JP6721288B2 - Wastewater treatment method and wastewater treatment system - Google Patents

Description

The present invention relates to a wastewater treatment method and a wastewater treatment system suitable for the wastewater treatment method.

Domestic wastewater and industrial wastewater are discharged to rivers and the like after being subjected to treatment to remove suspended substances and organic substances contained therein.
The membrane separation activated sludge method (MBR) is an effective means for treating wastewater containing organic substances as compared with the conventional standard activated sludge method. Here, MBR is a method of performing solid-liquid separation by a separation membrane without providing a final settling tank in the activated sludge method.

In MBR, a method of adding an amidine coagulant when treating wastewater has been proposed (for example, refer to Patent Document 1). The coagulant adsorbs on the surface of the sludge, and at the same time, adsorbs organic substances such as hardly decomposable substances that are difficult to decompose by MBR.

International Publication No. 2011/016482

However, when the coagulant is excessively added, or when the amount of sludge is smaller than the amount of the coagulant, the coagulant may remain in the treated water. Since the coagulant is an organic substance, the coagulant causes contamination of treated water. That is, BOD ₅ and COD _cr of the treated water rise, and the quality of the treated water deteriorates.
In addition, when the treated water is filtered by a reverse osmosis membrane or a nanofiltration membrane, if the hardly decomposable substance or the coagulant remains in the treated water, the hardly decomposable substance or the coagulant will block the membrane of the filtration membrane. There was a risk of causing it.

The present invention has been made in view of the above circumstances, and it is possible to obtain high-quality treated water, and it is possible to suppress the membrane clogging of the filtration membrane even when the treated water is filtered after being treated by the membrane separation activated sludge method. An object is to provide a wastewater treatment method and a wastewater treatment system.

The present invention has the following aspects.
[1] After treating the wastewater by adding a flocculant to the tank by a membrane separation activated sludge method in which biological treatment by microorganisms in activated sludge and solid-liquid separation treatment by a separation membrane are performed in the same tank, A method for treating wastewater, further comprising treating the membrane-separated water that has been subjected to solid-liquid separation by the membrane-separated activated sludge method by a biomembrane method in which the microorganisms attached to the carrier are used for biological treatment.
[2] The wastewater treatment method according to [1], wherein the BOD ₅ /COD _cr of the membrane separation treated water is 0.3 or less.
[3] The wastewater treatment method according to [1] or [2], wherein the biofilm method is a biological activated carbon treatment method.
[4] A wastewater treatment method, wherein the biofilm-treated water obtained by the wastewater treatment method according to any one of [1] to [3] is filtered by a reverse osmosis membrane or a nanofiltration membrane.
[5] The wastewater treatment method according to [4], wherein concentrated water generated by filtration is concentrated.
[6] Membrane separation activated sludge treatment device that performs biological treatment of wastewater by microorganisms in activated sludge and solid-liquid separation treatment using a separation membrane in the same tank, and solid-liquid separation by the membrane separation activated sludge treatment device A biofilm treatment device for biologically treating the treated membrane separation treated water with microorganisms attached to a carrier, wherein the membrane separation activated sludge treatment device comprises coagulant addition means for adding a coagulant to the tank, wastewater Processing system.
[7] The wastewater treatment system according to [6], wherein BOD ₅ /COD _cr of the membrane separation treated water is 0.3 or less.
[8] The wastewater treatment system according to [6] or [7], wherein the biofilm treatment device is a bioactive carbon treatment device.
[9] The method according to any one of [6] to [8], further including a reverse osmosis membrane filtration device or a nanofiltration membrane filtration device that performs filtration treatment on the biofilm treated water treated by the biofilm treatment device. Wastewater treatment system.
[10] The wastewater treatment system according to [9], further comprising an evaporative concentration device for concentrating the concentrated water generated by the reverse osmosis membrane filtration device or the nanofiltration membrane filtration device.

According to the wastewater treatment method and the wastewater treatment system of the present invention, it is possible to obtain treated water with high water quality, and further suppress the membrane clogging of the filtration membrane even when the treated water is filtered after being treated by the membrane separation activated sludge method. it can.

It is a schematic structure figure showing one embodiment of the wastewater treatment system of the present invention. It is a schematic block diagram which shows other embodiment of the wastewater treatment system of this invention.

[Wastewater treatment method]
The wastewater treatment method of the present invention is a method of adding a coagulant to a treatment tank (membrane separation tank) when treating wastewater by the membrane separation activated sludge method (MBR).
Hereinafter, the present invention will be described with reference to specific embodiments.

