TW201808819A - Membrane filtration method and membrane filtration system - Google Patents

Abstract

One aspect of the invention is a membrane filtration method in which an inorganic coagulant is added to a treated water, which is obtained by subjecting a water to be treated to coagulative precipitation or coagulative pressure flotation by adding an organic coagulant, and the resulting water is then subjected to at least one of an ultrafiltration membrane treatment and a microfiltration membrane treatment.

Description

Membrane filtration method and membrane filtration system

The invention relates to a membrane filtration method and a technology of a membrane filtration system.

Conventionally, it is known to add an organic coagulant to the water to be treated, and perform a coagulation and sedimentation treatment, and a pressurized floating treatment to treat the discharged water (for example, refer to Patent Document 1). [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 11-57313

[Problems to be Solved by the Invention] For the treated water obtained by the coagulation and sedimentation treatment and the pressure floatation treatment using an organic coagulant, if an ultrafiltration membrane or a precision filtration membrane is further used, the surface of the membrane may be polluted The phenomenon of clogging of pores (fouling) occurs. Therefore, an object of the present disclosure is to provide that the treated water obtained by the coagulation and sedimentation treatment and the pressure floatation treatment using an organic coagulant can suppress the scaling of ultrafiltration membranes and precision filtration membranes, and can Membrane filtration method and membrane filtration system for stable operation. [Means for solving problems]

(1) One aspect of this embodiment is a membrane filtration method in which an inorganic coagulant is added to treated water obtained by adding an organic coagulant to the water to be treated and performing coagulation precipitation treatment or coagulation pressure floatation treatment. Agent, and at least one of the ultrafiltration membrane treatment and the precision filtration membrane treatment is subjected to a membrane filtration treatment.

(2) In the membrane filtration method according to the above (1), it is preferable that at least one of the application of shearing force and the addition of an oxidizing agent is performed on the treated water during the membrane filtration treatment to condense the organic system in the treated water. The average molecular weight of the agent is preferably equal to or lower than the cut-off molecular weight of the membrane used in the membrane filtration treatment.

(3) In the membrane filtration method according to (1) or (2) above, the addition amount of the inorganic flocculant should preferably be 0.5 times to the concentration (mg / L) of the organic flocculant in the water to be treated. A range of 75 times is better.

(4) In the membrane filtration method according to any one of (1) to (3) above, it is desirable to respond to the polymer organic matter detected by LC-OCD in the treated water subjected to the coacervation precipitation treatment or cohesion pressure floatation treatment. The concentration of the inorganic coagulant is preferably controlled.

(5) In the membrane filtration method according to any one of (1) to (4) above, it is preferable to perform at least one of an activated carbon treatment and a reverse osmosis membrane treatment on the treated water of the membrane filtration treatment. .

(6) In the membrane filtration method according to any one of (1) to (5) above, it is preferable that the Langelier's index (LSI) of the treated water is less than 0 during the membrane filtration treatment. It is better to adjust the pH of the treated water.

(7) One aspect of this embodiment is a membrane filtration system, which includes the following means: an inorganic flocculant adding means, adding an organic flocculant to the water to be treated, and performing a coacervation precipitation treatment or a coacervation pressure floatation treatment. An inorganic flocculant is added to the obtained treated water; and a membrane filtration treatment method includes at least one of an ultrafiltration membrane and a precision filtration membrane, and a membrane filtration process is performed on the treated water to which the inorganic flocculant has been added.

(8) The membrane filtration system according to the above (7), preferably, at least one of a shearing force imparting means for imparting a shearing force to the treated water during the membrane filtration process and an oxidant adding means for adding an oxidant; From at least one of the application of the shear force and the addition of the oxidizing agent, it is preferable that the average molecular weight of the organic flocculant in the treated water is equal to or lower than the cut-off molecular weight of the membrane used in the membrane filtration treatment.

(9) In the membrane filtration system according to (7) or (8) above, the addition amount of the inorganic flocculant should preferably be 0.5 times to the concentration (mg / L) of the organic flocculant in the water to be treated. A range of 75 times is better.

(10) The membrane filtration system according to any one of (7) to (9) above, preferably has a post-treatment means for performing post-treatment on the treated water of the membrane filtration treatment; the post-treatment means includes activated carbon treatment means And at least one of the reverse osmosis membrane treatment means is preferable.

(11) The membrane filtration system according to any one of the above (7) to (10), it is preferable to adjust the membrane filtration process so that the blue index (LSI) of the treated water is less than 0 and adjusted. The pH adjustment method of the pH of the treated water is preferable. [Effect of the invention]

According to the membrane filtration method and membrane filtration system of the present embodiment, it is possible to suppress the formation of ultrafiltration membranes and precision filtration membranes in the treated water obtained by the coagulation sedimentation treatment and the pressure floatation treatment using an organic coagulant. Scale, and can run stably.

Hereinafter, embodiments of the present invention will be described. In addition, this embodiment is an example of implementing this invention, and this invention is not limited to this embodiment.

FIG. 1 is a schematic diagram showing an example of a configuration of a processing system according to this embodiment. The processing system 1 shown in FIG. 1 includes a coacervation system and a membrane filtration system. The coagulation and sedimentation system includes a first coagulation reaction tank 10, an organic coagulant addition line 12, and an coagulation and sedimentation tank 14. The membrane filtration system includes an inorganic flocculant adding device 15 and an inorganic flocculant adding line 16 as an example of an inorganic flocculant adding means, a second coalescing reaction tank 18, and a membrane filtering device 20 as an example of a membrane filtering processing means. .

