrane differential pressure after starting operation + 3 kPa to 50 kPa, the membrane module 35 A mode in which the acid washing step (f) is performed as it is without restarting the solid-liquid separation process.
(T) After the hypochlorite washing step (e) is completed, when the transmembrane pressure difference of the membrane module 35 is within the range of the transmembrane pressure difference after starting operation + 3 kPa to 50 kPa, the membrane module 35 The solid-liquid separation process is restarted, and the solid-liquid separation process by the membrane module 35 is interrupted again while the transmembrane differential pressure of the membrane module 35 is within the range of the transmembrane differential pressure after starting operation + 3 kPa to 50 kPa. A mode in which the washing step (f) is performed.
(U) After the hypochlorite washing step (e) is finished, when the transmembrane pressure difference of the membrane module 35 is lower than the transmembrane pressure difference after starting operation + 3 kPa, the solid-liquid separation process by the membrane module 35 is performed. When the transmembrane pressure difference of the membrane module 35 is in the range of 3 kPa to 50 kPa higher than the transmembrane pressure difference after the start of operation, the solid-liquid separation process by the membrane module 35 is interrupted again, and the acid cleaning step (f ).
In either case of adopting the conditions (A) and (B), the solid-liquid separation process by the membrane module 35 can be resumed after the end of the acid cleaning step (f).

Condition (b):
Since the interval from the end of step (e) to the start of the next step (f) is within 100 hours, washing is performed before the blockage by the inorganic plugging material generated by hypochlorite proceeds. It can be carried out. When the condition (a) is satisfied, the interval from the end of step (e) to the start of the next step (f) is preferably within 48 hours, and more preferably within 24 hours.

Condition (b):
By starting the step (f) when the transmembrane pressure difference of the membrane module 35 is equal to or higher than the transmembrane pressure difference after starting operation + 3 kPa, the frequency of interruption of the membrane separation step can be reduced, and the wastewater treatment efficiency is improved. improves. By starting step (f) when the transmembrane differential pressure of the membrane module 35 is equal to or lower than the transmembrane differential pressure after starting operation + 50 kPa, cleaning can be started without causing the membrane module to be blocked. When the condition (b) is satisfied, the timing of starting step (f) is preferably when the transmembrane differential pressure of the membrane module 35 is within the range of the transmembrane differential pressure after starting operation + 5 kPa to 40 kPa. More preferably, the transmembrane differential pressure of 35 is within the range of the transmembrane differential pressure after starting operation + 7 kPa to 35 kPa, and the transmembrane differential pressure of the membrane module 35 is within the range of transmembrane differential pressure after starting operation + 10 kPa to 30 kPa. More preferably, it is within.

  In the first invention of the present application, performing the acid cleaning step (f) a plurality of times between the hypochlorite cleaning step (e) and the next hypochlorite cleaning step (e) It is preferable from a viewpoint of improving, and it is more preferable to perform 3 times or more and 5 times or less.

  In the case where both of the conditions (b) and (b) are satisfied, the transmembrane differential pressure of the membrane module is preferably in the range of 5 to 30 kPa higher than the transmembrane differential pressure after the start of operation, more preferably 10 to 25 kPa higher. When in the range, more preferably in the range 15-25 kPa higher, it is desirable to start the first hypochlorite wash step (e).

  The frequency of performing the hypochlorite washing step (e) is, for example, preferably 1 to 6 times / 3 months, more preferably 1 to 5 times / 3 months, and even more preferably 1 to 4 times / month. It can be 3 months, particularly preferably 1 to 3 times / 3 months.

  In the above description regarding the first invention of the present application, after the operation of the solid-liquid separation process by the membrane module 35 in the membrane separation step (c) is started, the hypochlorite washing step (e) is first performed, Although the form which performs an acid washing step (f) was mainly illustrated and demonstrated, the 1st invention of this application is not limited to the said form. In the membrane separation step (c), after the operation of the solid-liquid separation process by the membrane module 35 is started, the acid washing step (f) is first performed, and then the hypochlorite washing step (e) is employed. Is also possible. Also in this form, after completion of the hypochlorite washing step (e), the next acid washing step (f) is started so as to satisfy the above condition (A) or (B). In the case of adopting such a configuration, the transmembrane differential pressure of the membrane module is preferably in the range of 5 to 30 kPa higher than the transmembrane differential pressure after the start of operation, more preferably in the range of 10 to 25 kPa, more preferably in the range of 15 to 25 kPa. When in the high range, it is desirable to start the first acid wash step (f).

According to the wastewater treatment method of the first invention of the present application, the heavy metal in the wastewater is recovered and the heavy metal concentration is reduced, so that (i) the washing load on the membrane module 35, particularly the load due to acid washing, is extremely small. Become. Furthermore, since the solid-liquid separation process by the membrane module 35 is performed in the aeration tank in the biological treatment, (ii) the conventional sedimentation tank is not required and maintenance management is facilitated, and (iii) the biological treatment is performed in only one stage. In spite of this, it is possible to obtain treated water quality equivalent to or higher than that of the conventional method with two stages of biological treatment, and (iv) SS (floating matter) even if there is no coagulation sedimentation tank required in the final stage in the past. ) Can be removed sufficiently, and (v) sand filtration or the like is necessary to pass the permeate through the reverse osmosis membrane in the conventional method, the permeate can be passed directly through the reverse osmosis membrane. As a result, even when wastewater with high COD _Cr is treated, the equipment (system) can be reduced in size as compared with the conventional one, so that the initial construction cost can be reduced.

The wastewater treatment method of the first invention of the present application further includes a washing step for washing the membrane module, and the washing step comprises a hypochlorite washing step for washing the membrane module with a hypochlorite aqueous solution. And (b) an interval from the end of the hypochlorite cleaning step to the start of the next acid cleaning step is within 100 hours. And / or (b) the acid cleaning step is started when the transmembrane pressure difference of the membrane module becomes 3 kPa to 50 kPa higher than the transmembrane pressure difference after the start of operation. Therefore, the transmembrane pressure difference of the membrane module 35 can be kept low while the wastewater containing COD _Cr and containing heavy metals is biologically treated and subjected to membrane separation treatment.
As described above, a membrane separation step may be performed between the hypochlorite washing step and the acid washing step.

(Other embodiment (1))
In the said description regarding the waste water treatment method of 1st invention of this application, although the form which uses the membrane separation activated sludge processing system of FIG. 2 or FIG. 5 was illustrated, 1st invention of this application is not limited to the said form. For example, the membrane separation activated sludge treatment apparatus 30 in FIGS. 2 and 5 is an integrated type that performs both the biological treatment by the aerobic microorganisms in the activated sludge and the solid-liquid separation treatment by the membrane module in one tank. Wastewater in a form using a membrane separation activated sludge treatment system equipped with a tank-separated membrane separation activated sludge treatment apparatus that performs biological treatment with aerobic microorganisms in activated sludge and solid-liquid separation treatment with a membrane module in separate tanks It is also possible to use a processing method.

  FIG. 7 is a schematic configuration diagram showing another aspect of the membrane separation activated sludge treatment system that can be used in the wastewater treatment method of the first invention of the present application. The membrane separation activated sludge treatment system of FIG. 7 includes a tank-separated membrane separation activated sludge treatment device 30 ′ instead of the integrated membrane separation activated sludge treatment device 30 in that FIG. 2 (and FIG. 5). ) Membrane separation activated sludge treatment system. The tank-separated membrane separation activated sludge treatment apparatus 30 ′ shown in FIG. 7 includes an activated sludge tank (first aeration tank) 38; a membrane separation tank 39; and an activated sludge tank (first aeration tank) 38. And two air diffusers 32 arranged near the bottom of the membrane separation tank 39; a blower 33 for supplying air to each air diffuser 32; and an air introduction tube 34 connecting each air diffuser 32 and the blower 33; A membrane module 35 disposed in the membrane separation tank 39 and above the diffuser tube 32; solid-liquid separation of sludge and permeate by being provided in the middle of the permeate flow channel 55 and reducing the pressure in the membrane module 35 A suction pump 36 that sends permeate to the downstream process; a backwash pump 37 that is provided in the middle of the chemical flow path 59 and sends a chemical solution for backwashing to the membrane module 35; and an activated sludge tank (first 1 aeration tank) 38 Comprising the activated sludge tank a portion of the excess sludge from the membrane separation tank 39 and the (first aeration tank) return sludge flow path back to 38; and mixed water passage for transporting the separation tank 39.

(Other embodiment (2))
In the above description regarding the first invention of the present application, the biological treatment (membrane separation activated sludge treatment) is performed by (i) biological treatment of treated wastewater or after biological treatment of treated wastewater, and then sludge and permeated water by the membrane module. However, the first invention of the present application is not limited to the above-described embodiment. . For example, the treated wastewater obtained by the heavy metal concentration reduction step may be once subjected to biological treatment and then subjected to the membrane separation step. That is, biological treatment (membrane separation activated sludge treatment)
(I) After performing the first-stage biological treatment of the treated wastewater and performing the second-stage biological treatment, or after performing the biological treatment of the treated wastewater in two stages, the membrane module converts the solid waste into sludge and permeate. A membrane separation step to separate;
(Ii) A wastewater treatment method having a washing step of washing the membrane module is also possible. Such other embodiments will be described below.

  FIG. 8: is a schematic block diagram which shows the one aspect | mode of the membrane separation activated sludge processing system in the waste water treatment method of 1st invention of this application which concerns on other embodiment. The membrane separation activated sludge treatment system of FIG. 8 includes an aeration tank 10 that biologically treats treated wastewater that has undergone the heavy metal concentration reduction step with aerobic microorganisms in the activated sludge; and an aeration tank mixed water that is biologically treated in the aeration tank 10. A sedimentation tank 20 for solid-liquid separation into sludge and supernatant liquid; and biological treatment of the supernatant liquid from the precipitation tank 20 by aerobic microorganisms in the activated sludge, and at the same time solid-liquid separation into sludge and permeated water by the membrane module 35 A membrane separation activated sludge treatment apparatus 30 that performs; a first chemical liquid tank 90 that stores a hypochlorite aqueous solution that cleans the membrane module 35; and a second chemical liquid tank 92 that stores an aqueous acid solution that cleans the membrane module 35 And; a control unit (not shown) for controlling the supply of the chemical solution from the first chemical solution tank 90 and the second chemical solution tank 92 to the membrane module 35; A drainage flow path 50 for supplying the treated wastewater to the aeration tank 10; an aeration tank mixed water flow path 51 for transferring the aeration tank mixed water biologically treated in the aeration tank 10 to the precipitation tank 20; and a supernatant liquid from the precipitation tank 20 A supernatant liquid channel 52 for transferring the excess sludge from the sedimentation tank 20 to the membrane separation activated sludge treatment apparatus 30; a part of the excess sludge from the sedimentation tank 20 to the aeration tank 10; A return sludge flow path 54 for returning; a permeate flow path 55 for discharging permeated water from the membrane separation activated sludge treatment apparatus 30; and an excess sludge flow path 56 for discharging excess sludge from the membrane separation activated sludge treatment apparatus 30; A chemical liquid channel 59 for supplying the chemical liquid from the first chemical liquid tank 90 and the second chemical liquid tank 92 to the membrane module 35 is provided.

  The aeration tank 10 includes: a tank body 11; a diffuser pipe 12 disposed in the vicinity of the bottom of the tank body 11; a blower 13 for supplying air to the diffuser pipe 12; and an air introduction for connecting the diffuser pipe 12 and the blower 13 Tube 14.

  The sedimentation tank 20 is not particularly limited as long as it can separate the aeration tank mixed water transferred from the aeration tank 10 into sludge and supernatant liquid by gravity sedimentation. The settling tank 20 may be a general settling tank.

  The membrane separation activated sludge treatment apparatus 30 has the same configuration as the membrane separation activated sludge treatment apparatus 30 in FIGS. 2 and 5 described above.

  As shown in FIG. 9, the membrane separation activated sludge treatment system includes a reverse osmosis membrane filtration device 40 that permeates the membrane module 35 and filters the permeate discharged from the permeate flow passage 55 through the reverse osmosis membrane; A purified water channel 57 that discharges purified water that has passed through the filtration device 40; and a concentrated water channel 58 that discharges concentrated water that has not passed through the reverse osmosis membrane filtration device 40 may be further provided. 9, the reverse osmosis membrane filtration device 40 has the same configuration as the reverse osmosis membrane filtration device 40 in FIG. 5 described above.

  The control unit has the same configuration as the control unit described above.

In addition to the following step (γ), the processing flow in the present embodiment includes the following steps (a) to (c), (e), when using the membrane separation activated sludge processing system having the configuration of FIG. And when using the membrane separation activated sludge processing system which has the structure of FIG. 9 and (f), it has the following steps (a)-(f), respectively.
(Γ) The heavy metal concentration reduction step for obtaining the treated waste water whose heavy metal concentration is reduced by collecting the heavy metal in the waste water as described above.
(A) A step of biologically treating the treated wastewater that has undergone the heavy metal concentration reduction step with aerobic microorganisms in the activated sludge in the aeration tank 10 (first-stage biological treatment).
(B) A precipitation step in which the aeration tank mixed water that has undergone biological treatment in the aeration tank 10 is solid-liquid separated in the precipitation tank 20.
(C) In the membrane-separated activated sludge treatment apparatus 30, the supernatant liquid from the sedimentation tank 20 is biologically treated by aerobic microorganisms in the activated sludge (second-stage biological treatment), and at the same time, the membrane module 35 permeates the sludge. A membrane separation step that separates solid and liquid into water.
(D) In the reverse osmosis membrane filtration device 40, reverse osmosis is performed by filtering the permeated water that has passed through the membrane module 35 with a reverse osmosis membrane and separating the purified water that has passed through the reverse osmosis membrane and the concentrated water that has not passed through Membrane filtration step.
(E) A hypochlorite cleaning step of cleaning the membrane module 35 with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module 35 with an aqueous acid solution.

  The properties of the wastewater to be treated and the heavy metal concentration reduction step (γ) are as described above. Hereinafter, the steps (e) to (f) will be described with reference mainly to FIGS. 8 and 9. In the following, a mode for treating wastewater discharged from a process for producing an aromatic carboxylic acid such as terephthalic acid will be described as a main example, but the first invention of the present application is not limited to this mode.

(First stage biological treatment (a))
The treated wastewater discharged when the aromatic carboxylic acid such as terephthalic acid is produced and passed through the step (γ) is supplied to the aeration tank 10 through the drainage flow path 50. Before supplying the treated wastewater to the aeration tank 10, coarse suspended solids, earth and sand, etc. may be removed from the treated wastewater in advance, the pH of the treated wastewater may be adjusted, or the treated wastewater may be diluted.

  In the aeration tank 10, the blower 13 is operated to introduce air from the diffuser pipe 12, and oxygen is given to the aerobic microorganisms in the activated sludge to perform biological treatment of the treated waste water. By this biological treatment, aromatic compounds (such as aromatic carboxylic acids) in the treated wastewater are decomposed into aliphatic carboxylic acids (such as acetic acid).

Examples of the aromatic compound include terephthalic acid, p-toluic acid, benzoic acid, 4-carboxybenzaldehyde, and salts thereof (alkali metal salt, alkaline earth metal salt, ammonium salt).
Aerobic microorganisms are bacteria etc. which can decompose | disassemble an aromatic compound etc. using oxygen. Examples of such bacteria include Alkaligenes and Rhodococcus.

  1000-10000 mg / L is preferable and, as for MLSS (mixed water floating substance) in the aeration tank 10, 2000-8000 mg / L is more preferable. If MLSS is less than 1000 mg / L, there is a possibility that aerobic microorganisms are insufficient and biological treatment of treated wastewater cannot be performed sufficiently. When MLSS exceeds 10,000 mg / L, there is a risk that the sludge floats on the water surface and the sludge flows out.

The aeration tank 10 is preferably operated so as to keep the COD _Cr volumetric load at 1 to 3 [COD _Cr -kg / m ³ / day]. If the COD _Cr volumetric load is less than 1 [COD _Cr -kg / m ³ / day], the processing time may be long. When the COD _Cr volumetric load exceeds 3 [COD _Cr -kg / m ³ / day], there is a possibility that biological treatment of waste water cannot be sufficiently performed. The COD _Cr volumetric load can be adjusted to the above range by adjusting the hydraulic residence time (HRT) depending on the COD _Cr in the waste water being processed per hour.

(Precipitation step (b))
The aeration tank mixed water biologically treated in the aeration tank 10 is transferred to the precipitation tank 20 through the aeration tank mixed water flow path 51. In the settling tank 20, the aeration tank mixed water is solid-liquid separated into sludge and supernatant liquid by gravity settling.

  The separated excess sludge is discharged through the excess sludge channel 53. Further, since the surplus sludge contains aerobic microorganisms, a part of the surplus sludge is returned to the aeration tank 10 via the return sludge flow path 54 and used again for biological treatment of waste water. In addition, since the kind of aerobic microorganisms in the aeration tank 10 is different from the kind of aerobic microorganisms in the membrane separation activated sludge treatment apparatus 30, excess sludge from the aeration tank 10 should not be transferred to the membrane separation activated sludge treatment apparatus 30. Is preferred.

The COD _{Cr in the} supernatant is preferably 200 mg / L or more. If the supernatant liquid COD _Cr is to be less than 200 mg / L, the burden of biological treatment in the aeration tank 10 may be too great. Moreover, in the membrane-separated activated sludge treatment apparatus 30, there is a fear that the organic matter that aerobic microorganisms use as an energy source is insufficient, and biological treatment becomes insufficient.

  After separating the sludge containing aerobic microorganisms in the sedimentation tank 20, the type of aerobic microorganisms in the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30 are transferred by transferring only the supernatant liquid to the membrane separation activated sludge treatment apparatus 30. The type of aerobic microorganisms in this is different. That is, since the kind of organic matter (aromatic compound or the like) in the aeration tank 10 is different from the kind of organic matter (aliphatic carboxylic acid or the like) in the membrane separation activated sludge treatment apparatus 30, the aeration tank 10 and the membrane separation activity naturally occur. In each of the sludge treatment apparatuses 30, different aerobic microorganisms that metabolize different organic substances preferentially will grow. Note that the precipitation tank 20 may be omitted, a membrane module may be installed in the aeration tank 10, and solid-liquid separation using a filtration membrane may be performed.

  If the aeration tank mixed water of the aeration tank 10 is directly transferred to the membrane separation activated sludge treatment apparatus 30 without passing through the settling tank 20, aerobic microorganisms different from the aeration tank 10 are present in the membrane separation activated sludge treatment apparatus 30. Since it becomes difficult to proliferate, the types of aerobic microorganisms in the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30 are almost the same. Therefore, in the membrane separation activated sludge treatment apparatus 30, different aerobic microorganisms that preferentially metabolize aliphatic carboxylic acid and the like are difficult to grow, and biological treatment of aliphatic carboxylic acid and the like in the membrane separation activated sludge treatment apparatus 30 is difficult. It may be sufficient.

(Membrane separation step (c))
The supernatant liquid of the sedimentation tank 20 is transferred to the membrane separation activated sludge treatment apparatus 30 via the supernatant liquid flow path 52.

In the membrane separation activated sludge treatment apparatus 30, the blower 33 is operated to introduce air from the air diffusion pipe 32, and oxygen is given to aerobic microorganisms in the activated sludge to perform biological treatment of the supernatant liquid. By this biological treatment, aliphatic carboxylic acid or the like (for example, acetic acid or the like) in the waste water is decomposed into carbon dioxide or the like.
Aerobic microorganisms are bacteria etc. which can decompose aliphatic carboxylic acid etc. using oxygen.

  3000-15000 mg / L is preferable and, as for MLSS (mixed water floating substance) in the membrane separation activated sludge processing apparatus 30, 5000-10000 mg / L is more preferable. When MLSS is less than 3000 mg / L, there is a possibility that aerobic microorganisms are insufficient and biological treatment of the supernatant liquid cannot be performed sufficiently. When MLSS exceeds 15000 mg / L, fluidity is deteriorated as the viscosity of the sludge increases, and the cleaning efficiency of the membrane surface is lowered and may be clogged.

The membrane separation activated sludge treatment apparatus 30 is preferably operated so as to keep the COD _Cr volumetric load at 0.1 to 0.5 [COD _Cr -kg / m ³ / day]. If the COD _Cr volumetric load is less than 0.1 [COD _Cr -kg / m ³ / day], the processing time may be long. If the COD _Cr volumetric load exceeds 0.5 [COD _Cr -kg / m ³ / day], there is a possibility that biological treatment of the supernatant liquid cannot be performed sufficiently. The COD _Cr volumetric load can be adjusted to the above range by adjusting the hydraulic residence time (HRT) depending on the COD _Cr of the supernatant liquid processed per hour.

  Further, in the membrane separation activated sludge treatment apparatus 30, the mixed water is solid-liquid separated into sludge and permeated water by operating the suction pump 36 to reduce the pressure in the membrane module 35. At this time, by introducing air into the membrane module 35 from the diffuser tube 32, solid-liquid separation can be performed efficiently while cleaning the surface of the hollow fiber membrane 76a (see FIG. 3).

  The separated excess sludge is discharged through the excess sludge channel 56. Further, since the excess sludge contains aerobic microorganisms, a part of the excess sludge may be returned to the membrane separation activated sludge treatment apparatus 30 and used again for biological treatment of the supernatant liquid. In addition, since the kind of aerobic microorganisms of the membrane separation activated sludge treatment apparatus 30 is different from the kind of aerobic microorganisms of the aeration tank 10, excess sludge from the membrane separation activated sludge treatment apparatus 30 should not be returned to the aeration tank 10. Is preferred.

The smaller the COD _Cr of the permeated water, the more preferable. Specifically, 80 mg / L or less is preferable. If the COD _{Cr of the} permeated water is 80 mg / L or less, the influence on the environment is sufficiently small.

  The reverse osmosis membrane filtration step (d) is the same as step (d) described above.

  The hypochlorite washing step (e) and the acid washing step (f) are performed in the same manner as the above-described step (e) and step (f).

According to the wastewater treatment method of the first invention of the present application relating to this embodiment, by performing the heavy metal concentration reduction treatment, (i) the load on the membrane module 35, particularly the load on acid cleaning, is extremely reduced. Furthermore, the treatment wastewater is biologically treated by aerobic microorganisms in the activated sludge in the aeration tank 10 in the biological treatment process, and is precipitated by the aerobic microorganisms in the activated sludge in the membrane separation activated sludge treatment apparatus 30. Since biological treatment of the supernatant liquid from the tank 20 is performed, COD _Cr of the permeated water can be efficiently reduced as compared with the conventional wastewater treatment method.
In addition, after separating the sludge containing aerobic microorganisms in the sedimentation tank 20, the type of aerobic microorganisms in the aeration tank 10 and the membrane separation activated sludge treatment are transferred by transferring only the supernatant liquid to the membrane separation activated sludge treatment apparatus 30. Since the type of aerobic microorganisms in the apparatus 30 is different, the biological treatment in the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30 can be efficiently performed by different aerobic microorganisms, and therefore the COD _Cr of the permeated water can be obtained. It can be reduced efficiently.
In addition, since the membrane separation treatment is performed using the membrane separation activated sludge treatment apparatus 30 instead of a pair of aeration tank and settling tank, the processing time is compared with the conventional wastewater treatment method using only the aeration tank and the precipitation tank. And (ii) the number of settling tanks can be reduced as compared with a conventional wastewater treatment method using two combinations of an aeration tank and a settling tank, and the installation area of the system can be reduced.

Moreover, the waste water treatment method of the first invention of the present application according to the present embodiment includes a cleaning step for cleaning the membrane module, and the cleaning step includes hypochlorite for cleaning the membrane module with a hypochlorite aqueous solution. An acid washing step and an acid washing step for washing the membrane module with an acid aqueous solution in this order, and (b) an interval from the end of the hypochlorite washing step to the start of the next acid washing step. The acid cleaning step is started when it is within 100 hours and / or (b) the transmembrane pressure difference of the membrane module is 3 kPa to 50 kPa higher than the transmembrane pressure difference before the start of operation. Therefore, the transmembrane pressure difference of the membrane module 35 can be kept low while the wastewater containing COD _Cr and containing heavy metals is biologically treated and subjected to membrane separation treatment.
As described above, a membrane separation step may be performed between the hypochlorite cleaning step and the acid cleaning step.

(Other embodiment (3))
In the above description regarding the wastewater treatment method of the first invention of the present application, the form using the membrane separation activated sludge treatment system of FIG. 8 or FIG. 9 is exemplified, but the first invention of the present application is not limited to this form. For example, the membrane separation activated sludge treatment apparatus 30 in FIGS. 8 and 9 is an integrated type that performs biological treatment with aerobic microorganisms in activated sludge and solid-liquid separation treatment with a membrane module in one tank. A tank-separated membrane separation activated sludge treatment apparatus (for example, a membrane separation activated sludge treatment apparatus 30 ′ in FIG. 7) that performs biological treatment by aerobic microorganisms in sludge and solid-liquid separation treatment by a membrane module in separate tanks. It is also possible to set it as the waste water treatment method of the form using the membrane separation activated sludge processing system which it comprises.

<2. Method for producing terephthalic acid>
The method for producing terephthalic acid according to the first invention of the present application includes a terephthalic acid production process and a wastewater treatment process for treating wastewater discharged in the terephthalic acid production process. Hereinafter, embodiments of the method for producing terephthalic acid according to the first invention of the present application will be described with reference to the drawings. In addition, embodiment shown below is an illustration of the manufacturing method of the terephthalic acid of 1st invention of this application, and the manufacturing method of terephthalic acid of 1st invention of this application is not limited to these embodiment. In particular, the combination of a heavy metal reduction treatment apparatus, a filtration membrane apparatus, and the like is not limited to these forms.

The industrial production method of terephthalic acid can be roughly classified into the following two types (A) and (B) depending on the quality (purity) required for terephthalic acid.
(A) A method for producing terephthalic acid by hydrorefining after the oxidation reaction.
(B) A method of producing terephthalic acid without hydrorefining by additionally conducting an oxidation reaction at high temperature and high pressure after the oxidation reaction.

(A. First representative method for producing terephthalic acid)
FIG. 10 is a diagram illustrating a process flow and a substance flow in the first representative method for producing terephthalic acid. The first representative method for producing terephthalic acid has a terephthalic acid production process having the following steps (i) to (vi) and a waste water treatment process (vii).
(I) A step of obtaining a crude terephthalic acid slurry by oxidizing p-xylene in hydrous acetic acid (hereinafter also referred to as “oxidation reaction step (i)”).
(Ii) A step of solid-liquid separation of the crude terephthalic acid slurry to recover a crude terephthalic acid cake (hereinafter also referred to as “first solid-liquid separation step (ii)”).
(Iii) A step of dissolving the crude terephthalic acid cake in water and performing a hydrogenation treatment (hereinafter, also referred to as “hydrogenation treatment step (iii)”).
(Iv) A step of crystallizing the hydrogenation treatment liquid to obtain a terephthalic acid slurry (hereinafter also referred to as “crystallization step (iv)”).
(V) A step of solid-liquid separation of the terephthalic acid slurry to obtain a terephthalic acid cake and a separated mother liquor (hereinafter also referred to as “second solid-liquid separation step (v)”).
(Vi) A step of drying the terephthalic acid cake to obtain terephthalic acid (hereinafter also referred to as “drying step (vi)”).
(Vii) The whole or part of the wastewater discharged from the steps (i) to (vi) is recovered by heavy metal concentration reduction treatment in the wastewater, followed by aerobic biological treatment, reverse osmosis membrane treatment, and adsorption treatment. Wastewater treatment process (hereinafter also referred to as “wastewater treatment process (vii)”)

(Oxidation reaction step (i))
The oxidation reaction step (i) is an oxidation reaction step in which p-xylene is oxidized in hydrous acetic acid to obtain a crude terephthalic acid slurry 211 ′. First, p-xylene and a solvent containing acetic acid or the like are mixed and sent to the oxidation reaction device 211, and p-xylene is oxidized using molecular oxygen in the presence of a catalyst in the solvent. Examples of the catalyst include compounds of transition metals such as cobalt and manganese and / or hydrogen halides such as hydrobromic acid. As a result, a crude terephthalic acid slurry 211 'is generated and sent to the first solid-liquid separation step (ii).

(First solid-liquid separation step (ii))
In the first solid-liquid separation step (ii), the crude terephthalic acid slurry 211 ′ is solid-liquid separated in the first solid-liquid separation device 212 to recover the crude terephthalic acid cake, followed by washing and drying to obtain crude terephthalic acid. This is a step of obtaining the acid 212 ′. Examples of the method for solid-liquid separation include a method in which a solid-liquid separator is used as it is. Since the crude terephthalic acid slurry 211 ′ is in a pressurized state, the dissolved crude terephthalic acid precipitates when the pressure is lowered. For this reason, the slurry 211 ′ may be sent to a crystallization tank (not shown) and cooled under pressure to precipitate the dissolved crude terephthalic acid, and then applied to a solid-liquid separator. “Relief pressure cooling” refers to expansion and vaporization of solvent components by introducing the target liquid into a crystallization tank set to a pressure condition lower than the pressure of the target liquid and releasing the pressure in the crystallization tank. Means cooling.

  The crude terephthalic acid cake thus obtained is washed with acetic acid, water, a mixture of acetic acid and water, and then dried to obtain crude terephthalic acid 212 '. The obtained crude terephthalic acid 212 'contains an oxidation intermediate such as 4-carboxybenzaldehyde (4CBA) as an impurity. In order to remove such impurities, the crude terephthalic acid 212 'is sent to the next hydrogenation treatment step (iii).

(Hydrogenation treatment step (iii))
The hydrogenation treatment step (iii) is a step in which the crude terephthalic acid 212 ′ is dissolved in water and reduced by hydrogenation in the hydrogenation treatment apparatus 213. Through the hydrogenation treatment step (iii), the impurity 4CBA is reduced to p-toluic acid. Since p-toluic acid has higher water solubility than terephthalic acid, it can be separated in the second solid-liquid separation step (v) described later. The separated p-toluic acid is returned to the oxidation reaction step (i) and used as a terephthalic acid raw material. The hydrogenation treatment liquid 213 ′ generated by the hydrogenation treatment step (iii) is sent to the next crystallization step (iv).

(Crystalling step (iv))
The crystallization step (iv) is a step of obtaining a terephthalic acid slurry 214 ′ by crystallizing the hydrogenation treatment liquid 213 ′ in the crystallizer 214. Examples of the crystallization method include a method of evaporating and removing water as a solvent and cooling, a method of cooling under pressure, and the like. In this step, since p-toluic acid is highly water-soluble as described above, many of them remain dissolved in the solvent without being precipitated. Therefore, p-toluic acid and terephthalic acid can be separated in the next second solid-liquid separation step (v).

(Second solid-liquid separation step (v))
In the second solid-liquid separation step (v), the terephthalic acid slurry 214 ′ is separated into a terephthalic acid cake 215 ′ and a terephthalic acid separation mother liquor 224 ′ in the second solid-liquid separation device 215. It is a process. As the separator, known methods such as filtration and centrifugation can be employed. The separated terephthalic acid cake has a mother liquor 224 ′ attached thereto, and impurities and the like dissolved in the mother liquor deteriorate the quality, so the terephthalic acid cake is washed with water. The terephthalic acid cake 215 ′ obtained by washing is sent to the next drying step (vi).

  Here, since the terephthalic acid separation mother liquor 224 ′ contains impurities such as p-toluic acid, a catalyst, terephthalic acid, and the like, the p-toluic acid and terephthalic acid are cooled by cooling in the recovery apparatus 220 such as p-toluic acid. Acid and the like are deposited and recovered. The recovered p-toluic acid, terephthalic acid and the like are returned to the oxidation reaction step (i). On the other hand, the separation mother liquor 225 'such as p-toluic acid is sent to a wastewater treatment process (vii) after collecting a heavy metal catalyst such as cobalt or manganese by a recovery device (not shown).

(Drying step (vi))
The drying step (vi) is a step of drying the terephthalic acid cake 215 ′ in the drying device 216 to obtain terephthalic acid 216 ′. In drying, a pressure dryer by pressure evaporation, a normal fluid dryer, or the like can be used.

(Wastewater treatment process (vii))
In the wastewater treatment process (vii), in the wastewater treatment system 221, first, the wastewater discharged from steps (i) to (vi) is first subjected to heavy metal concentration reduction treatment to recover heavy metals contained in the wastewater, and then organic matter Are decomposed by aerobic microorganisms in the presence of dissolved oxygen (aerobic biological treatment), and further processed as necessary. In addition, the waste water discharged | emitted from process (i)-(vi) is not necessarily sent directly to this waste water treatment system 221 and processed without necessarily performing any treatment. There is a case where a process corresponding to a drainage composition peculiar to each process is performed and sent to the wastewater treatment system 221.