<Embodiment of wastewater treatment system>
FIG. 1 is a schematic configuration diagram showing an embodiment of a wastewater treatment system of the present invention.
In this wastewater treatment system, wastewater from a raw water tank (not shown) is biologically treated by microorganisms in activated sludge, and at the same time, a solid-liquid separation treatment is performed by a membrane module 15 as a separation membrane into sludge and membrane separation treated water (permeate). The membrane separation activated sludge treatment device 10 and the biofilm treatment device 70 for biologically treating the membrane separation treated water that has been solid-liquid separated by the membrane separation activated sludge treatment device 10 by the microorganisms attached to the carrier.

(Membrane separation activated sludge treatment equipment)
The membrane separation activated sludge treatment device 10 includes a membrane separation tank (first aeration tank) 11, an air diffuser 12 arranged near the bottom of the membrane separation tank 11, and a blower 13 for supplying air to the air diffuser 12. An air introduction pipe 14 connecting the air diffuser 12 and the blower 13, a membrane module 15 arranged in the membrane separation tank 11 and above the air diffuser 12, and a coagulant addition for adding a coagulant to the membrane separation tank 11. Means 16; provided in the middle of the membrane separation treated water flow path 51, the solid-liquid separation of the sludge and the membrane separation treated water (permeate) is performed by reducing the pressure in the membrane module 15, and the membrane separation treated water is removed. A suction pump 18 for sending to the biofilm treatment device 70; a wastewater flow passage 50 for supplying wastewater from the raw water tank to the membrane separation activated sludge treatment device 10; and discharge of the membrane separation treated water from the membrane separation activated sludge treatment device 10. A membrane separation treated water channel 51; and an excess sludge channel 52 for discharging the excess sludge from the membrane separation activated sludge treatment device 10.

The membrane module 15 may be a known membrane module including a known filtration membrane. As the type of 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-shaped membrane. Of these, hollow fiber membranes are preferred because they allow a high degree of integration of the membrane area when compared on a volume basis.

Examples of the material of the filtration membrane include organic materials (cellulose, polyolefin, polysulfone, polyvinyl alcohol, polymethylmethacrylate, polyvinylidene fluoride, polytetrafluoroethylene, etc.), metals (stainless steel, etc.), inorganic materials (ceramics, etc.). To be The material of the filtration membrane is appropriately selected according to the properties of the wastewater.

The pore size of the filtration membrane may be appropriately selected according to the purpose of treatment. In MBR, the pore size of the filtration membrane is preferably 0.001 to 3 μm. When the pore diameter is 0.001 μm or more, it is possible to suppress an increase in the resistance of the film. When the pore diameter is 3 μm or less, activated sludge can be sufficiently separated, and the quality of treated water can be maintained in good condition. The pore size of the filtration membrane is more preferably 0.04 to 1.0 μm in the range of the microfiltration membrane.

In the membrane separation activated sludge treatment device 10, a membrane unit in which the air diffuser 12 and the membrane module 15 are integrated may be used. Examples of such a membrane unit include the membrane unit described in JP2013-202524A.

The coagulant adding means 16 includes a coagulant channel 16a for supplying the coagulant to the membrane separation tank 11; and a pump 16b provided in the middle of the coagulant channel 16a for feeding the coagulant to the membrane separation tank 11.

(Biofilm treatment equipment)
The biofilm treatment device 70 includes a biofilm tank (second aeration tank) 71; an air diffuser 72 arranged near the bottom of the biofilm tank 71; a blower 73 that supplies air to the air diffuser 72; An air introducing pipe 74 connecting the trachea 72 and the blower 73; and a biofilm treated water flow path 62 for discharging the biofilm treated water biologically treated in the biofilm tank 71 are provided.

The biofilm tank 71 contains a microorganism-attached carrier (not shown) in which microorganisms are attached to the carrier.
The microorganism-attached carrier may be fluidized in the biofilm tank 71 or may be fixed. The biofilm treatment device 70 that performs biological treatment while flowing the microorganism adhesion carrier in the biofilm tank 71 is referred to as a fluidized bed type biofilm treatment device, and organisms for biological treatment by fixing the microorganism adhesion carrier in the biofilm tank 71. The membrane treatment device 70 is referred to as a fixed bed biofilm treatment device.

Examples of the carrier include fixed bed carriers and fluidized bed carriers.
For example, examples of the fluidized bed carrier include activated carbon. In addition to activated carbon, a resin carrier such as polypropylene or polyvinyl alcohol, a ceramic carrier, or the like can be used as the carrier for the fluidized bed. Among these, activated carbon is preferable because it is excellent in decomposing a hardly decomposable substance or a coagulant, which is difficult to process by the membrane separation activated sludge method when it becomes a microorganism-attached carrier. Here, the biofilm treatment device 70 in which the microorganism adhesion carrier in which the microorganisms adhere to the activated carbon is stored in the biofilm tank 71 is also referred to as a bioactivated carbon treatment device.