An inlet of the first agglutination reaction tank 10 is connected to the treated water pipe 22. One end of the connection pipe 24a is connected to the outlet of the first condensation reaction tank 10, the other end is connected to the inlet of the condensation precipitation tank 14, one end of the connection pipe 24b is connected to the outlet of the condensation precipitation tank 14, and the other end is connected to the second condensation reaction. The inlet of the tank 18 is connected, one end of the connection pipe 24 c is connected to the outlet of the second condensation reaction tank 18, and the other end is connected to the inlet of the membrane filtration device 20. The outlet of the membrane filtration device 20 is connected to a treated water pipe 26. The organic flocculant addition line 12 is connected to the first flocculation reaction tank 10. One end of the inorganic flocculant addition line 16 is connected to the inorganic flocculant addition device 15, and the other end is connected to the second aggregation reaction tank 18.

The inorganic flocculant addition device 15 is composed of, for example, a storage tank containing the inorganic flocculant, a pump, a valve, and the like for discharging the inorganic flocculant. The inorganic flocculant supplied from the inorganic flocculant adding device 15 is supplied to the second flocculation reaction tank 18 through the inorganic flocculant adding line 16. Examples of the inorganic flocculant used in this embodiment include polyaluminum chloride (PAC), aluminum sulfate, iron (III) chloride, iron (III) sulfate, and aluminum chloride.

Examples of the organic coagulant used in the present embodiment include polypropylene fluorene amine coagulant, polysulfonic acid coagulant, polyacrylic coagulant, polyacrylate coagulant, polyamine coagulant, and polymethyl methacrylate. Polymeric coagulants such as acrylic acrylic coagulants, and low-molecular coagulants (coagulants) such as surfactants. The organic flocculant is, for example, supplied to the first flocculation reaction tank 10 through an organic flocculant adding line 12 from an organic flocculant adding device (not shown).

The membrane filtration device 20 may be provided with at least one of an UF membrane device having an ultrafiltration membrane and an MF membrane device having a precision filtration membrane. The UF membrane device and the MF membrane device include, for example, at least one module in which an ultrafiltration membrane and a precision filtration membrane are stored in a hermetically sealed container. The shape of the ultrafiltration membrane and precision filtration membrane is not particularly limited, and examples thereof include hollow fiber membranes, tubular membranes, flat membranes, and spiral membranes. The water passing method of the membrane filtering device 20 may be any water passing method such as an internal pressure type and an external pressure type, and any filtering method such as crossflow filtration or dead-end filtration may be adopted.

Examples of materials for ultrafiltration membranes and precision filtration membranes include organic membranes such as polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyether fluorene (PES), and cellulose acetate (CA), and ceramics. Made of inorganic films.

The cut-off molecular weight of the ultrafiltration membrane is, for example, in the range of 5,000 to 360,000, and preferably in the range of 10,000 to 360,000. The pore diameter of the ultrafiltration membrane is, for example, in a range of 0.01 to 0.1, and preferably in a range of 0.01 to 0.03. The pore diameter of the precision filtration membrane is, for example, in a range of 0.1 to 0.5, and preferably in a range of 0.1 to 0.2.

The water to be treated in the treatment system 1 is not particularly limited. For example, it is raw water containing impurities such as suspended matter, scale components such as calcium, etc., and specifically, industrial discharge water (for example, plating-type discharge water, etc.) , Tap water, groundwater (for example, well water, spring water, undulating water, etc.), surface water (for example, river water, lake water, etc.), etc.

An example of the operation of the processing system 1 according to this embodiment will be described.

The to-be-processed water is supplied to the 1st aggregation reaction tank 10 through the to-be-processed water pipe 22, and the organic flocculant is supplied to the 1st flocculation reaction tank 10 from the organic-type flocculant addition line 12. In the first agglutination reaction tank 10, the water to be treated and the organic coagulant are stirred by a stirrer 28a to flocculate impurities such as suspended matter in the water to be treated. Thereafter, the water to be treated containing the organic coagulant is supplied to the coagulation and sedimentation tank 14 through the connection pipe 24a, and impurities such as the flocculated suspended matter are precipitated in the form of sludge.

The supernatant, which is the treated water subjected to the coagulation and sedimentation treatment, is supplied to the second coagulation reaction tank 18 through the connection pipe 24b. The inorganic flocculant is supplied from the inorganic flocculant adding device 15 to the second flocculation reaction tank 18 through the inorganic flocculant adding line 16. In the second coagulation reaction tank 18, the treated water and the inorganic coagulant are stirred by a stirrer 28b, and the organic coagulant remaining in the treated water is brought into contact with the inorganic coagulant. The treated water to which the inorganic flocculant has been added is introduced into the membrane filtration device 20 through a connection pipe 24c. The impurities in the treated water are captured by the ultrafiltration membrane and the precision filtration membrane in the membrane filtering device 20, and the treated water from which the impurities have been removed is discharged from the treated water pipe 26. The obtained treated water can be used, for example, as washing water in food processing factories, chemical factories, semiconductor factories, machinery factories, and the like.

