JP5625705B2 - Method and apparatus for anaerobic treatment of wastewater containing terephthalic acid - Google Patents

Description

  The present invention relates to an anaerobic treatment method and treatment apparatus for terephthalic acid-containing wastewater, and more particularly to a method and apparatus for efficiently decomposing and removing hardly decomposable terephthalic acid in wastewater by anaerobic treatment.

  In the chemical industry and electronics industry, wastewater containing terephthalic acid may be discharged. For example, polyethylene terephthalate manufacturing process wastewater used as a raw material for PET bottles, films, magnetic tapes, clothing fibers and the like usually contains terephthalic acid, p-toluic acid, benzoic acid, and the like.

In general, when anaerobic treatment of wastewater from various industrial fields, nutrient salts, trace metals, etc. are necessary for bacterial cell synthesis in the anaerobic treatment system. For example, sulfate ions are converted into COD _Cr in the wastewater. On the other hand, about 1.5% is required as SO ₄ ^2- . Since chemical wastewater and electronic industrial wastewater contain almost no components necessary for the synthesis of these cells, anaerobic treatment of these wastewaters is performed by adding mineral components. However, sulfate ions are decomposed by sulfate-reducing bacteria in the methane fermentation tank to generate hydrogen sulfide gas, increasing the load of exhaust gas treatment, and methane fermentation is hindered by hydrogen sulfide, reducing the processing efficiency. Therefore, addition beyond the concentration required for cell synthesis is not performed.

  When trying to anaerobically treat terephthalic acid-containing wastewater, terephthalic acid is difficult to decompose and cannot be efficiently decomposed and removed. The same applies to p-toluic acid contained in the terephthalic acid-containing wastewater at the same time.

Conventionally, for the organic matter decomposition hardly persistent in anaerobic treatment, usually aerobic treatment is carried out, the anaerobic treatment is high load processing is possible running cost is lower compared to aerobic treatment, CO ₂ Since there is an advantage that the discharge amount is small, an anaerobic treatment is desired.

  Patent Document 1 proposes a method for anaerobic treatment after ozone treatment of terephthalic acid-containing wastewater in order to increase the decomposition efficiency of terephthalic acid in anaerobic treatment. However, although this method has high processing efficiency, there are problems that the apparatus for ozone treatment becomes complicated and the processing cost is high.

  In Patent Document 2, in anaerobic treatment, in order to prevent granulated sludge from floating and flowing out, an iron salt and a sulfate ion source are added to the waste water, and iron sulfide (FeS) is reacted by the reaction between the iron salt and the sulfate ion. ), And the granule sludge cavity is filled with iron sulfide. In this method, the added sulfate ion source is precipitated as FeS, and the sulfate ions in the anaerobic treatment tank are precipitated. It does not increase the concentration.

  As described above, in the anaerobic treatment, if the sulfate ion concentration in the system is increased, hydrogen sulfide gas is generated. Therefore, conventionally, in order to suppress the generation of hydrogen sulfide gas, the concentration is higher than that required for cell synthesis. The sulfate ion concentration is not increased.

Japanese Patent Laid-Open No. 6-269997 Japanese Patent No. 3814851

  The present invention highly efficiently decomposes and removes terephthalic acid by subjecting hardly-decomposable terephthalic acid-containing wastewater to anaerobic treatment efficiently at low cost without requiring complicated equipment and complicated operations. It is an object of the present invention to provide a method and an apparatus capable of performing the above.

As a result of intensive studies to solve the above problems, the present inventors have added a predetermined amount of sulfate radical (SO ₄ ²⁻ ) in the anaerobic treatment of terephthalic acid-containing wastewater, and decomposed terephthalic acid in the anaerobic treatment. It has been found that the efficiency is dramatically improved.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] In the method of anaerobically treating wastewater containing terephthalic acid, the anaerobic treatment is a biological anaerobic treatment having an acid generation step and a methane fermentation step, and the sulfate ion concentration in the anaerobic treatment water is An anaerobic treatment method for terephthalic acid-containing wastewater, wherein a sulfate radical is added to the wastewater so as to be 5 to 200 mg / L.