(Standard activated sludge treatment equipment)
As shown in FIG. 2, the wastewater treatment system further includes a standard activated sludge treatment device 20 upstream of the membrane separation activated sludge treatment device 10 for biologically treating the wastewater from a raw water tank (not shown) with microorganisms in the activated sludge. You may have.
In FIG. 2, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

The standard activated sludge treatment device 20 includes an activated sludge tank (third aeration tank) 21, an air diffusing pipe 22 arranged near the bottom of the activated sludge tank 21, and a blower 23 for supplying air to the air diffusing pipe 22; An air inlet pipe 24 connecting the air diffuser 22 and the blower 23; a settling tank 25 for solid-liquid separating the mixed water of the activated sludge tank biologically treated in the activated sludge tank 21 into sludge and supernatant liquid; from the raw water tank Waste water flow path 50 for supplying the waste water of the activated sludge tank 21 to the activated sludge tank 21; and an activated sludge tank mixed water flow path 53 for transferring the activated sludge tank mixed water biologically treated in the activated sludge tank 21 to the settling tank 25; Supernatant liquid flow path 54 for transferring the supernatant liquid from the above to the membrane separation activated sludge treatment device 10; excess sludge flow path 55 for discharging the excess sludge from the precipitation tank 25; and a part of the excess sludge from the precipitation tank 25 A return sludge flow path 56 for returning the activated sludge to the activated sludge tank 21.

The settling tank 25 is not particularly limited as long as it can solid-liquid separate the activated sludge tank mixed water transferred from the activated sludge tank 21 into a sludge and a supernatant liquid by gravity settling. The settling tank 25 may be a general settling tank.

(Filtration device)
As shown in FIG. 2, the wastewater treatment system may further include a filtration device 30 that performs biological treatment in the biofilm tank 71 and filters the biofilm-treated water discharged from the biofilm-treated water channel 62. Good.

The filtering device 30 includes a filtering device body 31, a purified water channel 58 for discharging the purified water that has passed through the filtering device body 31, and a concentrated water channel 59 for discharging the concentrated water that has not passed through the filtering device body 31. ..

Examples of the filtration device body 31 include those provided with a reverse osmosis membrane module or a nanofiltration membrane module. Here, the filtration device 30 including the reverse osmosis membrane module as the filtration device body 31 is also referred to as a reverse osmosis membrane filtration device, and the filtration device 30 including the nano filtration membrane module as the filtration device body 31 is also referred to as a nano filtration membrane filtration device.

The reverse osmosis membrane module is not particularly limited as long as it can separate 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 type reverse osmosis membrane module in which a cylindrical reverse osmosis membrane element in which a reverse osmosis membrane is wound around a water collection tube is housed in a cylindrical casing.
Examples of the material of the reverse osmosis membrane include polyamide, polysulfone, cellulose acetate, and the like, and aromatic polyamide or polyamide containing crosslinked aromatic polyamide is preferable.

The nanofiltration membrane module is not particularly limited as long as it can separate purified water that has passed through the nanofiltration membrane and concentrated water that does not pass through the nanofiltration membrane.
Examples of the nanofiltration membrane module include a so-called spiral nanofiltration membrane module in which a cylindrical nanofiltration membrane element having a nanofiltration membrane wound around a water collection tube is housed in a cylindrical casing.
Examples of the material of the nanofiltration membrane include polyethylene type, polyamide type including aromatic polyamide type and crosslinked polyamide type, aliphatic amine condensation type polymer, heterocyclic polymer type, polyvinyl alcohol type, cellulose acetate type polymer and the like.

(Evaporative concentrator)
As shown in FIG. 2, the wastewater treatment system may further include an evaporative concentrator 40 for concentrating the concentrated water that has not passed through the filter device body 31.

The evaporative concentration apparatus 40 includes an evaporator 41; a condensed water flow path 60 for discharging condensed water condensed and condensed in the evaporator 41; a concentrated waste water flow path for discharging concentrated waste water concentrated in the evaporator 41. And 61.

The evaporator 41 is not particularly limited as long as the concentrated water can be heated and concentrated.