The membrane filtration device 20 is periodically backwashed with the treated water or the like obtained by the membrane filtration treatment, and impurities accumulated on the membrane surface are discharged out of the system together with the backwash drainage water, or transported to the condensation sedimentation tank 14. For the backwash drainage water, consider the viewpoint that the suspended matter in the backwash drainage water can be settled and separated, and the water recovery rate (the amount of treated water / supply water, if it is discharged outside the system, the water recovery rate will decrease). It should be transported to the condensation sedimentation tank 14 preferably.

Generally, if the treated water containing an organic flocculant is subjected to membrane filtration treatment using an ultrafiltration membrane, a precision filtration membrane, or the like, the organic flocculant will accumulate on the surface of the membrane and easily cause membrane fouling. However, in this embodiment, it is considered that by contacting the inorganic flocculant with the organic flocculant, the inorganic flocculant adheres to the organic flocculant, and the organic flocculant becomes in a form that does not easily adhere to the surface of the film. In the form of being easily peeled from the film surface by backwashing or the like. Therefore, by adding an inorganic flocculant and performing a membrane filtration treatment, compared with a case where a membrane filtration process is not performed without adding an inorganic flocculant, scaling of the membrane is suppressed and stable operation can be performed. We have also considered adding an organic coagulant together with an organic coagulant to perform coagulation and precipitation in the coagulation and precipitation treatment using an organic coagulant, but even in such a system, there is still a certain amount of organic coagulant (For example, an organic flocculant without an inorganic flocculant attached) remains in the treated water obtained by the coacervation and precipitation treatment, so the inorganic flocculant is added to the treated water subjected to the flocculation and precipitation treatment as in this embodiment. The method of membrane filtration treatment is difficult to sufficiently suppress the fouling of the membrane, and it is difficult to perform a stable treatment.

The addition amount of the inorganic flocculant is not particularly limited as long as it is an amount capable of suppressing film scale. For example, the concentration (mg / L) of the organic flocculant relative to the water to be treated is preferably A range of 0.5 to 75 times is preferable, and in view of economy, a range of 0.5 to 2.5 times is more preferable. It is considered that if the addition amount of the inorganic coagulant is less than 0.5 times, it is not possible to suppress membrane fouling, and if it is more than 75 times, the filtration resistance due to flocs derived from the inorganic coagulant becomes large. Therefore, when the above range is satisfied, it is possible to effectively suppress the fouling of the membrane compared to the case where the above range is not satisfied.

In this embodiment, the treated water obtained by the coagulation and sedimentation treatment using an organic coagulant is exemplified. The same can be obtained with the treated water obtained by the coagulation and pressure floatation treatment using an organic coagulant. Effect. The agglomeration pressure floatation treatment is, for example, a conventionally known pressure floatation treatment or the like (for example, refer to Japanese Patent 5329653).

Considering the viewpoint of improving the contact rate between the organic coagulant and the inorganic coagulant, it is preferable to install a coagulation reaction tank (the second coagulation reaction tank 18 shown in FIG. 1). The viewpoint of reducing the installation space may also be considered. Like the processing system 2 shown in FIG. 2, an agglutination reaction tank is not provided, and an inorganic-based aggregating agent adding line 16 is provided in the connection pipe 24 b, and the inorganic aggregating agent is injected into the line.

FIG. 3 is a schematic diagram showing an example of a configuration of a processing system according to another embodiment. In the processing system 3 shown in FIG. 3, the same configurations as those of the processing system 1 shown in FIG. 1 are assigned the same reference numerals and descriptions thereof are omitted. The treatment system 3 shown in FIG. 3 is configured by adding an oxidizing agent to the treated water subjected to the coacervation treatment (or the coacervation pressure floatation treatment) during the membrane filtration process. Specifically, the processing system 3 shown in FIG. 3 includes an oxidant addition device 29 and an oxidant addition line 30 as oxidant addition means, and the oxidant is added from the oxidant addition device 29 to the second condensation reaction tank 18 through the oxidant addition line 30. In addition, the addition of oxidant can also be injected for the pipeline shown in FIG. 2.

As for the organic flocculant, for example, when a polymer flocculant such as a polypropylene amidant flocculant is used, the average molecular weight (weight average molecular weight or number average molecular weight) of the organic flocculant is usually higher than that of the ultrafiltration membrane in the later stage. 2. The cut-off molecular weight of the precision filtration membrane is larger. Therefore, if an organic flocculant having a molecular weight larger than the molecular weight cut off of the membrane remains in the treated water, it will affect the fouling of the membrane. In addition, the molecular weight cut-off is determined by the molecular weight equivalent to 90% of the blocking rate when a standard substance with a known molecular weight is penetrated. For example, for ultrafiltration membranes and precision filtration membranes with a molecular weight cut-off of 5,000, the molecular weight containing When treated water with a polymer flocculant exceeding 5,000, more than 90% of the polymer flocculant will be captured.

Therefore, in the treatment system 3 shown in FIG. 3, when an oxidizing agent is added to the treated water during the membrane filtration treatment, the molecular chain of the organic flocculant is cut, so that the molecular weight of the organic flocculant becomes an ultrafiltration membrane, The molecular weight cut-off of the precision filtration membrane is preferably smaller than the molecular weight cut-off. As a result, part of the organic flocculant is not captured by the membrane, but passes through the membrane together with the treated water. Therefore, the scale of the membrane can be further suppressed compared to the case where only the inorganic flocculant is added.

