JP5016827B2 - Membrane separation activated sludge treatment method - Google Patents

Description

  The present invention is a membrane-separated activated sludge that performs solid-liquid separation using a separation membrane by biochemically treating organic matter and its debris contained in industrial wastewater and domestic wastewater, or wastewater containing microorganisms and bacteria. It relates to the processing method.

  According to the conventional membrane separation activated sludge treatment apparatus, waste water (raw water) from which a relatively large solid content is removed by a fine screen is introduced into the raw water adjustment tank. In this raw water adjustment tank, the liquid level is measured by a liquid level gauge, and the first liquid feed pump is intermittently operated to adjust the liquid level height in the tank to be within a predetermined range. After the raw water sent by the first liquid feeding pump is introduced into the anaerobic tank, the raw water overflowing from the anaerobic tank is caused to flow into the adjacent aeration tank. A membrane filtration unit is immersed in this aeration tank. The treated water separated into activated sludge and treated water by this membrane filtration unit is sent to the treated water tank by a suction pump. On the other hand, solid content (suspended material) of sludge grown by aeration in an aeration tank settles to the bottom of the tank due to its own weight, while organic matter decomposed by oxidation floats in the sludge as suspended matter. To do. Excess sludge is stored in a sludge storage tank. A part of the sludge inside the aeration tank is returned to the anaerobic tank by the second liquid feed pump and circulated.

  The membrane filtration unit is, for example, a sheet-like hollow fiber membrane element in which a number of porous hollow fiber membranes are arranged in parallel on the same plane as disclosed in Japanese Patent Application Laid-Open No. 2000-51672 (Patent Document 1). Are provided with a hollow fiber membrane module obtained by arranging a plurality of them at a required interval, and an air diffuser provided below the hollow fiber membrane module. The hollow fiber membrane module is composed of a plurality of hollow fiber membrane elements, and the overall shape thereof is a substantially rectangular parallelepiped. On the other hand, for example, a plurality of diffuser tubes each having a hole formed in a pipe made of metal, resin, or the like are arranged in parallel, and one end of each diffuser tube is connected to an aeration blower. The air sent from the aeration blower is changed into bubbles through a diffuser and discharged into sludge. When treating sewage such as domestic wastewater and industrial wastewater, the organic matter in the aeration tank sludge is brought into contact with the air generated from the air diffuser in the presence of the aerobic microorganism, whereby the organic matter is brought into contact with the aerobic microorganism. It is adsorbed and metabolized to biologically sludge treatment.

  The hollow fiber membrane module and the air diffuser are surrounded by a shielding plate on all four sides. This shielding plate becomes a wall portion for generating a gas-liquid mixed flow by the rise of bubbles generated from the air diffuser and guiding the flow from the upward flow to the downward flow. The gas-liquid mixed flow generated from the diffuser does not scatter in an oblique direction, but rises straight and efficiently contacts the hollow fiber membrane module. At this time, the hollow fiber membrane is vibrated by the uniform dispersion of the gas-liquid mixed flow with respect to the membrane surface of the hollow fiber membrane module to uniformly wash the hollow fiber membrane elements. In addition, the biological treatment is efficiently performed by the gas-liquid mixed flow, and the sludge is separated into solid and water by the filtration function of the hollow fiber membrane. One end of a water collection pipe is connected to the membrane filtration unit, and a suction pump is connected to the other end, and treated water (filtered water) filtered by the membrane filtration unit is passed through the water collection pipe by a suction pump. It is sucked and transferred to the treated water tank.

  As a membrane module, it is not necessary to use a sheet-like hollow fiber membrane element having a porous hollow fiber membrane as a constituent member, as long as it has a filtration membrane having a plurality of fine pores. For example, a flat membrane type Various known separation membranes such as a tubular membrane type and a bag-like membrane type can be applied. Therefore, hollow fiber membrane modules using hollow fiber membrane elements have come to be used frequently because of the wide filtration area. Examples of the material include cellulose, polyolefin, polysulfone, PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and ceramics.

  The average pore size of the micropores formed in the porous hollow fiber membrane is generally 0.001 to 0.1 μm in the average pore size in a membrane generally called an ultrafiltration membrane, and 0.1 to 0.1 μm in the membrane generally called a microfiltration membrane. 1 μm. For example, when used for solid-liquid separation of activated sludge, the pore diameter is preferably 0.5 μm or less, and when sterilization is required as in the case of filtration of purified water, the pore diameter is preferably 0.1 μm or less.

  The membrane separation activated sludge treatment apparatus biologically purifies raw water with activated sludge in an anaerobic tank and an aeration tank (aerobic tank). Nitrogen is removed by a so-called nitrification / denitrification reaction by circulating sludge between an anaerobic tank and an aeration tank. The organic matter converted into BOD is aerobically oxidized and decomposed by the air released from the diffuser tube of the membrane filtration unit, which is mainly an aeration apparatus disposed in the aeration tank. The removal of phosphorus is performed by being taken into the microorganism as polyphosphoric acid by the action of microorganisms (phosphorus-accumulating bacteria) in the sludge. This microorganism takes up phosphorus in an aerobic state and releases phosphorus stored in the body in an anaerobic state. When repeatedly exposed to anaerobic and aerobic conditions, phosphorus-accumulating bacteria absorb more phosphorus in the aerobic state than the amount of phosphorus released in the anaerobic state.