<Embodiment of wastewater treatment method>
The wastewater treatment method using the wastewater treatment system of FIG. 1 has the following steps (b) and (c), and the wastewater treatment method using the wastewater treatment system of FIG. 2 has the following steps (b) and (c). ) And, if necessary, the following (a), (d), and (e).
(A) A step of biologically treating wastewater from a raw water tank (not shown) with microorganisms in the activated sludge in the standard activated sludge treatment device 20.
(B) In the membrane-separated activated sludge treatment device 10, wastewater from a raw water tank (not shown) or wastewater treated in step (a) (supernatant liquid) is biologically treated by microorganisms in the activated sludge, and at the same time, a membrane module. 15. A step of solid-liquid separation into sludge and treated water (permeate) by 15.
(C) A step of biologically treating the separated membrane-treated water (permeated water) that has permeated the membrane module 15 in the biological membrane treatment device 70.
(D) A step of filtering the biofilm-treated water that has been bioprocessed in the biofilm tank 71 with the filtration device 30 using a reverse osmosis membrane or a nanofiltration membrane.
(E) A step of concentrating concentrated water that has not permeated through the filtering device body 31 in the evaporative concentrator 40.

(Waste water)
The wastewater treated in the wastewater treatment system usually contains organic substances such as easily decomposable substances and hardly decomposable substances. Examples of such wastewater include domestic wastewater, industrial wastewater (chemical, pharmaceutical, papermaking, beverage, oil, semiconductor, electronic, etc.), and livestock wastewater.
The waste water may be subjected to removal of coarse floating substances, earth and sand, pH adjustment, or dilution in advance.

(Step (a))
The wastewater treated in step (b) may be treated in the standard activated sludge treatment device 20 in advance.
In step (a), first, the wastewater stored in a raw water tank (not shown) is supplied to the activated sludge tank 21 of the standard activated sludge treatment device 20 via the wastewater flow path 50.
In the activated sludge tank 21, the blower 23 is operated to introduce air from the air diffuser 22 to give oxygen to the microorganisms in the activated sludge to perform biological treatment of the wastewater.

Then, the activated sludge tank mixed water biologically treated in the activated sludge tank 21 is transferred to the settling tank 25 via the activated sludge tank mixed water flow path 53.
In the settling tank 25, the activated sludge tank mixed water is solid-liquid separated into sludge and a supernatant liquid by gravity settling.

The supernatant liquid of the settling tank 25 is transferred to the membrane separation activated sludge treatment device 10 via the supernatant liquid flow path 54 as waste water to be treated in step (b).
On the other hand, the separated excess sludge is discharged through the excess sludge channel 55. Since the excess sludge contains microorganisms, a part of the excess sludge is returned to the activated sludge tank 21 through the return sludge flow path 56 and used again for biological treatment of wastewater.

(Step (b))
When the wastewater treatment method does not include step (a), the wastewater stored in the raw water tank (not shown) is supplied to the membrane separation tank 11 of the membrane separation activated sludge treatment device 10 via the wastewater flow passage 50.
When the wastewater treatment method has step (a), the wastewater (supernatant liquid) treated in step (a) is supplied to the membrane separation tank 11 of the membrane separation activated sludge treatment device 10 via the supernatant liquid flow path 54. To do.

In the membrane separation tank 11, the blower 13 is operated to introduce air from the air diffuser 12 to give oxygen to the microorganisms in the activated sludge to perform biological treatment of the wastewater.
Further, in the membrane separation tank 11, the suction pump 18 is operated to reduce the pressure inside the membrane module 15 to perform solid-liquid separation of the mixed water into sludge and treated water (permeated water). At this time, by introducing air from the air diffuser 12 into the membrane module 15, solid-liquid separation can be efficiently performed while cleaning the surface of the separation membrane (for example, hollow fiber membrane) of the membrane module 15.

In step (b), the coagulant is added to the membrane separation tank 11 by the coagulant addition means 16 to treat the wastewater.
The amount of the aggregating agent added is not particularly limited as long as it is an amount capable of aggregating the organic matter (particularly the hardly decomposable substance) in the wastewater.

In step (b), it is preferable to treat the wastewater such that the BOD ₅ /COD _{cr of} the separation membrane-treated water (permeate) that has permeated the membrane module 15 is 0.3 or less. It is more preferable to treat the wastewater so that the membrane-treated water (permeate) has a BOD ₅ /COD _cr of 0.3 or less and an SS concentration of 25 mg/L or less.
If the BOD ₅ /COD _cr of the separation membrane-treated water is 0.3 or less, the concentration of the hardly decomposable substance (COD _cr −BOD ₅ ) in the biological membrane-treated water after biological treatment in step (c) is higher. Will be reduced. Therefore, treated water with higher water quality can be obtained. Moreover, when the biological membrane-treated water is filtered in step (d), the membrane clogging of the filtration membrane such as the reverse osmosis membrane or the nanofiltration membrane can be further suppressed.
If the SS concentration of the separation membrane-treated water is 25 mg/L or less, the biological treatment in step (c) can be performed more smoothly. In particular, when biological treatment is performed by the biological activated carbon treatment method in step (c), if the SS concentration of the separation membrane-treated water is 25 mg/L or less, clogging of the activated carbon can be suppressed, so the biological treatment should be performed more smoothly. You can

The BOD ₅ /COD _cr and SS concentrations of the separation membrane-treated water can be adjusted by the residence time in the membrane separation tank 11 and the addition amount of the coagulant. For example, the BOD ₅ /COD _cr and SS concentrations of the separation membrane-treated water tend to decrease as the residence time in the membrane separation tank 11 increases and the amount of the flocculant added increases. Also, by performing step (a) before step (b), the BOD ₅ /COD _cr of the separation membrane-treated water tends to decrease.