Examples of the oxidant include alkali metal salts of hypochlorite such as sodium hypochlorite and potassium hypochlorite; alkaline earth metal salts of hypochlorite such as calcium hypochlorite and barium hypochlorite; lithium chlorite, sodium chlorite, and potassium chlorite Alkali metal salts such as chlorite; Alkaline earth metal salts of chlorite such as calcium chlorite and barium chlorite; Other metal salts of chlorite such as nickel chlorite; Ammonium chlorate; Sodium chlorate Metal salts; chloric acid alkaline earth metal salts such as calcium chlorate.

The amount of the oxidant to be added is not particularly limited as long as the molecular weight of the organic flocculant is equal to or less than the molecular weight cut-off of the film. The concentration (mg / L) is preferably 0.5 to 75 times, and more preferably 0.5 to 2.5 times.

In addition, it is better to control the addition amount of the inorganic coagulant in accordance with the concentration of the polymer organic substance detected by LC-OCD in the treated water subjected to the coagulation precipitation treatment or the coagulation pressure floatation treatment. In the case of LC-OCD, organic matter is classified by molecular weight, and peaks of high molecular organic matter, humic matter, humic decomposition products, low molecular organic acids, low molecular organic matter, etc. are expressed according to residence time, and the respective concentrations can be quantified.

We believe that high molecular organics contribute to the occlusion of the membrane, so we can know the concentration of high molecular organics in detail from the organics in the treated water treated by agglomeration precipitation or agglomerated pressure floatation, and add the The addition amount of the inorganic coagulant is determined to be a more appropriate amount. In addition, the amount of the inorganic coagulant can be increased or decreased according to the height of the peak of the polymer organic substance detected by LC-OCD, thereby reducing the running cost.

As a method of reducing the molecular weight of the organic flocculant, in addition to the addition of an oxidizing agent, a method of imparting a shearing force to treated water may also be mentioned. As for the means for imparting a shearing force, for example, by agitating the treated water with a stirrer 28b provided in the second agglomeration reaction tank 18 and applying shearing force, the molecular chain of the organic agglomerating agent is cut to make the organic agglomerating agent. The molecular weight is below the cut-off molecular weight of ultrafiltration membranes and precision filtration membranes. For example, by adjusting the stirring speed, stirring time, etc., the molecular weight of the organic flocculant can be reduced to the molecular weight of the ultrafiltration membrane or the precision filtration membrane. The stirring speed set in order to reduce the molecular weight of the organic flocculant is, for example, in a range of 200 rpm to 1,000 rpm, and preferably in a range of 700 rpm to 1,000 rpm. The stirring time set to reduce the molecular weight of the organic flocculant is, for example, in the range of 5 minutes to 1 hour, and preferably in the range of 30 minutes to 1 hour.

FIG. 4 is a schematic diagram showing an example of a configuration of a processing system according to another embodiment. In the processing system 4 of FIG. 4, the same configurations as those of the processing system 1 shown in FIG. 1 are assigned the same reference numerals and descriptions thereof are omitted. The treatment system 4 shown in FIG. 4 includes an activated carbon device 32 filled with activated carbon and a reverse osmosis membrane device 34 provided with a reverse osmosis membrane at the rear stage of the membrane filtration device 20. One end of the treated water pipe 26 a is connected to the outlet of the membrane filtration device 20, and the other end is connected to the inlet of the activated carbon device 32. One end of the treated water pipe 26 b is connected to the outlet of the activated carbon device 32, and the other end is connected to the inlet of the reverse osmosis membrane device 34. The water-permeable outlet of the reverse osmosis membrane device 34 is connected to the water-permeable pipe 36, and the concentrated water outlet is connected to the concentrated water pipe 38.

The reverse osmosis membrane used in this embodiment is, for example, a membrane capable of removing ionic components in the treated water, and also includes a nanofiltration membrane (NF membrane). The shape of the reverse osmosis membrane is not particularly limited, and examples thereof include a hollow fiber membrane, a tubular membrane, a flat membrane, and a spiral membrane. Examples of the material of the reverse osmosis membrane include polyamines, Amines and cellulose acetate.

In the treatment system 4 shown in FIG. 4, the treated water discharged from the membrane filtration device 20 is supplied to the activated carbon device 32 through the treated water pipe 26 a. After the impurities in the treated water are removed by the activated carbon device 32, the treated water pipe 26b is supplied to the reverse osmosis membrane device 34 and separated into permeated water and concentrated water. The permeated water (processed water) obtained by the reverse osmosis membrane device 34 is discharged from the permeated water pipe 36. The obtained pervious water can be used not only as washing water in food processing factories, chemical factories, semiconductor factories, machinery factories, etc., but also can be used as, for example, dilution water, beverage water, reclaimed water, air conditioning water, raw water for pure water, and washing machines (rinser) Raw water, steam water, etc. The concentrated water obtained by the reverse osmosis membrane device 34 is discharged from the concentrated water pipe 38 and stored in, for example, a storage tank (not shown).

The treatment system 4 shown in FIG. 4 includes both an activated carbon device 32 and a reverse osmosis membrane device 34. However, as long as it is based on, for example, the target water quality of the finally obtained treated water, only the activated carbon device 32 and only reverse osmosis are selected. The membrane device 34 or both of the activated carbon device 32 and the reverse osmosis membrane device 34 may be provided. Although the description is omitted in the figure, an activated carbon device 32 and a reverse osmosis membrane device 34 may be provided in the processing system shown in FIGS. 2 and 3.