The wastewater treatment process (vii) includes, for example, the following steps (γ) and (a) to (f).
(Γ) A heavy metal concentration reduction step in which the heavy metal compound in the waste water from steps (i) to (vi) is recovered to reduce the heavy metal concentration in the waste water to obtain treated waste water.
(A) A step of biologically treating the treated wastewater that has undergone the heavy metal concentration reduction step with an aerobic microorganism in the activated sludge in an aeration tank (first-stage biological treatment).
(B) A precipitation step in which the aeration tank mixed water that has undergone biological treatment in the aeration tank is subjected to solid-liquid separation in the precipitation tank.
(C) In the membrane separation activated sludge treatment device, the supernatant liquid from the sedimentation tank is biologically treated with aerobic microorganisms in the activated sludge and / or after biological treatment, the membrane module converts the supernatant into sludge and permeate. A membrane separation step for solid-liquid separation.
(D) If necessary, in the reverse osmosis membrane filtration device, the permeated water that has permeated the membrane module is filtered by the reverse osmosis membrane, and separated into purified water that has permeated the reverse osmosis membrane and concentrated water that has not permeated. , Reverse osmosis membrane filtration step.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an aqueous acid solution.

  Steps (γ) and (a) to (f) are performed in the same manner as steps (γ) and (a) to (f) described above in relation to the wastewater treatment method of the first invention of the present application.

(Drainage)
Next, the type of wastewater discharged from the steps (i) to (vi) to the wastewater treatment process (vii) and the treatment route thereof will be described, and wastewater to be treated in the biological treatment of the wastewater treatment process (vii) for each step. Will be described.

(Drainage from oxidation reaction step (i))
From the oxidation reaction step (i), acetic acid as a solvent, water produced as a by-product, methyl acetate, methyl bromide, reaction intermediate, along with the molecular oxygen-containing gas introduced into the oxidation reaction device 211 for the oxidation reaction , Carbon monoxide, etc., unreacted p-xylene, and the like are discharged. By-product energy is recovered from the high-temperature and high-pressure gas as electric and thermal energy, and further acetic acid, methyl acetate and the like are recovered, and then methyl bromide and the like are combusted. After the exhaust gas after the combustion treatment is contact cleaned with alkaline water or the like, the gas is released to the atmosphere, and the oxidized exhaust gas cleaning water 217 ′ is sent to the waste water treatment system 221.

(Drainage from the first solid-liquid separation step (ii))
From the first solid-liquid separation step (ii), a solid-liquid separated mother liquor is generated. More than 50% of the mother liquor is recycled to the oxidation reaction step (i). The ratio of reusing the mother liquor is preferably 70% or more, but part of the mother liquor needs to be purged to prevent quality degradation due to impurity accumulation in the system. Therefore, the ratio of reusing the mother liquor is 95% or less, preferably 90% or less. Oxidation reaction mother liquor (purged) 218 ′ that is not reused is evaporated and concentrated by a solvent recovery device 217, and divided into an evaporation solvent 219 ′ and a mother liquor concentrated slurry 220 ′ containing an active ingredient. The mother liquor concentrated slurry 220 ′ is sent to the catalyst recovery / regeneration device 219, where the catalyst is recovered / regenerated. After the recovered and regenerated catalyst is subjected to solid-liquid separation, the regenerated catalyst recovery / separation mother liquor 222 ′ is sent to the waste water treatment system 221 together with the cleaning waste water generated from the deodorization tower. On the other hand, the evaporated solvent 219 ′ is sent to a recovery device 218 such as acetic acid, where acetic acid is concentrated and recovered in a dehydration tower (not shown), and then methyl acetate is recovered in a distillation tower (methyl acetate recovery tower) (not shown). Part of the remaining methyl acetate recovery tower bottom liquid 221 ′ is sent to the wastewater treatment system 221.

  The vent gas generated in the steps other than the oxidation reaction step (i) and the first solid-liquid separation step (ii) is collectively washed in a washing tower (not shown), and the waste water treatment system together with the oxidized exhaust gas washing water 217 ′. 221.

(Drainage from the hydrogenation process (iii))
Usually, no wastewater treatment object is generated from the hydrogenation treatment step (iii).

(Drainage from crystallization process (iv))
From the crystallization step (iv), condensed water 223 ′ generated at the time of crystallization generated by cooling the generated steam when crystallization is performed by depressurization cooling or cooling under reduced pressure is generated. Condensed water 223 ′ generated at the time of crystallization contains an organic substance such as p-toluic acid and is sent to the waste water treatment system 221.

(Drainage from second solid-liquid separation step (v) and drying step (vi))
In the second solid-liquid separation step (v), the terephthalic acid cake 215 ′ is solid-liquid separated and a terephthalic acid separation mother liquor 224 ′ is generated. The terephthalic acid separation mother liquor 224 ′ is sent to the recovery apparatus 220 for p-toluic acid and the like, and p-toluic acid, terephthalic acid and the like dissolved in the terephthalic acid separation mother liquor 224 ′ are deposited and separated by filtration under pressure relief. The cake precipitated and separated from the terephthalic acid separation mother liquor 224 ′ is slurried and then returned to the oxidation reaction step (i). After recovering heavy metals such as cobalt and manganese contained in the residual mother liquor of the precipitation separation with a metal recovery device (not shown), the remaining separation mother liquor 225 ′ such as p-toluic acid is cooled and sent to the waste water treatment system 221.
In addition to the second solid-liquid separation step (v) and the drying step (vi), vent gas cleaning water 226 ′ generated when the vent gas is collectively processed by the scrubber is sent to the waste water treatment system 221.

Step (i) ~ (vi) suspended solids in the waste water entering the waste water treatment system 221 from (SS), cobalt used as catalysts in oxidation reactions, heavy metals manganese, alkali metal, compound results in an increase in _{COD Cr} In addition, compounds that increase total nitrogen are contained. The concentration of insoluble substances in the waste water is 100 mg / L or less in terms of SS value and / or 100 NTU or less in terms of turbidity, and the concentration of water-soluble organic substances is 10,000 mg / L or less in terms of COD _Cr . However, the discharged water 227 ′ flowing out from the conventional waste water treatment system 221 cannot be reused as it is in the terephthalic acid production process from the viewpoint of water quality, and must be discharged in large quantities in public water areas.

  As a result of examining the method for treating the waste water discharged from the steps (i) to (vi), the first inventors of the present application have found that conventional waste water treatment in which only aerobic biological treatment is performed in the waste water treatment process (vii). Instead of performing a membrane separation process (and reverse osmosis membrane treatment if necessary) using a membrane module while performing a biological treatment and / or after performing a biological treatment after reducing the heavy metal concentration. The present inventors have found that a part or most of permeated water can be stably reused as industrial water (cooling water) or process water for producing terephthalic acid, and have completed the method for producing terephthalic acid according to the first invention of the present application. . When used as process water, it has also been found that the utility value of cooling water and / or process water can be further increased by improving the purification degree of water using various adsorbents as necessary. . In particular, by performing treatment to reduce the concentration of heavy metals such as Co before biological treatment, the adhesion of heavy metal compounds to the filtration membrane and reverse osmosis membrane filter is greatly reduced, and this deposit is removed. Labor saving of acid washing operation became possible.

  For biological treatment, aerobic microorganisms decompose organic substances in wastewater in the presence of oxygen by aerobic microorganisms, and / or organic substances in wastewater are decomposed by anaerobic microorganisms in a low oxygen concentration environment or in the absence of oxygen. Anaerobic biological treatment can be employed. Specifically, a form in which only aerobic biological treatment is performed and a form in which aerobic biological treatment and anaerobic biological treatment are combined are possible, but wastewater discharged from steps (i) to (vi) Since there are many cases where it is not necessary to denitrify because there are few nitrogen components, the form in which only aerobic biological treatment is performed is preferable because the facility becomes compact.

(A-1. First Embodiment in Production of Terephthalic Acid)
FIG. 11 shows the first representative method for producing terephthalic acid, in which the heavy metal compound recovery device of FIG. 1 described above is introduced in the uppermost stream of the waste water treatment system 2100 for treating the waste water discharged from the terephthalic acid production process. FIG. 5 is a diagram for explaining an embodiment in which a membrane separation process using a microfiltration membrane is performed during biological treatment after reducing the heavy metal concentration in wastewater. Hereinafter, a typical embodiment of the method for producing terephthalic acid according to the first invention of the present application will be described more specifically based on FIG.

  As a form of biological treatment that can be adopted in the method for producing terephthalic acid of the first invention of the present application, a form in which only aerobic biological treatment is performed, and a form in which aerobic biological treatment and anaerobic biological treatment are combined are carried out. Can be mentioned. According to the form of performing only aerobic biological treatment, the equipment can be simplified and the cost can be easily reduced. On the other hand, according to the form of combining aerobic biological treatment and anaerobic biological treatment, dephosphorization efficiency is improved. It is possible. For the sake of simplicity, a mode in which only the aerobic biological treatment is performed will be described here.

(Wastewater treatment system 2100)
In the wastewater treatment system 2100, a heavy metal compound recovery device that reduces the concentration of heavy metals, mainly Co and Mn, a microfiltration membrane module (hereinafter, the microfiltration membrane is referred to as “MF membrane”, and the microfiltration membrane module is referred to as “MF. Also referred to as “membrane module”). In the wastewater treatment system 2100, the aerobic biological treatment is performed in two stages after the heavy metal concentration is reduced by the heavy metal compound recovery device having the configuration shown in FIG. The aerobic biological treatment in the method for producing terephthalic acid according to the first invention of the present application is sufficient even in one stage, but water having a quality capable of using a large amount of waste water as at least industrial water (cooling water) and / or process water. From the viewpoint of making it easier to regenerate, it is preferable to perform biological treatment in two stages as described above. The wastewater treatment system 2100 includes at least a heavy metal compound recovery device, and a general aeration tank and precipitation tank. That is, the wastewater treatment system 2100 in FIG. 11 includes a heavy metal compound recovery device 2109, a first aeration tank 2101, a first precipitation tank 2102 connected to the first aeration tank 2101, and a first precipitation tank. A second aeration tank 2103, a reverse osmosis membrane filtration apparatus 2106, a reuse water tank 2107, and an adsorbent treatment apparatus 2108 are provided. Note that the second sedimentation tank 2104 indicated by the broken line is not used because it is not used. In the wastewater treatment system 2100, the wastewater passes through the heavy metal compound recovery device 2109 and is then biologically treated while being transferred in this order through the first aeration tank 2101, the first precipitation tank 2102, and the second aeration tank 2103. The

As an aeration method in the first aeration tank 2101 and the second aeration tank 2103, a known aeration method such as a complete mixing method, a plug flow method, and a step feed method can be employed without any particular limitation. As operating conditions of the first aeration tank 2101 and the second aeration tank 2103, MLSS (unit: mg / L) in the aeration tank is usually 1000 to 15000, preferably 3,000 to 7,000. The COD _Cr volumetric load (unit: COD _Cr -kg / m ³ / day) is usually 0.5 to 10, preferably 1 to 5. The COD _Cr removal rate is usually 95% to 99%, preferably 96% to 99.5%.

  In the wastewater treatment system 2100, an MF membrane module 2105 is disposed in the second aeration tank 2103. That is, the second aeration tank 2103 constitutes a membrane separation activated sludge treatment apparatus (membrane bioreactor, MBR). In a general wastewater treatment system that does not have a membrane module, if the sedimentation property deteriorates in the settling tank, solid-liquid separation becomes insufficient, and a bulking phenomenon may occur in which a large amount of suspended matter is mixed in the supernatant. According to the membrane separation activated sludge treatment apparatus, since this bulking phenomenon can be avoided, a sedimentation tank (second sedimentation tank 2104 in the wastewater treatment system 2100) is not required, and a high concentration operation of MLSS is possible. Further, there is an advantage that the processing equipment can be downsized.

  In the wastewater treatment system 2100, the supernatant liquid separated from the activated sludge in the first sedimentation tank 2102 after undergoing the biological treatment in the first aeration tank 2101 through the heavy metal compound recovery device 2109 is the second aeration tank 2103. Moved to. Since the MF membrane module 2105 is disposed in the second aeration tank 2103, activated sludge (microorganisms) and permeated water can be solid-liquid separated by a membrane without depending on precipitation. Therefore, since it is not necessary to install the second sedimentation tank 2104 in order to perform the final solid-liquid separation between the activated sludge and the permeated water, the installation area of the equipment can be reduced.

  In the wastewater treatment system 2100, the first aeration tank 2101 has MLSS (mg / L) of 1000 to 6000, the second aeration tank 2103 has MLSS (mg / L) of 6000 to 12000, and a membrane module. Compared to a general wastewater treatment system that does not have a low temperature, operation at a significantly higher concentration is possible.

(MF membrane module 2105)
In the wastewater treatment system 2100, an MF membrane is used for membrane separation. The MF membrane is a membrane that filters insoluble solids of approximately 0.1 μm to 10 μm. Examples of the material of the MF membrane include polymer materials such as polypropylene, polyethylene, cellulose acetate, aromatic polyamide, polyvinyl alcohol, polyvinylidene fluoride, polysulfone, and polycarbonate. The pore size of the MF membrane is usually 0.03 μm to 10 μm, but a finer membrane can be used depending on the application. For the membrane separation activated sludge treatment apparatus, an MF membrane having a pore diameter of 0.03 μm to 0.4 μm is preferable. The film material is particularly preferably polyethylene, polypropylene, polyvinylidene fluoride, or the like. As the form of the membrane module, a hollow fiber type, a flat membrane type, a tubular type, a spiral type and the like can be adopted without particular limitation. Among these, a hollow fiber type and a flat membrane type can be particularly preferably adopted. Specific examples of these include “Sterapore SADF (registered trademark)” (Mitsubishi Rayon Co., Ltd.), “Membray (registered trademark)” (Toray Industries, Inc.), “Mike”, which are commercially available for membrane separation activated sludge treatment equipment. Rosa (registered trademark) "(Asahi Kasei Chemicals Corporation).

  As a filtration method that can be used in the MF membrane module 2105, normal dead-end filtration (also referred to as total filtration) performed while depositing suspended substances on the filtration surface, a flow parallel to the membrane surface is created, and the flow direction is changed. There is cross-flow filtration that always re-disperses the suspended substance in a direction substantially orthogonal to the membrane permeation direction, and can be appropriately selected according to the installation method and the usage method. However, cross-flow filtration is preferable because it can reduce membrane contamination and concentration polarization, which can improve filtration efficiency. In the following description, it is assumed that cross flow filtration is performed.

  The membrane installation method in the MF membrane module 2105 can be appropriately selected from a suspension method and a flat placement method. In the suspension system, the membrane module is installed vertically in the aeration tank, and cross-flow filtration is performed on the surface of the membrane module by the upward air flow generated in the aeration tank. The air diffusion condition in the suspension system is preferably 50 m / hour to 100 m / hour in terms of linear velocity. In the flat placement method, air is diffused from the lower part of the installed flat membrane at a linear velocity of 50 m / hour to 100 m / hour, a crossflow flow is generated on the membrane surface, and crossflow filtration is performed.

  At the time of membrane filtration in the MF membrane module 2105, it is preferable to adopt a vacuum suction method. That is, it is preferable to reduce the pressure on the outlet side of the permeated water and increase the pressure difference that is the driving force for moving the water through the MF membrane. When the vacuum suction method is employed, it is preferable to operate the permeated water outlet pressure within a range of 15 kPa from the initial differential pressure. The filtration temperature is preferably 10 ° C to 50 ° C, more preferably 15 ° C to 40 ° C. The processing capacity (operating speed) is preferably 0.05 to 2.0, more preferably 0.1 to 1.0, and still more preferably 0.4 to 0 in terms of daily average flux (unit: m / day). It is preferable to operate at .6.

(Chemical tank)
The wastewater treatment system 2100 includes a first chemical liquid tank (not shown) for storing a hypochlorite aqueous solution for cleaning the MF membrane module 2105; and a second chemical liquid tank for storing an acid aqueous solution for cleaning the MF membrane module 2105. (Not shown); and a control unit (not shown) for controlling the supply of the chemical solution from the first chemical solution tank and the second chemical solution tank to the MF membrane module 2105. These first chemical liquid tank, second chemical liquid tank, and control unit have been described above with reference to FIGS. 2 and 5 in relation to the wastewater treatment method according to the first aspect of the first invention of the present application. It has the same configuration as the above.
In the MF membrane module 2105, prevention of clogging (fouling) due to deposition on the membrane surface is important. Although the deposition rate on the film surface can be reduced by crossflow or aerated air, clogging is unavoidable in the long term. As deposition on the film surface proceeds, the transmembrane pressure difference increases. If the transmembrane pressure exceeds a certain value, membrane cleaning with a chemical solution is required. As a chemical | medical solution which can be used for a film | membrane washing | cleaning, what was illustrated in the said description regarding the waste water treatment method of 1st invention of this application is mentioned. Membrane cleaning is performed in the same manner as steps (e) and (f) described above with respect to the wastewater treatment method of the first invention of the present application.

(RO membrane filtration device 2106)
The permeated water a separated by the MF membrane module 2105 passes through an intermediate tank (not shown), and is supplied with a reverse osmosis membrane filtration device 2106 (hereinafter referred to as “RO membrane” as a reverse osmosis membrane and “RO membrane” as a reverse osmosis membrane filtration device). It is also referred to as a “filtering device.”) And is subjected to removal of metal ions and residual organic substances by membrane separation treatment with an RO membrane. RO membrane materials used for RO membrane separation treatment include polyethylene, polyamides including aromatic polyamides and cross-linked aromatic polyamides, aliphatic amine condensation polymers, heterocyclic polymers, polyvinyl alcohol, and cellulose acetate polymer materials And can be appropriately selected from these. It is also possible to employ a mixture of two or more materials. In the first invention of the present application, aromatic polyamides and polyamides including cross-linked aromatic polyamides are particularly recommended because of their high separation performance. Examples of the membrane form of the RO membrane include an asymmetric membrane and a composite membrane, and can be appropriately selected from these. Two or more types of RO membranes can be used in combination. Further, a low fouling film with improved performance for preventing adhesion to the film surface can also be preferably used. Moreover, examples of the form of the membrane module used for the RO membrane separation treatment include a hollow fiber membrane type, a spiral membrane type, a tubular membrane type, a flat membrane type, and a pleated type, and one or two selected from these types More than one type of membrane module can be used. Among these, a spiral membrane type module is preferable from the viewpoint that the module has a large membrane area and is advantageous for downsizing the apparatus. Specific examples of these include the “Low-Pressure Spiral RO Membrane Element” series (Nitto Denko Corporation), the “Film Tech (registered trademark)” series (The Dow Chemical Company), “Romenbra (registered trademark)” ( Toray Industries, Inc.). In addition, it is desirable to install a prefilter at the entrance of the RO membrane module to protect the membrane.

  The permeability (permeated water weight / charged water weight × 100%) in the membrane separation process in the RO membrane filtration device 2106 is desirably 50% to 90%. More preferably, it is 60% to 80%. If the permeability is excessive, impurities in the permeated water increase, which may adversely affect the quality of the recovered water. The RO membrane separation process is performed under pressure. The required pressure in the RO membrane separation treatment is determined by the ion concentration and permeability in the permeated water that is passed through the RO membrane, but it is usually 0.5 MPaG to 5.5 MPaG, preferably 1.1 MPaG to 3.1 MPaG as a gauge pressure. Operated within range. The treatment temperature is preferably 10 ° C to 50 ° C, more preferably 15 ° C to 40 ° C. In determining the treatment temperature, it is necessary to pay attention to the heat resistance of the film material. Moreover, the linear velocity of the permeated water a in the cross flow is preferably 60 m / min to 240 m / min.

  When a drug is used in the RO membrane regeneration treatment, it is preferable to perform the membrane cleaning with the drug about once every two months to maintain the performance. Examples of agents usable as the RO membrane regeneration treatment include bisulfite, hypochlorite, citric acid, oxalic acid, peracetic acid and the like. In the first invention of the present application, among these, bisulfite, Hypochlorite, citric acid and the like are preferred. Moreover, since the pH of the permeated water a flowing into the RO membrane filtration device 2106 is high, it is preferable to perform an acidification treatment before contacting the RO membrane in order to prevent precipitation of salts. The preferred pH is usually 5.0 to 8.0, more preferably 6.0 to 7.5.

As described above, wastewater discharged from the terephthalic acid production process contains suspended solids (SS), heavy metals such as cobalt and manganese used in the oxidation reaction, alkali metals, COD, nitrogen-containing compounds, and the like. . The wastewater treated in the wastewater treatment process of the method for producing terephthalic acid according to the first invention of the present application, when flowing into the MF membrane module 2105, the concentration of insoluble substances in water is set to an SS value of 100 mg / L or less or turbidity 100NTU in the (Turbidity) below, the concentration of water-soluble organic substances in the and BOD ₅ below 100 mg / L in the _{COD Cr} 10 mg / L or less, the electrical conductivity as an indicator of the concentration of water-soluble inorganic substance is 500 to, It preferably has properties of 000 μS / cm and a pH of 5.0 to 9.5. The pH is usually 8 or more, indicating alkalinity, but in the first invention of the present application, treatment by membrane separation is possible if the pH is in the range of 5.0 to 9.5.

  When the waste water having the above-described properties is processed by the flow shown in FIG. 11 after the MF membrane module 2105, the RO membrane permeated water b having good water quality can be recovered from the RO membrane filtration device 2106. Although the water quality of the RO membrane permeated water b depends on the permeability, most of metal ions such as cobalt and manganese and residual organic substances are removed, and the water quality is high. The RO membrane permeated water b is stored in the reused water tank 2107 and supplied from the reused water tank 2107 to the terephthalic acid production process as industrial water (cooling water) d, or transferred to an adsorbent treatment device 2108 described later for further adsorption. It is supplied to the terephthalic acid production process as adsorbed purified water e through the agent treatment. The ratio of distributing the RO membrane permeate water b to the supply of industrial water (cooling water) d and the production of the adsorption purified water e can be selected as appropriate.

  In the prior art, it has been difficult to use the water after treating the waste water from the terephthalic acid production process as industrial water. According to 1st invention of this application, it becomes possible to reuse the water after waste water treatment in a terephthalic-acid manufacturing process. For example, in the terephthalic acid production process, it can be reused as industrial water including makeup water to the recooling tower. In particular, by performing a membrane separation process by combining a plurality of filtration membrane devices (for example, the MF membrane module 2105 and the RO membrane filtration device 2106 in the present embodiment), it becomes easier to achieve the effect.

  On the other hand, the RO membrane concentrated water c discharged from the RO membrane filtration device 2106 contains various impurities in a concentrated manner, but if the properties of the wastewater to be treated are within the above range, further treatment is performed. The water quality has been improved to such an extent that it can be released into public waters. Concentrated water may be discharged into public water areas after further ozone treatment as necessary. In addition, the method of monitoring light transmittance can be mentioned as a method of managing discharge | release water quality.

(Adsorbent processing device 2108)
When the RO membrane permeate b is used as process water, the degree of purification (purity) is further improved by performing adsorbent treatment using an adsorbent selected from various adsorbents in the adsorbent treatment apparatus 2108. Is possible. Thus, by improving the purity (water quality) of water, it is possible to expand the application range of recovered and reclaimed water. The adsorbed purified water e recovered from the adsorbent treatment device 2108 is supplied to the terephthalic acid production process and is more preferably used as process water. Examples of the use of the adsorbed purified water e as process water include use as part of a solvent used in the hydrogenation reaction in the hydrogenation treatment step (iii) and terephthalic acid in the second solid-liquid separation step (v). The use etc. which are used as a part of washing water in the solid-liquid separation process of this can be mentioned. The adsorbent processing waste water f discharged from the adsorbent processing apparatus 2108 is transferred to the first aeration tank 2101 and biologically processed again.

  Examples of the adsorbent usable in the adsorbent processing apparatus 2108 include activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, alkaline earth metal aluminate, and the like. Among these, at least one adsorbent can be selected and used. When two or more compounds selected from silica, alumina, silica alumina, synthetic zeolite, alkaline earth metal aluminate, etc. are used in combination, a mixture of these may be used as the adsorbent. A compound obtained by reacting the mixture may be used as an adsorbent.

  Examples of the adsorbent that can be used in the adsorbent treatment apparatus 2108 include wood-based activated carbon and coal-based activated carbon, and at least one of them can be selected and used. In addition, when combining 2 or more types of activated carbon, even if it mixes and uses these 2 or more types of activated carbon, you may divide and use it individually for a some packed tower, without mixing.

  Examples of the ion exchange resin that can be used in the adsorbent treatment apparatus 2108 include a cation exchange resin, an anion exchange resin, and an intermediate basic ion exchange resin. At least one selected from these can be used. be able to. When two or more types of ion exchange resins are used in combination, even if the two or more types of ion exchange resins are used in combination, each of them is divided into a plurality of packed towers without mixing. It may be used.

  The cation exchange resin that can be used in the adsorbent treatment apparatus 2108 includes a weak acid cation exchange resin having a weak acid group such as a carboxyl group as a functional group and a strong acid cation exchange resin having a strong acid group such as a sulfonic acid group. Any of them can be used in the first invention of the present application. However, in the first invention of the present application, it is preferable to use a strongly acidic cation exchange resin. Specific examples thereof include Diaion HP20 (registered trademark), Sepa beads SP825 (registered trademark), Sepa beads SP207 (registered trademark) (all manufactured by Mitsubishi Chemical Corporation), AMBERLITE XAD4 (registered trademark), and AMBERLITE XAD7 (registered trademark). Trademark) (all of which are manufactured by Rohm & Haas). As an anion exchange resin that can be used in the adsorbent treatment apparatus 2108, either a weakly basic anion exchange resin or a strongly basic anion exchange resin can be used. Specific examples of the strongly basic anion exchange resin include Diaion SA10A, SA12A, UBA120 (registered trademark) (all of which are manufactured by Mitsubishi Chemical Corporation). Specific examples of the weakly basic anion exchange resin include Diaion WA10, WA20, WA30 (registered trademark) (all of which are manufactured by Mitsubishi Chemical Corporation). Further, examples of the intermediate basic ion exchange resin that can be used in the adsorbent treatment apparatus 2108 include IONAC-365 (registered trademark) (Sybron Corp.) and the like.

  Examples of the synthetic zeolite that can be used in the adsorbent treatment apparatus 2108 include various synthetic zeolites such as sodalite, A type, X type, and Y type, and one or more of these are selected and used. be able to. Among these, A-type zeolite is preferable. Moreover, the preferable pore diameter of a synthetic zeolite is 0.2 nm-1.0 nm.

Specific examples of alkaline earth metal aluminates that can be used in the adsorbent processing apparatus 2108 include magnesium aluminate (Mg (AlO ₂ ) ₂ ), calcium aluminate (Ca (AlO ₂ ) ₂ ), and barium aluminate. (Ba (AlO ₂ ) ₂ ) and the like.

The adsorbent used in the adsorbent processing apparatus 2108 preferably has a large specific surface area. Specifically, the BET specific surface area is preferably 50 m ² / g or more, and more preferably 100 m ² / g or more. As the shape of the adsorbent used in the adsorbent processing apparatus 2108, a finely pulverized product (powdered product), a granulated product obtained by sieving, and the like are available, and any of them can be used. Industrially, in many cases, it is used by being filled in a fixed bed, fluidized bed, etc., and in consideration of pressure loss, a granular form is preferable. A mixture of a pulverized (powdered) adsorbent and a granular adsorbent may be used.

  In the adsorbent treatment apparatus 2108, various methods such as a method using a packed tower (packed tower method), a fluidized bed method, a moving tank method, and a stirring tank method are used as a method for bringing the adsorbent into contact with the RO membrane permeated water b. Can be used without particular limitation. However, from the viewpoint that it is easy to perform the adsorbent activation treatment described later in parallel with the adsorption treatment, the packed tower method is preferable.

  Note that, from the viewpoint of shortening the stop time of the adsorbent processing apparatus 2108 accompanying the saturation of the adsorption amount, it is preferable to activate the adsorbent in parallel with the adsorption. For example, when the adsorbent processing apparatus 2108 employs a packed tower system, a plurality of packed towers are installed, and other packed towers are activated while some of the packed towers are used for adsorption. A so-called merry-go-round driving method can be preferably employed.

  The activator used for activation of the adsorbent and the activation treatment conditions differ depending on the adsorbent used. In the case of an ion exchange resin, it varies depending on the type of ion exchange resin used, but generally in the case of a cation exchange resin, sulfuric acid, hydrochloric acid, hydrobromic acid, acetic acid and the like can be used. The temperature of the activation treatment is a maximum of 100 ° C., preferably around 80 ° C., from the viewpoint of heat resistance of the cation exchange resin. On the other hand, in the case of an anion exchange resin or an intermediate basic ion exchange resin, caustic soda, ammonia, sodium carbonate or the like can be used as an activator. The activation treatment temperature is a maximum of 80 ° C., and preferably 60 ° C.

  On the other hand, when using 1 type, or 2 or more types selected from silica, alumina, silica alumina, synthetic zeolite, and alkaline earth metal aluminate (when using a product obtained by mixing and reacting 2 or more types) In addition, as the activator, acetic acid, hydrobromic acid, steam and the like are preferable, and the activation treatment temperature is preferably 20 ° C to 60 ° C.

  From the viewpoint of the amount of wastewater discharged into public water areas, conventionally, a large amount of wastewater after biological treatment has been discharged to public water areas. However, according to the first invention of the present application, the wastewater can be recycled in the terephthalic acid production process through recovery and regeneration. Since the amount of water used is greatly increased, the amount of drainage can be reduced from one-half to about one-third compared to the conventional case. As a result, the amount of groundwater pumped up as a resource can be greatly reduced. Specifically, the wastewater discharged from the steps (i) to (vi) and used for biological treatment is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more. And can be used as cooling water and / or process water in the terephthalic acid production process.

(Other embodiments)
In the above description regarding the method for producing terephthalic acid according to the first invention of the present application, the method for producing terephthalic acid in a form in which the aerobic biological treatment is performed in two stages after the heavy metal concentration reducing step is exemplified. The manufacturing method of the terephthalic acid of invention is not limited to the said form. It is also possible to adopt a configuration in which the membrane treatment filtration system has only the first aeration tank and does not use the first precipitation tank and the second aeration tank (only one stage). Thus, when performing only in 1 step | paragraph, MF membrane module can be installed in a 1st aeration tank, as shown, for example in FIG. In this embodiment, instead of the above-described wastewater treatment process (vii), for example, a wastewater treatment process (vii ′) having the following steps (γ) and (c) to (f) can be employed.
(Γ) A heavy metal concentration reduction step in which the heavy metal compound in the waste water from steps (i) to (vi) is recovered to reduce the heavy metal concentration in the waste water to obtain treated waste water.
(C) The wastewater treated through the heavy metal concentration reduction step is solid-liquid separated into sludge and permeated water by the membrane module while biologically treating with the aerobic microorganisms in the activated sludge in the membrane separation activated sludge treatment device. Membrane separation step.
(D) Reverse osmosis membrane filtration in which the permeated water that has passed through the membrane module is filtered by the reverse osmosis membrane and separated into purified water that has permeated the reverse osmosis membrane and concentrated water that has not permeated. Step.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an aqueous acid solution.
Steps (γ) and (c) to (f) are performed in the same manner as steps (γ) and (c) to (f) described above in relation to the wastewater treatment method of the first invention of the present application.
However, from the viewpoint of improving the solid-liquid separation status of the activated sludge and reducing the inflow of suspended solids into the sedimentation tank, it is preferable to perform biological treatment in two stages as in the wastewater treatment system 2100 described above. In addition, when aerobic biological treatment is performed in one stage, the degree of contamination of the waste water that contacts the MF membrane is high, and the membrane cleaning frequency tends to increase because the treatment capability in the membrane separation treatment tends to decrease. . When constructing a new wastewater treatment system, a mode in which biological treatment is performed in only one stage after comparing the costs of increasing membrane cleaning costs by performing biological treatment in only one stage and reducing equipment costs, operating expenses, etc. It is only necessary to select which of the two-stage biological treatment is adopted.

In the above description of the method for producing terephthalic acid according to the first aspect of the present invention, an example of a method for producing terephthalic acid using the wastewater treatment system 2100 in which the MF membrane module 2105 is disposed in the second aeration tank 2103 is illustrated. However, the method for producing terephthalic acid according to the first invention of the present application is not limited to this form. The installation location of the MF membrane module is not limited to the inside of the aeration tank. One or more tanks (containers) having a small capacity are provided outside, and the membrane module is provided in the tank to dispose activated sludge. It is also possible to adopt a form of membrane separation while circulating externally. According to such a form, it becomes easy to reduce the maintenance work.
When biological treatment is performed in only one stage, the MF membrane module is placed at the outlet of the first sedimentation tank. When biological treatment is conducted in two stages, the MF membrane module is placed in the second precipitation tank. It is also possible to adopt a form in which it is disposed at the outlet. Specific examples of the MF membrane that can be used in such a form include “STELLAPORE LFB” (registered trademark), “STELLAPORE G” (registered trademark) (both manufactured by Mitsubishi Rayon Co., Ltd.), and “Trefill F” (registered trademark). ) (Manufactured by Toray Industries, Inc.), “Microza” (registered trademark) (manufactured by Asahi Kasei Chemical Co., Ltd.), and the like. However, from the viewpoints of eliminating the need for a sedimentation tank and enabling high-load processing of MLSS concentration in the aeration layer and reducing the size of the equipment, there is a need for an aeration tank (when biological treatment is performed in only one stage). In the case where the first aeration tank and biological treatment are performed in two stages, it is preferable to employ a membrane separation activated sludge treatment apparatus in which an MF membrane module is installed in the second aeration tank).