In addition, "COD _cr "is an oxygen consumption amount by potassium dichromate and is measured according to JIS K 0102.
"BOD ₅ "is a biochemical oxygen demand for 5 days, which is measured according to JIS K 0102.
The "SS concentration" is the concentration of suspended solids in water and is measured according to JIS K 0102.

The aggregating agent used in step (b) is not particularly limited, but a polymer aggregating agent is preferable. The polymer flocculant has a function of converting fine flocs into coarse flocs by crosslinking. Further, the polymer flocculants include nonionic, anionic and cationic types, depending on the adsorption active group of the flocculant. In particular, from the viewpoint of treatment efficiency, as the flocculant used in step (b), an amidine containing a cationic polymer having an amidine structural unit represented by the following formula (1) and/or (2) as an active ingredient. A system flocculant is preferred.
In the present invention, the "active ingredient" means the content of the cationic polymer in 100% by mass of the aggregating agent, and usually 10 to 100% by mass is preferable.

In formulas (1) and (2), R ^{1 to} R ⁴ are each a hydrogen atom or a methyl group, and may be the same or different.
X ⁻ and Y ⁻ are anions, and may be the same or different. Examples of the anion include Cl ⁻ , Br ⁻ , 1/2SO ₄ ²⁻ , CH ₃ (CO)O ⁻ , H(CO)O ^{− and the} like. Of these, Cl ⁻ is preferable.

The method for producing such a cationic polymer is not particularly limited, but for example, an ethylenically unsaturated monomer having a primary amino group or a substituted amino group capable of generating a primary amino group by a conversion reaction, and acrylonitrile or methacrylonitrile. A method of producing a copolymer with nitriles, acid hydrolysis, and then reacting a cyano group in the copolymer with a primary amino group to form an amidine is mentioned.

The cationic polymer is most typically a copolymer of N-vinylformamide and acrylonitrile, and the resulting copolymer is usually heated as an aqueous suspension in the presence of hydrochloric acid to form a substituted amino group. It is preferably prepared by forming an amidine structural unit from adjacent cyano groups. Then, a cationic polymer having various compositions can be obtained by selecting the molar ratio of N-vinylformamide and acrylonitrile to be subjected to copolymerization and the amidation condition of the copolymer.

The cationic polymer preferably contains 5 to 90 mol% of the amidine structural unit represented by the formula (1) and/or (2) as a repeating unit in 100 mol% of the cationic polymer. When the content of the amidine structural unit is less than 5 mol %, the content of the amidine structural unit is too small, and therefore the amount of the cationic polymer used as an aggregating agent increases. On the other hand, if the content of the amidine structural unit exceeds 90 mol %, it is difficult to produce it by the method described above. The lower limit of the content of the amidine structural unit is more preferably 10 mol% or more, further preferably 15 mol% or more, particularly preferably 20 mol% or more. The upper limit of the content of the amidine structural unit is more preferably 85 mol% or less, further preferably 80 mol% or less.

When produced by the above-mentioned method, the cationic polymer may contain units represented by the following formulas (3) to (5) in addition to the amidine structural unit.

In formulas (3) to (5), R ⁵ , R ⁷ , and R ⁸ are each a hydrogen atom or a methyl group, and may be the same or different.
R ⁶ is an alkyl group having 1 to 4 carbon atoms or a hydrogen atom.
Z ⁻ is an anion. The anion is the same as the anion exemplified above in the description of the formulas (1) and (2).

When the cationic polymer contains the units represented by the above formulas (3) to (5), the repeating unit represented by the above formula (3) is usually 0 to 100 mol% in the cationic polymer. 40 mol%, 0 to 70 mol% of the repeating unit represented by the above formula (4), and 0 to 70 mol% of the repeating unit represented by the above formula (5).

The composition of the amidine structural units represented by the above formulas (1) and/or (2) and the units represented by the above formulas (3) to (5) is determined by the polymerization mole of the ethylenically unsaturated monomer and the nitriles. It can be adjusted by the ratio and the conditions (temperature and time) of the amidination reaction.
Further, these compositions can be determined by measuring ¹³ C-NMR ( ¹³ C-nuclear magnetic resonance) of the cationic polymer, and specifically, ¹³ C-NMR spectra corresponding to each repeating unit. It can be calculated from the integrated value of the peak (signal).

