JP2005040747A - Sewage treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent adhesion of excessive polymer on a membrane surface by measuring the amount of organism-originating polymer in a mixed solution of activated sludge and timely reducing the amount of the polymer in an organism treatment tank (aerator), in a membrane separating activated sludge treatment method. <P>SOLUTION: In this sewage treatment apparatus, organic sewage is treated with activated sludge in the organism treatment tank 24; the mixed solution of the activated sludge is separated into solid and liquid by an immersed type membrane separation device 25 serving as a first separation means immersed in the tank 24; COD components containing the organism-originating polymer accumulated in the tank 24 by activated sludge treatment, are timely separated into solid and liquid by a second separation means 29; and a concentration of the polymer in the mixed solution is kept low, while keeping the activated sludge in the tank 24 at a high concentration. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for treating sewage, and relates to treatment of organic sewage, tank submerged membrane separation activated sludge process (MBR) in low water temperature areas.

  Membrane separation activated sludge treatment methods are widely used because the quality of treated water is stable and maintenance is easy. An example of a general water treatment system to which this membrane separation activated sludge treatment method is applied is shown in FIG. In FIG. 2, the sewage 1 flowing into the system is temporarily stored in the flow rate adjustment tank 3 after removing impurities by the pretreatment facility 2, and then transferred from the flow rate adjustment tank 3 to the biological treatment tank (aeration tank) 4 at a constant flow rate. In the biological treatment tank (aeration tank) 4, organic substances in the sewage are decomposed and removed by activated sludge in the biological treatment tank (aeration tank) 4, and the mixed liquid is solidified by the submerged membrane separation device 5 immersed in the biological treatment tank (aeration tank) 4. Liquid separation is performed, and the membrane filtrate that has permeated through the filtration membrane of the submerged membrane separator 5 is discharged as treated water.

  There are various types of submerged membrane separation devices 5. Here, a plurality of flat membrane cartridges 7 arranged in the vertical direction are arranged in parallel inside a case 6 that is open at the top and bottom. The membrane cartridge 7 has a flat membrane-like organic film attached to the front and back of the filter plate.

  In the biological treatment tank (aeration tank) 4, the air supplied by the blower 9 is diffused from the diffuser 8, and the mixed liquid of the sewage containing the pollutant and the activated sludge is produced by the upward flow of the solid-gas liquid mixed phase generated by the air. Oxygen is dissolved in the mixed solution while circulating in the tank, and organic matter in the pollutant is removed by biological treatment with microorganisms of activated sludge. The submerged membrane separation device 5 is supplied with the mixed liquid by cross flow along the membrane surface to the flow path between the membrane cartridges 7 by upward flow, and the upward flow acts on the membrane surface as a sweep flow. While washing the surface, a suction pressure is applied by a suction pump 10 as a driving force for filtration to separate the liquid mixture with the membrane cartridge 7, and the membrane filtrate that has passed through the membrane of the membrane cartridge 7 is removed from the sterilization tank 11. To be released.

  Patent Document 1 of the prior art document discloses a filtration method using a nonwoven fabric or a net. This method forms a dynamic membrane by depositing SS or floc (SS agglomerates such as activated sludge) in the holes of the nonwoven fabric or net, and is suitable for maintaining a stable filtration capacity. Since the formation and the control of the thickness are necessary, the filtration operation is stopped for a required time after the end of the reverse cleaning, and the filtration operation is resumed by growing flocs in the raw water.

  Patent Document 2 discloses that activated sludge particles become dispersed as the BOD load fluctuates as a problem of the dynamic membrane, and the flux of the dynamic membrane decreases. To solve this problem, dynamic membrane filtration is disclosed. Pull out sludge from the biological treatment tank located in the front of the tank, or acid-treat the separated sludge staying in the dynamic membrane filtration tank, and return the acid-treated separated sludge to the biological treatment tank after solubilization by physicochemical solubilization means ing.

Patent Document 3 discloses a coagulation state detection device that detects the amount of foaming of the dehydrated filtrate to detect the coagulation state of sludge, and when the amount of polymer added in the sludge coagulation process becomes excessive, Since the amount of residual polymer in the filtrate increases rapidly and foaming becomes intense, the amount of polymer added is determined by measuring the amount of foaming using a foam height meter or pressure gauge.
JP 2002-126734 A JP 2003-62591 A Japanese Utility Model Publication No. 7-24500

  By the way, when the target sewage water temperature is low in the water treatment using the membrane separation activated sludge treatment method, the activity of microorganisms decreases and the organic matter in the influent sewage is not completely decomposed, or the microorganisms themselves are abnormally metabolized. Products (undegraded organic matter) may be released outside the body. Such a metabolite is said to be a polymer mainly composed of glycoprotein having a molecular weight of thousands to hundreds of thousands. In order to distinguish the polymer derived from the metabolite (undegraded organic substance) of the microorganism from the polymer used for the conventional polymer flocculant or the like, in the present invention, the polymer is hereinafter referred to as a biological polymer.