  Some of the nitrogen compounds such as biological excrement and carcasses are assimilated into plants and bacteria as fertilizers. Some of these nitrogen compounds are oxidized to nitrous acid and nitric acid by autotrophic ammonia oxidizing bacteria and independent nitrite oxidizing bacteria under aerobic conditions with a lot of oxygen. On the other hand, under anaerobic conditions without oxygen, microorganisms called denitrifying bacteria produce nitrous acid from nitric acid instead of oxygen, and further reduce to dinitrogen monoxide and nitrogen gas. This reduction reaction is referred to as the nitrification denitrification reaction.

  When filtration is performed using a hollow fiber membrane module, suspended matter in the water, bacteria, and the like are removed by the fine pores of the membrane, and high-quality filtered water is obtained. However, if the filtration operation is performed continuously for a long time, the fine pores are blocked by suspended substances and the like, the amount of filtered water is reduced and the filtration pressure is increased, and the hollow fiber membrane module needs to be frequently replaced.

  In order to prevent early clogging of the hollow fiber membrane module, for example, a hollow fiber membrane or a hollow fiber membrane element using a gas-liquid mixed flow generated by bubbles released from the aeration diffuser Is subjected to so-called air scrubbing cleaning that peels and removes clogging substances adhering to the membrane surface, and further backwashing is performed to reversely pass filtered water from the hollow interior of the hollow fiber membrane to the outside. Recovery of filtration performance has been made.

In recent years, the daily treatment amount in industrial wastewater treatment and sludge treatment plants has increased to tens of thousands of tons, and development of a technique for efficiently treating this has been strongly desired. In order to meet this demand, for example, as described in US Pat. No. 5,944,997 (Patent Document 2), the aeration tank is enlarged and a large number of membrane filtrations are performed in a single aeration tank. Techniques are being developed to immerse units and place them side by side to allow activated sludge to flow in one direction and simultaneously perform a large amount of wastewater treatment. A plurality of membrane filtration units using the hollow fiber membrane module are immersed in an aeration tank in series with a required interval, and branch to each membrane filtration unit from a single water collection pipe (suction line) Connected through a branch pipe. The treated water filtered by the plurality of hollow fiber membrane modules is collected in the water collecting pipe and collected by a suction pump.
JP 2000-51672 A US Pat. No. 5,944,997

  Assuming that the depth dimension of the membrane filtration unit is 1552.5 mm, and as described in Patent Document 2, 20 membrane filtration units are provided in the aeration tank at intervals of 1/2 of the depth dimension. As a result, the total length of the water collecting pipe reaches 46575 mm or more. This means that the membrane surface from the inside of the porous hollow fiber membrane by sending back the treated water or the air main pipe arranged between the aeration generator and the aeration blower arranged for each membrane filtration unit. The same applies to the backwash pipe for washing, which means that a very long pipe is required. For example, even when two membrane filtration units are installed in parallel in the width direction of the aeration tank and 20 membrane filtration units are installed, the length in the treatment direction of the aeration tank is almost half of the whole. Although the length of the tank is longer, and the length of the drainage pipe is added to the width of the membrane filtration unit by the required interval, the total length of the pipe is less than when placed in series. The length becomes longer. When the pipe length is increased in this way, the change in pipe resistance in the length direction becomes extremely large.

  Here, the activated sludge concentration in the aeration tank gradually increases because the sludge treatment proceeds from the raw water introduction side to the drainage side. In general, since fresh raw water flows in the vicinity of the membrane filtration unit at the end of the raw water introduction side, the activated sludge concentration is low. On the other hand, in the vicinity of the membrane filtration unit at the drain side end, the activated sludge concentration is highest because the microorganisms are successively grown. On the other hand, when eight or more membrane filtration units are installed in the aeration tank, each of the filtered water suction main pipe, the air main pipe, and the backwash pipe from the fluid suction source and the supply source connecting each unit The distance to the branch pipe of the membrane filtration unit becomes gradually longer, and the farther away from the fluid suction source or supply source, the pipe resistance gradually increases, and at the same time, the fluid pressure becomes smaller.

  This means that, for example, if the diameter of each branch pipe is uniform, the fluid suction flow rate and supply flow rate for the membrane filtration unit arranged closest to the fluid suction source and supply source are the largest, and the amount is It means that it gradually decreases with distance from the fluid suction source and supply source. This flow rate gradient of the fluid forms a similar gradient in the filtered water suction capability, the dissolved oxygen amount, the scrubbing cleaning capability, and the back cleaning capability required for each. Such functional gradient in each membrane filtration unit spurs the concentration gradient of the above-mentioned activated sludge concentration. In biological sludge treatment, it is desirable that the activated sludge gradient naturally generated is unavoidable, but the flow rate gradient as described above is eliminated as much as possible and is uniform in all regions in the treatment direction. .