FIG. 5 is a schematic diagram showing an example of a configuration of a processing system according to another embodiment. In the processing system 5 of FIG. 5, the same configurations as those of the processing system 1 shown in FIG. 1 are assigned the same reference numerals and descriptions thereof are omitted. The processing system 5 shown in FIG. 5 is equipped with the pH adjustment system as an example of a pH adjustment means. The pH adjusting system includes a pH adjusting agent adding device 40, a pH adjusting agent adding pipe 42, a water quality detecting device 44, and a control unit 46.

The pH adjusting agent adding device 40 is constituted by, for example, a storage tank containing the pH adjusting agent, a pump, a valve, and the like for discharging the pH adjusting agent. One end of the pH adjusting agent adding pipe 42 is connected to the pH adjusting agent adding device 40, and the other end is connected to the second aggregation reaction tank 18.

The water quality detection device 44 includes a pH sensor, a temperature sensor, a conductivity sensor, a calcium hardness sensor, a total alkalinity sensor, and a pH value for the treated water in the second condensation reaction tank 18 , Water temperature, electrical conductivity, calcium hardness, total alkalinity.

The control unit 46 includes a processor and a memory, and includes a blue index calculation unit 48 and a pH-adjusted dose control unit 50 as functional blocks. Each of the detection values detected by the water quality detection device 44 is input to the Lanier index calculation unit 48. The pH adjustment dose control unit 50 calculates the addition amount of the pH adjuster based on the Blue's index calculated by the Lan's index calculation unit 48, and controls the addition amount of the pH adjuster by the pH adjuster adding device 40.

The processor of the control unit 46 executes various processes such as a process of calculating the Blue's index and a process of controlling the addition amount of the pH adjuster in accordance with a processing program stored in the memory. An example of the operation of the control unit 46 will be described below.

The Lan's index calculation unit 48 calculates a Lan's index of the treated water based on the detection value detected by the water quality detection device 44. The Lan's index (LSI) is usually obtained by the following formula (1). LSI = pH-pHs (1)

In the formula (1), the pH is the pH value of the treated water. In addition, pHs is a theoretical pH value at the equilibrium state where calcium carbonate neither dissolves nor precipitates in the treated water, and is calculated according to the following formula (2). pHs = 9.3 + A value + B value-C value-D value (2)

In formula (2), the A value is a correction value determined from the concentration of the evaporation residue. The evaporation residue concentration is related to the conductivity, so the evaporation residue concentration can be obtained from the conductivity using a predetermined conversion formula. The B value is a correction value determined by the water temperature. The C value is a correction value determined from the calcium hardness. The D value is a correction value determined from the total alkalinity. The A to D values can be obtained from the detection values of the water quality detection device 44 using a relational expression or by referring to a numerical table.

The blue index is a general index used to evaluate the tendency of scale formation in water systems. When the positive value is positive, the larger the absolute value is, the easier it is to precipitate calcium carbonate. When the negative value is negative, the larger the absolute value is, it indicates the calcium carbonate. The harder it is to separate out. In addition, when the Blue's index is 0, it is in an equilibrium state where calcium carbonate neither precipitates nor dissolves. Therefore, when the blue index of the treated water is less than 0, it is in a state that it is difficult to generate scale due to calcium carbonate on the membrane surface of the ultrafiltration membrane and the precision filtration membrane. On the contrary, when it exceeds 0, it is easy to form on the membrane surface. Scale up caused by calcium carbonate.

Therefore, when the calculated blue index of the treated water is 0 or more, the pH adjustment dose control unit 50 sets the added amount of the pH adjuster so that the blue index of the treated water does not reach 0. In addition, the pH adjusting agent adding device 40 adds a pH adjusting agent to the treated water according to the set amount of the pH adjusting agent, so that the blue index of the treated water becomes less than zero. As can be seen from the formula (1), the blue index of the treated water becomes smaller as the pH of the treated water decreases, and becomes larger as the pH increases. Therefore, the blue index of the treated water can be controlled by adjusting the pH of the treated water.

The treatment system 5 according to this embodiment is effective as a system for treating discharged water containing fluorine, for example. In a coalescing and sedimentation treatment or a pressure floatation treatment of fluorine-containing discharged water (to-be-treated water), a calcium agent may be added to the to-be-treated water together with an organic flocculant in order to recover fluorine. Calcium may be contained in the treated water obtained by such a coacervation treatment or pressure floatation treatment, and the blue index of the treated water may easily become 0 or more. As a result, scale may be generated on the surfaces of the ultrafiltration membrane and the precision filtration membrane. However, in the present embodiment, as described above, the pH of the treated water is adjusted so that the blue index of the treated water becomes less than 0 (a negative value), so that generation of scale can be suppressed. Therefore, fouling of the film can be further suppressed, and the operation can be more stable. Although illustration is omitted in the figure, a pH adjustment system may be provided in the processing system shown in FIGS. 2 to 4.