(Step (c))
The membrane separation treated water (permeated water) that has permeated the membrane module 15 is supplied to the biofilm treatment device 70 via the membrane separation treated water channel 51.
In the biofilm tank 71, the blower 73 is operated to introduce air from the air diffusing tube 72, and oxygen is given to the microorganisms attached to the carrier to perform the biological treatment of the membrane separation treated water. By this biological treatment, organic substances such as flocculants and persistent substances in the membrane separation treated water are decomposed by microorganisms.
It is preferable to biologically treat the membrane separation treated water by a bioactive carbon treatment method using a bioactive carbon treatment device as the biofilm treatment device 70 because it is excellent in decomposing the hardly decomposable substance and the coagulant.

(Step (d))
In step (c), the biofilm-treated water that has been biologically processed in the biofilm tank 71 may be discharged to the outside as it is, but is transferred to the filtration device 30 through the biofilm-treated water channel 62, and the reverse osmosis membrane. Alternatively, it is preferable to perform a filtration treatment with a nanofiltration membrane.
In the filtration device 30, the treated water that has passed through the reverse osmosis membrane or the nanofiltration membrane becomes purified water and is discharged from the purified water flow channel 58. On the other hand, the treated water that has not passed through the reverse osmosis membrane or the nanofiltration membrane becomes concentrated water and is discharged from the concentrated water channel 59.

(Step (e))
In step (d), the treated water (concentrated water) that has not permeated the reverse osmosis membrane or the nanofiltration membrane may be discharged to the outside as it is, but it is transferred to the evaporative concentration device 40 via the concentrated water flow channel 59, Concentration treatment is preferable.
In the evaporative concentration device 40, the concentrated water sent to the evaporator 41 is heated by a heat transfer device (not shown) to evaporate and become steam. The water vapor is cooled by a cooler (not shown) and condensed to become condensed water, which is discharged from the condensed water passage 60. The concentrated water concentrated in the evaporator 41 is discharged from the concentrated wastewater flow passage 61 as concentrated wastewater.
When the concentrated water is concentrated by the evaporative concentration device 40, an alkali such as sodium hydroxide may be added to the concentrated water for the purpose of preventing corrosion of the evaporative concentration device 40.
The concentrated wastewater may be discharged to the outside as it is, but it is usually dried and then made into a solid state before being discharged.

(Action effect)
In the wastewater treatment method and the wastewater treatment system of the present invention described above, after treating the wastewater by adding the flocculant by the MBR, the membrane-separated treated water solid-liquid separated by the MBR is treated by the biofilm method. Further processing. Therefore, even if the coagulant remains in the membrane separation treatment water due to excessive addition of the coagulant or the amount of sludge is smaller than the amount of the coagulant, the biofilm method is used to separate the coagulant into the membrane. Can be removed from treated water. The biofilm method can also remove organic substances such as hardly decomposable substances that are difficult to decompose by MBR. Therefore, the biofilm-treated water treated by the biofilm method has a low concentration of BOD ₅ , COD _cr , and hardly decomposable substances (COD _cr −BOD ₅ ), and high-quality treated water can be obtained.
Moreover, since the coagulant and the hardly decomposable substance can be removed by the biofilm method, even when the biofilm-treated water is filtered by a reverse osmosis membrane or a nanofiltration membrane, the membrane clogging of the filtration membrane can be suppressed.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

(Flocculant)
As the coagulant, a polyamidine-based polymer coagulant (“KP7000” manufactured by Mitsubishi Rayon Co., Ltd.) was used.

[Examples 1 to 5]
The wastewater discharged from the coke manufacturing process was used as the wastewater containing persistent substances. It is known that the wastewater discharged from the coke manufacturing process (coke wastewater) contains humic substances, etc., and generally contains a large amount of persistent substances that are difficult to bioprocess.
The COD _cr of the wastewater used in this example was 3500 mg/L, and the BOD ₅ was 500 mg/L. Therefore, the concentration of the hardly decomposable substance in the wastewater (COD _cr -BOD ₅ ) is 3000 mg/L, and the BOD ₅ /COD _cr is 0.14. COD _cr and BOD ₅ were measured according to JIS K 0102.

<Treatment by membrane separation activated sludge method>
(Preparation of Membrane Separation Treated Water (I))
Wastewater is treated by a membrane separation activated sludge method (MBR) using an activated sludge adjusted to an MLSS concentration of 8000 mg/L and a hollow fiber membrane (“Stellapore SADF” manufactured by Mitsubishi Rayon Co., Ltd.), and membrane separation treated water (I) Got In the treatment, aeration was carried out from below the hollow fiber membrane to aerobic conditions, and the hydraulic retention time was set to 24 hours.
When the COD _cr and BOD ₅ of the obtained membrane-separated water (I) were measured according to JIS K 0102, the COD _cr was 2000 mg/L, the BOD ₅ was 50 mg/L, and the concentration of the hardly decomposable substance. (COD _cr -BOD ₅ ) was 1950 mg/L.