  In the above description of the method for producing terephthalic acid according to the first invention of the present application, the method for producing terephthalic acid in the form using the wastewater treatment system 2100 having the MF membrane module 2105 that performs membrane separation by the MF membrane is exemplified. The method for producing terephthalic acid according to the first invention is not limited to this form. Instead of the MF membrane, a membrane separation may be performed using an ultrafiltration membrane (UF membrane) described later.

  In the above description of the method for producing terephthalic acid according to the first invention of the present application, the method for producing terephthalic acid in the form of performing membrane separation using the RO membrane in the RO membrane filtration device 2106 has been exemplified. The manufacturing method of the terephthalic acid of invention is not limited to the said form. Instead of the RO membrane, it is also possible to use a membrane positioned between the UF membrane and the RO membrane, which is also referred to as a loose RO membrane or a nanofiltration membrane (NF membrane). Such an NF membrane has an operating pressure of about 0.2 MPa to 1.5 MPa, and can be operated at a lower pressure than when the RO membrane is used. Therefore, a smaller pump can be used and the energy required for the operation can be reduced. It is possible to reduce. Even when an NF membrane is employed instead of the RO membrane, the membrane structure, material, manufacturing method, and the like can be the same as those of the RO membrane.

(A-2. Second embodiment in production of terephthalic acid)
FIG. 12 shows the first representative method for producing terephthalic acid, in which the heavy metal compound recovery apparatus shown in FIG. It is a figure explaining embodiment which performs the membrane separation process by an ultrafiltration membrane (UF membrane), after biologically treating the treated waste water which reduced the heavy metal density | concentration in waste_water | drain. As shown in FIG. 12, in the wastewater treatment process in the present embodiment, the heavy metal compound recovery device 2109, the first aeration tank 2101, the first precipitation tank 2102, the second aeration tank 2103a, and the second Sedimentation tank 2104a, UF membrane unit 2110 connected to second sedimentation tank 2104a, RO membrane filtration device 2106 connected to UF membrane unit 2110, and reused water tank 2107 connected to RO membrane filtration device 2106 And a wastewater treatment system 2200 comprising an adsorbent treatment device 2108 connected to the reused water tank 2107 is used. Of these, the second aeration tank 2103a, the second settling tank 2104a, the wastewater treatment system 2200, and the UF membrane unit 2110 are the same as those in the first embodiment described above with reference to FIG. 11, the same reference numerals as those in FIG.

(Wastewater treatment system 2200)
The wastewater treatment system 2200 includes a heavy metal compound recovery device 2109 having the configuration shown in FIG. 1, a first aeration tank 2101, a first settling tank 2102 connected to the first aeration tank 2101, A second aeration tank 2103a connected to the settling tank 2102, a second settling tank 2104a connected to the second aeration tank 2103a, a UF membrane unit 2110 connected to the second settling tank 2104a, and a UF An RO membrane filtration device 2106 connected to the membrane unit 2110, a reuse water tank 2107 connected to the RO membrane filtration device 2106, and an adsorbent treatment device 2108 connected to the reuse water tank 2107 are provided. The wastewater treatment system 2200 is different from the wastewater treatment system 2100 in FIG. 11 in that the MF membrane module 2105 is not disposed in the second aeration tank 2103a, the second precipitation tank 2104a is used, and The UF membrane unit 2110 is disposed on the exit side of the second sedimentation tank 2104a. In the wastewater treatment system 2200, wastewater is transferred through the first aeration tank 2101, the first precipitation tank 2102, the second aeration tank 2103 a, and the second precipitation tank 2104 a in this order, and aerobic biological treatment is performed in two stages. It is given in. The operating conditions and the like of the first and second aeration tanks 2101 and 2103a are the same as the operating conditions of the aeration tank in the wastewater treatment system 2100. The permeated water h, which is sequentially transferred through the first aeration tank 2101 to the second precipitation tank 2104a and subjected to the aerobic biological treatment in two stages, is a UF membrane unit connected to the second precipitation tank 2104a. 2110 is transferred.

(UF membrane unit 2110)
In the UF membrane unit 2110, the permeated water h is subjected to membrane separation treatment by an ultrafiltration membrane (UF membrane) module. The UF membrane permeated water i that has passed through the UF membrane is transferred to an RO membrane filtration device 2106 connected to the UF membrane unit 2110 via an intermediate tank (not shown).

  The UF membrane included in the UF membrane module has a pore diameter of approximately 2 nm to 200 nm, which is larger than the RO membrane and smaller than the microfiltration membrane (MF membrane). As the material of the UF membrane, one or a combination of two or more selected from polysulfone, polypropylene, polyethylene, polyvinylidene chloride, polyvinylidene fluoride, aromatic polyamide membrane, polyvinyl alcohol, cellulose acetate, and polyacrylonitrile can be used. . Among these, polypropylene, polyvinylidene fluoride, aromatic polyamide and the like are preferable from the viewpoint of being hardly affected by impurities in the waste water.

  As the UF membrane module included in the UF membrane unit 2110, one or a combination of two or more selected from a hollow fiber membrane type, a spiral membrane type, a tubular membrane type, and a flat membrane type can be used. Of these, hollow fiber membranes and / or spiral membrane type UF membrane modules are preferred. Specific examples of UF membrane modules that can be preferably used in the UF membrane unit 2110 include the “Treafil (registered trademark)” series (manufactured by Toray Industries, Inc.), the “capillary type UF membrane module” series (manufactured by Nitto Denko Corporation), Rosa (registered trademark) ”series (manufactured by Asahi Kasei Chemical Co., Ltd.), UF membrane module“ Molsep (registered trademark) ”(manufactured by Daisen Membrane Systems Co., Ltd.), and the like.

The UF membrane separation process is basically a process for solid-liquid separation of water, a solid substance (solid matter) insoluble in water, and a part of the water-soluble substance. The filtration (membrane separation) operation in the UF membrane unit 2110 can be performed under normal pressure, under pressure, or under reduced pressure, but industrially, it is preferably performed under pressure or under reduced pressure. As the pressure difference between the two spaces sandwiching the UF membrane is larger, the processing capability is improved. Moreover, as temperature which performs a UF membrane separation process, 10 to 50 degreeC is preferable, More preferably, it is 15 to 40 degreeC. As processing capacity (operation speed), it is preferable to operate at a daily average flux (unit: L / m ² · d) of the UF membrane permeated water i at 10 to 200.

  Although it is not impossible to use dead-end filtration (all-pass) as the filtration method, the pore size of the UF membrane is small. Therefore, when dead-end filtration is used, the membrane is clogged by deposition on the membrane surface. Ring) is likely to occur in a short time. For this reason, normally, the permeated water h is supplied along a surface of the UF membrane in a certain direction, and water (concentrated water) in which fine particles and impurities are concentrated is continuously discharged or returned to the liquid feeding side. It is preferable to employ a cross flow method in which membrane separation (filtration) is performed. The linear velocity of the permeate h when performing cross flow filtration is preferably 60 m / min to 240 m / min.

  When the compressibility of the solid matter is strong, the filtration rate is lowered and the time required for filtration is prolonged. Therefore, it is preferable to add a precoat material (filter aid) to suppress the reduction of the filtration rate. Generally, diatomaceous earth, pearlite, activated carbon, etc. can be used as the filter aid, but it is preferable to use inexpensive diatomaceous earth, pearlite, etc. from the viewpoint of easy cost reduction.

(Chemical tank)
The waste water treatment system 2200 includes a first chemical tank (not shown) for storing a hypochlorite aqueous solution for cleaning the UF membrane module of the UF membrane unit 2110; and an acid aqueous solution for cleaning the UF membrane module of the UF membrane unit 2110. A second chemical tank (not shown) for storing the chemical; and a controller (not shown) for controlling the supply of the chemical from the first chemical tank and the second chemical tank to the UF membrane module of the UF membrane unit 2110 It has further. These first chemical liquid tank, second chemical liquid tank, and control unit have been described above with reference to FIGS. 2 and 5 in relation to the wastewater treatment method according to the first aspect of the first invention of the present application. It has the same configuration as the above.
In the UF membrane module of the UF membrane unit 2110 as well, as the MF membrane module 2105 and the like in the embodiment of FIG. 11 described above, the deposition pressure on the membrane surface increases the transmembrane pressure difference. When the transmembrane pressure exceeds a certain value, membrane cleaning with a chemical solution is required. As a chemical | medical solution which can be used for a film | membrane washing | cleaning, what was illustrated in the said description regarding the waste water treatment method of 1st invention of this application is mentioned. Membrane cleaning is performed in the same manner as steps (e) and (f) described above with respect to the wastewater treatment method of the first invention of the present application.

(RO membrane filtration device 2106)
The UF membrane permeated water i obtained by the membrane separation process in the UF membrane unit 2110 is transferred to the RO membrane filtration device 2106 through an intermediate tank (not shown) to remove trace amounts of metal ions and residual organic substances. Applied. The UF membrane cleaning waste water o generated by the membrane cleaning of the UF membrane is transferred to the second aeration tank 2103a and processed.

As the water quality after the aerobic biological treatment of the wastewater treated in the present embodiment, the concentration of the insoluble substance in water is 50 mg / L or less in terms of SS value or turbidity when flowing into the UF membrane unit 2110. 50 NTU or less, the concentration of water-soluble organic substance is 100 mg / L or less for COD _Cr , 10 mg / L or less for BOD ₅ and the conductivity is 500 to 10,000 μS / cm as an index of the concentration of water-soluble inorganic substance, and the pH is It preferably has a property of 5.0 to 9.5. The pH is usually 8 or more, indicating alkalinity, but in the first invention of the present application, treatment by membrane separation is possible if the pH is in the range of 5.0 to 9.5.

When the wastewater having the above-described properties is processed by the flow shown in FIG. 12 after the UF membrane unit 2110, the RO membrane permeated water k with good water quality can be recovered from the RO membrane filtration device 2106. Although the water quality of the RO membrane permeated water k depends on the transmittance, most of the metal ions and residual organic substances are removed, and the water quality is high. The RO membrane permeated water k is stored in the reuse water tank 2107 and supplied from the reuse water tank 2107 to the terephthalic acid production process as industrial water 1 (cooling water) or transferred to an adsorbent treatment device 2108 described later for further adsorption. It is supplied to the terephthalic acid production process as adsorbed purified water m through the agent treatment. In addition, the ratio which distributes RO membrane permeate water k to supply of industrial water (cooling water) 1 and manufacture of adsorption purified water m can be selected as appropriate.
In particular, by performing a membrane separation process by combining a plurality of filtration membrane devices (for example, the UF membrane unit 2110 and the RO membrane filtration device 2106 in this embodiment), it becomes easier to achieve the above-described effects.

  On the other hand, the RO membrane concentrated water j discharged from the RO membrane filtration device 2106 contains various impurities in a concentrated manner. If the properties of the wastewater to be treated are within the above-described range, further treatment is performed. Water quality has been improved to such an extent that it can be discharged into public waters without applying water. The release of the RO membrane concentrated water j is the same as the RO membrane concentrated water c described above for the embodiment shown in FIG.

(Adsorbent processing device 2108)
When the RO membrane permeate k is used as process water, the degree of purification (purity) is further improved by applying an adsorbent treatment using an adsorbent selected from various adsorbents in the adsorbent treatment apparatus 2108. As a result, it is possible to expand the application range of the recovered and reclaimed water, as in the RO membrane permeated water b described above in relation to the first embodiment (FIG. 11). . The adsorbed purified water m recovered from the adsorbent treatment apparatus 2108 can be more preferably used as process water, similar to the adsorbed purified water e described above in relation to the first embodiment (FIG. 11). The details of the adsorbent and processing in the adsorbent processing apparatus 2108 have already been described. The adsorbent processing waste water n discharged from the adsorbent processing apparatus 2108 is transferred to the first aeration tank 2101 and biologically processed again.

  From the viewpoint of the amount of wastewater discharged into public water areas, a large amount of wastewater after biological treatment has been discharged into public water areas. Also in the present embodiment (FIG. 12), the amount of water reused in the terephthalic acid production process is greatly increased by the recovery and regeneration of water as in the first embodiment (FIG. 11). Compared to the conventional case, it can be reduced to about one-half to one-third. As a result, the amount of groundwater pumped up as a resource can be greatly reduced. Specifically, preferably 80% or more, more preferably 70% or more of wastewater discharged from the above steps (i) to (vi) of the terephthalic acid production process and used for biological treatment that has been conventionally performed. More preferably, 60% or more is recovered as membrane permeate and can be used as cooling water and / or process water in the terephthalic acid production process.

(B. Second representative method for producing terephthalic acid)
FIG. 13 is a diagram illustrating a process flow and a substance flow in a second representative method for producing terephthalic acid. The second representative method for producing terephthalic acid has a terephthalic acid production process having the following steps (viii) to (xii) and a waste water treatment process (xiii).
(Viii) Step of oxidizing p-xylene in hydrous acetic acid to obtain a crude terephthalic acid slurry (hereinafter also referred to as “oxidation reaction step (viii)”).
(Ix) A step of obtaining a terephthalic acid slurry by subjecting the crude terephthalic acid slurry to an additional oxidation reaction under high temperature conditions without supplying p-xylene (hereinafter also referred to as “additional oxidation step (ix)”) .)
(X) A step of solid-liquid separation of the terephthalic acid slurry to obtain a terephthalic acid cake (hereinafter also referred to as “solid-liquid separation step (x)”).
(Xi) A step of drying the terephthalic acid cake to obtain terephthalic acid (hereinafter also referred to as “drying step (xi)”).
(Xii) A step of recovering and regenerating valuable materials such as a catalyst and a solvent from the mother liquor after solid-liquid separation (hereinafter also referred to as “mother liquor recovery and regenerating step (xii)”).
(Xiii) The whole or a part of the waste water discharged from the steps (viii) to (xii) is subjected to a heavy metal concentration reduction treatment, followed by an aerobic biological treatment, a reverse osmosis membrane treatment, and an adsorbent treatment. The wastewater treatment process in which the permeate is recycled into the manufacturing process and the rest is discharged into the public water area (hereinafter also referred to as “wastewater treatment process (xiii)”).

(Oxidation reaction step (viii))
In the oxidation reaction step (viii), the oxidation reaction apparatus 2511 oxidizes p-xylene using hydrous acetic acid as a solvent and a molecular oxygen-containing gas in the presence of a catalyst. Examples of the catalyst include compounds of transition metals such as cobalt and manganese and / or hydrogen halides such as hydrobromic acid. Through the oxidation reaction step (viii), a crude terephthalic acid slurry 251 ′ is obtained. The reaction temperature is usually 180 ° C to 230 ° C, preferably 190 ° C to 210 ° C. The reaction pressure needs to be equal to or higher than the pressure at which the mixture can maintain the liquid phase at least at the reaction temperature. Specifically, the reaction pressure is preferably 0.3 MPa to 10 MPa (absolute pressure), more preferably 1 to 3 MPa (absolute pressure). .

  From the oxidation reaction step (viii), acetic acid as a solvent, water produced as a by-product in the reaction, other impurities, unreacted raw materials accompanying the molecular oxygen-containing gas introduced into the oxidation reaction device 2511 for the oxidation reaction A high-temperature high-pressure gas containing etc. is discharged. The high-temperature high-pressure gas is passed through an absorption tower (not shown) and the like. In the process, valuables, energy, etc. are recovered from the high-temperature high-pressure gas and reused, and then the remaining gas is burned. After the exhaust gas after the combustion treatment is cleaned by contact with alkaline water or the like, the gas is released into the atmosphere, and the remaining oxidized exhaust gas cleaning water 255 ′ is transferred to the waste water treatment system 2518.

(Additional oxidation process (ix))
The additional oxidation step (ix) is a step in which the crude terephthalic acid slurry 251 ′ obtained by the oxidation reaction is transferred to the additional oxidation reaction device 2512 and supplied with a molecular oxygen-containing gas to be further oxidized at a high temperature. . A terephthalic acid slurry 252 ′ is obtained by the additional oxidation step (ix). The reaction temperature is usually 235 ° C. to 290 ° C., preferably 240 ° C. to 280 ° C., and the pressure is usually preferably 3 MPa to 10 MPa (absolute pressure). A part of the terephthalic acid particles in the crude terephthalic acid slurry 251 ′ are dissolved, and the oxidized intermediates, unreacted raw materials, etc. in the particles are oxidized, and the impurity concentration is reduced to produce a purification effect. The high-temperature and high-pressure exhaust gas is treated in the same manner as the high-temperature and high-pressure gas generated from the oxidation reaction step (viii), and the remaining supplemental oxidation exhaust gas cleaning water 256 ′ is treated with wastewater together with the oxidation exhaust gas cleaning water 255 ′ of the oxidation reaction step (viii). Transported to system 2518.

(Solid-liquid separation step (x) and mother liquor recovery and regeneration step (xii))
The solid-liquid separation step (x) is a step of obtaining a terephthalic acid cake 253 ′ by solid-liquid separation of the terephthalic acid slurry 252 ′ in the solid-liquid separation device 2513. Examples of the method for solid-liquid separation include a method in which the terephthalic acid slurry 252 ′ is directly applied to a solid-liquid separator. Further, since the terephthalic acid slurry 252 'is in a pressurized state, dissolved terephthalic acid is deposited when the pressure is lowered. For this reason, the terephthalic acid slurry 252 ′ may be sent to a crystallization tank (not shown) and subjected to pressure reduction cooling to precipitate dissolved terephthalic acid, and then applied to a solid-liquid separator. Note that “relief cooling” refers to the expansion of the solvent component by introducing the target liquid into a crystallization tank set to a pressure condition lower than the pressure of the target liquid and releasing the pressure in the crystallization tank. It means cooling by vaporization.

  From the solid-liquid separation step (x), solid-liquid separated mother liquor and cleaning liquid (hereinafter also referred to as “mother liquor”) are generated. More than 50% of the mother liquor is returned to the oxidation reaction step (viii) and reused. The ratio of reusing the mother liquor or the like is preferably 70% or more, but it is necessary to partially purge the mother liquor in order to prevent quality degradation due to impurity accumulation in the system. Therefore, the ratio of reusing the mother liquor is 95% or less, preferably 90% or less. The oxidation reaction mother liquor (purged) 257 'that is not reused is sent to the solvent recovery device 2515 and is supplied to the mother liquor recovery and regeneration step (xii).

  In the mother liquor recovery and regeneration step (xii), the oxidation reaction mother liquor (purging portion) 257 'is evaporated and concentrated by a solvent recovery device 2515, and divided into an evaporation solvent 258' and a mother liquor concentrated slurry 259 'containing valuable components. The mother liquor concentrated slurry 259 'is sent to the catalyst recovery / regeneration device 2517, where the catalyst is recovered / regenerated. After the recovered and regenerated catalyst is subjected to solid-liquid separation, the regenerated catalyst recovery / separation mother liquor 261 ′ is sent to a wastewater treatment system 2518 together with cleaning wastewater generated from a deodorization tower (not shown). On the other hand, the evaporated solvent 258 ′ is sent to an acetic acid recovery device 2516, passed through a dehydrating tower (not shown), concentrated and recovered, and then recovered with a distillation tower (methyl acetate recovery tower) (not shown). Is done. A part of the remaining methyl acetate recovery tower bottom liquid 260 ′ is sent to the wastewater treatment system 2518.

  Note that vent gases generated in steps other than the oxidation reaction step (viii) and the additional oxidation step (ix) are collectively cleaned in a cleaning tower (not shown) to be oxidized exhaust gas cleaning water 255 ′ and additional oxidation exhaust gas cleaning water 256 ′. Are sent to the wastewater treatment system 2518.

(Drying process (xi))
The drying step (xi) is a step of drying the terephthalic acid cake 253 ′ with the drying device 2514 to obtain terephthalic acid 254 ′. The exhaust gas generated from the drying device 2514 is cleaned in a cleaning tower (not shown), and vent gas cleaning water 262 ′ generated by the cleaning is sent to a wastewater treatment system 2518.

(Wastewater treatment process (xiii))
Step (viii) ~ (xii) suspended solids in the waste water entering the waste water treatment system 2518 from (SS), heavy metals, alkali metal compounds results in an increase of _{COD Cr,} nitrogen-containing compounds resulting in an increase of the total nitrogen content Has been. The concentration of insoluble substances in the inflow wastewater is 100 mg / L or less in terms of SS value and / or 100 NTU or less in terms of turbidity, and the concentration of water-soluble organic substances is 10000 mg / L or less in terms of COD _Cr . However, the effluent 263 ′ flowing out from the conventional wastewater treatment system 2518 can be reused as it is in the terephthalic acid production process from the viewpoint of water quality, and has to be discharged in large quantities in public water areas.

The wastewater treatment process (xiii) includes, for example, the following steps (γ) and (a) to (g).
(Γ) A heavy metal concentration reduction step in which the heavy metal compound in the waste water from steps (i) to (vi) is recovered to reduce the heavy metal concentration in the waste water to obtain treated waste water.
(A) A step of biologically treating the treated wastewater that has undergone the heavy metal concentration reduction step with an aerobic microorganism in the activated sludge in an aeration tank (first-stage biological treatment).
(B) A precipitation step in which the aeration tank mixed water that has undergone biological treatment in the aeration tank is subjected to solid-liquid separation in the precipitation tank.
(C) In the membrane separation activated sludge treatment apparatus, the supernatant liquid from the sedimentation tank is biologically treated with aerobic microorganisms in the activated sludge, and / or after biological treatment, the membrane module converts the supernatant into sludge and permeate. A membrane separation step for solid-liquid separation.
(D ′) A step of filtering permeated water that has passed through the membrane module with a nanofiltration membrane with a nanofiltration membrane filtration device (a nanofiltration membrane treatment step) as necessary.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an aqueous acid solution.
(G) A step of further purifying the permeated water that has passed through the membrane module with the nanofiltration reverse osmosis membrane filtration device with an adsorbent, if necessary.

  Steps (γ), (a) to (c), and (e) to (f) are described above in relation to the first and second embodiments of the method for producing terephthalic acid of the first invention of the present application. The steps (γ), (a) to (c), and (e) to (f) are performed. Step (d ′) relates to the first and second embodiments of the method for producing terephthalic acid according to the first invention of the present application, except that a nanofiltration membrane is used as a membrane module instead of a reverse osmosis membrane. This is performed in the same manner as step (d) described above.

(B-1. Third Embodiment in Production of Terephthalic Acid)
FIG. 14 is a diagram for explaining an embodiment in which a second representative method for producing terephthalic acid is employed as the terephthalic acid production process in the method for producing terephthalic acid according to the first invention of the present application. Hereinafter, this embodiment will be described with reference to FIG.

  In the embodiment shown in FIG. 14, instead of the conventional wastewater treatment method in which only the aerobic biological treatment is performed, the membrane separation activity in which the MF membrane flat membrane is immersed in the aeration tank after reducing the heavy metal concentration in the wastewater. Biological treatment and MF membrane separation treatment are performed using a sludge treatment device, and the permeated water obtained by the MF membrane separation treatment is introduced into the nanofiltration membrane (NF membrane) separation device. Embodiment. Furthermore, since the water used as process water is supplied, the degree of purification (purity) can be improved by an adsorbent treatment described later, if necessary.

  In the embodiment shown in FIG. 14, in recovering and regenerating the wastewater from the terephthalic acid production process, the heavy metal compound recovery device 2109, the first aeration tank 21010, the first precipitation tank 21020, and the second aeration A tank 21030, an MF membrane module 21050 disposed in the second aeration tank 21030, and a nanofiltration membrane filtration device 21060 connected to the outlet side of the MF membrane module 21050 (hereinafter, the nanofiltration membrane is referred to as "NF membrane") The nanofiltration membrane filtration device is also referred to as “NF membrane filtration device”.), A reused water tank 21070 connected to the outlet side of the NF membrane filtration device 21060, and an adsorbent treatment device 21080 connected to the reused water tank 21070. A wastewater treatment system 21000 comprising:

(Wastewater treatment system 21000)
The wastewater treatment system 21000 includes a heavy metal compound recovery device 2109 having a configuration similar to that shown in FIG. 1, a first aeration tank 21010, and a first sedimentation tank 21020 connected to the first aeration tank 21010. The second aeration tank 21030 connected to the first precipitation tank 21020, the MF membrane module 21050 disposed in the second aeration tank 21030, and the NF membrane connected to the outlet side of the MF membrane module 21050 It includes a filtration device 21060, a reuse water tank 21070 connected to the outlet side of the NF membrane filtration device 21060, and an adsorbent treatment device 21080 connected to the reuse water tank 21070. The second settling tank 21040 indicated by a broken line in FIG. 14 is not used because it is not used. The wastewater that has flowed into the wastewater treatment system 21000 is subjected to aerobic biological treatment in two stages while being transferred through the first aeration tank 21010, the first precipitation tank 21020, and the second aeration tank 21030 in this order.
The wastewater treatment system 21000 includes a membrane separation activated sludge treatment apparatus. That is, the MF membrane module 21050 is disposed so as to be immersed in the second aeration tank 21030, and the wastewater that has undergone the second-stage aerobic biological treatment in the second aeration tank 21030 is the MF membrane module 21050. In the membrane separation treatment. Water that has permeated through the MF membrane included in the MF membrane module 21050 is taken out as permeated water r. The permeated water r is transferred to the NF membrane filtration device 21060 connected to the outlet side of the MF membrane module 21050.

(Chemical tank)
The wastewater treatment system 21000 includes a first chemical liquid tank (not shown) for storing a hypochlorite aqueous solution for cleaning the MF membrane module 21050; and a second chemical liquid tank for storing an acid aqueous solution for cleaning the MF membrane module 21050. (Not shown); and a controller (not shown) for controlling the supply of the chemical solution from the first chemical solution tank and the second chemical solution tank to the MF membrane module 21050. These first chemical liquid tank, second chemical liquid tank, and control unit have been described above with reference to FIGS. 2 and 5 in relation to the wastewater treatment method according to the first aspect of the first invention of the present application. It has the same configuration as the above.
In the MF membrane module 21050, prevention of fouling due to deposition on the membrane surface is important. Although the deposition rate on the film surface can be reduced by crossflow or aerated air, clogging is unavoidable in the long term. As deposition on the film surface proceeds, the transmembrane pressure difference increases. If the transmembrane pressure exceeds a certain value, membrane cleaning with a chemical solution is required. As a chemical | medical solution which can be used for a film | membrane washing | cleaning, what was illustrated in the said description regarding the waste water treatment method of 1st invention of this application is mentioned. Membrane cleaning is performed in the same manner as steps (e) and (f) described above with respect to the wastewater treatment method of the first invention of the present application.

(NF membrane filtration device 21060)
The NF membrane filtration device 21060 is a membrane filtration device including a nanofiltration membrane (NF membrane). The permeated water r flowing into the NF membrane filtration device 21060 is subjected to membrane separation processing by the NF membrane, and generates NF membrane permeated water s and NF membrane concentrated water t. The NF membrane is a liquid filtration membrane that blocks particles and polymers smaller than 2 nm, and has a pore diameter smaller than that of the MF membrane or UF membrane and larger than that of a general RO membrane. The NF membrane is also referred to as a loose RO membrane, and has a feature that it can be operated at a lower pressure than a general RO membrane.

  Examples of NF membrane materials that can be used in the NF membrane filtration apparatus 21060 include polyethylene, aromatic polyamide, and polyamides including crosslinked polyamides, aliphatic amine condensation polymers, heterocyclic polymers, polyvinyl alcohol, and cellulose acetate. Examples of the polymer may include one or a combination or mixture of two or more selected from these. In this embodiment, the separation performance of an NF membrane composed of a polyamide-based material including an aromatic polyamide or a crosslinked polyamide is particularly high, and can be preferably used.

  Many of the polyamide-based composite NF membranes have negative surface charges, and therefore, two types of NF membranes of the cation charge type and the anion charge type are controlled by controlling the surface charge. By combining the difference between the pore and the charge, it has the feature that the separation target of waste water can be expanded. In the NF membrane filtration apparatus 21060, it is possible to employ either a cationic charge type NF membrane or an anion charge type NF membrane.

  Examples of the NF membrane module that can be used in the NF membrane filtration device 21060 include a hollow fiber membrane type, a spiral membrane type, a tubular membrane type, a flat membrane type, and a pleated type. Two or more combinations can be selected and used. Among these, the spiral membrane type module is preferable from the viewpoint that the membrane area of the module per unit volume is large, which is advantageous for making the apparatus compact. Specific examples of these include “NTR-7250 (registered trademark)”, “NTR-7410 (registered trademark)” (all manufactured by Nitto Denko Corporation), “Film Tech (registered trademark)” NF series (The Dow Chemical Company) and the like. In addition, it is desirable to install a pre-filter on the entry side of the NF membrane module to protect the membrane.

  The operation pressure in the NF membrane filtration apparatus 21060 using an NF membrane is 0.2 MPa to 1.5 MPa, and can be operated at a lower pressure than a general RO membrane. Moreover, the water permeation | transmission flow velocity (flux) is large and it is possible to implement | achieve high processing efficiency.

The effluent from terephthalic acid production process to be processed in the present embodiment, suspended solids (SS), Co, heavy metals such as Mn, alkali metal, compound results in an increase of COD _Cr, nitrogen-containing compounds results in an increase in total nitrogen Etc. are contained. The water quality of the wastewater treated in the present embodiment after the aerobic biological treatment is such that when it flows into the NF membrane filtration device 21060, the concentration of insoluble substances in water is 100 mg / L or less in terms of SS value and / or turbidity. (Turbidity) of 100 NTU or less, the concentration of water-soluble organic substance is 100 mg / L or less for COD _Cr , 10 mg / L or less for BOD ₅ and the electric conductivity is 500 to 10,000 μS / cm as an indicator of the concentration of water-soluble inorganic substance. It is preferable that the pH is 5.0 to 9.5. The pH is usually 8 or more, indicating alkalinity, but in the first invention of the present application, treatment by membrane separation is possible if the pH is in the range of 5.0 to 9.5.

The water quality of the NF membrane permeated water s collected from the NF membrane filtration device 21060 depends on the permeability, but most of the metal ions and residual organic substances are removed, and the water quality is high. The NF membrane permeated water s is stored in the reuse water tank 21070 and is supplied from the reuse water tank 21070 to the terephthalic acid production process as industrial water (cooling water) u, or transferred to the adsorbent treatment device 21080 for further adsorbent treatment. Then, it is supplied to the terephthalic acid production process as adsorbed purified water v. Thus, it has been impossible in the past to regenerate wastewater from the terephthalic acid production process and supply it again to the terephthalic acid production process. In addition, the ratio which distributes NF membrane permeated water s to supply of industrial water (cooling water) u and manufacture of adsorption purified water v can be selected suitably.
In particular, by performing a membrane separation process by combining a plurality of filtration membrane devices (for example, the MF membrane module 21050 and the NF membrane filtration device 21060 in this embodiment), it becomes easier to achieve the effect.

  On the other hand, the NF membrane concentrated water t discharged from the NF membrane filtration device 21060 contains various impurities in a concentrated manner, but if the properties of the wastewater to be treated are within the above-described range, further treatment is performed. Water quality has been improved to such an extent that it can be discharged into public waters without applying water. The release of the NF membrane concentrated water t into the public water area is the same as the RO membrane concentrated water c described above in relation to the first embodiment (FIG. 11).

(Adsorbent processing device 21080)
When the NF membrane permeated water s is used as process water, the degree of purification (purity) is further improved by performing an adsorbent treatment using an adsorbent selected from various adsorbents in the adsorbent treatment apparatus 21080. As a result, it is possible to expand the application range of the collected and reclaimed water, as in the case of the RO membrane permeated water b described above in relation to the first embodiment (FIG. 11). It is. Adsorbents that can be used in the adsorbent processing apparatus 21080 can include the same adsorbents as those mentioned for the adsorbent processing apparatus 2108, and the operation of the adsorbent processing apparatus 21080 is the same as that of the adsorbent processing apparatus 2108. It can be carried out. The adsorbent processing waste water w generated from the adsorbent processing apparatus 21080 is returned to the first aeration tank 21010 and biologically processed again.

  From the viewpoint of the amount of wastewater discharged into public water areas, a large amount of wastewater after biological treatment has been discharged to public water areas in the past. In this embodiment (FIG. 14) as well, the first embodiment (FIG. 11) and the first embodiment Similar to the embodiment of FIG. 2 (FIG. 12), the amount of water reused in the terephthalic acid production process is greatly increased by recovery and regeneration. It can be reduced to about 1. As a result, the amount of groundwater pumped up as a resource can be greatly reduced. Specifically, it is preferable that 80% or more, more preferably 70% or more, more preferably 60% or more of the wastewater discharged from the steps (viii) to (xii) and used for biological treatment. And can be used as cooling water and / or process water in the terephthalic acid production process.