[2] Anaerobic treatment of terephthalic acid-containing wastewater according to [1], wherein a sulfate radical is added to the wastewater so that the content of the sulfate radical in the wastewater is 60 to 400 mg / L. Method.

[3] The sulfate according to [1] or [2], wherein a sulfate radical is added to the waste water so that a sulfate radical content is 10% by mass or more with respect to terephthalic acid in the waste water. Anaerobic treatment method for wastewater containing terephthalic acid.

[4] The anaerobic treatment method for terephthalic acid-containing wastewater according to any one of [1] to [3], wherein the wastewater contains 50 to 2000 mg / L of terephthalic acid.

[5] The anaerobic treatment method for terephthalic acid-containing wastewater according to any one of [1] to [4], wherein the wastewater further contains p-toluic acid.

[6] In the apparatus for anaerobic treatment of wastewater containing terephthalic acid, the anaerobic treatment is a biological anaerobic treatment having an acid generation step and a methane fermentation step, and the sulfate ion concentration in the anaerobic treatment water is An anaerobic treatment apparatus for terephthalic acid-containing wastewater, comprising means for adding a sulfate radical to the wastewater so as to be 5 to 200 mg / L.

[7] The terephthalic acid-containing wastewater according to [6], having means for adding a sulfate radical to the wastewater so that the content of the sulfate radical in the wastewater is 60 to 400 mg / L. Anaerobic treatment device.

[8] The sulfate according to [6] or [7], wherein a sulfate radical is added to the waste water so that a sulfate radical content is 10% by mass or more with respect to terephthalic acid in the waste water. Anaerobic treatment equipment for wastewater containing terephthalic acid.

[9] The anaerobic treatment apparatus for terephthalic acid-containing wastewater according to any one of [6] to [8], wherein the wastewater contains 50 to 2000 mg / L of terephthalic acid.

[10] The anaerobic treatment apparatus for terephthalic acid-containing wastewater according to any one of [6] to [9], wherein the wastewater further contains p-toluic acid.

According to the present invention, by adding sulfate radical (SO ₄ ²⁻ ) to the terephthalic acid-containing waste water so that the sulfate ion concentration in the anaerobic treated water is 5 to 200 mg / L, the hardly decomposable terephthalic acid is obtained. Can be efficiently decomposed and removed by anaerobic treatment to obtain high-quality treated water (claims 1 and 6).
The present invention can be carried out easily and at low cost with a simple device by simply adding a sulfate group such as sulfuric acid to waste water without requiring complicated equipment and complicated operations. The utility is extremely large.

  In the present invention, the sulfate radical is preferably added in an amount of 10% by mass or more with respect to terephthalic acid in the waste water, and the content in the waste water is 60 to 400 mg / L. , 8).

  The present invention is suitable for treating terephthalic acid-containing wastewater containing 50 to 2000 mg / L of terephthalic acid and further containing p-toluic acid (claims 4, 5, 9, and 10).

  Hereinafter, embodiments of the present invention will be described in detail.

  In the present invention, in the anaerobic treatment of terephthalic acid-containing wastewater, a predetermined amount of sulfate radical is added to the wastewater. Although the details of the mechanism of action by which the effect of improving the anaerobic treatment efficiency of terephthalic acid-containing wastewater is obtained by the addition of this predetermined amount of sulfate radicals are not clear in the present invention, the amount of wastewater is more than the amount necessary for cell synthesis. By adding an excessive amount of sulfate radicals, it is possible to promote the sulfate reduction reaction, thereby lowering the hydrogen partial pressure, resulting in the reduction of the anaerobic treatment system and the methane production reaction. It is believed that accelerated and persistent terephthalic acid is decomposed and removed.

[Terephthalic acid-containing wastewater]
The raw water to be treated in the present invention is effluent containing terephthalic acid, and includes terephthalic acid-containing effluent discharged from various industrial fields such as the chemical industry and the electronics industry, such as polyethylene terephthalate manufacturing process effluent. It is done.