  The present invention provides a membrane separation activated sludge treatment method that eliminates the effect of enlarging the pipe length due to an increase in the amount of sludge treatment and ensures an equal flow rate of various treatment fluids in the entire region in the treatment direction. It is an object.

  Such an object includes an anaerobic tank or an anaerobic tank and an aerobic tank, which are the main components of the present invention, and a membrane filtration unit is immersed in the aerobic tank, and the wastewater is biologically fed from the anaerobic tank side. A membrane separation activated sludge treatment method in which activated sludge is solid-liquid separated by sequential treatment, wherein 8 or more membrane filtration units are immersed and arranged in series at a predetermined interval in the aeration tank, Aspirating or supplying fluids simultaneously by a fluid suction source or supply source connected to the filtration unit via a branch line, and the amount of fluid suction or supply to all membrane filtration units arranged in the aeration tank It is effectively achieved by a membrane separation activated sludge treatment method characterized by maintaining and managing the flow rate adjusting valve so as to be substantially uniform.

  According to a preferred embodiment, the membrane filtration unit comprises a hollow fiber membrane module arranged in parallel with a predetermined interval with the membrane surface of a sheet-like membrane element composed of a plurality of porous hollow fiber membranes vertical. And a diffuser generating device that is arranged below the hollow fiber membrane module to release minute bubbles and generate a gas-liquid mixed flow rising toward the hollow fiber membrane module.

  On the other hand, when the fluid is filtered water that is solid-liquid separated by the membrane filtration unit and sucked under reduced pressure by a suction source through each branch pipe and the main suction pipe, the filtration sucked from each membrane filtration unit The water suction flow rate may be adjusted by a flow rate adjusting valve disposed in each branch pipe, and the processing suction amount from the entire membrane filtration unit may be maintained and managed substantially evenly.

  In addition, when the fluid is air discharged from each air diffuser connected via an air supply source and a branch pipe, the amount of air sent to each air diffuser is allocated to each branch pipe. It is desirable that the amount of air discharged toward each hollow fiber membrane module is maintained and managed substantially evenly by adjusting the flow rate adjusting valve. The fluid is filtered water sucked by the suction source, and each porous hollow fiber of the hollow fiber membrane module is fed back from the filtered water supply source to each yarn membrane module through the branch pipe. Adjust the supply flow rate of filtered water when cleaning each module from the inside of the membrane with the flow adjustment valve arranged in each branch pipe, and the supply amount of filtered water supplied to each membrane filtration unit is almost equal It is good to maintain.

  When eight or more membrane filtration units are immersed and arranged in series in the aeration tank with a predetermined interval, they are connected to each membrane filtration unit or are connected to each membrane filtration unit by a single main pipeline. When fluid such as filtered water, backwash filtered water, and air is sucked or supplied, the flow rate and fluid pressure flowing through the branch pipe are affected by the piping resistance, and the distance from the fluid suction source or supply source decreases. . As a result, the amount of fluid sucked and supplied to the membrane filtration unit increases from the upstream side to the downstream side in the processing direction in the aeration tank. Therefore, in the present invention, a flow rate adjusting valve is arranged in each branch pipe, and the suction flow rate and the supply flow rate are adjusted to be equal to all the eight or more membrane filtration units arranged from the downstream side to the upstream side. To do. Although this adjustment operation can be performed manually, it is preferable to automate it using a computer or the like because the operation in the sludge is difficult in terms of hygiene. However, this adjustment operation is only performed at the time of replacement of the membrane element of the membrane filtration unit, and normally there is no need for adjustment until the next module replacement.

  In this way, when the flow rate is adjusted, the suction amount and supply amount of the processing fluid to each membrane filtration unit are almost uniform in the entire region of the aeration tank, so that the dissolved oxygen amount becomes too small or vice versa. Eliminates problems such as lack of cleaning, enabling efficient activated sludge treatment over a long period of time.

  As a membrane element applied to the membrane filtration unit, it is preferable to employ a membrane element having a wide filtration area and capable of efficient filtration. On the other hand, the air diffuser that is one of the components of the membrane filtration unit is not particularly limited in its structure, but the size of the bubbles released from the air diffuser is made as small as possible. It is preferable to facilitate dissolution in the sludge and increase the amount of dissolved oxygen contained in the sludge because the biologically activated sludge treatment efficiency can be increased. For that purpose, the air discharge hole diameter of the air diffuser may be set to 10 μm to 10 mm.

  Examples of the fluid in the present invention include filtered water solid-liquid separated by the hollow fiber membrane module, air released from the aeration blower to the hollow fiber membrane module through the aeration generator, and sludge. There is filtered water that is fed back into the hollow part of the porous hollow fiber membrane of the element. Since these fluids act equally on all membrane filtration units, nitrification and phosphorus accumulation are ensured over the entire area, and scrubbing washing of the hollow fiber membrane modules of each membrane filtration unit is also backwashed with filtered water. Therefore, the activated sludge treatment can be efficiently performed over a long period of time.

Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.
FIG. 1 shows a schematic structure of a typical treatment apparatus for carrying out the membrane separation activated sludge treatment method of the present invention.

  According to this membrane separation activated sludge treatment apparatus, waste water (raw water) from which a relatively large solid content has been removed by the fine screen 1 is introduced into the raw water adjustment tank 2. Here, the liquid level is measured by a liquid level measuring instrument (not shown), and the first liquid feed pump P1 is intermittently operated to adjust the liquid level in the tank within a predetermined range. The raw water sent by the first liquid feeding pump P1 is introduced into the oxygen-free tank 3 and then flows into the adjacent aeration tank 4 using the raw water overflowing from the oxygen-free tank 3. A large number of membrane filtration units 5 are immersed in the aeration tank 4. The treated water separated into activated sludge and treated water by the membrane filtration unit 5 is sent to the treated water tank 8 by the suction pump Pv. On the other hand, the sludge solid matter (suspension material) consisting of microorganisms which have been aerated in the aeration tank 4 and propagated settles to the bottom of the tank under its own weight, and the excess sludge is stored in the sludge storage tank 7. The A part of the sludge inside the aeration tank 4 is returned to the anoxic tank 3 by the second liquid feed pump P2 and circulated.

  According to this membrane separation activated sludge treatment apparatus, raw water is biologically purified by activated sludge in the anoxic tank 3 and the aeration tank (aerobic tank) 4. Nitrogen is removed by a so-called nitrification denitrification reaction by circulating sludge between the anoxic tank 3 and the aeration tank 4. The organic matter converted to BOD (biochemical oxygen demand) is aerobic by the air released from the diffuser generator 15 of the membrane filtration unit 5 which is mainly an aeration apparatus disposed in the aeration tank 4. It is oxidized and decomposed. The removal of phosphorus is performed by being taken into the body of the microorganism as polyphosphoric acid by the action of microorganisms (phosphorus-accumulating bacteria) in the sludge. This microorganism takes up phosphorus in an aerobic state and releases phosphorus stored in the body in an anaerobic state. When repeatedly exposed to anaerobic and aerobic conditions, phosphorus-accumulating bacteria absorb more phosphorus in an aerobic state than the amount of phosphorus released in the anaerobic state.

  Part of nitrogen compounds such as biological excrement and debris is assimilated into plants and bacteria as fertilizer. Some of these nitrogen compounds are oxidized to nitrous acid and nitric acid by autotrophic ammonia oxidizing bacteria and independent nitrite oxidizing bacteria under aerobic conditions with a lot of oxygen. On the other hand, under anaerobic conditions without oxygen, microorganisms called denitrifying bacteria produce nitrous acid from nitric acid instead of oxygen, and further reduce to dinitrogen monoxide and nitrogen gas. This reduction reaction is referred to as the nitrification denitrification reaction.

  The circulation of sludge between the anaerobic tank 3 and the aeration tank 4 is not necessarily limited from which tank the liquid is fed using the pump, but normally the aeration tank using the second liquid feeding pump P2. From the oxygen-free tank 3 to the aeration tank 4 by overflow. In the present embodiment, the DO at the site where the circulating fluid from the aeration tank 4 enters the oxygen-free tank 3 is 0.2 mg / L or less, and the DO at the site where the circulating fluid is taken out from the aeration tank 4 is 0.5 mg / L. By making it below, the inflow of dissolved oxygen into the anoxic tank 3 is suppressed, and the anaerobic degree in the anoxic tank 3 is sufficiently maintained, thereby promoting the release of phosphorus.

  If dissolved oxygen, nitrate ions, and nitrite ions are not substantially present in the anoxic tank 3, the organic matter is decomposed anaerobically, and at this time, the polyphosphate accumulated in the bacteria is released out of the cells as phosphoric acid. . In this embodiment, the DO at the site where the circulating sludge is returned from the aeration tank 4 to the anaerobic tank 3 is preferably 0.2 mg / L or less, and if it is 1 mg / L or less, the phosphorus removability is more stable. Furthermore, 0.05 mg / L or less is preferable because of further stabilization. In addition, the measurement of DO can be measured using the normal DO meter by the diaphragm electrode method.

  In order to set the DO of the part where the circulating fluid (sludge) is taken out from the aeration tank 4 to 0.5 mg / L or less, the part where the sludge is taken out from the aeration tank 4 to the anoxic tank 3 is made a sludge retention part. Is preferred. The sludge retention part means a part that is not easily affected by sludge flow caused by aeration. For example, if a space is provided between the membrane filtration unit 5 and the bottom of the aeration tank 4, the sludge present in the lower part of the membrane filtration unit 5 is not well agitated, and thus becomes a retention part.

  Therefore, as shown in FIG. 1, the DO of the site 6 where the circulating fluid (sludge) is taken out from the aeration tank 4 can be made 0.5 mg / L or less by taking out the sludge from below the position of the membrane filtration unit 5. it can. In addition, when a plurality of membrane filtration units 5 are arranged in parallel in the aeration tank 4, the part from which the circulating fluid (sludge) is taken out is below the aeration apparatus. Further, the distance from the membrane filtration unit 5 to the site where the sludge is taken out is preferably 20 cm or more downward, more preferably 30 cm or more.