(Other embodiments)
In the above description of the third embodiment of the method for producing terephthalic acid according to the first invention of the present application, a heavy metal compound recovery device having the structure shown in FIG. Although an example in which an aerobic biological treatment is performed in two stages using one aeration tank 21010, a first precipitation tank 21020, and a second aeration tank 21030, the method for producing terephthalic acid according to the first invention of the present application Is not limited to this form. The aerobic biological treatment may be performed in only one stage. In such a case, the MF membrane module 21050 may be disposed in the first aeration tank 21010, and the first precipitation tank 21020 and Since the second aeration tank 21030 is not used, it becomes unnecessary. Even in such a case, the aspect of the MF membrane module 21050 can be the same.
In this embodiment, instead of the above-described wastewater treatment process (xiii), for example, a wastewater treatment process (xiii ′) having the following steps (γ) and (c) to (g) can be employed.
(Γ) A heavy metal concentration reduction step in which the heavy metal compound in the waste water from steps (i) to (vi) is recovered to reduce the heavy metal concentration in the waste water to obtain treated waste water.
(C) The wastewater treated through the heavy metal concentration reduction step is solid-liquid separated into sludge and permeated water by the membrane module while biologically treating with the aerobic microorganisms in the activated sludge in the membrane separation activated sludge treatment device. Membrane separation step.
(D ′) A step of filtering permeated water that has passed through the membrane module with a nanofiltration membrane with a nanofiltration membrane filtration device (a nanofiltration membrane treatment step) as necessary.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an aqueous acid solution.
(G) A step of further purifying the permeated water that has passed through the membrane module with the nanofiltration reverse osmosis membrane filtration device with an adsorbent, if necessary.
Steps (γ) and (c) are performed in the same manner as steps (γ) and (c) described above in relation to the wastewater treatment method of the first invention of the present application, and a series of subsequent steps (d ') To (g) are performed in the same manner as steps (d') to (g) described above.

  In the above description relating to the method for producing terephthalic acid of the first invention of the present application, an adsorbent treatment device 2108 is disposed downstream of the RO membrane filtration device 2106 and the adsorbent treatment is performed after the RO membrane separation treatment, and An example of the method for producing terephthalic acid in which the adsorbent treatment device 21080 is disposed downstream of the NF membrane filtration device 21060 and the adsorbent treatment is performed after the NF membrane separation treatment is described. The manufacturing method is not limited to these forms.

  Moreover, in the said description regarding the manufacturing method of the terephthalic acid of 1st invention of this application, installation using a heavy metal compound collection | recovery apparatus is essential, the form used in combination with a membrane separation activated sludge processing apparatus and RO membrane filtration apparatus, UF membrane unit And a method for producing terephthalic acid using a combination of an RO membrane filtration device and a membrane separation activated sludge treatment device and an NF membrane filtration device. The method for producing the acid is not limited to these forms. As a combination of the filtration membrane device, for example, in addition to the heavy metal compound recovery device, the membrane separation activated sludge treatment device and the UF membrane unit are used in combination, and the RO membrane filtration device and the NF membrane filtration device may not be used. It is possible. However, it is generally preferable to use an RO membrane filtration device. Even in such a case, the adsorbent treatment can be further performed in combination with the membrane separation treatment. The selection and combination of the filtration membrane device and the adsorbent treatment device can be appropriately determined in consideration of the relationship between the water quality desired for the recovered and reclaimed water and the reuse application.

  According to the method for producing terephthalic acid of the first invention of the present application, since the biological treatment and the membrane separation treatment are combined after reducing the heavy metal concentration in the waste water, the frequency of complicated membrane module regeneration treatment is greatly reduced. And stable operation becomes possible. Furthermore, a large amount of wastewater generated when producing terephthalic acid can be recycled as industrial water (cooling water) and / or process water, and the amount of new water intake from the water source and the amount of wastewater to the public water area can be reduced. It can be set as the manufacturing method of terephthalic acid which improved economic efficiency and environmental compatibility.

  In the method for producing terephthalic acid according to the first invention of the present application, after reducing the heavy metal concentration, terephthalic acid production is carried out by performing aerobic biological treatment or a combination of aerobic biological treatment and anaerobic biological treatment. Since it becomes easy to decompose organic substances contained in the process waste water, it becomes easy to regenerate a large amount of waste water generated when producing terephthalic acid.

  In the method for producing terephthalic acid according to the first invention of the present application, terephthalic acid is produced by performing the membrane separation treatment with at least one membrane module selected from the group consisting of an MF membrane module and a UF membrane module. It becomes easier to regenerate a large amount of drainage generated during the process.

  The method for producing terephthalic acid according to the first invention of the present application further comprises a step of subjecting at least a part of the permeated water to an adsorbent treatment to obtain adsorbed purified water, and a step of recovering the adsorbed purified water. It is possible not only to regenerate a large amount of wastewater generated during the production of acid to water having water quality that can be used as industrial water (cooling water), but also to water having water quality that can be used as process water. It is preferable.

  In the method for producing terephthalic acid according to the first aspect of the present invention, the method further comprises a step of subjecting at least a part of the permeated water to an adsorbent treatment to obtain adsorbed purified water and a step of recovering the adsorbed purified water. When producing terephthalic acid, preferably by performing the treatment with at least one adsorbent selected from the group consisting of activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, and alkaline earth metal aluminate. It is easy to regenerate a large amount of waste water generated in step 1 to water having water quality that can be used as process water.

The method for producing terephthalic acid according to the first invention of the present application described above includes a washing step for washing the membrane module, and the washing step comprises washing the membrane module with a hypochlorite aqueous solution. A chlorate washing step and an acid washing step for washing the membrane module with an aqueous acid solution in this order, and (b) an interval from the end of the hypochlorite washing step to the start of the next acid washing step. However, it is within 100 hours and / or (b) the acid cleaning step is started when the transmembrane pressure difference of the membrane module becomes 3 kPa to 50 kPa higher than the transmembrane pressure difference before the start of operation. Therefore, the transmembrane pressure difference of the membrane module 35 can be kept low while the wastewater containing COD _Cr and containing heavy metals is biologically treated and subjected to membrane separation treatment. As described above, by reducing the heavy metal concentration prior to the biological treatment, the frequency of these membrane regeneration treatments can be greatly reduced.

About 2nd invention of this application [The waste water treatment method of 2nd invention of this application]
The waste water treatment method of the second invention of the present application is a waste water treatment method for treating waste water having COD _Cr of 3000 mg / L to 10000 mg / L and a heavy metal concentration of 0.1 mass ppm to 200 mass ppm. Examples of the wastewater treatment method of the second invention of the present application include the following first and second aspects.
(Α) First aspect of the waste water treatment method of the second invention of the present application:
A wastewater treatment method comprising a membrane separation step for solid-liquid separation by a membrane module into sludge and permeate while performing biological treatment of wastewater and / or after biological treatment of wastewater, and a washing step for washing the membrane module .
(Β) Second aspect of the wastewater treatment method of the second invention of the present application:
Membrane for solid-liquid separation into sludge and permeated water by membrane module after performing biological treatment of the second stage after performing the biological treatment of the first stage of wastewater and / or after biological treatment of wastewater in two stages A wastewater treatment method comprising a separation step and a washing step for washing the membrane module.
Hereinafter, the first aspect and the second aspect of the wastewater treatment method of the second invention of the present application will be described with reference to specific embodiments.

<Α. Embodiment of Waste Water Treatment System in First Aspect>
FIG. 2: is a schematic block diagram which shows one Embodiment of the waste water treatment system in the 1st aspect of the waste water treatment method of 2nd invention of this application. The waste water treatment system biologically treats the waste water from the raw water tank (not shown) by the aerobic microorganisms in the activated sludge, and at the same time, the membrane separation activated sludge treatment apparatus 30 for solid-liquid separation into sludge and permeate by the membrane module 35 A first chemical tank 90 for storing a hypochlorite aqueous solution for cleaning the membrane module 35; a second chemical tank 92 for storing an acid aqueous solution for cleaning the membrane module 35; and a first chemical tank 90 and A control unit (not shown) for controlling the supply of the chemical solution from the second chemical solution tank 92 to the membrane module 35; a drainage flow path 50 for supplying wastewater from the raw water tank to the membrane separation activated sludge treatment device 30; A permeate flow path 55 for discharging permeated water from the separation activated sludge treatment apparatus 30; an excess sludge flow path 56 for discharging excess sludge from the membrane separation activated sludge treatment apparatus 30; and a first chemical tank 90 Beauty the chemical from the second chemical solution tank 92 and a liquid medicine flow channel 59 for supplying the membrane module 35.

(Membrane separation activated sludge treatment equipment)
The membrane separation activated sludge treatment apparatus 30 includes a tank main body 31 (first aeration tank); a diffuser pipe 32 disposed near the bottom in the tank main body 31 (first aeration tank); A blower 33 to be supplied; an air introduction pipe 34 connecting the diffuser pipe 32 and the blower 33; a membrane module 35 disposed in the tank body 31 (first aeration tank) and above the diffuser pipe 32; A suction pump 36 that is provided in the middle of the passage 55, performs solid-liquid separation of sludge and permeate by reducing the pressure in the membrane module 35, and sends the permeate to the reverse osmosis membrane filtration device 40; A backwash pump 37 is provided in the middle of the passage 59 and sends out a chemical solution for backwashing to the membrane module 35.

Examples of the membrane module 35 include a known membrane module including a known filtration membrane.
As the type of the filtration membrane, a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) is preferable. Examples of the shape of the filtration membrane include a hollow fiber membrane, a flat membrane, a tubular membrane, and a bag-like membrane. Of these, hollow fiber membranes are preferred because they can be highly integrated when compared on a volume basis.

  Examples of the material of the filter membrane include organic materials (cellulose, polyolefin, polysulfone, polyvinyl alcohol, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, etc.), metals (stainless steel, etc.), inorganic materials (ceramics, etc.). It is done. The material of the filtration membrane is appropriately selected according to the properties of the waste water.

  What is necessary is just to select the hole diameter of a filtration membrane suitably according to the objective of a process. In the membrane separation activated sludge method, the pore size of the filtration membrane is preferably 0.001 to 3 μm. When the pore diameter is less than 0.001 μm, the resistance of the film increases. If the pore diameter exceeds 3 μm, the activated sludge cannot be completely separated, and the water quality of the permeate may be deteriorated. The pore size of the filtration membrane is more preferably 0.04 to 1.0 μm, which is the range of the microfiltration membrane.

In the membrane separation activated sludge treatment apparatus 30, a membrane unit in which the air diffuser 32 and the membrane module 35 are integrated as shown in FIGS. 3 and 4 may be used.
The membrane unit includes a diffuser generating device 60; a membrane module 35 provided on the upper portion of the diffuser generating device 60;

  The air diffuser 60 includes a rectangular casing 61 that is open at the top and bottom; a column 62 that extends downward from the four corners of the casing 61; an outer wall of the casing 61; A connection pipe 63 for supplying air supplied through the casing 61; an air supply header 64 provided along the inner wall of the casing 61 and communicating with the connection pipe 63; an inner wall orthogonal to the air supply header 64 And a plurality of air diffusers 32 connected to 64a.

  The air diffuser 32 discharges air supplied from the blower 33 upward, and is composed of a single tube with a hole or a membrane type one end connected to an air supply header 64 and the other end closed. Yes.

  The membrane module 35 includes a frame 65 extending upward from four corners of the air diffuser 60; a plurality of hollow fiber membrane elements 70 supported by the frame 65 and arranged in parallel; and covers four side surfaces And a casing 66.

  The hollow fiber membrane element 70 has a passage (not shown) formed along the longitudinal direction inside, and has a permeated water outlet 71a formed at one end of the passage and communicating with the passage of the vertical rod 72. A pair of vertical rods 72, 73 that extend upward from both ends of the lower frame 71 and have a passage (not shown) formed along the longitudinal direction therein; and upper ends of the vertical rods 72, 73 An upper frame 74 having a passage (not shown) formed along the longitudinal direction and having a permeate outlet 74a formed at one end of the passage; and connected to the permeate outlet 74a. An L-shaped joint 75 that bends upward; a hollow fiber membrane sheet 76 composed of a number of hollow fiber membranes 76a arranged along the vertical rods 72 and 73 in a direction perpendicular to the water surface; and an upper frame 74 And the end of the hollow fiber membrane 76a is opened in the passage inside the lower frame 71. At state, the upper and lower ends of the hollow fiber membrane 76a, respectively on frame 74, secured in a liquid tight manner to the lower frame 71 comprises a potting material 77 which supports.

  The number of hollow fiber membranes 76 a constituting the hollow fiber membrane sheet 76 is preferably 500 to 3000 per one hollow fiber membrane sheet 76. If the number of the hollow fiber membranes 76a is less than 500, the membrane area of the hollow fiber membranes may be reduced, and the water permeation amount per unit volume may be reduced. When the number of the hollow fiber membranes 76a exceeds 3000, the installation area of the membrane unit becomes too large.

  It is preferable that the hollow fiber membranes 76a have a slack and are arranged in a substantially vertical direction with respect to the water surface. By arranging the hollow fiber membranes 76a in a substantially vertical direction with respect to the water surface, it becomes difficult for solids to accumulate on the surface of the hollow fiber membranes 76a, and the air from the diffuser tube 32 causes the surface of the hollow fiber membranes 76a to be deposited. It is cleaned efficiently. Further, since the hollow fiber membrane 76a has slackness, the air from the air diffuser 32 causes the hollow fiber membrane 76a to swing, and the surface of the hollow fiber membrane 76a is efficiently cleaned.

  The water collection header 80 is provided along the arrangement direction of the hollow fiber membrane elements 70. The water collecting header 80 includes a plurality of water collecting ports 80a formed along the longitudinal direction; one end is connected to the water collecting port 80a, and the other end is connected to the L-shaped joint 75 of the hollow fiber membrane element 70. A bent L-shaped joint 81; and a water suction port 80b provided on the upper surface of the water collecting header 80 and connected to the permeate flow passage 55.

(Reverse osmosis membrane filtration device)
As shown in FIG. 5, the wastewater treatment system includes a reverse osmosis membrane filtration device 40 that permeates the membrane module 35 and filters the permeate discharged from the permeate flow passage 55 through a reverse osmosis membrane; A purified water channel 57 that discharges purified water that has permeated through the reverse osmosis membrane; and a concentrated water channel 58 that discharges concentrated water that has not permeated through the reverse osmosis membrane filtration device 40.

The reverse osmosis membrane filtration device 40 includes one or more reverse osmosis membrane modules.
The reverse osmosis membrane module is not particularly limited as long as the purified water that has permeated through the reverse osmosis membrane and the concentrated water that does not permeate the reverse osmosis membrane can be separated.

Examples of the reverse osmosis membrane module include a so-called spiral reverse osmosis membrane module in which a cylindrical reverse osmosis membrane element in which a reverse osmosis membrane is wound around a water collection pipe is housed in a cylindrical casing.
Examples of the material of the reverse osmosis membrane include polyamide, polysulfone, cellulose acetate, and the like, and polyamides including aromatic polyamides or crosslinked aromatic polyamides are preferable.

  FIG. 6 is a perspective view and a partial cross-sectional view showing an example of a spiral type reverse osmosis membrane module. The spiral type reverse osmosis membrane module 41 folds the reverse osmosis membrane 42 in a state where a water collection pipe 43 having a plurality of water collection holes 43 a is placed at the center of the reverse osmosis membrane 42. 3 sides of the reverse osmosis membrane 42 overlapped with the liquid-permeable support fiber 44 sandwiched between them, and a double reverse osmosis membrane 42 with a mesh spacer 45 overlapped, and a double pipe centering on the water collecting pipe 43 A reverse osmosis membrane 42 is wound into a columnar shape to form a reverse osmosis membrane element 46, and the reverse osmosis membrane element 46 is accommodated in a cylindrical casing 47.

(Control part)
The control unit controls the interval from the end of the supply of the hypochlorite aqueous solution to the membrane module 35 to the start of the supply of the next aqueous acid solution to the membrane module 35 within 48 hours, and / or the membrane module When the transmembrane pressure difference 35 is 3 kPa to 30 kPa higher than the transmembrane pressure pressure after the start of operation, the supply of the acid aqueous solution to the membrane module 35 is started.

The control unit is schematically configured to include a processing unit and an interface unit, and controls operation start / stop of the backwash pump 37, opening / closing of a valve (not shown) of the chemical liquid channel 59, and the like.
The interface unit electrically connects the backwash pump 37, a valve, a pressure gauge (not shown), and the like to the processing unit.
The processing unit controls the start / stop of the operation of the backwash pump 37, the opening / closing of the valve, and the like based on the operation schedule input to the processing unit and the pressure signal from the pressure gauge.

The processing unit may be realized by dedicated hardware, and the processing unit is configured by a memory and a central processing unit (CPU), and a program for realizing the function of the processing unit is stored in the memory. The function may be realized by loading and executing.
In addition, an input device, a display device, and the like may be connected to the control unit as peripheral devices. The input device refers to an input device such as a display touch panel, a switch panel, or a keyboard, and the display device refers to a CRT or a liquid crystal display device.

<Α. Embodiment of Wastewater Treatment Method in First Aspect>
The wastewater treatment method using the wastewater treatment system of FIG. 2 has the following steps (c), (e), and (f), and the wastewater treatment method using the wastewater treatment system of FIG. c) to (f).
(C) Membrane separation activated solid sludge treatment apparatus 30 performs solid-liquid separation into sludge and permeate by membrane module 35 while biologically treating waste water from raw water tank (not shown) with aerobic microorganisms in activated sludge. Membrane separation step.
(D) A step of filtering the permeated water that has permeated through the membrane module 35 with a reverse osmosis membrane in the reverse osmosis membrane filtration device 40 as necessary.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an acid aqueous solution.

(Drainage)
The wastewater treated in the first aspect of the wastewater treatment method of the second invention of the present application has a COD _Cr of 3000 to 10000 mg / L and a heavy metal concentration of 0.1 to 200 ppm by mass.
When COD _Cr exceeds 10,000 mg / L, the burden of biological treatment in the membrane separation activated sludge treatment apparatus 30 becomes too large. When COD _Cr is low, there is no need to treat waste water according to the first aspect of the waste water treatment method of the second invention of the present application, so COD _Cr is 3000 mg / L or more. COD _Cr is preferably 4000 to 8000 mg / L.

When the heavy metal concentration exceeds 200 mass ppm, biological treatment of waste water may be hindered, and further, the clogging of inorganic substances into the membrane module may occur frequently. The heavy metal concentration is preferably 1 ppm by mass to 100 ppm by mass.
Examples of heavy metals include manganese and cobalt. The wastewater discharged in the terephthalic acid production process usually contains manganese and / or cobalt used as a catalyst.

The wastewater treated in the first aspect of the wastewater treatment method of the second invention of the present application preferably has a COD _Cr / BOD ₅ of 3 to 10.
If COD _Cr / BOD ₅ is within the above range, decomposition by biological treatment is easy, and the target treated water quality can be obtained even when the volume load is a normal load. When COD _Cr / BOD ₅ exceeds 10, it is difficult to decompose by biological treatment, so that it is not easy to treat by the first aspect of the wastewater treatment method of the second invention of the present application.

Examples of waste water that satisfies the above-mentioned ranges of COD _Cr and heavy metal concentrations include waste water discharged in the terephthalic acid production process. Is preferred. The terephthalic acid production process will be described in detail in the method for producing terephthalic acid described later.

(Step (c))
The wastewater stored in the raw water tank (not shown) is supplied to the membrane separation activated sludge treatment apparatus 30 via the drainage flow path 50.
About the waste_water | drain supplied to the membrane separation activated sludge processing apparatus 30, a coarse suspended solid, earth and sand, etc. may be removed beforehand, pH may be adjusted, or it may dilute.

  In the membrane separation activated sludge treatment apparatus 30, the blower 33 is operated to introduce air from the air diffuser 32, and oxygen is given to the aerobic microorganisms in the activated sludge to perform biological treatment of waste water. By this biological treatment, aromatic compounds (aromatic carboxylic acids, etc.) in waste water are decomposed into aliphatic carboxylic acids (acetic acid, etc.), and aliphatic carboxylic acids (acetic acid, etc.) are further decomposed into carbon dioxide, etc. .

Examples of the aromatic carboxylic acid include terephthalic acid, p-toluic acid, benzoic acid, 4-carboxybenzaldehyde, and salts thereof (alkali metal salt, alkaline earth metal salt, ammonium salt).
Aerobic microorganisms are bacteria etc. which can decompose | disassemble an aromatic compound etc. using oxygen. Examples of such bacteria include Alkaligenes and Rhodococcus.

  3000-15000 mg / L is preferable and, as for MLSS (mixed water floating substance) in the membrane separation activated sludge processing apparatus 30, 5000-10000 mg / L is more preferable. When MLSS is less than 3000 mg / L, there is a possibility that aerobic microorganisms are insufficient and biological treatment of waste water cannot be performed sufficiently. When MLSS exceeds 15000 mg / L, fluidity is deteriorated as the viscosity of the sludge increases, and the cleaning efficiency of the membrane surface is lowered and may be clogged.

The membrane separation activated sludge treatment apparatus 30 is preferably operated so as to maintain the COD _Cr volumetric load at 1 to 3 [COD _Cr -kg / m ³ / day]. If the COD _Cr volumetric load is less than 1 [COD _Cr -kg / m ³ / day], the processing time may be long. When the COD _Cr volumetric load exceeds 3 [COD _Cr -kg / m ³ / day], there is a possibility that biological treatment of waste water cannot be sufficiently performed. The COD _Cr volumetric load can be adjusted to the above range by adjusting the hydraulic residence time (HRT) depending on the COD _Cr of the waste water treated per hour.

  Further, in the membrane separation activated sludge treatment apparatus 30, the mixed water is solid-liquid separated into sludge and permeated water by operating the suction pump 36 to reduce the pressure in the membrane module 35. At this time, by introducing air into the membrane module 35 from the diffuser tube 32, solid-liquid separation can be efficiently performed while cleaning the surface of the hollow fiber membrane 76a.

  The separated excess sludge is discharged through the excess sludge channel 56. Further, since the surplus sludge contains aerobic microorganisms, a part of the surplus sludge may be returned to the membrane separation activated sludge treatment apparatus 30 and used again for biological treatment of waste water.

The smaller the COD _Cr of the permeated water, the more preferable. Specifically, 80 mg / L or less is preferable. If the COD _{Cr of the} permeated water is 80 mg / L or less, the influence on the environment is sufficiently small.

(Step (d))
The permeated water from the membrane separation activated sludge treatment apparatus 30 may be discharged to the outside as it is. However, the permeated water has high electrical conductivity because it contains metal ions derived from the catalyst used when producing terephthalic acid. Therefore, it is preferable that the permeated water from the membrane separation activated sludge treatment device 30 is transferred to the reverse osmosis membrane filtration device 40 through the permeate flow channel 55 and the ions in the permeated water are removed by the reverse osmosis membrane 42.

  In the spiral type reverse osmosis membrane module 41 of the reverse osmosis membrane filtration device 40, the permeated water is introduced into the permeated water inlet 41 a formed on one end face of the columnar reverse osmosis membrane element 46 and formed by the mesh spacer 45. Flow through the flow path. During this time, a part of the permeated water permeates through the reverse osmosis membrane 42 to become purified water, is led to the water collecting pipe 43 through the flow path formed by the liquid-permeable support fibers 44, and reaches the end of the water collecting pipe 43. It is discharged from the purified water outlet 41b. On the other hand, the permeated water that has not passed through the reverse osmosis membrane 42 becomes concentrated water and is discharged from the concentrated water outlet 41 c formed on the other end face of the reverse osmosis membrane element 46.

The purified water that has passed through the reverse osmosis membrane filtration device 40 is transferred to a terephthalic acid production facility or the like through the purified water passage 57 and reused as cooling water or the like.
The concentrated water that has not permeated through the reverse osmosis membrane filtration device 40 is discharged to the outside through the concentrated water channel 58. The concentrated water may be discharged after sterilizing with chlorine or the like.

(Steps (e) and (f))
When organic substances, inorganic substances, etc. present in the wastewater are adsorbed on the pores of the filtration membrane or deposited on the surface of the filtration membrane, the transmembrane differential pressure of the membrane module 35 increases. When the transmembrane pressure difference of the membrane module 35 increases to some extent, the efficiency of solid-liquid separation decreases. Therefore, step (e) or step (f) is performed in the middle of step (c), and a chemical solution is supplied from the first chemical solution tank 90 or the second chemical solution tank 92 to the membrane module 35 to clean the membrane module 35. .

By performing step (e), organic substances adsorbed on the pores of the filtration membrane or deposited on the surface of the filtration membrane can be decomposed by hypochlorite and removed from the filtration membrane.
Examples of hypochlorite include sodium hypochlorite and calcium hypochlorite.

The concentration of hypochlorite in the hypochlorite aqueous solution is preferably 300 to 10000 mg / L, more preferably 1000 to 5000 mg / L, from the viewpoint of the cleaning effect.
Passing liquid amount, in terms of protection of the cleaning effect and filtration membrane is preferably 0.5～10L / filtration membrane 1 m ^2, and more preferably 1.0～4.0L / filtration membrane 1 m ^2.
The passage time is preferably from 10 to 180 minutes, more preferably from 15 to 120 minutes, from the viewpoint of cleaning effect and time efficiency.
From the viewpoint of the cleaning effect, it is preferable that the membrane module 35 is allowed to stand for a while after the liquid is passed. The standing time is preferably 120 minutes or less, and more preferably 30 to 120 minutes. The end of step (e) (hypochlorite washing step) is the end of the standing time.

  Moreover, it is preferable that surfactant is contained in hypochlorite aqueous solution. Hypochlorous acid is a highly hydrophilic compound, and as it is, it is difficult to permeate oils or low-degradability coloring components such as hydrocarbon compounds and aromatic compounds with low hydrophilicity attached to the membrane, and the water permeability of the membrane It is difficult to remove deposits that lower the temperature. By allowing the surfactant to coexist in the hypochlorite aqueous solution, the permeability of the cleaning agent to the membrane used for filtration is improved, and the membrane deposits are decomposed and emulsified / dispersed. Therefore, it is possible to easily remove the dirt of the filtration membrane used for the treatment of waste water containing oils and coloring components such as hydrocarbon compounds and aromatic compounds.

  The surfactant is more preferably a low-foaming nonionic surfactant from the viewpoints of better cleaning performance of the filter membrane, cost merit, and handleability. Moreover, you may mix 1 or more types of anionic surfactant, a cationic surfactant, and an amphoteric surfactant.

  Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polystyryl phenyl ether, polyoxyethylene-polyoxypropylene glycol, polyoxyethylene-polyoxypropylene alkyl ether, polyvalent Alcohol fatty acid partial ester, polyoxyethylene polyhydric alcohol fatty acid partial ester, polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, polyoxyethylenated castor oil, fatty acid diethanolamide, polyoxyethylene alkylamine, triethanolamine fatty acid partial ester, Examples include trialkylamine oxide.

  Examples of the anionic surfactant include alkyl sulfonic acid, alkyl benzene sulfonic acid, alkyl carboxylic acid, alkyl naphthalene sulfonic acid, α-olefin sulfonic acid, dialkyl sulfosuccinic acid, α-sulfonated fatty acid, N-methyl-N-oleyl taurine, Petroleum sulfonic acid, alkyl sulfuric acid, sulfated oil and fat, polyoxyethylene alkyl ether sulfuric acid, polyoxyethylene styrenated phenyl ether sulfuric acid, alkyl phosphoric acid, polyoxyethylene alkyl ether phosphoric acid, polyoxyethylene alkyl phenyl ether phosphoric acid, naphthalene sulfone Examples include acid formaldehyde condensates and salts thereof.

  Cationic surfactants include primary to tertiary fatty amines, quaternary ammonium, tetraalkylammonium, trialkylbenzylammonium alkylpyridinium, 2-alkyl-1-alkyl-1-hydroxyethylimidazolinium, N, N -Dialkylmorpholinium, polyethylene polyamine fatty acid amide, urea condensate of polyethylene polyamine fatty acid amide, quaternary ammonium of urea condensate of polyethylene polyamine fatty acid amide, and salts thereof.

  Amphoteric surfactants include betaines (N, N-dimethyl-N-alkyl-N-carboxymethylammonium betaine, N, N, N-trialkyl-N-sulfoalkyleneammonium betaine, N, N-dialkyl-N N-bispolyoxyethylene ammonium sulfate betaine, 2-alkyl-1-carboxymethyl-1-hydroxyethylimidazolinium betaine, etc.), aminocarboxylic acids (N, N-dialkylaminoalkylene carboxylate, etc.), etc. Can be mentioned.

The concentration of the surfactant in the aqueous hypochlorite solution is preferably 0.05 to 3.0% by mass, and more preferably 0.3 to 1.5% by mass. If the surfactant concentration is not less than the lower limit, the filtration membrane can be sufficiently washed. However, even if the upper limit is exceeded, the effect of improving the cleaning performance reaches its peak, and the cost only increases.
Further, the ratio of the surfactant when the free chlorine concentration of chloric acid or a salt thereof is set to 1 is preferably 0.3 to 1.5 because higher detergency can be obtained.

By performing step (f), the inorganic substance adsorbed on the pores of the filtration membrane or deposited on the surface of the filtration membrane can be solubilized with an aqueous acid solution and removed from the filtration membrane.
Usable acid aqueous solutions include organic acid aqueous solutions and inorganic acids, and organic acid aqueous solutions are preferred because they have little influence on activated sludge.
Examples of the organic acid aqueous solution include a citric acid aqueous solution and an oxalic acid aqueous solution, and a citric acid aqueous solution is preferable.
Examples of inorganic acids include hydrochloric acid and sulfuric acid.

The concentration of the acid in the acid aqueous solution is preferably 0.5 to 5% by mass and more preferably 1 to 3% by mass from the viewpoint of the cleaning effect.
Passing liquid amount, in terms of protection of the cleaning effect and filtration membrane is preferably 0.5～10L / filtration membrane 1 m ^2, and more preferably 1～4L / filtration membrane 1 m ^2.
The passage time is preferably from 10 to 180 minutes, more preferably from 15 to 120 minutes, from the viewpoint of cleaning effect and time efficiency.
From the viewpoint of the cleaning effect, it is preferable that the membrane module 35 is allowed to stand for a while after the liquid is passed. The standing time is preferably 180 minutes or less, and more preferably 30 to 120 minutes. The end of step (f) (acid cleaning step) means the end of the standing time.

  In the first aspect of the wastewater treatment method of the second invention of the present application, as the cleaning step, step (e) is first performed, and then step (f) is performed within a specific time. By performing each step in this order, it is possible to remove the inorganic material generated by step (e) and closing the membrane module 35 by step (f).

In the first aspect of the wastewater treatment method of the second invention of the present application, step (f) is performed after step (e) so as to satisfy the following condition (1) and / or condition (2).
(1) The interval from the end of step (e) to the start of step (f) is within 48 hours.
(2) Step (f) is started when the transmembrane differential pressure of the membrane module 35 becomes 3 kPa to 30 kPa higher than the transmembrane differential pressure after the start of operation.

Condition (1):
If the interval from the end of step (e) to the start of the next step (f) is within 48 hours, washing is performed before the membrane module 35 is blocked by the inorganic material generated in step (e). Can do. The interval from the end of step (e) to the start of the next step (f) is preferably within 48 hours, more preferably within 24 hours.

Condition (2):
If the step (f) is started when the transmembrane pressure difference of the membrane module 35 is equal to or higher than the transmembrane pressure difference after starting operation + 3 kPa, the frequency of interruption of the membrane separation step can be reduced and the wastewater treatment efficiency is improved. To do. If step (f) is started when the transmembrane differential pressure of the membrane module 35 is not more than the transmembrane differential pressure after starting operation + 30 kPa, step (c) (membrane separation step) can be performed stably for a long period of time. .
The timing when the step (f) is started is preferably in the range of the transmembrane pressure difference of the membrane module 35 +10 kPa to 20 kPa.

  In the 1st form of the waste water treatment method of the 2nd invention of this application, it is preferred from a point with a big cleaning effect to perform Step (f) in multiple times between Step (e) and the following Step (e). .

(Function and effect)
In the first aspect of the wastewater treatment method of the second invention of the present application described above, since a solid-liquid separation process by the membrane module 35 is performed, a conventional sedimentation tank is not necessary. As a result, the facility (system) can be reduced in size compared to the prior art even when wastewater with high COD _Cr is treated.
In addition, by introducing the membrane separation activated sludge treatment apparatus 30, a treated water quality equivalent to or higher than that of the conventional one in which the biological treatment is in two stages can be obtained although the biological treatment is in only one stage.
In addition, the equipment (system) becomes compact, and the initial construction cost is reduced.
In addition, no settling tank is required, and maintenance is easy.
In addition, SS can be sufficiently removed even without a coagulation sedimentation tank conventionally required for the final stage.
Moreover, the permeated water from the membrane separation activated sludge treatment apparatus 30 can be directly passed through the reverse osmosis membrane.
In the conventional case, in order to pass the permeated water through the reverse osmosis membrane, sand filtration or the like is separately required.

In the first aspect of the wastewater treatment method of the second invention of the present application described above, the membrane module has a washing step for washing the membrane module, and the washing step is performed with a hypochlorite aqueous solution. A hypochlorite washing step for washing the membrane module and an acid washing step for washing the membrane module with an aqueous acid solution in this order, and from the end of the hypochlorite washing step to the start of the next acid washing step. The acid washing step is started when the interval is within 48 hours and / or when the transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than the transmembrane pressure difference after the start of operation. Therefore, the transmembrane pressure difference of the membrane module 35 can be kept low during the biological treatment of the wastewater containing COD _Cr and containing heavy metals and performing the membrane separation treatment.
A membrane separation step may be performed between the hypochlorite cleaning step and the acid cleaning step.