  When the amount of the biological polymer increases, the viscosity of the activated sludge mixed liquid increases and the fluidity thereof decreases. In addition, the biological polymer is deposited not only on the activated sludge (SS) but also on the filtration membrane, but the biological polymer itself is deposited directly on the surface of the filtration membrane to form a gel layer, The small biological polymer stays in the filtration membrane while clogging through the filtration membrane and becomes clogged, so that the filtration resistance of the filtration membrane becomes abnormally large, and a sufficient permeation flux cannot be obtained at normal filtration pressure. For this reason, back-pressure cleaning of the filtration membrane (washing off deposits on the membrane surface) is required, but if the frequency of this cleaning is too high, the process itself using the membrane will not be established. In addition, when surplus sludge is extracted from the biological treatment tank (aeration tank) to reduce the bio-derived polymer in the biological treatment tank (aeration tank), it is necessary to extract the excess sludge more than the amount extracted during normal operation. The microorganisms flow out of the tank together with the excess sludge, leading to a decrease in the activated sludge concentration in the activated sludge mixed liquid.

  On the other hand, an appropriate amount of bio-derived polymer improves the floc formation of microorganisms, improves the sludge filterability, and forms an appropriate polymer layer on the membrane surface to filter the membrane itself (fractionation performance). Dynamic membrane function that improves

  It is difficult to accurately know the amount of biological polymer in the activated sludge mixture, and it is difficult to control the amount of biological polymer contained in the activated sludge mixed liquid in the biological treatment tank (aeration tank) by changing the operating conditions. very difficult.

  In the bath immersion type membrane separation activated sludge method (MBR), a microfiltration membrane (pore diameter 0.4 μm) is usually used in order to obtain a sufficient permeation flux at a low pressure. In order to easily control the cake layer (polymer amount) deposited and deposited on the film surface necessary for functioning as a dynamic film, the flat film type has become the mainstream.

  The present invention measures the amount of biological polymer in the activated sludge mixed solution in the membrane separation activated sludge treatment method, and reduces the amount of biological polymer in the biological treatment tank (aeration tank) in a timely manner so that excess polymer is present on the membrane surface. It prevents it from adhering.

  In order to solve the above-mentioned problem, a method for treating sewage according to claim 1 of the present invention is a soaking method in which an organic sludge is treated with activated sludge in a biological treatment tank, and the first separation means is immersed in the biological treatment tank. The activated sludge mixed solution is solid-liquid separated by the mold membrane separation device, and the COD containing the biological polymer accumulated in the biological treatment tank by the activated sludge treatment is solid-liquid separated from the activated sludge mixed solution at the appropriate time by the second separation means. Thus, while maintaining the activated sludge amount in the biological treatment tank at a high concentration, the biological polymer amount in the activated sludge mixed solution is maintained at a low concentration.

  With the above-described configuration, the organic sewage BOD is decomposed by the biological treatment of microorganisms by treating the organic sewage with activated sludge in the biological treatment tank. Microorganisms decompose BOD and release metabolites (undegraded organic substances) outside the body. This bioprotein-based polymer, mainly composed of glycoproteins, has an unusually low microbial activity, especially when the temperature of the target sewage is low, along with the undegraded organic matter that remains because the microbial activity is reduced and the organic matter in the influent sewage is not completely decomposed. Increased by releasing.

  Solid-liquid separation of the normal activated sludge mixed liquid in the biological treatment tank is performed by the submerged membrane separation apparatus that constitutes the first separation means, and the activated sludge and biological polymer are left in the biological treatment tank so that the submerged membrane separation apparatus The membrane filtrate that has passed through the filtration membrane is taken out of the tank as treated water.

  If the concentration of the biological polymer in the biological treatment tank increases too much, the amount of biological polymer adhering to the filtration membrane of the submerged membrane separator becomes excessive and the membrane resistance of the filtration membrane becomes abnormally large. Inhibits.