(Reference example) FIG. 6 is a schematic diagram showing a configuration of a processing system in a reference example. In the processing system 6 shown in FIG. 6, the same configurations as those of the processing system 1 shown in FIG. 1 are assigned the same reference numerals and descriptions thereof are omitted. In the processing system 6 shown in FIG. 6, an inorganic flocculant is not added to the treated water subjected to the coacervation and sedimentation process (or cohesive pressure floatation process) during the membrane filtration process, and the oxidant is passed from the oxidant adding device 29 The oxidant addition line 30 is configured to be added to the second agglutination reaction tank 18. In addition, the addition of oxidant can also be injected for the pipeline shown in FIG. 2.

In the treatment system 6 shown in FIG. 6, during the membrane filtration process, an oxidant is added to the treated water to cut the molecular chain of the organic flocculant, so that the molecular weight of the organic flocculant becomes an ultrafiltration membrane and precision filtration. The cut-off molecular weight of the film is preferably smaller than the cut-off molecular weight. As a result, part of the organic flocculant is not captured by the membrane, but passes through the membrane together with the treated water. Therefore, the scale of the membrane can be further suppressed compared to the case where only the inorganic flocculant is added.

The amount of the oxidant to be added is not particularly limited as long as the molecular weight of the organic flocculant is equal to or less than the molecular weight cut-off of the membrane. For example, the concentration of the organic flocculant in the water to be treated (mg / L) is preferably 2.5 to 100 times, and more preferably 20 to 50 times.

As a method of reducing the molecular weight of the organic flocculant, in addition to the addition of an oxidizing agent, a method of imparting a shearing force to treated water may also be mentioned. As for the means for imparting a shearing force, for example, by agitating the treated water with a stirrer 28b provided in the second agglomeration reaction tank 18 and applying shearing force, the molecular chain of the organic agglomerating agent is cut to make the organic agglomerating agent. The molecular weight is below the cut-off molecular weight of ultrafiltration membranes and precision filtration membranes. The stirring speed set in order to reduce the molecular weight of the organic flocculant is, for example, in a range of 200 rpm to 1,000 rpm, and preferably in a range of 700 rpm to 1,000 rpm. The stirring time set to reduce the molecular weight of the organic flocculant is, for example, in the range of 5 minutes to 1 hour, and preferably in the range of 30 minutes to 1 hour. In addition, although the description is omitted in the figure, the processing system shown in FIG. 6 may be applied to the processing systems shown in FIGS. 2 to 5. [Example]

Hereinafter, the present invention will be described more specifically and in detail with examples and comparative examples, but the present invention is not limited to the following examples.

(Example 1) The treatment system shown in FIG. 1 was used to treat the drainage water of the plating quality shown in Table 1.

【Table 1】

The membrane filtration device of Example 1 used a UF membrane device. The details of the UF membrane device are shown below. Size: outer diameter 230mm × height 2400mm Filter area (membrane area): 77m ² Ultrafiltration membrane: hollow fiber membrane, made of PVDF, nominal pore size 0.01μm (nominal cut-off molecular weight 360,000Da) Filtration method: external pressure end-point filtration process : 9.6m ³ / h

1.0 ppm of a polyacrylamide polymer as an organic aggregating agent was added to the water-based plating-type drainage water shown in Table 1, and an aggregation-precipitation treatment was performed, and then the supernatant water was supplied to the second agglutination reaction tank. 75 ppm of ferric chloride as an inorganic flocculant was added to the second agglutination reaction tank, and water was passed through the membrane filtration device (UF membrane device) to perform membrane filtration treatment.

(Example 2) Except having changed the inorganic flocculant (ferric chloride) from 75 ppm to 10 ppm, the same process as Example 1 was performed.

(Comparative example 1) Except not having added an inorganic flocculant (ferric chloride), the same process as Example 1 was performed.

(Comparative Example 2) The same procedure as in Example 1 was performed except that the organic flocculant (polyacrylamide polymer) was changed from 1.0 ppm to 0.5 ppm, and no inorganic flocculant (ferric chloride) was added. Processing.

Table 2 shows the water quality results of the treated water obtained from the membrane filtration treatments of Examples 1 to 2 and Comparative Examples 1 to 2. The results of the filtration resistance (1 / m) of the membrane filtration device in Examples 1 to 2 and Comparative Examples 1 to 2 with respect to the filtration amount (m ³ / m ² ) are shown in FIG. 7.

【Table 2】

As shown in FIG. 7, Examples 1 and 2 in which an inorganic coagulant was added to the treated water obtained by the coagulation and precipitation treatment using an organic coagulant and the membrane filtration treatment was performed were compared with those in which no inorganic coagulant was added In Comparative Examples 1 and 2 in which a membrane agglomerating agent was directly applied to the membrane filtration treatment, an increase in filtration resistance was suppressed even if the amount of filtration was increased. The increase rate of the filtration resistance with respect to the increase in the filtration amount indicates a decrease in the filtration performance due to the fouling of the membrane. Therefore, it is shown that the treatment methods of Examples 1 and 2 can suppress film fouling and can operate stably. In addition, in Comparative Example 1 in which the amount of the organic coagulant was added more than that in Comparative Example 2, the increase in the filtration resistance was higher than that in Comparative Example 2. It can be said that the organic coagulant remaining in the treated water helped Fouling of the membrane. On the other hand, in Examples 1 and 2, although the same amount of organic flocculant as in Comparative Example 1 was added, even if the amount of filtration was increased, the filtration resistance was hardly increased, and membrane fouling was suppressed. The reason is considered to be that the addition of the inorganic coagulant causes the organic coagulant in the treated water to be in a state that it is difficult to adhere to the film surface.