(Other embodiments)
In addition, the 1st aspect of the waste water treatment method of 2nd invention of this application is not limited to the waste water treatment system of the example of illustration, and the waste water treatment method using this.
For example, if the permeated water from the membrane separation activated sludge treatment apparatus 30 is not reused as cooling water or the like, the reverse osmosis membrane filtration apparatus 40 may be omitted.

  Further, as shown in the illustrated example, the membrane separation activated sludge treatment apparatus may be an integrated type in which biological treatment by aerobic microorganisms in activated sludge and solid-liquid separation treatment by a membrane module are performed in one tank. A separate tank type may be used in which biological treatment with aerobic microorganisms in sludge and solid-liquid separation treatment with a membrane module are performed in separate tanks.

FIG. 7: is a schematic block diagram which shows other embodiment of the waste water treatment system in the 1st aspect of the waste water treatment method of 2nd invention of this application which used the membrane separation activated sludge processing apparatus as the tank separate type.
The tank-separated membrane separation activated sludge treatment apparatus 30 includes an activated sludge tank (first aeration tank) 38; a membrane separation tank 39; an activated sludge tank (first aeration tank) 38 and a membrane separation tank 39. Two air diffusers 32 respectively disposed near the bottom; a blower 33 for supplying air to each air diffuser 32; an air introduction tube 34 for connecting each air diffuser 32 and the blower 33; A membrane module 35 disposed above the diffuser pipe 32; provided in the middle of the permeate flow channel 55, and by reducing the pressure inside the membrane module 35, the sludge and the permeate are separated from each other, and the permeate is separated. A suction pump 36 that is sent to the reverse osmosis membrane filtration device 40; a backwash pump 37 that is provided in the middle of the chemical liquid channel 59 and sends a chemical solution for backwashing to the membrane module 35; and an activated sludge tank (first aeration tank). Tank) Biologically treated mixed water in 38 A mixed water channel for transporting the vessel 39; comprising a membrane activated sludge tank a portion of the excess sludge from the separation tank 39 the return sludge flow path to return to the (first aeration tank) 38.

<Β. Embodiment of Wastewater Treatment System in Second Aspect>
FIG. 8: is a schematic block diagram which shows one Embodiment of the waste water treatment system which concerns on the 2nd aspect of the waste water treatment method of 2nd invention of this application. The waste water treatment system includes an aeration tank 10 for biologically treating waste water from a raw water tank (not shown) with aerobic microorganisms in activated sludge; aeration tank mixed water biologically treated in the aeration tank 10 A sedimentation tank 20 for solid-liquid separation; biological treatment of the supernatant from the sedimentation tank 20 by aerobic microorganisms in the activated sludge, and simultaneous membrane separation activated sludge treatment for solid-liquid separation into sludge and permeated water by the membrane module 35 A first chemical solution tank 90 for storing a hypochlorite aqueous solution for cleaning the membrane module 35; a second chemical solution tank 92 for storing an acid aqueous solution for cleaning the membrane module 35; A control unit (not shown) for controlling the supply of the chemical solution from the tank 90 and the second chemical solution tank 92 to the membrane module 35; a drainage flow path 50 for supplying wastewater from the raw water tank to the aeration tank 10; An aeration tank mixed water flow path 51 for transferring the aeration tank mixed water biologically treated in the tank 10 to the precipitation tank 20; A surplus sludge flow path 53 for discharging surplus sludge from the settling tank 20; a return sludge flow path 54 for returning a part of the surplus sludge from the settling tank 20 to the aeration tank 10; and a membrane separation activated sludge treatment apparatus 30 Permeate flow path 55 for discharging permeated water from the wastewater; surplus sludge flow path 56 for discharging surplus sludge from the membrane-separated activated sludge treatment device 30; chemical liquid from the first chemical liquid tank 90 and the second chemical liquid tank 92 And a chemical flow path 59 for supplying the membrane module 35 to

(Aeration tank)
The aeration tank 10 includes: a tank body 11; a diffuser pipe 12 disposed in the vicinity of the bottom of the tank body 11; a blower 13 for supplying air to the diffuser pipe 12; and an air introduction for connecting the diffuser pipe 12 and the blower 13 Tube 14.

(Settling tank)
The sedimentation tank 20 is not particularly limited as long as it can separate the aeration tank mixed water transferred from the aeration tank 10 into sludge and supernatant liquid by gravity sedimentation. The settling tank 20 may be a general settling tank.

(Membrane separation activated sludge treatment equipment)
The membrane separation activated sludge treatment apparatus 30 has the same configuration as the membrane separation activated sludge treatment apparatus 30 in the first aspect, and a description thereof is omitted.

(Reverse osmosis membrane filtration device)
As shown in FIG. 9, the waste water treatment system includes a reverse osmosis membrane filtration device 40 that permeates the membrane module 35 and filters the permeate discharged from the permeate flow channel 55 through a reverse osmosis membrane; A purified water channel 57 that discharges purified water that has permeated through the reverse osmosis membrane; and a concentrated water channel 58 that discharges concentrated water that has not permeated through the reverse osmosis membrane filtration device 40.

  The reverse osmosis membrane filtration device 40 has the same configuration as the reverse osmosis membrane filtration device 40 in the first embodiment, and a description thereof is omitted.

(Control part)
The control unit has the same configuration as the control unit in the first aspect, and a description thereof is omitted.

<Β. Embodiment of Wastewater Treatment Method in Second Aspect>
The wastewater treatment method using the wastewater treatment system of FIG. 8 has the following steps (a) to (c), (e), and (f), and the wastewater treatment method using the wastewater treatment system of FIG. The following steps (a) to (f) are included.
(A) In the aeration tank 10, a step of biologically treating the waste water from the raw water tank (not shown) with aerobic microorganisms in the activated sludge (first-stage biological treatment).
(B) A step of solid-liquid separation of the aeration tank mixed water biologically treated in the aeration tank 10 in the precipitation tank 20.
(C) In the membrane-separated activated sludge treatment apparatus 30, while the supernatant liquid from the sedimentation tank 20 is biologically treated by aerobic microorganisms in the activated sludge (second-stage biological treatment), the membrane module 35 permeates the sludge. A membrane separation step for solid-liquid separation with water.
(D) A step of filtering the permeated water that has permeated through the membrane module 35 with a reverse osmosis membrane in the reverse osmosis membrane filtration device 40 as necessary.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an acid aqueous solution.

(Drainage)
The wastewater treated in the second aspect of the wastewater treatment method of the second invention of the present application has a COD _Cr of 3000 to 10000 mg / L and a heavy metal concentration of 0.1 to 200 ppm by mass.
When COD _Cr exceeds 10,000 mg / L, the burden of biological treatment in the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30 becomes too large. When COD _Cr is low, there is no need to treat waste water according to the second aspect of the waste water treatment method of the second invention of the present application, so COD _Cr is 3000 mg / L or more. COD _Cr is preferably 4000 to 8000 mg / L.

When the heavy metal concentration exceeds 200 mass ppm, biological treatment of waste water may be hindered, and further, the clogging of inorganic substances into the membrane module may occur frequently. The heavy metal concentration is preferably 1 ppm by mass to 100 ppm by mass.
Examples of heavy metals include manganese and cobalt. The wastewater discharged in the terephthalic acid production process usually contains manganese and / or cobalt used as a catalyst.

The wastewater treated in the second aspect of the wastewater treatment method of the second invention of the present application preferably has a COD _Cr / BOD ₅ of 3 to 10.
If COD _Cr / BOD ₅ is within the above range, it can be easily decomposed by biological treatment, and can be decomposed only in one stage. The target treated water quality is obtained. If COD _Cr / BOD ₅ exceeds 10, it is difficult to decompose by biological treatment, so that it is not easy to treat by the second aspect of the wastewater treatment method of the second invention of the present application.

Examples of the wastewater that satisfies the above-mentioned ranges of COD _Cr and heavy metal concentrations include wastewater discharged in the terephthalic acid production process, and the wastewater treatment system and wastewater according to the second aspect of the wastewater treatment method of the second invention of the present application. The treatment method is suitable for the treatment of this waste water. The terephthalic acid production process will be described in detail in the method for producing terephthalic acid described later.

(Step (a))
Drainage discharged when producing aromatic carboxylic acid such as terephthalic acid and stored in the raw water tank (not shown) is supplied to the aeration tank 10 via the drainage channel 50.
About the waste_water | drain supplied to the aeration tank 10, a coarse suspended solid, earth and sand, etc. may be removed previously, pH may be adjusted, or it may dilute.

  In the aeration tank 10, the blower 13 is operated to introduce air from the air diffuser 12, and oxygen is given to aerobic microorganisms in the activated sludge to perform biological treatment of the waste water. By this biological treatment, aromatic compounds (such as aromatic carboxylic acids) in the wastewater are decomposed into aliphatic carboxylic acids (such as acetic acid).

Examples of the aromatic carboxylic acid include terephthalic acid, p-toluic acid, benzoic acid, 4-carboxybenzaldehyde, and salts thereof (alkali metal salt, alkaline earth metal salt, ammonium salt).
Aerobic microorganisms are bacteria etc. which can decompose | disassemble an aromatic compound etc. using oxygen. Examples of such bacteria include Alkaligenes and Rhodococcus.

  1000-10000 mg / L is preferable and, as for MLSS (mixed water floating substance) in the aeration tank 10, 2000-8000 mg / L is more preferable. When MLSS is less than 1000 mg / L, there is a possibility that aerobic microorganisms are insufficient and biological treatment of waste water cannot be performed sufficiently. When MLSS exceeds 10,000 mg / L, there is a risk that the sludge floats on the water surface and the sludge flows out.

The aeration tank 10 is preferably operated so as to keep the COD _Cr volumetric load at 1 to 3 [COD _Cr -kg / m ³ / day]. If the COD _Cr volumetric load is less than 1 [COD _Cr -kg / m ³ / day], the processing time may be long. When the COD _Cr volumetric load exceeds 3 [COD _Cr -kg / m ³ / day], there is a possibility that biological treatment of waste water cannot be sufficiently performed. The COD _Cr volumetric load can be adjusted to the above range by adjusting the hydraulic residence time (HRT) depending on the COD _Cr in the waste water being processed per hour.

(Step (b))
The aeration tank mixed water biologically treated in the aeration tank 10 is transferred to the precipitation tank 20 through the aeration tank mixed water flow path 51.
In the settling tank 20, the aeration tank mixed water is solid-liquid separated into sludge and supernatant liquid by gravity settling.

  The separated excess sludge is discharged through the excess sludge channel 53. Further, since the surplus sludge contains aerobic microorganisms, a part of the surplus sludge is returned to the aeration tank 10 via the return sludge flow path 54 and used again for biological treatment of waste water. In addition, since the kind of aerobic microorganisms in the aeration tank 10 is different from the kind of aerobic microorganisms in the membrane separation activated sludge treatment apparatus 30, excess sludge from the aeration tank 10 should not be returned to the membrane separation activated sludge treatment apparatus 30. Is preferred.

The COD _{Cr in the} supernatant is preferably 200 mg / L or more. If it is attempted to reduce the COD _Cr of the supernatant liquid to less than 200 mg / L, the burden of biological treatment in the aeration tank 10 becomes too large. In addition, there is a risk that the biological treatment becomes insufficient due to a shortage of organic matter that is used as an energy source by the aerobic microorganisms in the membrane separation activated sludge treatment apparatus 30.

After separating the sludge containing aerobic microorganisms in the sedimentation tank 20, the type of aerobic microorganisms in the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30 are transferred by transferring only the supernatant liquid to the membrane separation activated sludge treatment apparatus 30. The type of aerobic microorganisms in this is different. That is, since the kind of organic matter (aromatic compound or the like) in the aeration tank 10 is different from the kind of organic matter (aliphatic carboxylic acid or the like) in the membrane separation activated sludge treatment apparatus 30, the aeration tank 10 and the membrane separation activity naturally occur. In each of the sludge treatment apparatuses 30, different aerobic microorganisms that prefer different organic substances will grow.
Note that the precipitation tank 20 may be omitted, a membrane module may be installed in the aeration tank 10, and solid-liquid separation using a filtration membrane may be performed.

  If the aeration tank mixed water of the aeration tank 10 is transferred to the membrane separation activated sludge treatment apparatus 30 without passing through the settling tank 20, aerobic microorganisms different from the aeration tank 10 grow in the membrane separation activated sludge treatment apparatus 30. Therefore, the types of aerobic microorganisms in the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30 are almost the same. Therefore, in the membrane separation activated sludge treatment apparatus 30, different aerobic microorganisms that favor aliphatic carboxylic acids and the like are difficult to grow, and biological treatment such as aliphatic carboxylic acids in the membrane separation activated sludge treatment apparatus 30 is insufficient. Become.

(Step (c))
The supernatant liquid of the sedimentation tank 20 is transferred to the membrane separation activated sludge treatment apparatus 30 via the supernatant liquid flow path 52.
The supernatant liquid from the sedimentation tank 20 may be mixed with other liquids (such as other wastewater with high COD _Cr ) as long as the mixed COD _Cr and BOD ₅ do not exceed the above-described drainage range. Good.

In the membrane separation activated sludge treatment apparatus 30, the blower 33 is operated to introduce air from the air diffusion pipe 32, and oxygen is given to aerobic microorganisms in the activated sludge to perform biological treatment of the supernatant liquid. By this biological treatment, the aliphatic carboxylic acid (such as acetic acid) in the wastewater is decomposed into carbon dioxide.
Aerobic microorganisms are bacteria etc. which can decompose aliphatic carboxylic acid etc. using oxygen.

  3000-15000 mg / L is preferable and, as for MLSS (mixed water floating substance) in the membrane separation activated sludge processing apparatus 30, 5000-10000 mg / L is more preferable. When MLSS is less than 3000 mg / L, there is a possibility that aerobic microorganisms are insufficient and biological treatment of the supernatant liquid cannot be performed sufficiently. When MLSS exceeds 15000 mg / L, fluidity is deteriorated as the viscosity of the sludge increases, and the cleaning efficiency of the membrane surface is lowered and may be clogged.

The membrane separation activated sludge treatment apparatus 30 is preferably operated so as to keep the COD _Cr volumetric load at 0.1 to 0.5 [COD _Cr -kg / m ³ / day]. If the COD _Cr volumetric load is less than 0.1 [COD _Cr -kg / m ³ / day], the processing time may be long. If the COD _Cr volumetric load exceeds 0.5 [COD _Cr -kg / m ³ / day], there is a possibility that biological treatment of the supernatant liquid cannot be performed sufficiently. The COD _Cr volumetric load can be adjusted to the above range by adjusting the hydraulic residence time (HRT) depending on the COD _Cr of the supernatant liquid processed per hour.

  Further, in the membrane separation activated sludge treatment apparatus 30, the mixed water is solid-liquid separated into sludge and permeated water by operating the suction pump 36 to reduce the pressure in the membrane module 35. At this time, by introducing air into the membrane module 35 from the diffuser tube 32, solid-liquid separation can be efficiently performed while cleaning the surface of the hollow fiber membrane 76a.

  The separated excess sludge is discharged through the excess sludge channel 56. Further, since the excess sludge contains aerobic microorganisms, a part of the excess sludge may be returned to the membrane separation activated sludge treatment apparatus 30 and used again for biological treatment of the supernatant liquid. In addition, since the kind of aerobic microorganisms of the membrane separation activated sludge treatment apparatus 30 is different from the kind of aerobic microorganisms of the aeration tank 10, excess sludge from the membrane separation activated sludge treatment apparatus 30 should not be returned to the aeration tank 10. Is preferred.

The smaller the COD _Cr of the permeated water, the more preferable. Specifically, 80 mg / L or less is preferable. If the COD _{Cr of the} permeated water is 80 mg / L or less, the influence on the environment is sufficiently small.

(Step (d))
Step (d) is the same step as step (d) in the first embodiment, and a description thereof is omitted.

(Steps (e) and (f))
Steps (e) and (f) are the same steps as step (d) in the first aspect, and a description thereof will be omitted.

(Function and effect)
In the second aspect of the wastewater treatment method of the second invention of the present application described above, the wastewater is biologically treated with aerobic microorganisms in the activated sludge in the aeration tank 10, and the membrane separation activated sludge treatment is performed. Since the apparatus 30 performs biological treatment of the supernatant liquid from the sedimentation tank 20 by aerobic microorganisms in the activated sludge, the permeated water (treatment liquid) COD _Cr is sufficient compared to conventional wastewater treatment systems and wastewater treatment methods. Can be reduced.
In addition, after separating the sludge containing aerobic microorganisms in the sedimentation tank 20, the type of aerobic microorganisms in the aeration tank 10 and the membrane separation activated sludge treatment are transferred by transferring only the supernatant liquid to the membrane separation activated sludge treatment apparatus 30. Since the types of aerobic microorganisms in the apparatus 30 are different, the biological treatment in the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30 can be efficiently performed by different aerobic microorganisms. COD _Cr can be sufficiently reduced.
Moreover, since it processes in the membrane separation activated sludge processing apparatus 30, processing time can be shortened compared with the conventional waste water treatment system and waste water treatment method of only an aeration tank and a sedimentation tank.
In addition, since the membrane separation activated sludge treatment device 30 is used instead of the aeration tank and the settling tank, the number of settling tanks is reduced compared to the conventional wastewater treatment system and the wastewater treatment method having two stages of the combination of the aeration tank and the settling tank, System installation area can be reduced.

In the second aspect of the waste water treatment method of the second invention of the present application described above, the membrane module includes a washing step for washing the membrane module, and the washing step is performed with a hypochlorite aqueous solution. A hypochlorite washing step for washing the membrane module and an acid washing step for washing the membrane module with an aqueous acid solution in this order, and from the end of the hypochlorite washing step to the start of the next acid washing step. The acid washing step is started when the interval is within 48 hours and / or when the transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than the transmembrane pressure difference after the start of operation. Therefore, the transmembrane pressure difference of the membrane module 35 can be kept low during the biological treatment of the wastewater containing COD _Cr and containing heavy metals and performing the membrane separation treatment.
A membrane separation step may be performed between the hypochlorite cleaning step and the acid cleaning step.

(Other embodiments)
In addition, the 2nd aspect of the waste water treatment method of 2nd invention of this application is not limited to the waste water treatment system of the example of illustration, and the waste water treatment method using this.
For example, if the permeated water from the membrane separation activated sludge treatment apparatus 30 is not reused as cooling water or the like, the reverse osmosis membrane filtration apparatus 40 may be omitted.

  Further, as shown in the illustrated example, the membrane separation activated sludge treatment apparatus may be an integrated type in which biological treatment by aerobic microorganisms in activated sludge and solid-liquid separation treatment by a membrane module are performed in one tank. A separate tank type may be used in which biological treatment with aerobic microorganisms in sludge and solid-liquid separation treatment with a membrane module are performed in separate tanks (see FIG. 7).

[Method for producing terephthalic acid of the second invention of the present application]
The method for producing terephthalic acid according to the second invention of the present application includes a terephthalic acid production process and a wastewater treatment process for treating wastewater discharged in the terephthalic acid production process.
Hereinafter, embodiments of the method for producing terephthalic acid of the second invention of the present application will be described with reference to the drawings. In addition, embodiment shown below is an illustration of the manufacturing method of the terephthalic acid of 2nd invention of this application, and the manufacturing method of terephthalic acid of 2nd invention of this application is not limited to these embodiment. In particular, the combination of the filtration membrane device and the like is not limited to these forms.

The industrial production method of terephthalic acid can be roughly classified into the following two types (A) and (B) depending on the quality (purity) required for terephthalic acid.
(A) A method for producing terephthalic acid by hydrorefining after the oxidation reaction.
(B) A method of producing terephthalic acid without hydrorefining by additionally conducting an oxidation reaction at high temperature and high pressure after the oxidation reaction.

<A. First representative method for producing terephthalic acid>
FIG. 10 is a diagram illustrating a process flow and a substance flow in the first representative method for producing terephthalic acid. The first representative method for producing terephthalic acid has a terephthalic acid production process having the following steps (i) to (vi) and a waste water treatment process (vii).
(I) A step of obtaining a crude terephthalic acid slurry by oxidizing p-xylene in hydrous acetic acid (hereinafter also referred to as “oxidation reaction step (i)”).
(Ii) A step of solid-liquid separation of the crude terephthalic acid slurry to recover a crude terephthalic acid cake (hereinafter also referred to as “first solid-liquid separation step (ii)”).
(Iii) A step of dissolving the crude terephthalic acid cake in water and performing a hydrogenation treatment (hereinafter, also referred to as “hydrogenation treatment step (iii)”).
(Iv) A step of crystallizing the hydrogenation treatment liquid to obtain a terephthalic acid slurry (hereinafter also referred to as “crystallization step (iv)”).
(V) A step of solid-liquid separation of the terephthalic acid slurry to obtain a terephthalic acid cake and a separated mother liquor (hereinafter also referred to as “second solid-liquid separation step (v)”).
(Vi) A step of drying the terephthalic acid cake to obtain terephthalic acid (hereinafter also referred to as “drying step (vi)”).
(Vii) A wastewater treatment process (hereinafter referred to as “wastewater treatment process (vii)”) in which all or part of the wastewater discharged from the steps (i) to (vi) is recovered after aerobic biological treatment.
).

(Oxidation reaction step (i))
The oxidation reaction step (i) is an oxidation reaction step in which p-xylene is oxidized in hydrous acetic acid to obtain a crude terephthalic acid slurry 211 ′. First, p-xylene and a solvent containing acetic acid or the like are mixed and sent to the oxidation reaction device 211, and p-xylene is oxidized using molecular oxygen in the presence of a catalyst in the solvent. Examples of the catalyst include compounds of transition metals such as cobalt and manganese and / or hydrogen halides such as hydrobromic acid. As a result, a crude terephthalic acid slurry 211 'is generated and sent to the first solid-liquid separation step (ii).

(First solid-liquid separation step (ii))
In the first solid-liquid separation step (ii), the crude terephthalic acid slurry 211 ′ is solid-liquid separated in the first solid-liquid separation device 212 to recover the crude terephthalic acid cake, followed by washing and drying to obtain crude terephthalic acid. This is a step of obtaining the acid 212 ′. Examples of the method for solid-liquid separation include a method in which a solid-liquid separator is used as it is. Since the crude terephthalic acid slurry 211 ′ is in a pressurized state, the dissolved crude terephthalic acid precipitates when the pressure is lowered. For this reason, the crude terephthalic acid slurry 211 ′ may be sent to a crystallization tank (not shown), cooled under pressure to precipitate the dissolved crude terephthalic acid, and then applied to a solid-liquid separator. “Relief pressure cooling” refers to expansion and vaporization of solvent components by introducing the target liquid into a crystallization tank set to a pressure condition lower than the pressure of the target liquid and releasing the pressure in the crystallization tank. Means cooling.

  The crude terephthalic acid cake thus obtained is washed with acetic acid, water, a mixture of acetic acid and water, and then dried to obtain crude terephthalic acid 212 '. The obtained crude terephthalic acid 212 'contains an oxidation intermediate such as 4-carboxybenzaldehyde (4CBA) as an impurity. In order to remove such impurities, the crude terephthalic acid 212 'is sent to the next hydrogenation treatment step (iii).

(Hydrogenation treatment step (iii))
The hydrogenation treatment step (iii) is a step in which the crude terephthalic acid 212 ′ is dissolved in water and reduced by hydrogenation in the hydrogenation treatment apparatus 213. Through the hydrogenation treatment step (iii), the impurity 4CBA is reduced to p-toluic acid. Since p-toluic acid has higher water solubility than terephthalic acid, it can be separated in the second solid-liquid separation step (v) described later. The separated p-toluic acid is returned to the oxidation reaction step (i) and used as a terephthalic acid raw material. The hydrogenation treatment liquid 213 ′ generated by the hydrogenation treatment step (iii) is sent to the next crystallization step (iv).

(Crystalling step (iv))
The crystallization step (iv) is a step of obtaining a terephthalic acid slurry 214 ′ by crystallizing the hydrogenation treatment liquid 213 ′ in the crystallizer 214. Examples of the crystallization method include a method of evaporating and removing water as a solvent and cooling, a method of cooling under pressure, and the like. In this step, since p-toluic acid is highly water-soluble as described above, many of them remain dissolved in the solvent without being precipitated. Therefore, p-toluic acid and terephthalic acid can be separated in the next second solid-liquid separation step (v).

(Second solid-liquid separation step (v))
In the second solid-liquid separation step (v), the terephthalic acid slurry 214 ′ is separated into a terephthalic acid cake 215 ′ and a terephthalic acid separation mother liquor 224 ′ in the second solid-liquid separation device 215. It is a process. As the separator, known methods such as filtration and centrifugation can be employed. The separated terephthalic acid cake has a terephthalic acid separation mother liquor 224 ′ attached thereto, and impurities and the like dissolved in the mother liquor deteriorate the quality, and are washed with water. The terephthalic acid cake 215 ′ obtained by washing is sent to the next drying step (vi).

  Here, since the terephthalic acid separation mother liquor 224 ′ contains impurities such as p-toluic acid, a catalyst, terephthalic acid, and the like, the p-toluic acid and terephthalic acid are cooled by cooling in the recovery apparatus 220 such as p-toluic acid. Acid and the like are deposited and recovered. The recovered p-toluic acid, terephthalic acid and the like are returned to the oxidation reaction step (i). On the other hand, the separation mother liquor 225 'such as p-toluic acid is sent to a wastewater treatment process (vii) after collecting a heavy metal catalyst such as cobalt or manganese by a recovery device (not shown).

(Drying step (vi))
The drying step (vi) is a step of drying the terephthalic acid cake 215 ′ in the drying device 216 to obtain terephthalic acid 216 ′. In drying, a pressure dryer by pressure evaporation, a normal fluid dryer, or the like can be used.

(Wastewater treatment process (vii))
In the wastewater treatment process (vii), in the wastewater treatment system 221, organic substances and the like contained in the wastewater discharged from the steps (i) to (vi) are decomposed by aerobic microorganisms in the presence of dissolved oxygen (aerobic biological treatment). And, if necessary, other processes are performed. The wastewater treatment system 221 has a general settling tank and aeration tank combination. The discharged water 227 ′ having been subjected to the biological treatment is discharged to the outside. In addition, the waste water discharged | emitted from process (i)-(vi) is not necessarily sent directly to this waste water treatment system 221 and processed without necessarily performing any treatment. There is a case where a process corresponding to a drainage composition peculiar to each process is performed and sent to the wastewater treatment system 221.

The wastewater treatment process (vii) includes, for example, the following steps (a) to (f) or steps (c) to (f).
(A) A step of biologically treating the waste water from steps (i) to (vi) with aerobic microorganisms in activated sludge in an aeration tank.
(B) Solid-liquid separation of the aeration tank mixed water biologically treated in the aeration tank in the precipitation tank.
(C) In the membrane-separated activated sludge treatment apparatus, while biologically treating the supernatant liquid from the sedimentation tank or the waste water from steps (i) to (vi) with aerobic microorganisms in the activated sludge and / or A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module after treatment
(D) A step of filtering the permeated water that has passed through the membrane module with a reverse osmosis membrane with a reverse osmosis membrane filtration device as necessary.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an acid aqueous solution.

  Steps (a) to (f) are the same steps as steps (a) to (f) in the first and second aspects of the wastewater treatment method of the second invention of the present application, and a description thereof is omitted.

(Drainage)
Next, the wastewater type discharged from the steps (i) to (vi) to the wastewater treatment process (vii) and the treatment route thereof will be described, and each step will be a treatment target of the biological treatment of the wastewater treatment process (vii). The drainage will be explained.

(Drainage from oxidation reaction step (i))
From the oxidation reaction step (i), acetic acid as a solvent, water produced as a by-product, methyl acetate, methyl bromide, reaction intermediate, along with the molecular oxygen-containing gas introduced into the oxidation reaction device 211 for the oxidation reaction , Carbon monoxide, etc., unreacted p-xylene, and the like are discharged. By-product energy is recovered from the high-temperature and high-pressure gas as electric and thermal energy, and further acetic acid, methyl acetate and the like are recovered, and then methyl bromide and the like are combusted. After the exhaust gas after the combustion treatment is cleaned by contact with alkaline water or the like, the gas is released into the atmosphere, and the oxidized exhaust gas cleaning water 217 ′ is sent to the waste water treatment system 221.

(Drainage from the first solid-liquid separation step (ii))
From the first solid-liquid separation step (ii), a solid-liquid separated mother liquor is generated. More than 50% of the mother liquor is recycled to the oxidation reaction step (i). The ratio of reusing the mother liquor is preferably 70% or more, but part of the mother liquor needs to be purged to prevent quality degradation due to impurity accumulation in the system. Therefore, the ratio of reusing the mother liquor is 95% or less, preferably 90% or less. Oxidation reaction mother liquor (purged) 218 ′ that is not reused is evaporated and concentrated by a solvent recovery device 217, and divided into an evaporation solvent 219 ′ and a mother liquor concentrated slurry 220 ′ containing an active ingredient. The mother liquor concentrated slurry 220 ′ is sent to the catalyst recovery / regeneration device 219, where the catalyst is recovered / regenerated. After the recovered and regenerated catalyst is subjected to solid-liquid separation, the regenerated catalyst recovery / separation mother liquor 222 ′ is sent to the waste water treatment system 221 together with the cleaning waste water generated from the deodorization tower. On the other hand, the evaporated solvent 219 ′ is sent to a recovery device 218 such as acetic acid, where acetic acid is concentrated and recovered in a dehydration tower (not shown), and then methyl acetate is recovered in a distillation tower (methyl acetate recovery tower) (not shown). Part of the remaining methyl acetate recovery tower bottom liquid 221 ′ is sent to the wastewater treatment system 221.

  The vent gas generated in the steps other than the oxidation reaction step (i) and the first solid-liquid separation step (ii) is collectively washed in a washing tower (not shown), and the waste water treatment system together with the oxidized exhaust gas washing water 217 ′. 221.

(Drainage from the hydrogenation process (iii))
Usually, no wastewater treatment object is generated from the hydrogenation treatment step (iii).

(Drainage from crystallization process (iv))
From the crystallization step (iv), condensed water 223 ′ generated at the time of crystallization generated by cooling the generated steam when crystallization is performed by depressurization cooling or cooling under reduced pressure is generated. Condensed water 223 ′ generated at the time of crystallization contains an organic substance such as p-toluic acid and is sent to the waste water treatment system 221.

(Drainage from second solid-liquid separation step (v) and drying step (vi))
In the second solid-liquid separation step (v), the terephthalic acid cake 215 ′ is solid-liquid separated and a terephthalic acid separation mother liquor 224 ′ is generated. The terephthalic acid separation mother liquor 224 ′ is sent to the recovery apparatus 220 for p-toluic acid and the like, and p-toluic acid, terephthalic acid and the like dissolved in the terephthalic acid separation mother liquor 224 ′ are deposited and separated by filtration under pressure relief. The cake precipitated and separated from the terephthalic acid separation mother liquor 224 ′ is slurried and then returned to the oxidation reaction step (i). After recovering heavy metals such as cobalt and manganese contained in the residual mother liquor of the precipitation separation with a metal recovery device (not shown), the remaining separation mother liquor 225 ′ such as p-toluic acid is cooled and sent to the waste water treatment system 221.
In addition to the second solid-liquid separation step (v) and the drying step (vi), vent gas cleaning water 226 ′ generated when the vent gas is collectively processed by the scrubber is sent to the waste water treatment system 221.

Step (i) ~ (vi) suspended solids in the waste water entering the waste water treatment system 221 from (SS), cobalt used as catalysts in oxidation reactions, heavy metals manganese, alkali metal, compound results in an increase in _{COD Cr} In addition, compounds that increase total nitrogen are contained. The concentration of insoluble substances in the waste water is 100 mg / L or less in terms of SS value and / or 100 NTU or less in terms of turbidity, and the concentration of water-soluble organic substances is 10,000 mg / L or less in terms of COD _Cr . However, the discharged water 227 ′ flowing out from the waste water treatment system 221 cannot be reused as it is in the terephthalic acid production process from the viewpoint of water quality, and must be discharged in large quantities in public water areas.

  As a result of examining the method for treating the wastewater discharged from the steps (i) to (vi), the present inventors have found that in the wastewater treatment process (vii), instead of only the conventional aerobic biological treatment, during the biological treatment and / or Alternatively, by introducing a membrane module after biological treatment and performing membrane separation treatment, it is found that part or most of the permeated water can be recycled as industrial water (cooling water) or process water for producing terephthalic acid. The terephthalic acid production method of the invention has been completed. When used as process water, it has also been found that the utility value of cooling water and / or process water can be further increased by improving the purification degree of water using various adsorbents as necessary. .

  For biological treatment, aerobic microorganisms decompose organic substances in wastewater in the presence of oxygen by aerobic microorganisms, and / or organic substances in wastewater are decomposed by anaerobic microorganisms in a low oxygen concentration environment or in the absence of oxygen. Anaerobic biological treatment can be employed. Specifically, a form in which only aerobic biological treatment is performed and a form in which aerobic biological treatment and anaerobic biological treatment are combined are possible, but the wastewater discharged from steps (i) to (vi) Since there are few nitrogen components, it is not necessary to denitrify in many cases, and the form which performs only an aerobic biological treatment from a compact facility is preferable.