  For this reason, the activated sludge in the biological treatment tank is caused to flow out of the tank by solid-liquid separating the COD containing the biological polymer accumulated in the biological treatment tank by the second separation means from the activated sludge mixed solution in a timely manner. While maintaining the high concentration without removing the biological polymer in the activated sludge mixture, the biological polymer amount is maintained at a low concentration. This operation prevents an increase in membrane resistance due to an excessive amount of biological polymer, improves the floc formation of microorganisms with an appropriate amount of biological polymer and improves the sludge filterability, An appropriate polymer layer can be formed on the membrane surface to provide a dynamic membrane function that improves the filtration performance (fractionation performance) of the membrane itself.

  As the second separation means, there is a membrane filtration device immersed in a biological treatment tank, and the membrane filtration device has a pore diameter larger than the pores of the filtration membrane of the immersion membrane separation device (more than 10 times by pore ratio). A filtration membrane made of a non-woven fabric or the like is attached, the activated sludge is prevented from permeating, and the activated sludge mixed solution is solid-liquid separated by passing the COD containing the biological polymer.

  Alternatively, when a centrifuge installed outside the biological treatment tank is adopted as the second separation means, the activated sludge mixed liquid in the biological treatment tank is centrifuged to separate and remove the liquid phase containing the biological polymer. The solid content is returned to the biological treatment tank.

  In the method for treating sewage according to claim 2 of the present invention, the COD in the membrane filtrate permeated through the submerged membrane separator is measured, and the pores having a predetermined pore size larger than the pores of the filter membrane of the submerged membrane separator The COD in the filtration means filtrate obtained by filtering the activated sludge mixed liquid in the biological treatment tank with a filtration means having a COD difference value obtained by subtracting the COD in the membrane filtrate from the COD in the filtration means filtrate is predetermined. When the value is equal to or greater than the value, the COD containing the biological polymer is separated from the activated sludge mixed solution by the second separation means.

  In the configuration described above, the present inventors adopt COD as an index for estimating the amount of biological polymer because it is difficult to directly measure the amount of biological polymer contained in the activated sludge mixed liquid in the biological treatment tank. Decided to do. However, the COD in the activated sludge mixed solution in the biological treatment tank is not only a biological polymer produced as a microbial metabolite (undegraded organic substance) in the biological treatment tank, but also the chromaticity flowing from outside the system into the biological treatment tank. Therefore, the COD in the activated sludge mixed solution cannot be used as an index of the amount of biological polymer contained in the activated sludge mixed solution.

  For this reason, the inventors do not allow most of the biological polymer to permeate through the filtration membrane of a submerged membrane separation device composed of a microfiltration membrane having a small pore size (pore size 0.4 μm), etc. A filter paper (pore size 1.0 μm) with pores larger than the filter membrane of the device prevents the permeation of solids corresponding to activated sludge (microorganisms) and permeates soluble polymers including biological polymers. In view of the above, the COD in the membrane filtrate that has passed through the filtration membrane of the submerged membrane separator is measured, and the pores of the same activated sludge mixed solution are larger than the pores of the filtration membrane of the submerged membrane separator. Filter the activated sludge mixture in the biological treatment tank with filtration means such as filter paper, measure the COD in the filtration means filtrate that has passed through the filtration means, and compare the two to compare the metabolites of microorganisms (undegraded organic matter) Indirectly measure the amount of polymer due to the glycoprotein The inventors have found that this can be determined.

  Based on the knowledge, the COD difference value obtained by subtracting the COD in the membrane filtrate from the COD in the filtration means filtrate is estimated as the amount of the biological polymer in the biological treatment tank, and the second value is obtained when the COD difference value is equal to or larger than a predetermined value. By performing solid-liquid separation of the activated sludge mixed liquid by the separation means, the biological polymer is separated from the activated sludge mixed liquid in a timely manner, and an appropriate amount of biological polymer is left in the biological treatment tank.

  The sewage treatment apparatus according to claim 3 of the present invention is the first separation means for separating the activated sludge mixed liquid into a biological treatment tank for treating the activated sewage with the activated sludge, and taking out the membrane filtrate as the treated water. And a second separation means for taking out the membrane filtrate containing the biological polymer accumulated in the biological treatment tank by solid-liquid separation of the activated sludge mixed liquid.

  With the above-described configuration, a normal solid-liquid separation operation is performed by the first separation means, and the membrane filtrate is taken out as treated water, and the COD containing the biological polymer accumulated in the biological treatment tank by the second separation means is appropriately timed. In addition, the solid-liquid separation from the activated sludge mixture allows the biological polymer amount to be maintained at a low level while maintaining the activated sludge amount in the tank at a high concentration, and the increase in membrane resistance caused by the excessive amount of biological polymer. Of the dynamic membrane that improves the filtration performance (fractionation performance) with the proper polymer layer formed on the membrane surface. The function can be demonstrated.

  Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, organic waste water 21 flowing into the system is temporarily stored in a flow rate adjusting tank 23 after removing contaminants by a pretreatment facility 22, and a biological treatment tank (aeration tank) at a constant flow rate from the flow rate adjusting tank 23. 24.

  In the biological treatment tank (aeration tank) 24, the organic substance (BOD) contained in the organic sewage 21 is decomposed and removed by biological treatment with activated sludge. Solid-liquid separation of the normal activated sludge mixed liquid in the biological treatment tank (aeration tank) 24 is performed by the submerged membrane separator 25 that constitutes the first separation means immersed in the tank, and the filtration membrane of the submerged membrane separator 25. The membrane filtrate 26 that has permeated is taken out, disinfected in a sterilization tank 27, and discharged as treated water 28.

  Various devices can be applied to the submerged membrane separator 25, and there are flat membrane organic membranes, tube-like organic membranes, ceramic membranes, etc. as filtration membranes. Here, the filtration membrane has a small pore diameter. Are used in the same configuration as the submerged membrane separation device 5 described above with reference to FIG.

  In the biological treatment tank (aeration tank) 24, the microorganisms decompose BOD and release metabolites (undecomposed organic substances) to the outside of the body. This bioprotein-based polymer, mainly composed of glycoproteins, has an unusually low microbial activity, especially when the temperature of the target sewage is low, along with the undegraded organic matter that remains because the microbial activity is reduced and the organic matter in the influent sewage is not completely decomposed. Increased by releasing.

  The submerged membrane separation device 25 leaves the activated sludge and the biological polymer in the biological treatment tank (aeration tank) 24 and removes the membrane filtrate 26 as treated water from the tank, so that the biological treatment tank (aeration tank) 24 If the concentration of the biological polymer is excessively increased, the amount of the biological polymer adhering to the filtration membrane of the submerged membrane separation device 25 becomes excessive, and the membrane resistance of the filtration membrane becomes abnormally large, thereby inhibiting the solid-liquid separation operation.

  For this reason, the activated sludge mixed liquid is solid-liquid separated by driving the suction pressure of the suction pump 30 through the membrane filtration device 29 constituting the second separation means immersed in the biological treatment tank (aeration tank) 24 in a timely manner. The amount of biological polymer in the activated sludge mixture is maintained while maintaining the activated sludge amount in the biological treatment tank (aeration tank) 24 at a high concentration. Is maintained at a low concentration.

  The membrane filtrate 31 that has permeated through the membrane filtration device 29 is normally diluted with the membrane filtrate 26 of the submerged membrane separation device 25 and discharged. However, when the COD regulation value is exceeded even after dilution, a coagulation treatment ( Agglomeration and sedimentation) 32, COD is reduced within the regulation value and discharged.

  The membrane filtration device 29 uses a non-woven fabric in which pores having a large pore size 10 times or more in terms of pore ratio than the microfiltration membrane (pore size 0.4 μm) of the submerged membrane separation device 25 are used as a filtration membrane. The pore diameter of the non-woven fabric is selected so that a cake layer is formed on the membrane surface when used for a long time and the pore diameter is substantially several μm even in the state of cake filtration.

  As the second separation means, a centrifuge installed outside the biological treatment tank (aeration tank) 24 can also be adopted. In this case, the activated sludge mixed liquid is centrifuged to separate and remove the liquid phase containing the biological polymer, and the solid content is returned to the biological treatment tank.

  This operation prevents an increase in membrane resistance due to an excessive amount of biological polymer, improves the floc formation of microorganisms with an appropriate amount of biological polymer and improves the sludge filterability, An appropriate polymer layer can be formed on the membrane surface to provide a dynamic membrane function that improves the filtration performance (fractionation performance) of the membrane itself.

The timing at which the COD containing the biological polymer is separated from the activated sludge mixed solution by the membrane filtration device 29 of the second separation means is detected by the following measurement.
In the present invention, since it is difficult to directly measure the amount of biological polymer contained in the activated sludge mixed liquid of the biological treatment tank (aeration tank) 24, COD is adopted as an index for estimating the amount of biological polymer. Yes. The COD in the activated sludge mixed liquid is not only a biological polymer produced as a microbial metabolite (undecomposed organic matter) in the biological treatment tank (aeration tank) 24, but also the chromaticity flowing into the biological treatment tank from outside the system. Since COD is also included, COD in the activated sludge mixed solution cannot be used as an indicator of the amount of biological polymer contained in the activated sludge mixed solution.