(Preparation of membrane separation treated water (II))
The wastewater was treated under the same conditions as in the preparation of the membrane separation treated water (I) except that the coagulant was continuously added to the wastewater so that the concentration was 500 mg/L, to obtain a membrane separation treated water (II).
The COD _cr and BOD ₅ of the obtained membrane-separated water (II) were measured according to JIS K 0102. The COD _cr was 1500 mg/L, the BOD ₅ was 50 mg/L, and the concentration of the hardly decomposable substance. (COD _cr -BOD ₅ ) was 1450 mg/L.

<Treatment by the biofilm method>
Membrane separation water and _{(II) (COD cr = 1500mg} / L, BOD 5 = 50mg / L, COD cr -BOD 5 = 1450mg / L), domestic wastewater _{(COD cr = 500mg / L,} BOD 5 = 425mg / L , COD _cr −BOD ₅ =75 mg/L, BOD ₅ /COD _cr =0.85) and pure water were mixed to obtain mixed raw water. The mixing ratios of the membrane separation treated water (II), domestic wastewater, and pure water were such that COD _cr , BOD ₅ /COD _cr , and SS concentration in the mixed raw water were the values shown in Table 1. Table 1 also shows BOD ₅ and COD _cr -BOD _{5 in the} mixed raw water. The SS concentration was measured according to JIS K 0102.

While aerating the inside of a column (diameter 50 mm, length 20 cm) packed with 200 mL of activated carbon (“DIAMALUS SAC” manufactured by Mitsubishi Rayon Co., Ltd., effective porosity 75%), the space velocity of mixed raw water was SV=0.042. Water was passed under the condition of /hr. The column filled with the above activated carbon was allowed to pass through the membrane separation treated water (I) in advance for 1 month under the condition of 0.021/hr while aerating the membrane separation treated water (I) to attach and grow microorganisms on the surface of the activated carbon. The cells were sufficiently acclimated to become microbial activated carbon (carrier with attached microorganisms).
Treated water (biofilm-treated water) after 240 hours from the start of water flow is collected, COD _cr and BOD ₅ are measured, and the concentration of the hardly decomposable substance in the biofilm-treated water (COD _cr −BOD ₅ ) is measured. I asked. The results are shown in Table 1.
Note that Examples 1 to 3 correspond to Examples, and Examples 4 and 5 correspond to Reference Examples .

As is clear from the results in Table 1, by treating the mixed raw water by the biofilm method, it was possible to remove the hardly decomposable substance contained in the mixed raw water. In particular, when the mixed raw water with BOD ₅ /COD _cr of 0.3 or less was used (Examples 1 to 3), the hardly decomposable substance could be largely removed. This means that high BOD ₅ /COD _cr means that the ratio of easily decomposable substances in the mixed raw water is high, and when the mixed raw water with high BOD ₅ /COD _cr is treated by the biofilm method, it is easily decomposed. Degradation of substances tends to be prioritized. Therefore, it can be considered that the concentration of the hardly decomposable substance in the biofilm-treated water becomes higher than that in the case where the mixed raw water having a low BOD ₅ /COD _cr is treated by the biofilm method.

From these results, after the coagulant is added by MBR to treat the wastewater, the treated water (membrane separation treated water) is further treated by the biofilm method so that the organic substances such as the coagulant and the hardly decomposable substance are formed into a membrane. It can be said that it is possible to obtain treated water with high water quality (treated biofilm) by removing it from the separated treated water.
Generally, when biological treatment of wastewater containing easily decomposable substances and hardly decomposable substances, microorganisms that decompose easily decomposable substances grow preferentially, and bacteria that decompose hardly decomposed substances grow. Tend to be suppressed. According to the present invention, when biologically treating wastewater containing a relatively large amount of hardly decomposable substances, microorganisms decomposing easily decomposable substances do not grow preferentially, and microorganisms decomposing hardly decomposable substances are used. The stable growth of the soybean allows stable treatment of the hardly decomposable substance.
In particular, if the BOD ₅ /COD _cr of the membrane separation treated water is 0.3 or less, it can be said that the hardly decomposable substance is largely removed and the treated water with higher water quality can be obtained. Further, it can be said that even when the obtained biofilm-treated water is subjected to a filtration treatment with a reverse osmosis membrane or a nanofiltration membrane, the membrane clogging of the filtration membrane can be more easily suppressed.