The flow of sludge in the aeration tank 4 mainly increases in the region by the membrane filtration unit 5 as the bubbles rise from the gas discharge holes of the air diffuser, and the sludge falls in the non-aerated portion. Thus, the whole is stirred. At this time, if the oxygen utilization rate (r _r ) of the sludge in the aeration tank 4 is kept high, oxygen is rapidly consumed in the non-aerated area, so that the dissolved oxygen is low in the aeration tank 4. It becomes easy to form the part which becomes. Here, the oxygen utilization rate (r _r ) of the sludge in the aeration tank 4 refers to the oxygen utilization rate of the sludge taken from the aerated portion of the aeration tank 4, and the measuring method is the sewer test method ( 1997, according to the Japan Sewerage Association.

  FIG. 2 shows a typical example of a normal membrane filtration unit 5. As shown in the figure, the membrane filtration unit 5 includes a hollow fiber membrane module 9 in which a plurality of hollow fiber membrane elements 10 arranged in a direction perpendicular to the yarn length are supported and fixed in parallel, and the hollow fiber membrane module 9 And a diffuser generating device 15 arranged at a predetermined interval below. The hollow fiber membrane element 10 has an upper end opening end portion of a membrane sheet 11 in which a large number of porous hollow fiber membranes 10a are arranged in parallel, and is communicated with and supported by a filtered water discharge pipe 12 via a potting material 11a. And is fixed and supported by the lower frame 13 through the potting material 11a, and both ends of the filtered water outlet pipe 12 and the lower frame 13 are supported by a pair of vertical rods 14. A large number of hollow fiber membrane elements 10 are accommodated and supported in parallel in substantially the entire volume of a rectangular cylindrical upper wall member 20 whose upper and lower end surfaces are open with the sheet surface vertical. Here, in the hollow fiber membrane element 10, generally, as shown in FIG. 3, a plurality of porous hollow fiber membranes 10a are arranged in parallel on the same plane with the same gap.

In this embodiment, the hollow fiber membrane 10a is made of a PVDF (polyvinylidene fluoride) porous hollow fiber membrane that is hollow in the longitudinal direction along the center, and the pore diameter of the filtration hole is 0.4 μm. The effective membrane area per sheet is 25 m ² . The sheet-like hollow fiber membrane element 10 is used in 20 pieces per membrane filtration unit 5 and has a depth of 30 mm, a width of 1250 mm, and a length from the upper surface of the filtrate extraction pipe 12 to the lower surface of the lower frame 13. Is 2000 mm. The size of the single membrane filtration unit 5 including the air diffuser 15 is 1552.5 mm in depth, 1447 mm in width, and 3043.5 mm in height. The filtered water extraction pipe 12 has a length of 1280 mm, its material is ABS resin, and the vertical rod 14 is made of SUS304.

  However, the material such as the porous hollow fiber membrane 10a, the filtrate extraction pipe 12 and the vertical rod 14, the size of the hollow fiber membrane element 10, the size of the membrane filtration unit 5, and the number of the hollow fiber membrane elements 10 per unit The number of sheets can be variously changed according to the application. For example, in terms of the number of hollow fiber membrane elements 10, it can be arbitrarily set to 20, 40, 60,... According to the processing amount, or the material of the porous hollow fiber membrane 10a can be cellulose, polyolefin, Conventionally known ones such as polysulfone, polyvinyl alcohol, polymethyl methacrylate, and polyfluorinated ethylene can be applied.

  An outlet 12a for high-quality filtered water (treated water) filtered by each porous hollow fiber membrane 10a is formed at one end of the filtrate outlet tube 12 of each hollow fiber membrane element 10. In this embodiment, L-shaped joints 12b are attached to the respective outlets 12a in a liquid-tight manner through a sealing material, similarly to the membrane filtration unit 5 shown in FIG. Moreover, as shown in FIG. 3, the water collection header pipe | tube 21 is installed horizontally along the edge by the side in which the said outlet 12a is formed in the upper end of the said upper wall material 20. As shown in FIG. The water collecting header pipe 21 is formed with water collecting ports 21a at positions corresponding to the plurality of outlets 12a, and an L-shaped joint 21b similar to the outlet 12a serves as a sealing material in each water collecting port 21a. It is liquid-tightly attached. The treated water outlet 12a of the filtered water outlet 12 and the water outlet 21a of the water header 21 are connected to each other by connecting the L-shaped joints 12b and 21b attached to each other. . A water suction port 21 c connected to the suction pump Pv via the suction pipe line 22 is formed at one end of the water collection header pipe 21. As shown in FIG. 1, the water suction port 21 c formed for each water collecting header pipe 21 and the suction pipe 22 are flow rates interposed in the branch pipes 22 a respectively branched from the suction pipe 22. The adjustment valve 23 is connected.