  Therefore, the COD contained in the membrane filtrate 26 that has passed through the microfiltration membrane (pore diameter 0.4 μm) of the submerged membrane separator 25 is measured, and the pores (pore diameter) of the microfiltration membrane of the submerged membrane separator 25 are measured. Filter the activated sludge mixed liquid in the biological treatment tank (aeration tank) 24 using filter paper having a predetermined pore size larger than 0.4 μm) (pore size 1 to 3 μm) as a filtering means, and measure the COD in the filtered filter paper filtrate. The COD difference value obtained by subtracting the COD of the membrane filtrate from the COD of the filter paper filtrate is assumed to indirectly indicate the amount of polymer derived from the glycoprotein derived from the microbial metabolite (undegraded organic matter). Is equal to or greater than a predetermined value (5 mg / L or more is an effective value), the membrane filtration device 29 of the second separation means separates the COD containing the biological polymer from the activated sludge mixed solution.

  This is because most of the biological polymer does not permeate through the microfiltration membrane of the submerged membrane separation device 25, and the filter paper having pores having a larger pore size than the microfiltration membrane has a solid substance corresponding to activated sludge (microorganisms). This is in view of preventing permeation and allowing soluble polymers including biological polymers to permeate.

In the present embodiment, COD is adopted as an index for estimating the amount of biological polymer, but UV ₂₆₀ (ultraviolet absorption) can also be adopted as an index for estimating the amount of biological polymer. Since the measurement method of UV ₂₆₀ (ultraviolet absorption) is performed by a known technique, the description thereof is omitted. In this case, the correlation between the amount of biological polymer and UV ₂₆₀ (ultraviolet absorption) is obtained in advance by experiments, and the amount of biological polymer is estimated from the value of UV ₂₆₀ (ultraviolet absorption) actually measured during operation.

  In the above-described configuration, when the waste water is targeted at a low water temperature of 8 to 12 ° C., it was necessary to wash the membrane once every 2 to 3 weeks. As a result, the cleaning frequency of the film became once every two to three months. Even when filtration with a non-woven fabric was performed for one day per week, almost the same result was obtained. The COD of the membrane filtrate 26 of the submerged membrane separator 25 at this time was 6 to 9 mg / L, and the COD of the membrane filtrate 31 filtered with a nonwoven fabric was 15 to 40 mg / L.

It is a block diagram which shows the processing method of the sewage in embodiment of this invention. It is a block diagram which shows the processing method of the conventional sewage.

Explanation of symbols

6 Case 7 Flat membrane cartridge 8 Air diffuser 9 Blower 10 Suction pump 21 Organic sewage 22 Pretreatment equipment 23 Flow control tank 24 Biological treatment tank (aeration tank)
25 Submerged membrane separator 26 Membrane filtrate 27 Sterilization tank 28 Treated water 29 Membrane filtration device 30 Suction pump 31 Membrane filtrate 32 Aggregation treatment (aggregation precipitation)

Claims (3)

Organic sludge is treated with activated sludge in a biological treatment tank, and the activated sludge mixed solution is solid-liquid separated with an immersion type membrane separation device that forms a first separation means immersed in the biological treatment tank. The COD containing the biological polymer accumulated in the solid is separated from the activated sludge mixed liquid in a timely manner by the second separation means, and the activated sludge mixed liquid is maintained while maintaining a high concentration of activated sludge in the biological treatment tank. A method for treating sewage, characterized in that the amount of the biological polymer therein is maintained at a low concentration. 2. The method for treating sewage according to claim 1, wherein the COD in the membrane filtrate permeated through the submerged membrane separator is measured, and the filtration has a pore having a predetermined diameter larger than the pores of the filter membrane of the submerged membrane separator. The COD in the filtration means filtrate obtained by filtering the activated sludge mixed liquid in the biological treatment tank is measured, and the COD difference value obtained by subtracting the COD in the membrane filtrate from the COD in the filtration means filtrate is a predetermined value or more. In some cases, the second separation means separates COD containing the biological polymer from the activated sludge mixed solution, and a method for treating wastewater. In the biological treatment tank for treating activated sludge with organic sludge, the first separation means for separating the activated sludge mixed liquid into solid-liquid separation and taking out the membrane filtrate as treated water, and the biological treatment with solid-liquid separation of the activated sludge mixed liquid. A wastewater treatment apparatus, wherein a second separation means for taking out a membrane filtrate containing a biological polymer accumulated in a tank is immersed and installed.

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