  Although there is no restriction | limiting in particular about the terephthalic acid density | concentration in a terephthalic-acid containing waste water, Usually, 50-2000 mg / L, Preferably it is about 100-1000 mg / L. When the concentration of terephthalic acid in the waste water is less than this lower limit, the significant difference from the normal treatment becomes small, and when it exceeds this upper limit, terephthalic acid tends to crystallize and the processing efficiency may be reduced.

  The terephthalic acid-containing wastewater may further contain easily degradable organic substances such as p-toluic acid, benzoic acid, sugar, and organic acids.

In particular, the addition of sulfate radicals in the anaerobic treatment in the present invention is also effective in improving the anaerobic treatment efficiency of p-toluic acid, and shows a good treatment effect even for wastewater containing p-toluic acid together with terephthalic acid.
In this case, although there is no restriction | limiting in particular about content of the paratoluic acid in waste_water | drain, Usually, 50-5000 mg / L, Preferably it is 100-2000 mg / L.
The present invention is particularly advantageous in terms of treatment effect in the treatment of wastewater having a paratoluic acid concentration in the above range.

[Sulfate]
In the present invention, the agent for adding sulfate radical (SO ₄ ²⁻ ) to the waste water is not particularly limited as long as it can increase the concentration of SO ₄ ²⁻ in the waste water. Examples thereof include SO ₄ ^2- containing acidic solutions such as sulfuric acid, iron (I) sulfate, iron (II) sulfate, and polysulfate, and soluble sulfates such as ammonium sulfate, aluminum sulfate, sodium sulfate, and potassium sulfate.
In addition, although calcium sulfate, magnesium sulfate, etc. are hardly soluble in water, the sulfate ion concentration in the waste water can be increased by adding as a dilute solution. One kind of these sulfate radical agents may be used alone, or two or more kinds may be used in combination.

It is preferable to add a sulfate source drug such as sulfuric acid as an aqueous solution having a SO ₄ ²⁻ concentration of 5 to 30% by mass in terms of handleability, operability of adding to drainage, and the like.

If the amount of sulfate radical added to the wastewater is too small, the effect of the present invention by adding the sulfate radical cannot be sufficiently obtained, and if too large, hydrogen sulfide gas is generated in a large amount, which is not preferable.
Therefore, the sulfate radical addition amount to the wastewater, that is, SO ₄ ²⁻ addition amount is preferably 30 to 400 mg / L, more preferably 50 to 200 mg / L, and within the range of this addition amount, SO ₄ in the wastewater. ^2- It is preferable to add so that a density | concentration may be 60-400 mg / L, especially 70-200 mg / L.

  Moreover, it is preferable to add a sulfate radical so that it may become content of 10 mass% or more especially 15-30 mass% especially with respect to the terephthalic acid in waste_water | drain. If the content of sulfate radicals relative to terephthalic acid in the wastewater is too small, the decomposition efficiency of terephthalic acid may not be sufficiently increased.

  Moreover, when the wastewater to be treated contains terephthalic acid and p-toluic acid, the sulfate radical has a content of 10% by mass or more, particularly 15 to 30% by mass with respect to the total amount of terephthalic acid and p-toluic acid in the waste water. It is preferable to add such that.

  The sulfate radical is added so that the sulfate ion concentration in the treated water obtained by anaerobic treatment is 5 to 200 mg / L, preferably 10 to 20 mg / L. When the sulfate ion concentration is such that the sulfate ion concentration of the anaerobic treated water is less than the above lower limit, the effect of adding the sulfate radical according to the present invention cannot be sufficiently obtained. However, if the sulfate ion concentration of the anaerobic treated water is excessively high, the amount of hydrogen sulfide gas generated is increased, the water quality of the anaerobic treated water itself is deteriorated, and the load of the subsequent treatment process is increased.

  The location of the sulfate radical added to the wastewater will be described later.

[Anaerobic treatment]
There is no particular limitation on the anaerobic treatment method in the present invention, even if it is a single-phase system in which the acid production process by acid-producing bacteria and the methane fermentation process by methanogenic bacteria are performed in the same tank, these are performed in separate tanks. A two-phase system may be used.