<A-1. First Embodiment in Production of Terephthalic Acid>
FIG. 11 is a diagram illustrating an embodiment in which a membrane separation process using a microfiltration membrane is performed during biological treatment in the first representative method for producing terephthalic acid. Hereinafter, a representative example of the embodiment of the method for producing terephthalic acid according to the second invention of the present application will be described more specifically based on FIG.

  In the present embodiment, a microfiltration membrane module (hereinafter, the microfiltration membrane is also referred to as “MF membrane” and the microfiltration membrane module is also referred to as “MF membrane module”) is disposed in the wastewater treatment system 2100. Examples of the biological treatment method that can be adopted in the second invention of the present application include a form in which only aerobic biological treatment is performed, and a form in which aerobic biological treatment and anaerobic biological treatment are combined. According to the form of performing only aerobic biological treatment, the equipment can be simplified and the cost can be easily reduced. On the other hand, according to the form of combining aerobic biological treatment and anaerobic biological treatment, dephosphorization efficiency is improved. It is possible. For the sake of simplicity, a mode in which only the aerobic biological treatment is performed will be described here.

(Wastewater treatment system 2100)
In the wastewater treatment system 2100, aerobic biological treatment is performed in two stages. The aerobic biological treatment in the method for producing terephthalic acid according to the second invention of the present application is sufficient even in one stage, but water having a quality capable of using a large amount of waste water as at least industrial water (cooling water) and / or process water. From the viewpoint of making it easier to reproduce the image, it is preferable to carry out the process in two stages. The wastewater treatment system 2100 includes at least a general aeration tank and a precipitation tank. That is, as shown in FIG. 11, the waste water treatment system 2100 is connected to the first aeration tank 2101, the first precipitation tank 2102 connected to the first aeration tank 2101, and the first precipitation tank 2102. A second aeration tank 2103, a reverse osmosis membrane filtration device 2106, a reuse water tank 2107, and an adsorbent treatment device 2108 are provided. Note that the second sedimentation tank 2104 indicated by the broken line is not used because it is not used. In the wastewater treatment system 2100, wastewater is biologically treated while being transferred through the first aeration tank 2101, the first settling tank 2102, and the second aeration tank 2103 in this order.

As an aeration method in the first aeration tank 2101 and the second aeration tank 2103, a known aeration method such as a complete mixing method, a plug flow method, and a step feed method can be employed without any particular limitation. As operating conditions of the first aeration tank 2101 and the second aeration tank 2103, MLSS (unit: mg / L) in the aeration tank is usually 1000 to 15000, preferably 3,000 to 7,000. The COD _Cr volumetric load (unit: COD _Cr -kg / m ³ / day) is usually 0.5 to 10, preferably 1 to 5. The COD _Cr removal rate is usually 95% to 99%, preferably 96% to 99.5%.

  In the wastewater treatment system 2100, an MF membrane module 2105 is disposed in the second aeration tank 2103. An apparatus in which the membrane module is immersed in the aeration tank in this way is called a membrane separation activated sludge treatment apparatus. Also called membrane bioreactor (MBR). In a general wastewater treatment system that does not have a membrane module, if the sedimentation property deteriorates in the settling tank, solid-liquid separation becomes insufficient, and a bulking phenomenon may occur in which a large amount of suspended matter is mixed in the supernatant. According to the membrane separation activated sludge treatment apparatus, since this bulking phenomenon can be avoided, a sedimentation tank (second sedimentation tank 2104 in the wastewater treatment system 2100) is not required, and a high concentration operation of MLSS is possible. Further, there is an advantage that the processing equipment can be downsized.

  In the wastewater treatment system 2100, after the biological treatment is performed in the first aeration tank 2101, the supernatant liquid separated from the activated sludge in the first sedimentation tank 2102 is transferred to the second aeration tank 2103. Since the MF membrane module 2105 is disposed in the second aeration tank 2103, activated sludge (microorganisms) and permeated water can be solid-liquid separated by a membrane without depending on precipitation. Therefore, since it is not necessary to install the second sedimentation tank 2104 in order to perform the final solid-liquid separation between the activated sludge and the permeated water, the installation area of the equipment can be reduced.

  In the wastewater treatment system 2100, the first aeration tank 2101 has MLSS (mg / L) of 1000 to 6000, the second aeration tank 2103 has MLSS (mg / L) of 6000 to 12000, and a membrane module. Compared to a general wastewater treatment system that does not have a low temperature, operation at a significantly higher concentration is possible.

(MF membrane module 2105)
In the wastewater treatment system 2100, an MF membrane is used for membrane separation. The MF membrane is a membrane that filters insoluble solids of approximately 0.1 μm to 10 μm. Examples of the material of the MF membrane include polymer materials such as polypropylene, polyethylene, cellulose acetate, aromatic polyamide, polyvinyl alcohol, polyvinylidene fluoride, polysulfone, and polycarbonate. The pore size of the MF membrane is usually 0.03 μm to 10 μm, but a finer membrane can be used depending on the application. For the membrane separation activated sludge treatment apparatus, an MF membrane having a pore diameter of 0.03 μm to 0.4 μm is preferable. The film material is particularly preferably polyethylene, polypropylene, polyvinylidene fluoride, or the like. As the form of the membrane module, a hollow fiber type, a flat membrane type, a tubular type, a spiral type and the like can be adopted without particular limitation. Among these, a hollow fiber type and a flat membrane type can be particularly preferably adopted. Specific examples of these include “Sterapore SADF (registered trademark)” (Mitsubishi Rayon Co., Ltd.), “Membray (registered trademark)” (Toray Industries, Inc.), “Mike”, which are commercially available for membrane separation activated sludge treatment equipment. Rosa (registered trademark) "(Asahi Kasei Chemicals Corporation).

  As a filtration method that can be used in the MF membrane module 2105, normal dead-end filtration (also referred to as total filtration) performed while depositing suspended substances on the filtration surface, a flow parallel to the membrane surface is created, and the flow direction is changed. There is cross-flow filtration that always re-disperses the suspended substance in a direction substantially orthogonal to the membrane permeation direction, and can be appropriately selected according to the installation method and the usage method. However, cross-flow filtration is preferable because it can reduce membrane contamination and concentration polarization, which can improve filtration efficiency. In the following description, it is assumed that cross flow filtration is performed.

  The membrane installation method in the MF membrane module 2105 can be appropriately selected from a suspension method and a flat placement method. In the suspension system, the membrane module is installed vertically in the aeration tank, and cross-flow filtration is performed on the surface of the membrane module by the upward air flow generated in the aeration tank. The air diffusion condition in the suspension system is preferably 50 m / hour to 100 m / hour in terms of linear velocity. In the flat placement method, air is diffused from the lower part of the installed flat membrane at a linear velocity of 50 m / hour to 100 m / hour, a crossflow flow is generated on the membrane surface, and crossflow filtration is performed.

  At the time of membrane filtration in the MF membrane module 2105, it is preferable to adopt a vacuum suction method. That is, it is preferable to reduce the pressure on the outlet side of the permeated water and increase the pressure difference that is the driving force for moving the water through the MF membrane. When the reduced pressure suction method is adopted, it is preferable to operate within the range where the pressure on the permeate discharge side is increased by 3 kPa from the initial differential pressure. The filtration temperature is preferably 10 ° C to 50 ° C, more preferably 15 ° C to 40 ° C. The processing capacity (operating speed) is preferably 0.05 to 2.0, more preferably 0.1 to 1.0, and still more preferably 0.4 to 0 in terms of daily average flux (unit: m / day). It is preferable to operate at .6.

(Chemical tank)
The wastewater treatment system 2100 includes a first chemical liquid tank (not shown) for storing a hypochlorite aqueous solution for cleaning the MF membrane module 2105; and a second chemical liquid tank for storing an acid aqueous solution for cleaning the MF membrane module 2105. (Not shown); and a control unit (not shown) for controlling the supply of the chemical solution from the first chemical solution tank and the second chemical solution tank to the MF membrane module 2105. A control part is a thing of the same structure as the control part in the 1st-2nd aspect of the waste water treatment method of 2nd invention of this application, and abbreviate | omits description.
In the MF membrane module 2105, prevention of clogging (fouling) due to deposition on the membrane surface is important. Although the deposition rate on the film surface can be reduced by crossflow or aerated air, clogging is unavoidable in the long term. As deposition on the film surface proceeds, the transmembrane pressure difference increases. If the transmembrane pressure exceeds a certain value, membrane cleaning with a chemical solution is required. As a chemical | medical solution which can be used for film | membrane washing | cleaning, what was illustrated in the 1st-2nd aspect of the waste water treatment method of 2nd invention of this application is mentioned. Membrane cleaning is performed in the same manner as steps (e) and (f) in the first and second aspects of the wastewater treatment method of the second invention of the present application.

(RO membrane filtration device 2106)
The permeated water a separated by the MF membrane module 2105 passes through an intermediate tank (not shown), and is supplied with a reverse osmosis membrane filtration device 2106 (hereinafter referred to as “RO membrane” as a reverse osmosis membrane and “RO membrane” as a reverse osmosis membrane filtration device). It is also referred to as a “filtering device.”) And is subjected to removal of metal ions and residual organic substances by membrane separation treatment with an RO membrane. RO membrane materials used for RO membrane separation treatment include polyethylene, polyamides including aromatic polyamides and cross-linked aromatic polyamides, aliphatic amine condensation polymers, heterocyclic polymers, polyvinyl alcohol, and cellulose acetate polymer materials And can be appropriately selected from these. It is also possible to employ a mixture of two or more materials. In the second invention of the present application, among these, polyamides including aromatic polyamides and cross-linked aromatic polyamides are recommended as preferable because of their high separation performance. Examples of the membrane form of the RO membrane include an asymmetric membrane and a composite membrane, and can be appropriately selected from these. Two or more types of RO membranes can be used in combination. Further, a low fouling film with improved performance for preventing adhesion to the film surface can also be preferably used. Moreover, examples of the form of the membrane module used for the RO membrane separation treatment include a hollow fiber membrane type, a spiral membrane type, a tubular membrane type, a flat membrane type, and a pleated type, and one or two selected from these types More than one type of membrane module can be used. Among these, a spiral membrane type module is preferable from the viewpoint that the module has a large membrane area and is advantageous for downsizing the apparatus. Specific examples of these include the “Low-Pressure Spiral RO Membrane Element” series (Nitto Denko Corporation), the “Film Tech (registered trademark)” series (The Dow Chemical Company), “Romenbra (registered trademark)” ( Toray Industries, Inc.). In addition, it is preferable to install a prefilter at the entrance of the RO membrane module to protect the membrane.

  The transmittance (permeated water weight / charged water weight × 100%) in the membrane separation process in the RO membrane filtration device 2106 is preferably 50% to 90%. More preferably, it is 60% to 80%. If the permeability is excessive, impurities in the permeated water increase, which may adversely affect the quality of the recovered water. The RO membrane separation process is performed under pressure. The required pressure in the RO membrane separation treatment is determined by the ion concentration and permeability in the permeated water that is passed through the RO membrane, but it is usually 0.5 MPaG to 5.5 MPaG, preferably 1.1 MPaG to 3.1 MPaG as a gauge pressure. Operated within range. The treatment temperature is preferably 10 ° C to 50 ° C, more preferably 15 ° C to 40 ° C. In determining the treatment temperature, it is necessary to pay attention to the heat resistance of the film material. Moreover, the linear velocity of the permeated water a in the cross flow is preferably 60 m / min to 240 m / min.

  When a drug is used in the RO membrane regeneration treatment, it is preferable to perform the membrane cleaning with the drug about once every two months to maintain the performance. Examples of the agent usable as the RO membrane regeneration treatment include bisulfite, hypochlorite, citric acid, oxalic acid, peracetic acid and the like. In the second invention of the present application, among these, bisulfite, Hypochlorite, citric acid and the like are preferred. Moreover, since the pH of the permeated water a flowing into the RO membrane filtration device 2106 is high, it is preferable to perform an acidification treatment before contacting the RO membrane in order to prevent precipitation of salts. The preferred pH is usually 5.0 to 8.0, more preferably 6.0 to 7.5.

As described above, the wastewater targeted by the second invention of the present application contains suspended solids (SS), heavy metals such as cobalt and manganese used in the oxidation reaction, alkali metals, COD, nitrogen-containing compounds, and the like. ing. The wastewater treated in the wastewater treatment process of the method for producing terephthalic acid according to the second invention of the present application, when flowing into the MF membrane module 2105, the concentration of insoluble substances in water is set to an SS value of 100 mg / L or less or turbidity 100NTU in the (Turbidity) below, the concentration of water-soluble organic substances in the and BOD ₅ below 100 mg / L in the _{COD Cr} 10 mg / L or less, the electrical conductivity as an indicator of the concentration of water-soluble inorganic substance is 500 to, It preferably has properties of 000 μS / cm and a pH of 5.0 to 9.5. The pH is usually 8 or more, indicating alkalinity, but in the second invention of the present application, treatment by membrane separation is possible if the pH is in the range of 5.0 to 9.5.

  When the wastewater having the properties described above is processed by the flow shown in FIG. 11 after the MF membrane module 2105, the RO membrane permeated water b having good water quality can be recovered from the RO membrane filtration device 2106. Although the water quality of the RO membrane permeated water b depends on the permeability, most of metal ions such as cobalt and manganese and residual organic substances are removed, and the water quality is high. The RO membrane permeated water b is stored in the reused water tank 2107 and supplied from the reused water tank 2107 to the terephthalic acid production process as industrial water (cooling water) d, or transferred to an adsorbent treatment device 2108 described later for further adsorption. It is supplied to the terephthalic acid production process as adsorbed purified water e through the agent treatment. The ratio of distributing the RO membrane permeate water b to the supply of industrial water (cooling water) d and the production of the adsorption purified water e can be selected as appropriate.

  In the prior art, it has been difficult to use the water after treating the waste water from the terephthalic acid production process as industrial water. According to 2nd invention of this application, it becomes possible to reuse the water after waste water treatment in a terephthalic-acid manufacturing process. For example, in the terephthalic acid production process, it can be reused as industrial water including makeup water to the recooling tower. In particular, by performing a membrane separation process by combining a plurality of filtration membrane devices (for example, the MF membrane module 2105 and the RO membrane filtration device 2106 in the present embodiment), it becomes easier to achieve the effect.

  On the other hand, the RO membrane concentrated water c discharged from the RO membrane filtration device 2106 contains various impurities in a concentrated manner. If the properties of the wastewater to be treated are within the above range, further treatment is performed. The water quality has been improved to such an extent that it can be released into public waters. Concentrated water may be discharged into public water areas after further ozone treatment as necessary. In addition, the method of monitoring light transmittance can be mentioned as a method of managing discharge | release water quality.

(Adsorbent processing device 2108)
When the RO membrane permeate b is used as process water, the degree of purification (purity) is further improved by performing adsorbent treatment using an adsorbent selected from various adsorbents in the adsorbent treatment apparatus 2108. Is possible. Thus, by improving the purity (water quality) of water, it is possible to expand the application range of recovered and reclaimed water. The adsorbed purified water e recovered from the adsorbent treatment device 2108 is supplied to the terephthalic acid production process and is more preferably used as process water. Examples of the use of the adsorbed purified water e as process water include use as part of a solvent used in the hydrogenation reaction in the hydrogenation treatment step (iii) and terephthalic acid in the second solid-liquid separation step (v). The use etc. which are used as a part of washing water in the solid-liquid separation process of this can be mentioned. The adsorbent processing waste water f discharged from the adsorbent processing apparatus 2108 is transferred to the first aeration tank 2101 and biologically processed again.

  Examples of the adsorbent usable in the adsorbent processing apparatus 2108 include activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, alkaline earth metal aluminate, and the like. Among these, at least one adsorbent can be selected and used. When two or more compounds selected from silica, alumina, silica alumina, synthetic zeolite, alkaline earth metal aluminate, etc. are used in combination, a mixture of these may be used as the adsorbent. A compound obtained by reacting the mixture may be used as an adsorbent.

  Examples of the adsorbent that can be used in the adsorbent treatment apparatus 2108 include wood-based activated carbon and coal-based activated carbon, and at least one of them can be selected and used. In addition, when combining 2 or more types of activated carbon, even if it mixes and uses these 2 or more types of activated carbon, you may divide and use it individually for a some packed tower, without mixing.

  Examples of the ion exchange resin that can be used in the adsorbent treatment apparatus 2108 include a cation exchange resin, an anion exchange resin, and an intermediate basic ion exchange resin. At least one selected from these can be used. be able to. When two or more types of ion exchange resins are used in combination, even if the two or more types of ion exchange resins are used in combination, each of them is divided into a plurality of packed towers without mixing. It may be used.

  The cation exchange resin that can be used in the adsorbent treatment apparatus 2108 includes a weak acid cation exchange resin having a weak acid group such as a carboxyl group as a functional group and a strong acid cation exchange resin having a strong acid group such as a sulfonic acid group. Any of them can be used in the second invention of the present application. However, in the second invention of the present application, it is preferable to use a strongly acidic cation exchange resin. Specific examples thereof include Diaion HP20 (registered trademark), Sepa beads SP825 (registered trademark), Sepa beads SP207 (registered trademark) (all manufactured by Mitsubishi Chemical Corporation), AMBERLITE XAD4 (registered trademark), and AMBERLITE XAD7 (registered trademark). Trademark) (all of which are manufactured by Rohm & Haas). As an anion exchange resin that can be used in the adsorbent treatment apparatus 2108, either a weakly basic anion exchange resin or a strongly basic anion exchange resin can be used. Specific examples of the strongly basic anion exchange resin include Diaion SA10A, SA12A, UBA120 (registered trademark) (all of which are manufactured by Mitsubishi Chemical Corporation). Specific examples of the weakly basic anion exchange resin include Diaion WA10, WA20, WA30 (registered trademark) (all of which are manufactured by Mitsubishi Chemical Corporation). Further, examples of the intermediate basic ion exchange resin that can be used in the adsorbent treatment apparatus 2108 include IONAC-365 (registered trademark) (Sybron Corp.) and the like.

  Examples of the synthetic zeolite that can be used in the adsorbent treatment apparatus 2108 include various synthetic zeolites such as sodalite, A type, X type, and Y type, and one or more of these are selected and used. be able to. Among these, A-type zeolite is preferable. Moreover, the preferable pore diameter of a synthetic zeolite is 0.2 nm-1.0 nm.

Specific examples of alkaline earth metal aluminates that can be used in the adsorbent processing apparatus 2108 include magnesium aluminate (Mg (AlO ₂ ) ₂ ), calcium aluminate (Ca (AlO ₂ ) ₂ ), and barium aluminate. (Ba (AlO ₂ ) ₂ ) and the like.

The adsorbent used in the adsorbent processing apparatus 2108 preferably has a large specific surface area. Specifically, the BET specific surface area is preferably 50 m ² / g or more, and more preferably 100 m ² / g or more. As the shape of the adsorbent used in the adsorbent processing apparatus 2108, a finely pulverized product (powdered product), a granulated product obtained by sieving, and the like are available, and any of them can be used. Industrially, in many cases, it is used by being filled in a fixed bed, fluidized bed, etc., and in consideration of pressure loss, a granular form is preferable. A mixture of a pulverized (powdered) adsorbent and a granular adsorbent may be used.

  In the adsorbent treatment apparatus 2108, various methods such as a method using a packed tower (packed tower method), a fluidized bed method, a moving tank method, and a stirring tank method are used as a method for bringing the adsorbent into contact with the RO membrane permeated water b. Can be used without particular limitation. However, from the viewpoint that it is easy to perform the adsorbent activation treatment described later in parallel with the adsorption treatment, the packed tower method is preferable.

  Note that, from the viewpoint of shortening the stop time of the adsorbent processing apparatus 2108 accompanying the saturation of the adsorption amount, it is preferable to activate the adsorbent in parallel with the adsorption. For example, when the adsorbent processing apparatus 2108 employs a packed tower system, a plurality of packed towers are installed, and other packed towers are activated while some of the packed towers are used for adsorption. A so-called merry-go-round driving method can be preferably employed.

  The activator used for activation of the adsorbent and the activation treatment conditions differ depending on the adsorbent used. In the case of an ion exchange resin, it varies depending on the type of ion exchange resin used, but generally in the case of a cation exchange resin, sulfuric acid, hydrochloric acid, hydrobromic acid, acetic acid and the like can be used. The temperature of the activation treatment is a maximum of 100 ° C., preferably around 80 ° C., from the viewpoint of heat resistance of the cation exchange resin. On the other hand, in the case of an anion exchange resin or an intermediate basic ion exchange resin, caustic soda, ammonia, sodium carbonate or the like can be used as an activator. The activation treatment temperature is a maximum of 80 ° C., and preferably 60 ° C.

  On the other hand, when using 1 type, or 2 or more types selected from silica, alumina, silica alumina, synthetic zeolite, and alkaline earth metal aluminate (when using a product obtained by mixing and reacting 2 or more types) In addition, as the activator, acetic acid, hydrobromic acid, steam and the like are preferable, and the activation treatment temperature is preferably 20 ° C to 60 ° C.

  From the viewpoint of the amount of wastewater discharged into public water areas, conventionally, a large amount of wastewater after biological treatment has been discharged to public water areas. According to the second invention of the present application, the wastewater can be recycled in the terephthalic acid production process through recovery and regeneration. Since the amount of water used is greatly increased, the amount of drainage can be reduced from one-half to about one-third compared to the conventional case. As a result, the amount of groundwater pumped up as a resource can be greatly reduced. Specifically, preferably 60% or more, more preferably 70% or more, more preferably 80% or more of the wastewater discharged from the steps (i) to (vi) and used for biological treatment is recovered as permeated water. However, it can be used as cooling water and / or process water in the terephthalic acid production process.

(Other embodiments)
In the above description of the method for producing terephthalic acid according to the second invention of the present application, the method for producing terephthalic acid in a form in which the aerobic biological treatment is performed in two stages is exemplified, but production of terephthalic acid according to the second invention of the present application is exemplified. The method is not limited to this form. It is also possible to adopt a configuration in which the waste water treatment system has only the first aeration tank and does not use the first precipitation tank and the second aeration tank (only one stage). Thus, when performing only in one step, the MF membrane module can be installed in the first aeration tank. However, from the viewpoint of improving the solid-liquid separation state of the activated sludge and reducing the inflow of suspended substances to the sedimentation tank, it is preferable to carry out in two stages as in the wastewater treatment system 2100 described above. In addition, when aerobic biological treatment is performed in one stage, the degree of contamination of the waste water that contacts the MF membrane is high, and the membrane cleaning frequency tends to increase because the treatment capability in the membrane separation treatment tends to decrease. . When constructing a new wastewater treatment system, whether only one stage or two stages will be adopted after comparing the cost of increasing the membrane cleaning cost with only one stage and reducing the equipment and operating costs. It only has to be selected.

In the above description of the method for producing terephthalic acid according to the second aspect of the present invention, an example of the method for producing terephthalic acid using the wastewater treatment system 2100 in which the MF membrane module 2105 is disposed in the second aeration tank 2103 is illustrated. However, the method for producing terephthalic acid of the second invention of the present application is not limited to this form. The installation location of the MF membrane module is not limited to the inside of the aeration tank. One or more tanks (containers) having a small capacity are provided outside, and the membrane module is provided in the tank to dispose activated sludge. It is also possible to adopt a form of membrane separation while circulating externally. According to such a form, it becomes easy to reduce the maintenance work.
When biological treatment is performed in only one stage, the MF membrane module is placed at the outlet of the first sedimentation tank. When biological treatment is conducted in two stages, the MF membrane module is placed in the second precipitation tank. It is also possible to adopt a form in which it is disposed at the outlet. Specific examples of the MF membrane that can be used in such a form include “STELLAPORE LFB” (registered trademark), “STELLAPORE G” (registered trademark) (both manufactured by Mitsubishi Rayon Co., Ltd.), and “Trefill F” (registered trademark). ) (Manufactured by Toray Industries, Inc.), “Microza” (registered trademark) (manufactured by Asahi Kasei Chemical Co., Ltd.), and the like. However, from the viewpoints of eliminating the need for a sedimentation tank and enabling high-load processing of MLSS concentration in the aeration layer and reducing the size of the equipment, there is a need for an aeration tank (when biological treatment is performed in only one stage). In the case where the first aeration tank and biological treatment are performed in two stages, it is preferable to employ a membrane separation activated sludge treatment apparatus in which an MF membrane module is installed in the second aeration tank).

  In the above description of the method for producing terephthalic acid according to the second invention of the present application, the terephthalic acid production method using the wastewater treatment system 2100 having the MF membrane module 2105 for performing membrane separation by the MF membrane is exemplified. The method for producing terephthalic acid according to the second invention is not limited to this form. Instead of the MF membrane, a membrane separation may be performed using an ultrafiltration membrane (UF membrane) described later.

  In the above description of the method for producing terephthalic acid according to the second invention of the present application, the method for producing terephthalic acid in the form of performing membrane separation using the RO membrane in the RO membrane filtration device 2106 has been exemplified. The manufacturing method of the terephthalic acid of invention is not limited to the said form. Instead of the RO membrane, it is also possible to use a membrane positioned between the UF membrane and the RO membrane, which is also referred to as a loose RO membrane or a nanofiltration membrane (NF membrane). Such an NF membrane has an operating pressure of about 0.2 MPa to 1.5 MPa, and can be operated at a lower pressure than when the RO membrane is used. Therefore, a smaller pump can be used and the energy required for the operation can be reduced. It is possible to reduce. Even when an NF membrane is employed instead of the RO membrane, the membrane structure, material, manufacturing method, and the like can be the same as those of the RO membrane.

<A-2. Second Embodiment in Production of Terephthalic Acid>
FIG. 12 is a diagram illustrating an embodiment in which a membrane separation process using an ultrafiltration membrane (UF membrane) is performed after biological treatment in the first representative method for producing terephthalic acid. As shown in FIG. 12, in the wastewater treatment process according to this embodiment, the first aeration tank 2101, the first precipitation tank 2102, the second aeration tank 2103 a, the second precipitation tank 2104 a, UF membrane unit 2110 connected to second sedimentation tank 2104a, RO membrane filtration device 2106 connected to UF membrane unit 2110, reused water tank 2107 connected to RO membrane filtration device 2106, and reused water tank 2107 A wastewater treatment system 2200 having an adsorbent treatment device 2108 connected to the slag is used. Among these, since the second aeration tank 2103a, the second settling tank 2104a, the waste water treatment system 2200, and the UF membrane unit 2110 are the same as those in the first embodiment, the same reference numerals as those in FIG. The description will be omitted as appropriate.

(Wastewater treatment system 2200)
The wastewater treatment system 2200 includes a first aeration tank 2101, a first precipitation tank 2102 connected to the first aeration tank 2101, a second aeration tank 2103 a connected to the first precipitation tank 2102, A second settling tank 2104a connected to the second aeration tank 2103a, a UF membrane unit 2110 connected to the second settling tank 2104a, an RO membrane filtration device 2106 connected to the UF membrane unit 2110, and RO A reuse water tank 2107 connected to the membrane filtration apparatus 2106 and an adsorbent treatment apparatus 2108 connected to the reuse water tank 2107 are provided. The wastewater treatment system 2200 is different from the wastewater treatment system 2100 in that the MF membrane module 2105 is not disposed in the second aeration tank 2103a, the second precipitation tank 2104a is used, and the second precipitation The UF membrane unit 2110 is disposed at the outlet of the tank 2104a. In the wastewater treatment system 2200, wastewater is sequentially transferred through the first aeration tank 2101 to the second settling tank 2104a, and aerobic biological treatment is performed in two stages. The operating conditions of both aeration tanks are the same as those of the wastewater treatment system 2100. The permeated water h, which is sequentially transferred through the first aeration tank 2101 to the second precipitation tank 2104a and subjected to the aerobic biological treatment in two stages, is a UF membrane unit 2110 connected to the second precipitation tank 2104a. It is transferred to.

(UF membrane unit 2110)
In the UF membrane unit 2110, the permeated water h is subjected to membrane separation treatment by an ultrafiltration membrane (UF membrane) module. The UF membrane permeated water i that has passed through the UF membrane is transferred to an RO membrane filtration device 2106 connected to the UF membrane unit 2110 via an intermediate tank (not shown).

  The UF membrane included in the UF membrane module has a pore diameter of approximately 2 nm to 200 nm, which is larger than the RO membrane and smaller than the microfiltration membrane (MF membrane). As the material of the UF membrane, one or a combination of two or more selected from polysulfone, polypropylene, polyethylene, polyvinylidene chloride, polyvinylidene fluoride, aromatic polyamide membrane, polyvinyl alcohol, cellulose acetate, and polyacrylonitrile can be used. . Among these, polypropylene, polyvinylidene fluoride, aromatic polyamide and the like are preferable from the viewpoint of being hardly affected by impurities in the waste water.

  As the UF membrane module included in the UF membrane unit 2110, one or a combination of two or more selected from a hollow fiber membrane type, a spiral membrane type, a tubular membrane type, and a flat membrane type can be used. Of these, hollow fiber membranes and / or spiral membrane type UF membrane modules are preferred. Specific examples of UF membrane modules that can be preferably used in the UF membrane unit 2110 include the “Treafil (registered trademark)” series (manufactured by Toray Industries, Inc.), the “capillary type UF membrane module” series (manufactured by Nitto Denko Corporation), Rosa (registered trademark) ”series (manufactured by Asahi Kasei Chemical Co., Ltd.), UF membrane module“ Molsep (registered trademark) ”(manufactured by Daisen Membrane Systems Co., Ltd.), and the like.

The UF membrane separation process is basically a process for solid-liquid separation of water, a solid substance (solid matter) insoluble in water, and a part of the water-soluble substance. The filtration (membrane separation) operation in the UF membrane unit 2110 can be performed under normal pressure, under pressure, or under reduced pressure, but industrially, it is preferably performed under pressure or under reduced pressure. As the pressure difference between the two spaces sandwiching the UF membrane is larger, the processing capability is improved. Moreover, as temperature which performs a UF membrane separation process, 10 to 50 degreeC is preferable, More preferably, it is 15 to 40 degreeC. As processing capacity (operation speed), it is preferable to operate at a daily average flux (unit: L / m ² · d) of the UF membrane permeated water i at 10 to 200.

  Although it is not impossible to use dead-end filtration (all-pass) as the filtration method, the pore size of the UF membrane is small. Therefore, when dead-end filtration is used, the membrane is clogged by deposition on the membrane surface. Ring) is likely to occur in a short time. For this reason, normally, the permeated water h is supplied along a surface of the UF membrane in a certain direction, and water (concentrated water) in which fine particles and impurities are concentrated is continuously discharged or returned to the liquid feeding side. It is preferable to employ a cross flow method in which membrane separation (filtration) is performed. The linear velocity of the permeate h when performing cross flow filtration is preferably 60 m / min to 240 m / min.

  When the compressibility of the solid matter is strong, the filtration rate is lowered and the time required for filtration is prolonged. Therefore, it is preferable to add a precoat material (filter aid) to suppress the reduction of the filtration rate. Generally, diatomaceous earth, pearlite, activated carbon, etc. can be used as the filter aid, but it is preferable to use inexpensive diatomaceous earth, pearlite, etc. from the viewpoint of easy cost reduction.

(Chemical tank)
The waste water treatment system 2200 includes a first chemical tank (not shown) for storing a hypochlorite aqueous solution for cleaning the UF membrane module of the UF membrane unit 2110; and an acid aqueous solution for cleaning the UF membrane module of the UF membrane unit 2110. A second chemical tank (not shown) for storing the chemical; and a controller (not shown) for controlling the supply of the chemical from the first chemical tank and the second chemical tank to the UF membrane module of the UF membrane unit 2110 It has further. A control part is a thing of the same structure as the control part in the 1st-2nd aspect of the waste water treatment method of 2nd invention of this application, and abbreviate | omits description.
In the UF membrane module of the UF membrane unit 2110 as well, as the MF membrane module 2105 and the like, as the deposition on the membrane surface proceeds, the transmembrane pressure difference increases. When the transmembrane pressure exceeds a certain value, membrane cleaning with a chemical solution is required. As a chemical | medical solution which can be used for film | membrane washing | cleaning, what was illustrated in the 1st-2nd aspect of the waste water treatment method of 2nd invention of this application is mentioned. Membrane cleaning is performed in the same manner as steps (e) and (f) in the first and second aspects of the wastewater treatment method of the second invention of the present application.

(RO membrane filtration device 2106)
The UF membrane permeated water i obtained by the membrane separation process in the UF membrane unit 2110 is transferred to the RO membrane filtration device 2106 through an intermediate tank (not shown), where metal ions and residual organic substances are removed. The The UF membrane cleaning waste water o generated by the membrane cleaning of the UF membrane is transferred to the second aeration tank 2103a and processed.

As the water quality after the aerobic biological treatment of the wastewater treated in the present embodiment, the concentration of the insoluble substance in water is 50 mg / L or less in terms of SS value or turbidity when flowing into the UF membrane unit 2110. 50 NTU or less, the concentration of water-soluble organic substance is 100 mg / L or less for COD _Cr , 10 mg / L or less for BOD ₅ and the conductivity is 500 to 10,000 μS / cm as an index of the concentration of water-soluble inorganic substance, and the pH is It preferably has a property of 5.0 to 9.5. The pH is usually 8 or more, indicating alkalinity, but in the second invention of the present application, treatment by membrane separation is possible if the pH is in the range of 5.0 to 9.5.