As shown in Table 2, the TOC of the treated water in Examples 1 and 2 was decreased, and it was confirmed that the remaining organic flocculant had been treated.

(Example 3) Except for the organic flocculant (polyacrylamide polymer) was changed from 1.0 ppm to 5.0 ppm, and the inorganic flocculant (ferric chloride) was changed from 75 ppm to 2.5 ppm. Example 1 The same process.

(Comparative Example 3) To the plating-type drainage water of the water quality shown in Table 1, 5.0 ppm (polyacrylamide polymer) as an organic flocculant was added, and 1 ppm of ferric chloride was added as an inorganic flocculant. , Performing a coacervation treatment, and then directly passing the supernatant water to a membrane filtration device (the aforementioned UF membrane device) to perform a membrane filtration treatment.

Table 3 shows the water quality results of the treated water obtained by the membrane filtration treatment of Example 3 and Comparative Example 3.

【table 3】

The results of the filtration resistance (1 / m) of the membrane filtration device in Example 3 and Comparative Example 3 with respect to the filtration amount (m ³ / m ² ) are shown in FIG. 8. The rate of increase in the filtration resistance of Example 3 is the same as that of Examples 1 and 2. On the other hand, the increase rate of the filtration resistance of Comparative Example 3 was higher than that of Example 3 in which the same amount of inorganic flocculant was added, compared to Comparative Example 1 and no inorganic flocculant added. 2, for lower results. From these results, it can be said that, in order to suppress the fouling of the membrane, it is necessary to add an inorganic coagulant to the treated water obtained by coagulation and precipitation treatment using an organic coagulant.

(Example 4) The same treatment as in Example 1 was performed except that the inorganic flocculant was replaced with ferric chloride and polyaluminum chloride (PAC), and the addition amount was changed from 75 ppm to 50 ppm.

(Comparative example 4) Except changing the sampling time of raw water, the same process as Example 1 was performed.

The results of the filtration resistance (1 / m) of the membrane filtration device in Example 4 and Comparative Example 4 with respect to the filtration amount (m ³ / m ² ) are shown in FIG. 9. In Example 4 using PAC as an inorganic agglomerating agent, as in Examples 1 to 3, even if the filtration amount was increased, the filtration resistance was hardly increased, and the film scale was suppressed. On the other hand, in Comparative Example 4 in which no inorganic flocculant was added, the filtration resistance increased as the amount of filtration increased.

(Examples 5 to 10) The treatment system shown in FIG. 1 was used to treat the simulated discharged water. The simulated drainage system was obtained by dispersing bentonite 10mg / L in tap water. The membrane filtration device was a UF membrane device as in Example 1.

In Example 5, 1.0 ppm of a polyacrylic polymer (OX-304 (cationic polymer) manufactured by Olugaonau) was added as an organic flocculant to the simulated discharge water, and a coacervation treatment was performed. Supernatant water was supplied to the second aggregation reaction tank. 10 ppm of PAC as an inorganic flocculant was added to the second aggregation reaction tank, and then water was passed through a membrane filtration device (UF membrane device) to perform membrane filtration treatment.

In Example 6, the organic flocculant was replaced by a polyacrylic polymer (manufactured by Olurkanau, OX-304 (cationic polymer)) with an acrylamide polymer (manufactured by Olurkanau, Except for AP-1 (anionic polymer)), membrane filtration was performed in the same manner as in Example 5.

In Example 7, the organic flocculant was replaced by a polyacrylic polymer (manufactured by Olurkanau, OX-304 (cationic polymer)) by a polyacrylamide polymer (manufactured by Olurkanau). Except for ON-1H (non-ionic polymer)), membrane filtration was performed in the same manner as in Example 5.

In Example 8, the membrane filtration treatment was performed in the same manner as in Example 5 except that the inorganic coagulant was replaced with PAC and ferric chloride (FeCl ₃ ).

In Example 9, a membrane filtration treatment was performed in the same manner as in Example 6 except that the inorganic coagulant was replaced with PAC and ferric chloride (FeCl ₃ ).

In Example 10, membrane filtration was performed in the same manner as in Example 7 except that the inorganic coagulant was replaced with PAC and ferric chloride (FeCl ₃ ).

(Comparative Examples 5 to 7) In Comparative Example 5, a membrane filtration treatment was performed in the same manner as in Example 5 except that no inorganic flocculant was added.

In Comparative Example 6, a membrane filtration treatment was performed in the same manner as in Example 6 except that no inorganic coagulant was added.

In Comparative Example 7, a membrane filtration treatment was performed in the same manner as in Example 7 except that no inorganic coagulant was added.

In Examples 5 to 10 and Comparative Examples 5 to 7, the time (filtration time) from when water was passed through the membrane filtration device until 200 ml of filtrate was obtained was measured. The results are shown in Table 4. The longer the filtration time, the faster the filtration resistance rises.

【Table 4】

In Examples 5 to 10 in which the organic-based coagulant and the inorganic-based coagulant were added, the filtration time was shortened compared to Comparative Examples 5 to 7 in which only the organic-based coagulant was added. That is, it can be said that in Examples 5 to 10, the increase in filtration resistance was suppressed compared to Comparative Examples 5 to 7.