  There is also no particular limitation on the type of reaction tank for anaerobic treatment, and fixed bed type, fluidized bed type, UASB (Upflow Anaerobic Sludge Blanket; upflow anaerobic) capable of high load treatment with granule of methanogenic bacteria. (Sludge bed) method, EGSB (Expanded Granule Sludge Bed) method, and the like, and the UASB method and EGSB method capable of high load treatment are preferable.

In the case of single-phase anaerobic treatment, the sulfate radical may be added to either the anaerobic treatment tank or the raw water flowing into the anaerobic treatment tank, but when adding sulfuric acid as the sulfate radical, addition of sulfuric acid When the pH adjustment tank is provided, it is preferable to add it at the preceding stage.
In addition, in the case of the two-phase system, the location of sulfate radical addition differs depending on the amount of the material to be treated in the wastewater. If there are many easily decomposable substances in the wastewater, add them at a position close to the methane fermentation tank. When there is little easily decomposable substance in the waste water, it is preferable to add in the former stage, for example, an acid generation tank. This is because if the easily decomposable substance is consumed, the effect of promoting the decomposition of terephthalic acid or p-toluic acid is reduced.
In any case, when sulfuric acid is added as a sulfate radical, the pH is lowered by the addition of sulfuric acid. Therefore, when a pH adjusting tank is provided, it is preferably added at the preceding stage.

The conditions of anaerobic treatment vary depending on the method employed, but usually pH 6-8, temperature 25-39 ° C., residence time 4 hours-3 days, anaerobic sludge concentration 10,000-40,000 mg-VSS / L, load amount It is preferable to set it as 1-15 kg-BOD / m < ³ > * day, CODcr load 2-30 kg-CODcr / m < ³ > * day.

  Anaerobic treated water can be further subjected to aerobic treatment such as activated sludge treatment and other post-treatments in order to decompose the remaining organic matter. According to the present invention, since terephthalic acid that is hardly decomposable can be efficiently decomposed and removed by anaerobic treatment in anaerobic treatment, the load is reduced even when aerobic treatment is performed in the subsequent stage. And the processing cost can be reduced.

[Treatment of hydrogen sulfide gas]
In the present invention, since the sulfate radical is added to the terephthalic acid-containing wastewater in the above-described limited amount, the generation of hydrogen sulfide gas is suppressed to the extent that methane fermentation is not inhibited, and terephthalic acid is then added. Although the decomposition efficiency of can be increased, a small amount of hydrogen sulfide gas may be generated. In this case, hydrogen sulfide in exhaust gas may be treated by biological desulfurization treatment or the like. When biodesulfurization is performed, if the concentration of hydrogen sulfide in the gas to be treated fluctuates, the sulfur-oxidizing bacteria do not grow stably and the treatment becomes unstable, but in the present invention, even when hydrogen sulfide gas is generated, By adding a predetermined amount of sulfate radicals to the waste water, exhaust gas with a stable hydrogen sulfide concentration is discharged, so there is no such problem, and a stable biological desulfurization treatment can be performed.

As the biological desulfurization treatment of hydrogen sulfide-containing exhaust gas, as described in Japanese Patent No. 3235131, the hydrogen sulfide-containing exhaust gas is brought into contact with a cleaning liquid, for example, a treatment liquid in aerobic microbial oxidation of an organic substance. And a method in which the obtained absorption liquid is oxidized aerobically by microorganisms, and the hydrogen sulfide is oxidized to sulfate ions or elemental sulfur by the oxidizing action of sulfur-oxidizing bacteria to render them harmless.
According to this method, desulfurization can be performed at a high desulfurization rate without reducing the content of methane gas, efficiently at low cost, and without generating a new waste liquid accompanying desulfurization.
However, the method for treating hydrogen sulfide gas is not limited to this method.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

  In the following examples and comparative examples, the quality of raw water subjected to anaerobic treatment is as follows.

<Raw water quality>
COD _Cr : 4050 mg / L
Terephthalic acid concentration: 400 mg / L
Palatoluic acid concentration: 620 mg / L
SO ₄ ²⁻ concentration: 30 to 40 mg / L
pH: 10

[Examples 1 to 3, Comparative Examples 1 and 2]
A two-phase anaerobic treatment device equipped with an acid production tank and an EGSB methane fermentation tank, after introducing and treating raw water into the acid production tank, treating it in the methane fermentation tank, and a part of the treated water in the methane fermentation tank Was circulated to the acid generation tank and the remainder was taken out as treated water to perform anaerobic treatment of the raw water.