When the wastewater having the above-described properties is processed by the flow shown in FIG. 12 after the UF membrane unit 2110, the RO membrane permeated water k with good water quality can be recovered from the RO membrane filtration device 2106. Although the water quality of the RO membrane permeated water k depends on the transmittance, most of the metal ions and residual organic substances are removed, and the water quality is high. The RO membrane permeated water k is stored in the reuse water tank 2107 and supplied from the reuse water tank 2107 to the terephthalic acid production process as industrial water 1 (cooling water) or transferred to an adsorbent treatment device 2108 described later for further adsorption. It is supplied to the terephthalic acid production process as adsorbed purified water m through the agent treatment. In addition, the ratio which distributes RO membrane permeate water k to supply of industrial water (cooling water) 1 and manufacture of adsorption purified water m can be selected as appropriate.
In particular, by performing a membrane separation process by combining a plurality of filtration membrane devices (for example, the UF membrane unit 2110 and the RO membrane filtration device 2106 in this embodiment), it becomes easier to achieve the above-described effects.

  On the other hand, the RO membrane concentrated water j discharged from the RO membrane filtration device 2106 contains various impurities in a concentrated manner. If the properties of the wastewater to be treated are within the above-described range, further treatment is performed. Water quality has been improved to such an extent that it can be discharged into public waters without applying water. The release of the RO membrane concentrated water j is the same as the RO membrane concentrated water c.

(Adsorbent processing device 2108)
When the RO membrane permeate k is used as process water, the degree of purification (purity) is further improved by applying an adsorbent treatment using an adsorbent selected from various adsorbents in the adsorbent treatment apparatus 2108. As a result, it is possible to expand the application range of the recovered and reclaimed water as in the RO membrane permeated water b. The adsorbed purified water m recovered from the adsorbent treatment apparatus 2108 can be more preferably used as process water, like the adsorbed purified water e. The details of the adsorbent and processing in the adsorbent processing apparatus 2108 are the same as those already described. The adsorbent processing waste water n discharged from the adsorbent processing apparatus 2108 is transferred to the first aeration tank 2101 and biologically processed again.

  From the viewpoint of the amount of wastewater discharged into public water areas, a large amount of wastewater after biological treatment has been discharged to public water areas in the past, but this embodiment (FIG. 12) is the same as in the first embodiment (FIG. 11). In addition, since the amount of water reused in the terephthalic acid production process is greatly increased by recovery and regeneration, the amount of wastewater can be reduced to about one-half to one-third compared to the conventional case. As a result, the amount of groundwater pumped up as a resource can be greatly reduced. Specifically, the wastewater discharged from the steps (i) to (vi) and used for biological treatment is preferably 80% or more, more preferably 70% or more, and still more preferably 60% or more as membrane permeated water. It can be recovered and used as cooling water and / or process water in the terephthalic acid production process.

<B. Second representative method for producing terephthalic acid>
FIG. 13 is a diagram illustrating a process flow and a substance flow in a second representative method for producing terephthalic acid. The second representative method for producing terephthalic acid has a terephthalic acid production process having the following steps (viii) to (xii) and a waste water treatment process (xiii).
(Viii) Step of oxidizing p-xylene in hydrous acetic acid to obtain a crude terephthalic acid slurry (hereinafter also referred to as “oxidation reaction step (viii)”).
(Ix) A step of obtaining a terephthalic acid slurry by subjecting the crude terephthalic acid slurry to an additional oxidation reaction under high temperature conditions without supplying p-xylene (hereinafter also referred to as “additional oxidation step (ix)”) .)
(X) A step of solid-liquid separation of the terephthalic acid slurry to obtain a terephthalic acid cake (hereinafter also referred to as “solid-liquid separation step (x)”).
(Xi) A step of drying the terephthalic acid cake to obtain terephthalic acid (hereinafter also referred to as “drying step (xi)”).
(Xii) A step of recovering and regenerating valuable materials such as a catalyst and a solvent from the mother liquor after solid-liquid separation (hereinafter also referred to as “mother liquor recovery and regenerating step (xii)”).
(Xiii) Wastewater treatment process (hereinafter referred to as “wastewater treatment process (xiii)”) that discharges all or part of the wastewater discharged from the steps (viii) to (xii) to public water after aerobic biological treatment .)

(Oxidation reaction step (viii))
In the oxidation reaction step (viii), the oxidation reaction apparatus 2511 oxidizes p-xylene using hydrous acetic acid as a solvent and a molecular oxygen-containing gas in the presence of a catalyst. Examples of the catalyst include compounds of transition metals such as cobalt and manganese and / or hydrogen halides such as hydrobromic acid. Through the oxidation reaction step (viii), a crude terephthalic acid slurry 251 ′ is obtained. The reaction temperature is usually 180 ° C to 230 ° C, preferably 190 ° C to 210 ° C. The reaction pressure needs to be equal to or higher than the pressure at which the mixture can maintain the liquid phase at least at the reaction temperature. Specifically, the reaction pressure is preferably 0.3 MPa to 10 MPa (absolute pressure), more preferably 1 to 3 MPa (absolute pressure). .

  From the oxidation reaction step (viii), acetic acid as a solvent, water produced as a by-product in the reaction, other impurities, unreacted raw materials accompanying the molecular oxygen-containing gas introduced into the oxidation reaction device 2511 for the oxidation reaction A high-temperature high-pressure gas containing etc. is discharged. The high-temperature high-pressure gas is passed through an absorption tower (not shown) and the like. In the process, valuables, energy, etc. are recovered from the high-temperature high-pressure gas and reused, and then the remaining gas is burned. After the exhaust gas after the combustion treatment is cleaned by contact with alkaline water or the like, the gas is released into the atmosphere, and the remaining oxidized exhaust gas cleaning water 255 ′ is transferred to the waste water treatment system 2518.

(Additional oxidation process (ix))
The additional oxidation step (ix) is a step in which the crude terephthalic acid slurry 251 ′ obtained by the oxidation reaction is transferred to the additional oxidation reaction device 2512 and supplied with a molecular oxygen-containing gas to be further oxidized at a high temperature. . A terephthalic acid slurry 252 ′ is obtained by the additional oxidation step (ix). The reaction temperature is usually 235 ° C. to 290 ° C., preferably 240 ° C. to 280 ° C., and the pressure is usually preferably 3 MPa to 10 MPa (absolute pressure). A part of the terephthalic acid particles in the crude terephthalic acid slurry 251 ′ are dissolved, and the oxidized intermediates, unreacted raw materials, etc. in the particles are oxidized, and the impurity concentration is reduced to produce a purification effect. The high-temperature and high-pressure exhaust gas is treated in the same manner as the high-temperature and high-pressure gas generated from the oxidation reaction step (viii), and the remaining supplemental oxidation exhaust gas cleaning water 256 ′ is treated with wastewater together with the oxidation exhaust gas cleaning water 255 ′ of the oxidation reaction step (viii). Transported to system 2518.

(Solid-liquid separation step (x) and mother liquor recovery and regeneration step (xii))
The solid-liquid separation step (x) is a step of obtaining a terephthalic acid cake 253 ′ by solid-liquid separation of the terephthalic acid slurry 252 ′ in the solid-liquid separation device 2513. Examples of the method for solid-liquid separation include a method in which the terephthalic acid slurry 252 ′ is directly applied to a solid-liquid separator. Further, since the terephthalic acid slurry 252 'is in a pressurized state, dissolved terephthalic acid is deposited when the pressure is lowered. For this reason, the terephthalic acid slurry 252 ′ may be sent to a crystallization tank (not shown) and subjected to pressure reduction cooling to precipitate dissolved terephthalic acid, and then applied to a solid-liquid separator. Note that “relief cooling” refers to the expansion of the solvent component by introducing the target liquid into a crystallization tank set to a pressure condition lower than the pressure of the target liquid and releasing the pressure in the crystallization tank. It means cooling by vaporization.

  From the solid-liquid separation step (x), solid-liquid separated mother liquor and cleaning liquid (hereinafter also referred to as “mother liquor”) are generated. More than 50% of the mother liquor is returned to the oxidation reaction step (viii) and reused. The ratio of reusing the mother liquor or the like is preferably 70% or more, but it is necessary to partially purge the mother liquor in order to prevent quality degradation due to impurity accumulation in the system. Therefore, the ratio of reusing the mother liquor is 95% or less, preferably 90% or less. The oxidation reaction mother liquor (purged) 257 'that is not reused is sent to the solvent recovery device 2515 and is supplied to the mother liquor recovery and regeneration step (xii).

  In the mother liquor recovery and regeneration step (xii), the oxidation reaction mother liquor (purging portion) 257 'is evaporated and concentrated by a solvent recovery device 2515, and divided into an evaporation solvent 258' and a mother liquor concentrated slurry 259 'containing valuable components. The mother liquor concentrated slurry 259 'is sent to the catalyst recovery / regeneration device 2517, where the catalyst is recovered / regenerated. After the recovered and regenerated catalyst is subjected to solid-liquid separation, the regenerated catalyst recovery / separation mother liquor 261 ′ is sent to a wastewater treatment system 2518 together with cleaning wastewater generated from a deodorization tower (not shown). On the other hand, the evaporated solvent 258 ′ is sent to an acetic acid recovery device 2516, passed through a dehydrating tower (not shown), concentrated and recovered, and then recovered with a distillation tower (methyl acetate recovery tower) (not shown). Is done. A part of the remaining methyl acetate recovery tower bottom liquid 260 ′ is sent to the wastewater treatment system 2518.

  Note that vent gases generated in steps other than the oxidation reaction step (viii) and the additional oxidation step (ix) are collectively cleaned in a cleaning tower (not shown) to be oxidized exhaust gas cleaning water 255 ′ and additional oxidation exhaust gas cleaning water 256 ′. Are sent to the wastewater treatment system 2518.

(Drying process (xi))
The drying step (xi) is a step of drying the terephthalic acid cake 253 ′ with the drying device 2514 to obtain terephthalic acid 254 ′. The exhaust gas generated from the drying device 2514 is cleaned in a cleaning tower (not shown), and vent gas cleaning water 262 ′ generated by the cleaning is sent to a wastewater treatment system 2518.

(Wastewater treatment process (xiii))
Step (viii) ~ (xii) suspended solids in the waste water entering the waste water treatment system 2518 from (SS), heavy metals, alkali metal compounds results in an increase of _{COD Cr,} nitrogen-containing compounds resulting in an increase of the total nitrogen content Has been. The concentration of insoluble substances in the inflow wastewater is 100 mg / L or less in terms of SS value and / or 100 NTU or less in terms of turbidity, and the concentration of water-soluble organic substances is 10000 mg / L or less in terms of COD _Cr . However, the discharged water 263 ′ flowing out from the waste water treatment system 2518 can be reused as it is in the terephthalic acid production process from the viewpoint of water quality, and must be discharged in large quantities in public water areas.

The wastewater treatment process (xiii) includes, for example, the following steps (a) to (f) or steps (c) to (f).
(A) A step of biologically treating the waste water from steps (i) to (vi) with aerobic microorganisms in activated sludge in an aeration tank.
(B) Solid-liquid separation of the aeration tank mixed water biologically treated in the aeration tank in the precipitation tank.
(C) In the membrane-separated activated sludge treatment apparatus, while biologically treating the supernatant liquid from the sedimentation tank or the waste water from steps (i) to (vi) with aerobic microorganisms in the activated sludge and / or A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module after treatment
(D ′) A step of filtering permeated water that has permeated through the membrane module with a nanofiltration membrane in a nanofiltration membrane filtration device as necessary.
(E) A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution.
(F) An acid cleaning step of cleaning the membrane module with an acid aqueous solution.

  Steps (a) to (c), (e), and (f) are the same steps as steps (a) to (c), (e), and (f) in the first and second aspects, and the description thereof is omitted. To do.

<B-1. Third Embodiment in Production of Terephthalic Acid>
FIG. 14 is a diagram for explaining an embodiment of a second representative method for producing terephthalic acid. Hereinafter, an embodiment of the method for producing terephthalic acid according to the second invention of the present application for reducing the amount of wastewater flowing into the wastewater treatment system 2518 to the public water area will be described with reference to FIG.

  The embodiment described in FIG. 14 employs a membrane separation activated sludge treatment device in which an MF membrane flat membrane is immersed in an aeration tank instead of the conventional aerobic biological treatment method, and the permeated water obtained by the MF membrane separation treatment. Is introduced into a nanofiltration membrane (NF membrane) separation device to obtain water quality water that can be used for industrial water. Furthermore, in order to supply water used as process water, the degree of purification (purity) is improved by the adsorbent treatment described later.

  In the embodiment described in FIG. 14, in collecting and regenerating waste water from the terephthalic acid production process, the first aeration tank 21010, the first precipitation tank 21020, the second aeration tank 21030, and the second An MF membrane module 21050 disposed in the aeration tank 21030, and a nanofiltration membrane filtration device 21060 connected to the outlet side of the MF membrane module 21050 (hereinafter referred to as “NF membrane” as a nanofiltration membrane, a nanofiltration membrane filtration device) A wastewater treatment system comprising: a reuse water tank 21070 connected to the outlet side of the NF membrane filtration apparatus 21060; and an adsorbent treatment device 21080 connected to the reuse water tank 21070. 21000 is used.

(Wastewater treatment system 21000)
The wastewater treatment system 21000 includes a first aeration tank 21010, a first precipitation tank 21020 connected to the first aeration tank 21010, a second aeration tank 21030 connected to the first precipitation tank 21020, MF membrane module 21050 disposed in second aeration tank 21030, NF membrane filtration device 21060 connected to the exit side of MF membrane module 21050, and reuse connected to the exit side of NF membrane filtration device 21060 A water tank 21070 and an adsorbent treatment apparatus 21080 connected to the reuse water tank 21070 are provided. The second settling tank 21040 indicated by a broken line in FIG. 14 is not used because it is not used. The wastewater that has flowed into the wastewater treatment system 21000 undergoes aerobic biological treatment in two stages while being sequentially transferred from the first aeration tank 21010 to the second aeration tank 21030.
The wastewater treatment system 21000 includes a membrane separation activated sludge treatment apparatus. That is, the MF membrane module 21050 is disposed so as to be immersed in the second aeration tank 21030, and the wastewater that has undergone the second-stage aerobic biological treatment in the second aeration tank 21030 is the MF membrane module 21050. In the membrane separation treatment. Water that has permeated through the MF membrane included in the MF membrane module 21050 is taken out as permeated water r. The permeated water r is transferred to the NF membrane filtration device 21060 connected to the outlet side of the MF membrane module 21050.

(Chemical tank)
The wastewater treatment system 21000 includes a first chemical liquid tank (not shown) for storing a hypochlorite aqueous solution for cleaning the MF membrane module 21050; and a second chemical liquid tank for storing an acid aqueous solution for cleaning the MF membrane module 21050. (Not shown); and a controller (not shown) for controlling the supply of the chemical solution from the first chemical solution tank and the second chemical solution tank to the MF membrane module 21050. A control part is a thing of the same structure as the control part in the 1st-2nd aspect of the waste water treatment method of 2nd invention of this application, and abbreviate | omits description.
In the MF membrane module 21050, prevention of fouling due to deposition on the membrane surface is important. Although the deposition rate on the film surface can be reduced by crossflow or aerated air, clogging is unavoidable in the long term. As deposition on the film surface proceeds, the transmembrane pressure difference increases. If the transmembrane pressure exceeds a certain value, membrane cleaning with a chemical solution is required. As a chemical | medical solution which can be used for film | membrane washing | cleaning, what was illustrated in the 1st-2nd aspect of the waste water treatment method of 2nd invention of this application is mentioned. Membrane cleaning is performed in the same manner as steps (e) and (f) in the first and second aspects of the wastewater treatment method of the second invention of the present application.

(NF membrane filtration device 21060)
The NF membrane filtration device 21060 is a membrane filtration device including a nanofiltration membrane (NF membrane). The permeated water r flowing into the NF membrane filtration device 21060 is subjected to membrane separation processing by the NF membrane, and generates NF membrane permeated water s and NF membrane concentrated water t. The NF membrane is a liquid filtration membrane that blocks particles and polymers smaller than 2 nm, and has a pore diameter smaller than that of the MF membrane or UF membrane and larger than that of a general RO membrane. The NF membrane is also referred to as a loose RO membrane, and has a feature that it can be operated at a lower pressure than a general RO membrane.

  Examples of NF membrane materials that can be used in the NF membrane filtration apparatus 21060 include polyethylene, aromatic polyamide, and polyamides including crosslinked polyamides, aliphatic amine condensation polymers, heterocyclic polymers, polyvinyl alcohol, and cellulose acetate. Examples of the polymer may include one or a combination or mixture of two or more selected from these. In the third aspect of the second invention of the present application, the separation performance of an NF membrane composed of a polyamide-based material including an aromatic polyamide-based material or a crosslinked polyamide-based material is particularly high, and can be preferably employed.

  Many of the polyamide-based composite NF membranes have negative surface charges, and therefore, two types of NF membranes of the cation charge type and the anion charge type are controlled by controlling the surface charge. By combining the difference between the pore and the charge, it has the feature that the separation target of waste water can be expanded. In the NF membrane filtration apparatus 21060, it is possible to employ either a cationic charge type NF membrane or an anion charge type NF membrane.

  Examples of the NF membrane module that can be used in the NF membrane filtration device 21060 include a hollow fiber membrane type, a spiral membrane type, a tubular membrane type, a flat membrane type, and a pleated type. Two or more combinations can be selected and used. Among these, the spiral membrane type module is preferable from the viewpoint that the membrane area of the module per unit volume is large, which is advantageous for making the apparatus compact. Specific examples of these include “NTR-7250 (registered trademark)”, “NTR-7410 (registered trademark)” (all manufactured by Nitto Denko Corporation), “Film Tech (registered trademark)” NF series (The Dow Chemical Company) and the like. In addition, it is preferable to install a prefilter on the entrance side of the NF membrane module to protect the membrane.

  The operation pressure in the NF membrane filtration apparatus 21060 using an NF membrane is 0.2 MPa to 1.5 MPa, and can be operated at a lower pressure than a general RO membrane. Moreover, the water permeation | transmission flow velocity (flux) is large and it is possible to implement | achieve high processing efficiency.

The wastewater from the terephthalic acid production process treated in the present embodiment contains suspended solids (SS), heavy metals, alkali metals, compounds that increase COD _Cr , nitrogen-containing compounds that increase total nitrogen, and the like. Yes. The water quality of the wastewater treated in the present embodiment after the aerobic biological treatment is such that when it flows into the NF membrane filtration device 21060, the concentration of insoluble substances in water is 100 mg / L or less in terms of SS value and / or turbidity. (Turbidity) of 100 NTU or less, the concentration of water-soluble organic substance is 100 mg / L or less for COD _Cr , 10 mg / L or less for BOD ₅ and the electric conductivity is 500 to 10,000 μS / cm as an indicator of the concentration of water-soluble inorganic substance. It is preferable that the pH is 5.0 to 9.5. The pH is usually 8 or more, indicating alkalinity, but in the second invention of the present application, treatment by membrane separation is possible if the pH is in the range of 5.0 to 9.5.

The water quality of the NF membrane permeated water s collected from the NF membrane filtration device 21060 depends on the permeability, but most of the metal ions and residual organic substances are removed, and the water quality is high. The NF membrane permeated water s is stored in the reuse water tank 21070 and is supplied from the reuse water tank 21070 to the terephthalic acid production process as industrial water (cooling water) u, or transferred to the adsorbent treatment device 21080 for further adsorbent treatment. Then, it is supplied to the terephthalic acid production process as adsorbed purified water v. Thus, it has been impossible in the past to regenerate wastewater from the terephthalic acid production process and supply it again to the terephthalic acid production process. In addition, the ratio which distributes NF membrane permeated water s to supply of industrial water (cooling water) u and manufacture of adsorption purified water v can be selected suitably.
In particular, by performing a membrane separation process by combining a plurality of filtration membrane devices (for example, the MF membrane module 21050 and the NF membrane filtration device 21060 in this embodiment), it becomes easier to achieve the effect.

  On the other hand, the NF membrane concentrated water t discharged from the NF membrane filtration device 21060 contains various impurities in a concentrated manner, but if the properties of the wastewater to be treated are within the above-described range, further treatment is performed. Water quality has been improved to such an extent that it can be discharged into public waters without applying water. The release of the NF membrane concentrated water t to the public water area is the same as the RO membrane concentrated water c.

(Adsorbent processing device 21080)
When the NF membrane permeated water s is used as process water, the degree of purification (purity) is further improved by performing an adsorbent treatment using an adsorbent selected from various adsorbents in the adsorbent treatment apparatus 21080. As a result, it is possible to expand the application range of the recovered and reclaimed water as in the RO membrane permeated water b. Adsorbents that can be used in the adsorbent processing apparatus 21080 can include the same adsorbents as those mentioned for the adsorbent processing apparatus 2108, and the operation of the adsorbent processing apparatus 21080 is the same as that of the adsorbent processing apparatus 2108. It can be carried out. The adsorbent processing waste water w generated from the adsorbent processing apparatus 21080 is returned to the first aeration tank 21010 and biologically processed again.

  From the viewpoint of the amount of wastewater discharged into public water areas, a large amount of wastewater after biological treatment has been discharged to public water areas in the past. In this embodiment (FIG. 14) as well, the first embodiment (FIG. 11) and the first embodiment Similar to the embodiment of FIG. 2 (FIG. 12), the amount of water reused in the terephthalic acid production process is greatly increased by recovery and regeneration. It can be reduced to about 1. As a result, the amount of groundwater pumped up as a resource can be greatly reduced. Specifically, preferably 80% or more, more preferably 70% or more, more preferably 60% or more of the wastewater discharged from the steps (viii) to (xii) and used for biological treatment is used as membrane permeated water. It can be recovered and used as cooling water and / or process water in the terephthalic acid production process.

(Other embodiments)
In the above description of the method for producing terephthalic acid according to the second aspect of the present invention, the first aeration tank 21010, the first settling tank 21020, and the second aeration tank are used for recovering and regenerating waste water from the terephthalic acid production process. Although the form which performs aerobic biological treatment in two steps using 21030 was illustrated, the manufacturing method of the terephthalic acid of 2nd invention of this application is not limited to the said form. The aerobic biological treatment may be performed in only one stage. In such a case, the MF membrane module 21050 may be disposed in the first aeration tank 21010, and the first precipitation tank 21020 and Since the second aeration tank 21030 is not used, it becomes unnecessary. Even in such a case, the aspect of the MF membrane module 21050 can be the same.

  In the above description of the method for producing terephthalic acid of the second invention of the present application, an adsorbent treatment device 2108 is disposed downstream of the RO membrane filtration device 2106, and the adsorbent treatment is performed after the RO membrane separation treatment, and An example of the method for producing terephthalic acid in which the adsorbent treatment device 21080 is disposed downstream of the NF membrane filtration device 21060 and the adsorbent treatment is performed after the NF membrane separation treatment is illustrated. The method for producing the acid is not limited to these forms. An adsorbent treatment device may be disposed upstream of a filtration membrane device such as an RO membrane filtration device or an NF membrane filtration device, and the adsorbent treatment may be performed prior to the membrane separation treatment.

  Moreover, in the description regarding the manufacturing method of the terephthalic acid of 2nd invention of this application mentioned above, it combines the form which uses a membrane separation activated sludge processing apparatus and RO membrane filtration apparatus, and combines a UF membrane unit and RO membrane filtration apparatus. Although the form to use and the manufacturing method of the terephthalic acid of the form which uses a membrane separation activated sludge processing apparatus and the NF membrane filtration apparatus in combination were illustrated, the manufacturing method of the terephthalic acid of 2nd invention of this application is in these forms It is not limited. As a combination of the filtration membrane device, for example, a membrane separation activated sludge treatment device and a UF membrane unit may be used in combination, and the RO membrane filtration device and the NF membrane filtration device may not be used. Even in such a case, it goes without saying that the adsorbent treatment can be further performed in combination with the membrane separation treatment. The selection and combination of the filtration membrane device and the adsorbent treatment device can be appropriately determined in consideration of the relationship between the water quality desired for the recovered and reclaimed water and the reuse application.

(Function and effect)
According to the method for producing terephthalic acid of the second invention of the present application, since biological treatment and membrane separation treatment are combined, a large amount of waste water generated when producing terephthalic acid is used as industrial water (cooling water) and / or A process for producing terephthalic acid with improved economic efficiency and environmental compatibility, which can be recycled as process water and can reduce the amount of new water taken from the water source and the amount of water discharged to public water bodies.

  In the method for producing terephthalic acid according to the second invention of the present application, the biological treatment is included in the wastewater from the terephthalic acid production process by using an aerobic biological treatment or a combination of an aerobic biological treatment and an anaerobic biological treatment. Since it becomes easy to decompose organic substances, it becomes easy to regenerate a large amount of waste water generated when terephthalic acid is produced.

  In the method for producing terephthalic acid of the second invention of the present application, terephthalic acid is produced by performing the membrane separation treatment with at least one membrane module selected from the group consisting of an MF membrane module and a UF membrane module. It becomes easier to regenerate a large amount of drainage generated during the process.

  In the method for producing terephthalic acid according to the second invention of the present application, preferably, the method further comprises a step of subjecting at least a part of the permeated water to an adsorbent treatment to obtain adsorbed purified water, and a step of recovering the adsorbed purified water. In addition to regenerating large amounts of wastewater generated during the production of terephthalic acid to water having water quality that can be used as industrial water (cooling water), it is also necessary to regenerate water that has water quality that can be used as process water. Is possible.

  In the method for producing terephthalic acid according to the second aspect of the present invention, the method further comprises a step of subjecting at least a part of the permeated water to an adsorbent treatment to obtain an adsorbed purified water and a step of recovering the adsorbed purified water. When producing terephthalic acid, preferably by performing the treatment with at least one adsorbent selected from the group consisting of activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, and alkaline earth metal aluminate. It is easy to regenerate a large amount of waste water generated in step 1 to water having water quality that can be used as process water.

Moreover, in the manufacturing method of the terephthalic acid of 2nd invention of this application demonstrated above, it has the washing | cleaning step which wash | cleans a membrane module, and wash | cleans a membrane module with hypochlorite aqueous solution as this washing | cleaning step. It has a hypochlorite washing step and an acid washing step for washing the membrane module with an acid aqueous solution in this order, and the interval from the end of the hypochlorite washing step to the start of the next acid washing step is The acid washing step is started when it is within 48 hours and / or when the transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than the transmembrane pressure difference after the start of operation. Therefore, the transmembrane pressure difference of the membrane module 35 can be kept low during the biological treatment of the wastewater containing COD _Cr and containing heavy metals and performing the membrane separation treatment.
A membrane separation step may be performed between the hypochlorite cleaning step and the acid cleaning step.

  Hereinafter, the first invention of the present application will be specifically described by way of examples. However, the present invention is not limited to these examples.

<Experimental Examples 1-1 to 1-2>
(Drainage)
Cobalt acetate and manganese acetate were used as catalysts, and p-xylene was subjected to liquid phase oxidation in a solvent containing water and acetic acid in the presence of hydrogen bromide as a cocatalyst to obtain a crude terephthalic acid slurry. Next, the crude terephthalic acid slurry was subjected to solid-liquid separation to obtain a mother liquor and a crude terephthalic acid cake. The crude terephthalic acid cake was washed with water, dried and recovered as crude terephthalic acid. The recovered crude terephthalic acid and water were put into a hydrogenation reactor and subjected to hydrogenation treatment to form a slurry containing terephthalic acid, and then terephthalic acid was recovered. After recovering the catalyst from the mother liquor separated in the solid-liquid separation, waste water discharged together with the washing waste water was prepared. Table 1 shows the properties of this waste water.

(Experimental example 1-1)
The wastewater treatment system has a configuration in which a heavy metal concentration reduction treatment system using a chelate resin having the configuration shown in FIG. 1 is installed, and treated wastewater that has been treated by the system is introduced into a wastewater treatment system having the configuration shown in FIG. did.
In the heavy metal concentration reduction step, first, the pH of the waste water is set to 5.5 in the pH adjustment tank 101, and the chelate resin shown in Table 2 (Lewatit (registered trademark) Monoplus TP 207, manufactured by Symphonic Chemicals Inc. A LANXESS COMPANY) is filled. The chelate resin towers 102 and 103 were passed through. Incidentally, the chelate resin ions are converted into sodium-type by theoretical amount. The wastewater contains 5 ppm by weight of Co as a heavy metal, and contains trace amounts of Mn and terephthalic acid and p-toluic acid as organic compounds. The chelate resin towers 102 and 103 are both fixed bed flow reactors having a substantially cylindrical shape, and the ratio of the inner diameter and the height of the portion filled with the chelate resin is 1.0: 0.7, The chelate resin particles were filled up to 50% of the height. The liquid flow through the chelate resin towers 102 and 103 is a circulation system, and two (102, 103) are arranged in parallel and can be switched. For the chelate resin tower 102 or 103 that has reached the breakthrough region, operations such as regeneration, washing, and ion exchange, which will be described later, are performed.
The temperature of the waste water adjusted to pH 5.5 was 55 ° C., and the solution was passed through the chelate resin tower 102 at a linear velocity of 8.9 m / hr. The waste water after the liquid passing treatment was sent to the storage tank 104 and stored, and then sent to the waste water treatment system (FIG. 2). When the Co concentration in the effluent at the outlet of the chelate resin tower 102 was 1 ppm by weight or more, it was regarded as a breakthrough region, and the liquid flow was continuously performed by switching to the chelate resin tower 103.
In addition, the Co concentration in the treated waste water after passing was about 0.01 to 0.04 ppm by weight in the initial stage of operation. Thereafter, the Co concentration in the treated waste water after passing through gradually increased, but could be maintained at less than 1 ppm by weight as described above. From this result, the Co concentration in the wastewater sent to the wastewater treatment system shown in FIG. 8 is normally 5 ppm by weight, but can be suppressed to less than 1 ppm by performing heavy metal reduction treatment. It was. (In this experimental example, the breakthrough region is defined when the Co concentration is 1 ppm by weight or more. However, the breakthrough region can be appropriately set as long as it exceeds the initial Co concentration. For example, it can be set as appropriate according to the regulation of drainage.)
Next, in order to regenerate (desorb) the adsorbed Co and other heavy metals on the chelate resin tower 102 that has reached the breakthrough region, a regenerant tank is used with a 10 wt% aqueous solution of hydrogen bromide as a regenerant. The solution was passed through 106. The temperature of the regenerant at this time was room temperature, and the liquid flow rate was 5 m / hr. By passing the liquid for 1 hour or longer, 90% or more of the adsorbed Co was desorbed. The regenerated heavy metal compound such as Co was stored in the catalyst secondary recovery liquid tank 105 together with the hydrogen bromide water as a regenerant, and was reused as a catalyst secondary recovery liquid in the oxidation reaction step of p-xylene.
After completion of the regeneration operation with hydrogen bromide water, washing was performed by passing water through the chelate resin tower 102 to remove trace metals remaining in the resin. Thereafter, in order to prepare for the next adsorption, a 5% by weight aqueous caustic soda solution was passed from the caustic soda tank 108 and the reserve tank 109 into the chelate resin tower 102 which was made into a hydrogen form by the regenerating solution (hydrogen bromide aqueous solution). This liquid flow was an up flow, the linear velocity was 5 m / hr, and the temperature of the liquid was 35 ° C.
The heavy metal reduction treatment was continuously performed by switching the chelating resin adsorption, washing, regeneration (desorption), washing, and ionization in a series of repetition operations in the chelate resin towers 102 and 103.
As the membrane unit, the membrane unit shown in FIG. 3 in which the air diffuser 32 and the membrane module 35 were integrated was used.
Table 1 shows water tank capacities of the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30.

Wastewater treatment was performed on the treated wastewater subjected to the heavy metal reduction step using a wastewater treatment system having the configuration shown in FIG. (Examples 1-1 and 1-2)
The properties of waste water and treated waste water and the amount of treated water are shown in Table 1.
The MLSS concentration, HRT (hydraulic residence time), and COD _Cr volumetric load of the aeration tank 10 were as shown in Table 1.
MLSS concentration of the membrane separation activated sludge treatment apparatus 30, HRT (hydraulic retention time), _{COD Cr} volumetric loading was set to values shown in Table 1.
The amount of returned sludge from the settling tank 20 was the amount shown in Table 1.
Table 1 shows the properties of the supernatant from the settling tank 20 and the permeated water from the membrane module 35.

(Experimental example 1-2)
Change the properties of wastewater and treated wastewater and the amount of treated water to the values shown in Table 1, change the HRT (hydraulic residence time) and COD _Cr volume load of the aeration tank 10 to the values shown in Table 1, and membrane separation activated sludge Except that the HRT (hydraulic residence time) and COD _Cr volumetric load of the treatment apparatus 30 were changed to the values shown in Table 1, wastewater treatment was performed in the same manner as in Experimental Example 1-1.
Table 1 shows the properties of the supernatant from the settling tank 20 and the permeated water from the membrane module 35.

(result)
In Experimental Examples 1-1 and 1-2, the water quality of the permeated water was very good, the treatment could be performed continuously, and the residence time was short. A short residence time means that the installation area can be reduced.