  On the other hand, as shown in FIG. 4, the air diffuser 15 is composed of a rectangular cylindrical body that is coupled to the lower end of the upper wall member 20 and that is open at the top and bottom, and extends downward from the lower ends of the four corners. It is accommodated and fixed at the bottom of the lower wall member 24 provided with the column 24a. The air diffuser 15 extends horizontally in the width direction along the front-side inner wall surface of the lower wall member 24, and includes an aeration blower B and an air main pipe 18 arranged outside as shown in FIG. The air introduction pipe 16 which is a branch pipe connected via the air introduction pipe 16 is arranged at a predetermined interval in the length direction of the air introduction pipe 16, one end is fixed, and the other end is an inner side of the rear side. And a plurality of air diffusers 17 fixed horizontally along the wall surface. The end of the diffuser pipe 17 connected to the air inlet pipe 16 communicates with the inside of the air inlet pipe 16, and the other end of the diffuser pipe 17 is closed.

  According to the illustrated example, the main body of the air diffuser 17 is composed of a rubber tube with a slit, and a slit (not shown) that communicates inward and outward along the length direction is formed on a horizontally disposed lower surface. . The air diffuser 15 is preferably arranged at a distance of 45 cm downward from the lower end of the hollow fiber membrane element 10, and the column 24a protrudes downward from the lower wall member 24 to be exposed to the outside. This is desirable for smooth sludge flow. At this time, in order to set the DO of the part where the circulating fluid (sludge) is taken out from the aeration tank 4 to 0.5 mg / L or less, the distance from the membrane filtration unit 5 to the part where the sludge is taken out is 20 cm or more downward as described above. It is preferable that the distance is 30 cm or more. In addition, the air diffuser 15 according to the present embodiment is arranged corresponding to each of the plurality of membrane filtration units 5, and in order to divert the air sent from the same aeration blower B to each air diffuser 15, The main air pipe 18 directly connected to the aeration blower B is connected to each air diffuser 15 from the main air pipe 18 through an air introduction pipe 16 which is a branch pipe.

  In the present invention, eight or more membrane filtration units 5 having the above-described configuration illustrated are immersed in the same aeration tank 4 and juxtaposed, and sludge is removed between the anaerobic tank 3 and the aeration tank 4. It is assumed that a large amount of biological activated sludge treatment as described above is performed while circulating. Therefore, as described above, the membrane filtration units 5 are connected to the same suction conduit 22 via the flow rate adjusting valve 23. However, when this sludge treatment is continued for a long period of time, clogging proceeds on the surface of the membrane of the membrane filtration unit 5, so that the filtration flow rate decreases or the transmembrane pressure difference increases.

  In order to suppress such an increase in the transmembrane pressure difference, a biological treatment is performed using a mixed fluid of air and sludge discharged from the air diffuser 15 disposed below the hollow fiber membrane element 10. At the same time, so-called air scrubbing is performed, and each hollow fiber membrane 10a is vibrated to peel off and remove the suspended substances adhering to the surface, thereby performing physical cleaning. However, in this air scrubbing, the filtered water is actively sucked from the external suction pump Pv through the hollow portion of the hollow fiber membrane 10a at the same time as the air scrubbing to separate the sludge and the filtered water, so that the treatment takes a long time. As usual, suspended substances are sucked onto the membrane surface, resulting in clogging and a decrease in filtration flow rate. As a result, it was necessary to temporarily stop the sludge treatment and periodically perform extensive washing.

  By the way, if the depth dimension of the membrane filtration unit is 1552.5 mm as described above, and 25 membrane filtration units are arranged in parallel in the aeration tank with an interval of 1/2 of the depth dimension, The total length of the air main pipe 18 reaches 58219 mm or more. The same applies to the backwashing conduit 25 described later for cleaning the membrane surface from the inside of the porous hollow fiber membrane by feeding back the suction conduit 22 arranged for each membrane filtration unit and the treated water. I can say that. Thus, when the pipe length becomes extremely long, the change in pipe resistance in the length direction also becomes very large. As a result, in the air scrubbing cleaning, the amount of air released from the diffuser generator 15 closest to the aeration blower B is significantly larger than the amount of air released from the diffuser generator 15 closest to the anaerobic tank 3. .

  This is not only because there is a difference in the cleaning effect of air scrubbing cleaning that is affected by the amount of released air, but also the amount of dissolved oxygen in the periphery of the membrane filtration unit 5 changes greatly. It means that the gradient becomes large and efficient activated sludge treatment is not performed. Therefore, in the present embodiment, a flow rate adjustment valve 19 is arranged in the air introduction pipe 16 branched from the air main pipe 18, and the opening degree of the flow rate adjustment valve 19 is adjusted to be generated from all the air diffusers 15. The amount of released air is made uniform. The adjustment operation of the opening degree of the flow rate adjusting valve 19 can be performed manually because the decrease in the air discharge amount is caused by the pipe resistance. However, when the adjustment is always performed while monitoring the flow rate, the illustration is omitted. However, it is preferable to automatically adjust the opening degree of each flow rate adjusting valve 19 through a computer (not shown) by a measurement signal from the flow meter and the same flow meter.