  The specifications and processing conditions of each tank are as follows, and the raw water flow rate is 5 L / day.

Acid production tank Capacity: 0.5L
Acid generation tank pH: 6.5 to 7.5
Methane fermentation tank Capacity: 2L
Methane fermenter pH: 7-8
Methane fermentation tank Sludge concentration: 67g / L as VSS
Methane fermenter temperature: 35 ℃
Circulating water amount from the methane fermentation tank to the acid generation tank: 1Q (= 5 L / day) was circulated with respect to the raw water flow rate Q (= 5 L / day).

In such anaerobic treatment, sulfuric acid was added to the SO ₄ ²⁻ addition amount shown in Table 1 in the previous stage of the acid generation tank (however, in Comparative Example 1, sulfuric acid was not added). Sulfuric acid was added as a 20% by mass aqueous solution. Moreover, since pH falls by addition of a sulfuric acid, after adding a sulfuric acid, alkali (sodium hydroxide) was added suitably and pH adjustment was carried out. By the addition of this sulfuric acid, the SO ₄ ²⁻ content in the wastewater subjected to anaerobic treatment including SO ₄ ²⁻ contained in the raw water was as shown in Table 1.

  Table 1 shows the quality of treated water obtained by such anaerobic treatment, the activity of sludge determined from the result of the treatment, and the presence or absence of hydrogen sulfide gas.

  From Table 1, it can be seen that according to the present invention, it is possible to efficiently anaerobically treat hardly-decomposable terephthalic acid-containing wastewater to obtain high-quality treated water.

Claims (10)

In the method of anaerobically treating wastewater containing terephthalic acid, the anaerobic treatment is a biological anaerobic treatment having an acid generation step and a methane fermentation step, and the sulfate ion concentration in the anaerobic treatment water is 5 to 200 mg. An anaerobic treatment method for terephthalic acid-containing wastewater, wherein a sulfate radical is added to the wastewater so as to be / L.   The method for anaerobic treatment of terephthalic acid-containing wastewater according to claim 1, wherein a sulfate radical is added to the wastewater so that the content of the sulfate radical in the wastewater is 60 to 400 mg / L.   The terephthalic acid-containing wastewater according to claim 1 or 2, wherein a sulfate radical is added to the wastewater such that the sulfate radical content is 10 mass% or more with respect to the terephthalic acid in the wastewater. Anaerobic treatment method.   The method for anaerobic treatment of terephthalic acid-containing wastewater according to any one of claims 1 to 3, wherein the wastewater contains 50 to 2000 mg / L of terephthalic acid.   The method for anaerobic treatment of wastewater containing terephthalic acid according to any one of claims 1 to 4, wherein the wastewater further contains p-toluic acid. In the apparatus for anaerobically treating wastewater containing terephthalic acid, the anaerobic treatment is a biological anaerobic treatment having an acid generation step and a methane fermentation step, and the sulfate ion concentration in the anaerobic treatment water is 5 to 200 mg. An anaerobic treatment apparatus for terephthalic acid-containing wastewater, comprising means for adding a sulfate radical to the wastewater so as to be / L.   The anaerobic treatment of terephthalic acid-containing wastewater according to claim 6, further comprising means for adding a sulfate radical to the wastewater so that the content of the sulfate radical in the wastewater is 60 to 400 mg / L. apparatus.   The terephthalic acid-containing wastewater according to claim 6 or 7, wherein a sulfate radical is added to the wastewater so that the content of the sulfate radical is 10% by mass or more with respect to the terephthalic acid in the wastewater. Anaerobic treatment equipment.   The anaerobic treatment apparatus for terephthalic acid-containing wastewater according to any one of claims 6 to 8, wherein the wastewater contains 50 to 2000 mg / L of terephthalic acid.   The anaerobic treatment apparatus for terephthalic acid-containing wastewater according to any one of claims 6 to 9, wherein the wastewater further contains p-toluic acid.