<Examples 1-1 to 1-2>
(Example 1-1)
Wastewater treatment was performed in the same wastewater treatment system as in Experimental Example 1-1.
The transmembrane pressure difference of the membrane module 35 after the start of operation was 10 kPa.
175 days after the start of operation, when the transmembrane pressure of the membrane module 35 reached 37 kPa, the membrane separation step was interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution was passed through the membrane module 35 through ² L / filtration membrane 1 m ² . The membrane module was washed by passing the liquid over 30 minutes and allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 14 kPa.
The membrane separation step was resumed at the same conditions.
Ten hours after the end of the first washing, when the transmembrane pressure difference of the membrane module 35 reached 14 kPa, the membrane separation step was interrupted, and 2 L of citric acid aqueous solution was added to the membrane module 35 by 2 L / filtration membrane 1 m ^2. The membrane module was washed by letting it pass over 30 minutes and allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 14 kPa.
The membrane separation step was resumed at the same conditions.
480 hours after the end of the second washing, when the transmembrane pressure of the membrane module 35 reaches 26 kPa, the membrane separation step is interrupted, and 2% citric acid aqueous solution is added to the membrane module 35 by 2 L / filtration membrane 1 m ^2. The membrane module was washed by letting it pass over 30 minutes and allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 21 kPa.
The membrane separation step was resumed at the same conditions.
720 hours after the end of the third washing, when the transmembrane pressure of the membrane module 35 reaches 22 kPa, the membrane separation step is interrupted, and 2 L of citric acid aqueous solution is added to the membrane module 35 by 2 L / filtration membrane 1 m ^2. The membrane module was washed by letting it pass over 30 minutes and allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 21 kPa.
The membrane separation step was resumed at the same conditions.
720 hours after the end of the fourth washing, when the transmembrane pressure of the membrane module 35 reaches 21 kPa, the membrane separation step is interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution is filtered into the membrane module 35 at 2 L / filter. The membrane module was washed by passing through the membrane at a rate of 1 m ² over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 20 kPa.
The membrane separation step was resumed at the same conditions.
Ten hours after the end of the fifth washing, when the transmembrane pressure of the membrane module 35 reaches 20 kPa, the membrane separation step is interrupted, and 2 L of citric acid aqueous solution is added to the membrane module 35 by 2 L / filtration membrane 1 m ^2. The membrane module was washed by letting it pass over 30 minutes and allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 21 kPa.
The membrane separation step was resumed at the same conditions.

(Example 1-2)
Wastewater treatment was performed in the same wastewater treatment system as in Experimental Example 1-1.
The transmembrane pressure difference of the membrane module 35 after the start of operation was 10 kPa.
4200 hours after the start of operation, when the transmembrane pressure of the membrane module 35 reached 23 kPa, the membrane separation step was interrupted, and 3000 mg / L sodium hypochlorite aqueous solution was added to the membrane module 35 at ² L / filtration membrane 1 m ² . The membrane module was washed by passing the solution over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 23 kPa.
The membrane separation step was resumed at the same conditions.
Ten hours after the completion of the first washing, when the transmembrane pressure of the membrane module 35 reaches 23 kPa, the membrane separation step is interrupted, and 2% by weight of citric acid aqueous solution is added to the membrane module 35 at 2 L / filtration membrane 1 m ^2. The membrane module was washed by letting it pass over 30 minutes and allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 24 kPa.
The membrane separation step was resumed at the same conditions.
456 hours after the end of the second washing, when the transmembrane pressure of the membrane module 35 reaches 17 kPa, the membrane separation step is interrupted, 2 L of citric acid aqueous solution is added to the membrane module 35 at 2 L / filtration membrane 1 m ^2. The membrane module was washed for 30 minutes with the flow rate of and then left for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 16 kPa.
The membrane separation step was resumed at the same conditions.
864 hours after the end of the third washing, the membrane separation step was interrupted when the transmembrane pressure difference of the membrane module 35 reached 18 kPa, and 2 L of citric acid aqueous solution was added to the membrane module 35 at 2 L / filtration membrane 1 m ^2. The membrane module was washed by letting it pass over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 17 kPa.
The membrane separation step was resumed at the same conditions.
480 hours after the end of the fourth washing, when the transmembrane pressure of the membrane module 35 reaches 24 kPa, the membrane separation step is interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution is filtered into the membrane module 35 at 2 L / filter. The membrane module was washed by passing through the membrane at a rate of 1 m ² over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 20 kPa.
The membrane separation step was resumed at the same conditions.

Hereinafter, although the 2nd invention of this application is concretely explained by an example, the present invention is not limited to these.
<Experimental example and comparative experimental example>
(Drainage)
Cobalt acetate and manganese acetate were used as catalysts, and p-xylene was subjected to liquid phase oxidation in a solvent containing water and acetic acid in the presence of hydrogen bromide as a cocatalyst to obtain a crude terephthalic acid slurry. Next, the crude terephthalic acid slurry was made into a mother liquor and a crude terephthalic acid cake by solid-liquid separation. The crude terephthalic acid cake was washed with water, dried and recovered as crude terephthalic acid. The recovered crude terephthalic acid and water were put into a hydrogenation reactor and subjected to hydrogenation treatment using hydrogen to form a slurry containing terephthalic acid, and then terephthalic acid was recovered. After recovering the catalyst from the mother liquor separated in the solid-liquid separation, waste water discharged together with the washing waste water was prepared. Table 3 shows the properties of this drainage.

(Experimental example 2-1)
As the waste water treatment system, the waste water treatment system of FIG. 8 was used.
As the membrane unit, the membrane unit shown in FIG. 3 in which the air diffuser 32 and the membrane module 35 were integrated was used.
Table 3 shows the water tank capacities of the aeration tank 10 and the membrane separation activated sludge treatment apparatus 30.

Wastewater treatment was performed using this drainage system.
The amount of treated water was the amount of water shown in Table 3.
The MLSS concentration, HRT (hydraulic residence time), and COD _Cr volumetric load in the aeration tank 10 were as shown in Table 3.
MLSS concentration of the membrane separation activated sludge treatment apparatus 30, HRT (hydraulic retention time), _{COD Cr} volumetric loading was set to values shown in Table 3.
The amount of returned sludge from the settling tank 20 was the amount shown in Table 3.
Table 3 shows the properties of the supernatant from the settling tank 20 and the permeated water from the membrane module 35.

(Experimental Examples 2-2 to 2-3)
The amount of treated water was changed to the amount of water shown in Table 3, the HRT (hydraulic residence time) of the aeration tank 10 and the COD _Cr volumetric load were changed to the values shown in Table 3, and the HRT (water The waste water treatment was performed in the same manner as in Experimental Example 2-1, except that the physical residence time) and the COD _Cr volumetric load were changed to the values shown in Table 3.
Table 3 shows the properties of the supernatant from the settling tank 20 and the permeated water from the membrane module 35.

(Comparative Experimental Example 2-1)
As the wastewater treatment system, a conventional wastewater treatment system shown in FIG. 15 was used.
Table 3 shows the water tank capacities of the first aeration tank 1010 and the second aeration tank 1030.

Wastewater treatment was performed using this drainage system.
The amount of treated water was the amount of water shown in Table 3.
MLSS concentration in the first aeration tank 1010, HRT (hydraulic retention time), _{COD Cr} volumetric loading was set to values shown in Table 3.
MLSS concentration in the second aeration tank 1030, HRT (hydraulic retention time), _{COD Cr} volumetric loading was set to values shown in Table 3.
The amount of returned sludge from the first settling tank 1020 and the amount of returned sludge from the second settling tank 1040 were as shown in Table 3.
Table 3 shows the properties of the supernatant liquid from the first precipitation tank 1020 and the supernatant liquid from the second precipitation tank 1040.

(result)
In Experimental Examples 2-1 to 2-3, the quality of treated water is good and the residence time is small, so the installation area is small. On the other hand, in Comparative Experimental Example 2-1, which does not use membrane separation, the quality of the treated water is somewhat worse than in Experimental Example 2-1, but the installation area increases because the second sedimentation tank is used.

<Example>
(Example 2-1)
Waste water treatment was performed in the same waste water treatment system as in Experimental Example 2-1.
The transmembrane pressure difference of the membrane module 35 after the start of operation was 10 kPa.
After 3744 hours from the start of operation, when the transmembrane pressure of the membrane module 35 reached 20 kPa, the membrane separation step was interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution was added to the membrane module 35 at 2 L / filtration membrane 1 m. ^The membrane module 35 was washed by passing the solution at a flow rate of ² over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 14 kPa.
The membrane separation step was resumed at the same conditions.
Ten hours after the first washing, when the transmembrane pressure of the membrane module 35 reached 14 kPa, the membrane separation step was interrupted, and 2 L of a 2% by mass citric acid aqueous solution was added to the membrane module 35 at 1 m ^{2 of} filtration membrane. The membrane module 35 was washed by passing the solution for 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 13 kPa.
The membrane separation step was resumed at the same conditions.
888 hours after the second washing, when the transmembrane pressure of the membrane module 35 reached 19 kPa, the membrane separation step was interrupted, and 2 L of a 2% by mass citric acid aqueous solution was added to the membrane module 35 at a rate of 2 L / filtration membrane 1 m ² . The membrane module 35 was washed by passing the liquid through over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 18 kPa.
The membrane separation step was resumed at the same conditions.
480 hours after the third washing, when the transmembrane pressure of the membrane module 35 reached 26 kPa, the membrane separation step was interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution was filtered into the membrane module 35 at 2 L / filter. The membrane module 35 was washed by passing through the membrane in an amount of 1 m ² over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 15 kPa.
The membrane separation step was resumed at the same conditions.
One hour after the fourth washing, when the transmembrane pressure of the membrane module 35 reached 15 kPa, the membrane separation step was interrupted, and 2% by mass of a 2% by mass citric acid aqueous solution was added to the membrane module 35/1 m ^{2 of} filtration membrane. The membrane module 35 was washed by passing the solution for 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 14 kPa.
The membrane separation step was resumed at the same conditions.
After 1440 hours from the fifth washing, when the transmembrane pressure of the membrane module 35 reaches 19 kPa, the membrane separation step is interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution is filtered into the membrane module 35 at 2 L / filter. The membrane module 35 was washed by passing through the membrane in an amount of 1 m ² over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 18 kPa.
The membrane separation step was then resumed under the same conditions.

(Example 2-2)
Waste water treatment was performed in the same waste water treatment system as in Experimental Example 2-1.
The transmembrane pressure difference of the membrane module 35 after the start of operation was 10 kPa.
After 3696 hours from the start of operation, when the transmembrane pressure of the membrane module 35 reached 20 kPa, the membrane separation step was interrupted, and 2% by mass of citric acid aqueous solution was passed through the membrane module 35 through 2 L / filtration membrane 1 m ² . The membrane module 35 was washed by passing the liquid over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 18 kPa.
The membrane separation step was resumed at the same conditions.
216 hours after the first washing, when the transmembrane pressure of the membrane module 35 reached 53 kPa, the membrane separation step was interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution was filtered into the membrane module 35 at 2 L / filter. The membrane module 35 was washed by passing through the membrane in an amount of 1 m ² over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 16 kPa.
The membrane separation step was resumed at the same conditions.
5 hours after the second wash, where the transmembrane pressure of the membrane module 35 becomes 16 kPa, membrane separation step is interrupted, the membrane module 35, a 2 mass% aqueous citric acid 2L / filtration membrane 1 m ² The membrane module 35 was washed by passing the solution for 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 14 kPa.
The membrane separation step was resumed at the same conditions.
480 hours after the third washing, when the transmembrane pressure difference of the membrane module 35 reached 26 kPa, the membrane separation step was interrupted, and 2 L of a 2% by mass citric acid aqueous solution was added to the membrane module 35 at 2 L / filtration membrane 1 m ² . The membrane module 35 was washed by passing the liquid through over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 21 kPa.
The membrane separation step was resumed at the same conditions.
After 744 hours from the fourth washing, when the transmembrane pressure difference of the membrane module 35 reached 22 kPa, the membrane separation step was interrupted, and 2 L of a 2% by mass citric acid aqueous solution was added to the membrane module 35 at a filtration membrane of 1 m ² . The membrane module 35 was washed by passing the liquid through over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 20 kPa.
The membrane separation step was resumed at the same conditions.
816 hours after the fifth washing, when the transmembrane pressure difference of the membrane module 35 reached 21 kPa, the membrane separation step was interrupted, and 2% citric acid aqueous solution was passed through the membrane module 35 through 2 L / filtration membrane 1 m ² . The membrane module 35 was washed by passing the liquid over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 20 kPa.
The membrane separation step was resumed at the same conditions.
Five hours after the sixth washing, when the transmembrane pressure difference of the membrane module 35 reached 20 kPa, the membrane separation step was interrupted, and 3000 mg / L of sodium hypochlorite aqueous solution was filtered into the membrane module 35 at 2 L / filter. The membrane module 35 was washed by passing through the membrane in an amount of 1 m ² over 30 minutes, and then allowed to stand for 90 minutes. The transmembrane pressure difference of the membrane module 35 was 21 kPa.
The membrane separation step was resumed at the same conditions.

<Experimental examples 3-1 to 3-3>
(Experimental example 3-1)
Experimental Example 3-1 is for confirming that heavy metal in wastewater affects the blockage of the membrane module in the membrane separation step in which sludge and permeated water are obtained by performing solid-liquid separation with respect to wastewater. This is an experiment.
In Experimental Example 3-1, solid-liquid separation was performed in the membrane separation tank for the wastewater from which the heavy metal cobalt was almost removed (Example 3-1) and the wastewater to which cobalt was added (Comparative Example 3-1). The transmembrane pressure difference of the membrane module in the membrane separation tank was measured over time.
The experimental flow is as shown in FIG. 16, and will be described in detail below. In Experimental Example 3-1, the hypochlorite washing step and the acid washing step are not performed.

<Example 3-1>
First, wastewater from which cobalt was almost removed (cobalt concentration in wastewater: 0.5 mg / L) was filled in an existing aeration tank shown in FIG. The waste water filled in the aeration tank is supplied from the second aeration tank (31 in FIGS. 8 and 16) to the membrane separation tank 31 ′ of the experimental apparatus shown in FIG. did. In order to avoid excessive concentration in the membrane separation tank 31 ′, the amount to be supplied was set to 3 times or more of the amount of filtered water, and the excess was discharged from the membrane separation tank 31 ′ by overflow 56 ′. In the membrane separation tank 31 ', the drainage was solid-liquid separated into sludge and permeated water by operating the suction pump 36' to reduce the pressure inside the membrane module. At this time, air was introduced into the membrane module 35 ′ from the diffuser tube 32 ′, and solid-liquid separation was performed while washing the surface of the hollow fiber membrane of the membrane module 35 ′. The transmembrane pressure difference of the membrane module 35 ′ during the solid-liquid separation was measured over time. The permeated water obtained by the solid-liquid separation was separated from the sludge through the permeated water flow path 56 ′ by the suction pump 36 ′.

The details of each condition in the experiment are as follows.
・ Cobalt concentration in waste water in existing aeration tank: 0.5 mg / L
・ Drainage flow rate from existing aeration tank: 9L / min
Membrane area of membrane module in membrane separation tank: 0.073 m ² (PVDF hollow fiber membrane, nominal pore diameter 0.4 μm)
・ Flux (flux): 0.5m / day (suction for 7 minutes, stop for 1 minute)
・ Suction flow rate: 29 mL / min (0.073 m ² × 0.8 m / day × 8/7)
・ Air flow rate: 20L / min
The measurement results are shown in FIG.

(Comparative Example 3-1)
In Comparative Example 3-1, the waste water from which cobalt was almost removed (Cobalt content 0.5 mg / L) in Example 3-1 was supplied to the membrane separation tank 31 ′, and then the aqueous cobalt acetate solution was supplied to the membrane separation tank. Example 3-1 was repeated except that the cobalt acetate aqueous solution was added from the tank 91 ′ containing the water by a pump so that the cobalt concentration in the waste water in the membrane separation tank 31 ′ was 5 mg / L.
The measurement results are shown in FIG.

  As shown in FIG. 17, in Example 3-1, the cobalt in the wastewater was almost removed, so that even though the number of filtration days had elapsed, the transmembrane differential pressure of the membrane module was low and stable. In Comparative Example 3-1, in which cobalt was added, the transmembrane pressure difference increased by 15 kPa or more in about 2 weeks after the start of filtration. From the above results, it can be seen that by removing cobalt in the wastewater as a pre-stage for solid-liquid separation of the wastewater, it is possible to avoid clogging of the membrane module and perform the subsequent membrane separation step efficiently. It was.

(Experimental example 3-2)
Experimental Example 3-2 is a cleaning step for cleaning the membrane module 35 ′. This is an experiment for confirming that the (interval) affects the blockage of the membrane module.
In this experiment, wastewater from which cobalt was almost removed (cobalt concentration in wastewater: 0.5 mg / L) was used, and cobalt acetate was not added to the wastewater.

In Experimental Example 3-2, after solid-liquid separation of waste water was performed as in Experimental Example 3-1, 0.3% by mass from the first chemical liquid tank 90 ′ in FIG. 16 through the chemical liquid flow path 59 ′. The membrane module 35 'was washed by supplying the aqueous hypochlorite solution to the membrane module 35' by a pump 37 '(hypochlorite washing step). The amount of the hypochlorite aqueous solution passed was ² L / filter membrane 1 m ² and passed for 30 minutes. After the passage of the hypochlorite aqueous solution, the membrane module 35 'was allowed to stand for the following time. After the membrane module 35 'is left still, the membrane module 35' is cleaned by supplying 2% by mass of citric acid from the second chemical tank 92 'through the chemical channel 59' to the membrane module 35 'by the pump 37'. (Acid wash step).
The experimental conditions in the solid-liquid separation are as follows: flux (flux) is 0.8 m / day (suction for 7 minutes, stop for 1 minute), and suction flow rate is 46 mL / min (0.073 m ² × 0.8 m / day ×). The experimental conditions are the same as those in Experimental Example 3-1, except that 8/7).

In Example 3-2, a hypochlorite washing step was performed at 26 kPa where the transmembrane pressure difference of the membrane module 35 ′ was in the range of 3 to 30 kPa (11 days after the start of filtration), and hypochlorite was obtained. The acid wash step was started 24 hours after the end of the wash step.
In Comparative Example 3-2, the hypochlorite washing step was performed at 40 kPa where the transmembrane pressure difference of the membrane module 35 ′ exceeded 30 kPa (58 days after the start of filtration), and at the end of the hypochlorite washing step The acid wash step was started 60 hours after 48 hours.
The measurement results are shown in FIGS.

As shown in FIG. 18, the hypochlorite washing step is performed within the range where the transmembrane pressure difference of the membrane module 35 ′ is 3 to 30 kPa, and the acid washing step is performed within 48 hours from the end of the hypochlorite washing step. In Example 3-2 that started the process, the membrane pressure difference of the membrane module 35 ′ was stable even after the cleaning step, and the subsequent filtration treatment could be continued.
On the other hand, as shown in FIG. 19, in Comparative Example 3-2 in which the hypochlorite cleaning step was performed after the transmembrane pressure difference of the membrane module 35 ′ exceeded 30 kPa, the transmembrane difference of the membrane module 35 ′. The pressure increased excessively, and the transmembrane pressure did not decrease sufficiently even after washing. In Comparative Example 3-2, since the acid cleaning step is started over 48 hours from the end of the hypochlorite cleaning step, the transmembrane differential pressure temporarily decreases, but increases immediately. As a result.

(Experimental example 3-3)
Experimental Example 3-3 was the same as Comparative Example 3-1, except that cobalt acetate was added to the wastewater in the membrane separation tank 31 ′, so that the cobalt concentration in the wastewater in the membrane separation tank 31 ′ was 5 mg / L. Repeated Experimental Example 3-2.
In Comparative Example 3-3-1, a hypochlorite washing step was performed at 20 kPa where the transmembrane pressure difference of the membrane module 35 ′ was in the range of 3 to 30 kPa (14 days after the start of filtration). The acid wash step was started 24 hours after the end of the acid salt wash step.
In Comparative Example 3-3-2, the hypochlorite washing step was performed at 41 kPa where the transmembrane pressure difference of the membrane module 35 ′ exceeded 30 kPa (15 days after the start of filtration), and the hypochlorite washing step The acid wash step was started 60 hours later than 48 hours from the end.
The measurement results are shown in FIGS.

  As shown in FIG. 20, in Comparative Example 3-3-1, the hypochlorite washing step was performed within the range where the transmembrane differential pressure of the membrane module 35 ′ was 3 to 30 kPa. Therefore, even if acid cleaning is performed 24 hours after the end of hypochlorite cleaning, the transmembrane differential pressure of the membrane module 35 'temporarily decreases, but the subsequent transmembrane differential pressure increases. The speed has increased. In addition, as shown in FIG. 21, in Comparative Example 3-3-2, the cleaning effect was hardly obtained even after acid cleaning after hypochlorite cleaning and after the transmembrane differential pressure increased. It became.

The wastewater treatment method of the present invention is useful for treating wastewater that is high in COD _Cr and contains heavy metals (for example, wastewater discharged in a terephthalic acid production process).
The method for producing terephthalic acid according to the present invention can be suitably used for industrial production of terephthalic acid in recent years where cost savings are required by protecting the global environment and saving water resources.

DESCRIPTION OF SYMBOLS 10 Aeration tank 20 Precipitation tank 30 Membrane separation activated sludge processing apparatus 35 Membrane module 40 Reverse osmosis membrane filtration apparatus 42 Reverse osmosis membrane 90 1st chemical | medical solution tank 92 2nd chemical | medical solution tank 101 pH adjustment tank (regulation tank)
102 Treatment tower (chelate resin tower)
103 Treatment tower (chelate resin tower)
104 Disposal wastewater tank (storage tank)
105 Catalyst secondary recovery liquid tank (recovered liquid tank)
106 Regenerant tank 107 Desorption operation final liquid tank 108 Caustic soda tank 109 Caustic soda preliminary tank 211 Oxidation reactor 212 First solid-liquid separator 213 Hydrogenation processor 214 Crystallizer 215 Second solid-liquid separator 216 Dryer 217 Solvent recovery device 218 Acetic acid recovery device 219 Catalyst recovery / regeneration device 220 p-Toluic acid recovery device 221 Wastewater treatment system 211 ′ Crude terephthalic acid slurry 212 ′ Crude terephthalic acid 213 ′ Hydrogenation treatment liquid 214 ′ Terephthalic acid slurry 215 ′ Terephthalic acid cake 216 'Terephthalic acid 217' Oxidation exhaust gas cleaning water 218 'Oxidation reaction mother liquor (for purging)
219 'Evaporating solvent 220' Mother liquor concentrated slurry 221 'Methyl acetate recovery tower bottom liquid 222' Regenerated catalyst recovery separation mother liquor 223 'Condensed water generated during crystallization 224' Terephthalic acid separation mother liquor 225 'Separated mother liquor such as p-toluic acid 226' Vent gas Washing water 227 ′ Discharged water 2511 Oxidation reaction device 2512 Additional oxidation reaction device 2513 Solid-liquid separation device 2514 Drying device 2515 Solvent recovery device 2516 Acetic acid recovery device 2517 Catalyst recovery / regeneration device 2518 Wastewater treatment system 251 ′ Crude terephthalic acid slurry 252 ′ Terephthalic acid slurry 253 'Terephthalic acid cake 254' Terephthalic acid 255 'Oxidation exhaust gas cleaning water 256' Additional oxidation exhaust gas cleaning water 257 'Oxidation reaction mother liquor (purged)
258 'Evaporating solvent 259' Mother liquor concentrated slurry 260 'Methyl acetate recovery tower bottom liquid 261' Regenerated catalyst recovery separation mother liquor 262 'Vent gas cleaning water 263' Effluent water 2100, 2200, 21000 Wastewater treatment system 2101, 21010 First aeration tank 2102 21020 First sedimentation tank 2103, 2103a, 21030 Second aeration tank 2104, 2104a, 21040 Second sedimentation tank 2105, 21050 MF membrane module 2106 RO membrane filtration device 2107, 21070 Reuse water tank 2108, 21080 Adsorbent treatment Equipment 2110 UF membrane unit 21060 NF membrane filtration device a, h, r treated water b, k RO membrane permeated water c, j RO membrane concentrated water d, l, u Industrial water (cooling water)
e, m, v Adsorbed purified water f, n, w Adsorbent-treated wastewater i UF membrane permeated water o UF membrane washed water s NF membrane permeated water t NF membrane concentrated water 1010 First aeration tank 1020 First sedimentation tank 1030 Second aeration tank 1040 Second settling tank

Claims (50)

A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10,000 mg / L and a heavy metal concentration of 0.1 to 200 ppm by weight,
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) having a washing step for washing the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The waste water treatment method, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours. A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10,000 mg / L and a heavy metal concentration of 0.1 to 200 ppm by weight,
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) having a washing step for washing the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The waste water treatment method, wherein the acid cleaning step is started when a transmembrane differential pressure of the membrane module becomes 3 kPa to 30 kPa higher than a transmembrane differential pressure after the start of operation.   The wastewater treatment method according to claim 1 or 2, wherein the heavy metal is cobalt and / or manganese.   The wastewater treatment method according to any one of claims 1 to 3, wherein the wastewater is wastewater discharged in a terephthalic acid production process.   The waste water treatment method according to any one of claims 1 to 4, wherein the acid is citric acid.   The wastewater treatment according to any one of claims 1 to 5, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step. Method.   The wastewater treatment method according to claim 1, wherein a surfactant is contained in the hypochlorite aqueous solution. A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) having a washing step for washing the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The method for producing terephthalic acid, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours. A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
(1) A heavy metal concentration reduction step for recovering heavy metals in the waste water to be treated waste water;
(2) A membrane separation step for obtaining sludge and permeate by performing solid-liquid separation with a membrane module while performing biological treatment of the treated wastewater or after biological treatment of the treated wastewater;
(3) a cleaning step of cleaning the membrane module;
The washing step includes
A hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution;
The membrane module is washed with an acid aqueous solution, and has an acid washing step in the order described above.
The method for producing terephthalic acid, characterized in that the acid washing step is started when a transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than a transmembrane pressure difference after starting operation.   The method for producing terephthalic acid according to claim 8 or 9, wherein the aqueous acid solution is an aqueous citric acid solution. The COD _Cr in the waste water is 3000 mg / L to 10000 mg / L, and the heavy metal concentration in the waste water is 0.1 wt ppm to 200 wt ppm. A method for producing terephthalic acid according to Item 1.   The terephthalic acid according to any one of claims 8 to 11, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step. Manufacturing method.   The method for producing terephthalic acid according to any one of claims 8 to 12, wherein the heavy metal is cobalt and / or manganese.   The method for producing terephthalic acid according to any one of claims 8 to 13, wherein a cobalt concentration in the treated waste water is 1/10 or less of a cobalt concentration in the waste water.   15. The heavy metal in the waste water is recovered by bringing the waste water into contact with the chelate resin and recovering the heavy metal in the waste water to the chelate resin in the heavy metal concentration reduction step. A process for producing terephthalic acid according to claim 1.   The method for producing terephthalic acid according to claim 15, wherein the pH of the waste water is 5.1 or more and 5.9 or less.   The method for producing terephthalic acid according to claim 15 or 16, wherein a flow rate of the waste water to the chelate resin when the waste water is brought into contact with the chelate resin is 5 m / hr or more and 14 m / hr or less. .   The method for producing terephthalic acid according to any one of claims 15 to 17, wherein a uniformity coefficient of the chelate resin is 1.4 or less.   The method for producing terephthalic acid according to any one of claims 15 to 18, wherein a reduction rate of Cu adsorption amount of the chelate resin is 11% / month or less.   20. The method according to claim 15, further comprising a step of regenerating the chelate resin by causing a regenerative agent to act on the chelate resin from which the heavy metal has been recovered to obtain a regenerated liquid containing heavy metal. A method for producing terephthalic acid according to 1.   The method for producing terephthalic acid according to claim 20, wherein the regenerant is hydrogen bromide having a concentration of 7.1 wt% or more and 19 wt% or less.   The method for producing terephthalic acid according to any one of claims 8 to 21, further comprising a step of separating the permeated water into membrane concentrated water and membrane permeated water by performing reverse osmosis membrane treatment.   The method for producing terephthalic acid according to claim 22, further comprising the step of further performing an adsorbent treatment on at least a part of the membrane permeated water to obtain adsorbed purified water.   The adsorbent treatment is performed with at least one adsorbent selected from the group consisting of activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, and alkaline earth metal aluminate. The method for producing terephthalic acid according to 23. The terephthalic acid production process comprises
oxidizing p-xylene to crude terephthalic acid;
The method for producing terephthalic acid according to any one of claims 8 to 24, further comprising a step of purifying the crude terephthalic acid to form terephthalic acid.   The method for producing terephthalic acid according to claim 25, wherein the step of purifying the crude terephthalic acid to form terephthalic acid includes a step of performing hydrogenation treatment on the crude terephthalic acid.   The method for producing terephthalic acid according to claim 25, wherein the step of purifying the crude terephthalic acid to form terephthalic acid includes a step of performing an additional oxidation reaction on the crude terephthalic acid.   28. At least a part of the membrane permeated water and / or at least a part of the adsorbed purified water are used as cooling water and / or process water in the terephthalic acid production process. A method for producing terephthalic acid according to Item 1.   The method for producing terephthalic acid according to any one of claims 8 to 28, wherein a surfactant is contained in the hypochlorite aqueous solution. A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10000 mg / L and a heavy metal concentration of 0.1 mass ppm to 200 mass ppm,
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The waste water treatment method, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours. A wastewater treatment method for treating wastewater having COD _Cr of 3000 mg / L to 10000 mg / L and a heavy metal concentration of 0.1 mass ppm to 200 mass ppm,
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The wastewater treatment method, wherein the acid cleaning step is started when a transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than a transmembrane pressure difference after the start of operation.   The wastewater treatment method according to claim 30 or 31, wherein the heavy metal is at least one selected from the group consisting of manganese and cobalt.   The wastewater treatment method according to any one of claims 30 to 32, wherein the wastewater is wastewater discharged in a terephthalic acid production process.   The wastewater treatment method according to any one of claims 30 to 33, wherein the acid is citric acid.   The wastewater treatment method according to any one of claims 30 to 34, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step.   The wastewater treatment method according to any one of claims 30 to 35, wherein a surfactant is contained in the hypochlorite aqueous solution. A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The method for producing terephthalic acid, wherein an interval from the end of the hypochlorite washing step to the start of the acid washing step is within 48 hours. A method for producing terephthalic acid having a wastewater treatment process for treating wastewater discharged in a terephthalic acid production process,
The wastewater treatment process
A membrane separation step for solid-liquid separation into sludge and permeate by a membrane module while performing biological treatment of the wastewater and / or after biological treatment of the wastewater;
A washing step for washing the membrane module,
As the cleaning step, first, perform a hypochlorite cleaning step of cleaning the membrane module with a hypochlorite aqueous solution, then perform an acid cleaning step of cleaning the membrane module with an aqueous acid solution,
The method for producing terephthalic acid, wherein the acid washing step is started when the transmembrane pressure difference of the membrane module becomes 3 kPa to 30 kPa higher than the transmembrane pressure difference after the start of operation.   The method for producing terephthalic acid according to claim 37 or 38, wherein the acid is citric acid. The method for producing terephthalic acid according to any one of claims 37 to 39, wherein COD _{Cr of the} waste water is 3000 mg / L to 10000 mg / L, and the heavy metal concentration is 0.1 mass ppm to 200 mass ppm. . The terephthalic acid production process comprises
oxidizing p-xylene into crude terephthalic acid;
The method for producing terephthalic acid according to any one of claims 37 to 40, comprising a step of purifying the crude terephthalic acid to form terephthalic acid.   The method for producing terephthalic acid according to claim 41, wherein the step of purifying the crude terephthalic acid includes a step of performing a hydrogenation treatment.   42. The method for producing terephthalic acid according to claim 41, wherein the step of purifying the crude terephthalic acid includes a step of performing an additional oxidation reaction.   44. The method for producing terephthalic acid according to any one of claims 37 to 43, wherein the acid washing step is performed a plurality of times between the hypochlorite washing step and the next hypochlorite washing step. The wastewater treatment process
45. The method for producing terephthalic acid according to any one of claims 37 to 44, further comprising a step of filtering the permeated water that has permeated through the membrane module with a reverse osmosis membrane filtration device. The wastewater treatment process
At least a part of the permeated water is further subjected to an adsorbent treatment to obtain purified purified water;
The method for producing terephthalic acid according to any one of claims 37 to 45, further comprising: recovering the adsorbed purified water.   The terephthalate according to claim 46, wherein the adsorbent treatment is performed with at least one adsorbent selected from the group consisting of activated carbon, ion exchange resin, synthetic zeolite, silica alumina, bentonite, and alkaline earth metal aluminate. Acid production method.   The method for producing terephthalic acid according to any one of claims 37 to 47, wherein at least a part of the recovered permeated water is used as cooling water and / or process water in the terephthalic acid production process.   48. The method for producing terephthalic acid according to claim 46 or 47, wherein at least a part of the recovered purified purified water is used as cooling water and / or process water in the terephthalic acid production process.   The method for producing terephthalic acid according to any one of claims 37 to 49, wherein the aqueous hypochlorite solution contains a surfactant.