  Even if the opening degree of the flow rate adjusting valve 19 is adjusted, the cleaning effect by air scrubbing can be obtained. However, when the clogging is severe and the forced cleaning is required, the processing amount is 1000 t / day or less. If the amount is small, the operation can be stopped once, and each membrane filtration unit 5 can be pulled out of the tank to perform sufficient cleaning. However, if the daily throughput exceeds 2500 t and the number of membrane filtration units 5 exceeds 8, when all of these operations are stopped, the planned throughput within the period until the next cleaning is performed. It becomes difficult to manage. In particular, if the amount of wastewater discharged per day is almost constant as in the case of industrial wastewater treatment, a predetermined amount of wastewater treatment cannot be performed unless there is another buffer.

  Therefore, in the present embodiment, the membrane filtration unit 5 having a total number of n of 8 or more is arranged in one tank. Among these, the base n ′ of the membrane filtration unit 5 to be cleaned is set to a base of 0.1 × n to 0.25 × n. At the time of cleaning, the operation of the air diffuser 15 of the n′-based membrane filtration unit 5 is not stopped, but only the suction by the suction pump Pv is stopped to perform physical cleaning by air scrubbing. Therefore, the flow rate adjusting valve 23 interposed in the branch line 22a that connects the n′-based membrane filtration unit 5 that stops suction by the suction pump Pv and the suction line 22 is temporarily closed. The opening / closing operation of the flow rate adjusting valve 23 may be performed manually, but considering that it is an operation in a sludge tank, hygiene can be performed by automatic operation according to a sequence stored in advance in a computer (not shown). It is desirable because it is efficient and efficient.

  At the time of this washing, the remaining nn′-based membrane filtration unit 5 continues normal suction by the common suction pump Pv, and the biological activated sludge treatment is performed. Since suction from the filtration unit 5 is not performed, the total amount of suction of the nn′-based membrane filtration unit 5 is n / (n−n ′) times, and the entire treatment in the aeration tank 4 is performed. There is no change in quantity. Moreover, since the amount of dissolved oxygen supplied to the aeration tank 4 is not changed, the amount of activated sludge that grows does not change. In addition to these effects, the hollow fiber membrane 10a of the n'-based membrane filtration unit 5 does not have a suction action, so it does not have a suction action for suspended substances and the like. As a result, the amount of adhering to the surface is also greatly reduced, and effective cleaning by air scrubbing can be performed.

  Temporarily, using the membrane filtration unit 5 with a throughput of 400 t / day per unit, a large amount of sludge treatment of 10,000 t / day or more is performed, and all membrane filtration units 5 are washed with membranes. If cleaning is performed at least once every 15 days per unit for 2 hours, the total number n needs to be at least 25 units, while the number n ′ of the membrane filtration unit 5 to be cleaned is changed to the membrane filtration unit 5. Assuming that 10% of the total cardinal number n, n ′ is 3, and the time required for cleaning the entire membrane filtration unit 5 is (25 ÷ 3) × 2 = 17 hours. Experiments have shown that a maximum cleaning interval of only aeration is preferably every 15 hours. From this, it can be seen that in this case, the number n ′ of membrane filtration units to be cleaned at the same time is small with three units. Therefore, if the washing time for one washing is not changed to 2 hours and the radix n ′ of the membrane filtration unit to be washed is 15% of the total radix n, the radix n ′ of the membrane filtration unit to be washed is 25 ×. 0.15 = 3.75, that is, 4 groups. In this case, the total time required for cleaning the entire membrane filtration unit 5 is (25 ÷ 4) × 2 = 12.5 hours, which falls within the range of 15 hours that do not require cleaning.

  FIG. 5 schematically shows an example of the operation procedure of the membrane cleaning device of the membrane filtration unit according to the present embodiment. In the illustrated example, for ease of understanding, the total number n of the membrane filtration unit 5 is four, and the number n ′ of the membrane filtration unit 5 to be cleaned is one. It is interposed in each branch line 22a that connects the suction line 22 connected to the suction pump Pv and each water collection header pipe 21 (see FIG. 3) of each of the first to fourth membrane filtration units 5a to 5d. Further, the membrane surface cleaning of the hollow fiber membrane elements 10 of all the membrane filtration units 5a to 5d is performed by sequentially opening and closing the four first to fourth flow rate adjusting valves 23a to 23d. Even during this cleaning, air from the aeration blower B is introduced into all the air diffuser 15 and the air is continuously released.

  Specifically, as shown in FIG. 5A, the first flow rate adjusting valve 23a is first closed, and the suction action by the suction pump Pv is stopped. Also at this time, the same amount of air as that of the other second to fourth diffuser generators 15b to 15d is ejected from the first diffuser generator 15a. The air-liquid mixed flow of air and sludge acts on the surface of the hollow fiber membrane 10a of the hollow fiber membrane element 10 due to the ejection of the air, vibrates the hollow fiber membrane 10a, and the suspended matter adhering to the membrane surface. Remove from the membrane surface. At this time, dissolved oxygen in the air that does not contribute to sludge filtration oxidizes and decomposes surrounding organic substances, and aerobic microorganisms such as polyphosphate accumulating bacteria accumulate phosphorus in the bacteria. Moreover, the 2nd-4th membrane filtration units 5b-5d which are not made into the washing | cleaning object simultaneously discharge | emit filtered water (process water) out of the system by the suction pump Pv continuously. As for the pump capacity at the time of this suction, the operation is continued on the premise of the total capacity when the entire membrane filtration unit 5 is fully operated. Therefore, since the first membrane filtration unit has stopped filtration for washing, the amount of treatment that should be 1/4 times the total amount of treatment N should be reduced. The other second to fourth membrane filtration units 5b Since ~ 5d covers and processes, there is no change in the daily scheduled processing amount.