1 ～ 6‧‧‧processing system
10‧‧‧The first condensation reaction tank
12‧‧‧Organic flocculant addition pipeline
14‧‧‧Condensation and sedimentation tank
15‧‧‧Inorganic flocculant addition device
16‧‧‧Inorganic flocculant addition pipeline
18‧‧‧ 2nd condensation reaction tank
20‧‧‧ membrane filtration device
22‧‧‧ Pipeline for treated water
24a ～ 24c‧‧‧Connection piping
26, 26a, 26b ‧‧‧ treatment water piping
28a, 28b‧‧‧mixer
29‧‧‧oxidant adding device
30‧‧‧Oxidant adding pipeline
32‧‧‧ activated carbon device
34‧‧‧ reverse osmosis membrane device
36‧‧‧ Permeable piping
38‧‧‧ Concentrated water piping
40‧‧‧pH adjusting agent adding device
42‧‧‧pH adjusting agent adding pipe
44‧‧‧Water Quality Testing Device
46‧‧‧Control Department
48‧‧‧Lan's Index Calculation Department
50‧‧‧pH adjustment dose control unit

[FIG. 1] A schematic diagram showing an example of a configuration of a processing system according to this embodiment. FIG. 2 is a schematic diagram showing an example of a configuration of a processing system according to another embodiment. 3 is a schematic diagram showing an example of a configuration of a processing system according to another embodiment. FIG. 4 is a schematic diagram showing an example of a configuration of a processing system according to another embodiment. FIG. 5 is a schematic diagram showing an example of a configuration of a processing system according to another embodiment. 6 is a schematic diagram showing a configuration of a processing system in a reference example. FIG. 7 is a graph showing the results of the filtration resistance (1 / m) with respect to the filtration amount (m ³ / m ² ) of the membrane filtration devices in Examples 1 to 2 and Comparative Examples 1 to 2. FIG. FIG. 8 is a graph showing the results of the filtration resistance (1 / m) of the membrane filtration device in Example 3 and Comparative Example 3 with respect to the filtration amount (m ³ / m ² ). FIG. 9 is a graph showing the results of the filtration resistance (1 / m) of the membrane filtration devices in Example 4 and Comparative Example 4 with respect to the filtration amount (m ³ / m ² ).

no

Claims (11)

A membrane filtration method characterized by adding an inorganic flocculant to the treated water obtained by adding an organic flocculant to the treated water and subjecting it to a coacervation precipitation treatment or a flocculation pressure floatation treatment, and performing an ultrafiltration membrane treatment And at least one kind of membrane filtration treatment among precision filtration membrane treatment. For example, in the membrane filtration method according to the first patent application scope, at the time of the membrane filtration treatment, at least one of the application of shearing force and the addition of an oxidizing agent is performed on the treated water to make the organic flocculant in the treated water The average molecular weight is equal to or lower than the cut-off molecular weight of the membrane used in the membrane filtration treatment. For example, the membrane filtration method according to item 1 or 2 of the patent application range, wherein the addition amount of the inorganic coagulant is 0.5 to 75 times the concentration (mL / g) of the organic coagulant in the water to be treated. range. For example, the membrane filtration method according to item 1 or 2 of the scope of patent application, wherein the inorganic polymer is controlled in accordance with the concentration of the high molecular organic matter detected by LC-OCD in the treated water subjected to agglomeration precipitation treatment or agglomerated pressure floatation treatment. The amount of coagulant added. For example, the membrane filtration method according to item 1 or 2 of the patent application scope, wherein at least one of an activated carbon treatment and a reverse osmosis membrane treatment is performed on the treated water treated by the membrane filtration. For example, the membrane filtration method according to item 1 or 2 of the scope of patent application, in which the treated water is adjusted in such a way that the Langelier's index (LSI) of the treated water becomes less than 0 during the membrane filtration The pH. A membrane filtration system is characterized in that it includes the following means: an inorganic coagulant adding means for adding an inorganic coagulant to treated water obtained by adding an organic coagulant to the water to be treated and performing coagulation precipitation treatment or coagulation pressure floatation treatment; Coagulant; and membrane filtration treatment means, which has at least one of an ultrafiltration membrane and a precision filtration membrane, and performs membrane filtration treatment on the treated water to which an inorganic coagulant has been added. For example, the membrane filtration system according to item 7 of the scope of patent application includes at least one of a shearing force imparting means for imparting a shearing force to the treated water during the membrane filtration process, and an oxidant adding means for adding an oxidant; At least one of the application of the shear force and the addition of the oxidizing agent is such that the average molecular weight of the organic flocculant in the treated water is equal to or lower than the cut-off molecular weight of the membrane used in the membrane filtration treatment. For example, the membrane filtration system according to item 7 or 8 of the scope of patent application, wherein the addition amount of the inorganic coagulant is 0.5 to 75 times the concentration (mL / g) of the organic coagulant in the water to be treated. range. For example, the membrane filtration system with the scope of patent application No. 7 or 8 has a post-treatment means for post-treating the treated water of the membrane filtration treatment; the post-treatment means includes at least one of activated carbon treatment means and reverse osmosis membrane treatment means. One. For example, the membrane filtration system for item 7 or 8 of the scope of patent application includes a pH adjustment means for adjusting the pH of the treated water so that the blue index (LSI) of the treated water becomes less than 0 during the membrane filtration treatment. .