[Examples 6 to 10]
Membrane separation water and _{(II) (COD cr = 1500mg} / L, BOD 5 = 50mg / L, COD cr -BOD 5 = 1450mg / L), domestic wastewater _{(COD cr = 500mg / L,} BOD 5 = 425mg / L , COD _cr −BOD ₅ =75 mg/L, BOD ₅ /COD _cr =0.85) and pure water were mixed to obtain mixed raw water. The mixing ratio of the membrane separation treated water (II), domestic wastewater, and pure water was such that COD _{cr in the} mixed raw water was 500 mg/L and BOD ₅ was 100 mg/L. Further, activated sludge was added so that the SS concentration of the mixed raw water became the value shown in Table 2.

While aerating the inside of a column (diameter 50 mm, length 20 cm) packed with 200 mL of activated carbon (“DIAMALUS SAC” manufactured by Mitsubishi Rayon Co., Ltd., effective porosity 75%), the space velocity of mixed raw water was SV=0.042. Water was passed under the condition of /hr. The column filled with the above activated carbon was allowed to pass through the membrane separation treated water (I) in advance for 1 month under the condition of 0.021/hr while aerating the membrane separation treated water (I) to attach and grow microorganisms on the surface of the activated carbon. The cells were sufficiently acclimated to become microbial activated carbon (carrier with attached microorganisms).
As the pressure applied to the column, the distance from the upper surface of the activated carbon in the column to the water surface was measured. The time required for this distance to reach 20 cm was measured. The results are shown in Table 2.
Note that Examples 6 and 7 correspond to Examples, and Examples 8 to 10 correspond to Reference Examples .

The increase in the pressure applied to the column means that the activated carbon is clogged, and an operation such as back washing is usually required. The longer the time it takes for the distance from the upper surface of the activated carbon to the water surface in the column to reach 20 cm, the smoother the treatment of the mixed raw water by the biofilm method without clogging of the activated carbon.
As is clear from the results in Table 2, in each example, the mixed raw water could be smoothly treated by the biofilm method for 7 hours or more. In particular, when mixed raw water having an SS concentration of 25 mg/L or less was used (Examples 6 and 7), the activated carbon was not clogged even after 240 hours, and the mixed raw water was stably treated by the biofilm method. We were able to.

From these results, after treating the wastewater by adding the coagulant by MBR, when the treated water (membrane separation treated water) is further treated by the biofilm method, the SS concentration of the membrane separation treated water is 25 mg/L or less. If so, it can be said that the clogging of activated carbon can be effectively suppressed and the membrane separation treated water can be smoothly treated.

10 Membrane Separation Activated Sludge Treatment Device 11 Membrane Separation Tank 15 Membrane Module 16 Coagulant Addition Means 20 Standard Activated Sludge Treatment Device 30 Filtration Device 40 Evaporative Concentration Device 70 Biofilm Treatment Device

Claims (6)

Biological treatment by microorganisms in activated sludge, and solid-liquid separation treatment by a separation membrane by the membrane separation activated sludge method performed in the same tank, after treating the wastewater by adding a flocculant to the tank,
Solid-liquid separation by the membrane separation activated sludge method to obtain BOD ₅ /COD _cr of 0.3 or less and SS concentration of 25 mg/L or less of the membrane-separated treated water into the activated carbon packed in the column. processed by Lisa et biofilm process a biological activated carbon treatment method for performing a biological process by adhering microorganisms, waste water treatment method. A wastewater treatment method, wherein the biofilm-treated water obtained by the wastewater treatment method according to claim 1 is filtered by a reverse osmosis membrane or a nanofiltration membrane. The wastewater treatment method according to claim 2 , wherein the concentrated water generated by the filtration treatment is concentrated. A membrane separation activated sludge treatment device that performs biological treatment of wastewater with microorganisms in activated sludge and solid-liquid separation treatment with a separation membrane in the same tank,
Solid-liquid separation was carried out in the membrane separation activated sludge treatment device , and the membrane separation treated water having a BOD ₅ /COD _cr of 0.3 or less and an SS concentration of 25 mg/L or less was filled in the column with activated carbon. And a biofilm treatment device which is a bioactive carbon treatment device for biological treatment with microorganisms attached to
The said membrane separation activated sludge process equipment is a wastewater treatment system provided with the coagulant|flocculant addition means which adds a coagulant|flocculant to the said tank. The wastewater treatment system according to claim 4 , further comprising a reverse osmosis membrane filtration device or a nanofiltration membrane filtration device that filters the biofilm treatment water treated by the biofilm treatment device. The wastewater treatment system according to claim 5 , further comprising an evaporative concentration device for concentrating the concentrated water generated by the reverse osmosis membrane filtration device or the nanofiltration membrane filtration device.

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