  When the membrane cleaning by aeration of the first membrane filtration unit 5a is completed, the first flow rate adjustment valve 23a is opened and the second flow rate adjustment valve 23b is closed as shown in FIG. The first membrane filtration unit 5a resumes normal processing, and at the same time, the second membrane filtration unit 5b performs aeration cleaning by blowing air from the second air diffuser 15b. When the membrane cleaning of the second membrane filtration unit 5b is completed, as shown in FIG. 5C, the second flow rate adjusting valve 23b is opened simultaneously with the same operation as shown in FIG. The unit 5b is switched to the membrane cleaning of the third membrane filtration unit 5c. Subsequently, the membrane cleaning of the fourth membrane filtration unit 5d is similarly performed, and one cycle is completed. By repeating this cycle, the membrane filtration units 5a to 5d are periodically subjected to membrane cleaning by aeration without changing the total throughput.

  By the way, as already described, when the number of the membrane filtration units exceeds 8, the suction pipe length from the suction pump Pv becomes 58219 mm or more, and thus the pipe resistance cannot be ignored. Actually, if the diameters of the suction pipes 22 are made uniform and the diameters of the branch pipes 22a are the same, the pressure loss of filtrate water sucked from the membrane filtration unit 5 closest to the suction pump and the closest to the oxygen-free tank 3 There is a difference of 1/10 or more with the pressure loss difference of filtrate water sucked from the membrane filtration unit 5. This means that the suction amount of filtered water per day, that is, the scheduled processing amount of activated sludge per day, is greatly reduced. Therefore, in this embodiment, when the hollow fiber membrane module 9 of the whole membrane filtration unit 5 is replaced, for example, the opening degree of all the flow rate adjustment valves 23 is adjusted.

  Although this adjustment can also be performed manually, it is used for a flow meter and a computer (not shown) as in the air scrubbing cleaning, and based on a correlation table between a flow rate and a valve opening stored in advance in the computer, The opening degree of each flow rate adjusting valve 23 can be automatically adjusted. During this automatic adjustment, the flow rate can always be adjusted. Therefore, the adjustment is not limited to when the membrane element 10 of the hollow fiber membrane module 9 is replaced. By adjusting in this way, the same amount of filtered water can be sucked from all the membrane filtration units 5 regardless of the distance from the suction pump Pv. The sludge concentration gradient from the vicinity of the membrane filtration unit 5 farthest from the suction pump to the vicinity of the nearest membrane filtration unit 5 can be suppressed to the minimum.

  FIG. 6 shows an example of a reverse cleaning apparatus for carrying out the membrane separation activated sludge treatment method according to the second embodiment of the present invention. As a cleaning method for detaching suspended substances (solid matter) adhering to the membrane surface from the membrane surface, reverse cleaning is known in addition to so-called air scrubbing by aeration as described above. This backwashing is a state in which the suction pump Pv is stopped, the treated water in the treated water tank 8 in which treated water is stored is pumped up by the backfeed pump Pr, and the suction line 22 is backwashed to each membrane filtration unit. 5 is sent to the hollow portion of each porous hollow fiber membrane 10a of each hollow fiber membrane element 10 through the water collecting header pipe 21, and the treated water is flowed from the inside of the porous hollow fiber membrane to the outside through the filtration hole, This is a cleaning method in which the solid matter adhering to the membrane surfaces of the porous hollow fiber membrane 10a and the hollow fiber membrane element 10 is peeled off and washed. At this time, the suction pump Pv is naturally stopped, and suction of filtered water is also stopped.

  Conventionally, the backwashing was simultaneously performed on the treated water tank 8 with respect to the plurality of membrane filtration units 5 immersed in a single aeration tank. Usually, the suction of the treated water (filtered water) by the suction pump Pv is performed for 10 minutes and is intermittently operated for about 1 minute. On the other hand, the back washing time is 30 seconds to just over 1 minute. Therefore, it is reasonable to perform the reverse cleaning during the idle time period of the suction pump Pv. For example, as shown in FIG. 6, this reverse cleaning device has an open / close valve 22b adjacent to the upstream side of the suction pump Pv in the suction line 22, and the treated water suction port of the reverse feed pump Pr via a pipe. The backwash pipe 25 that is erected in the treated water tank 8 and connected to the treated water discharge port of the back feed pump Pr is joined to the suction pipe 22 upstream of the opening / closing valve 22b. The backwash pipe 25 is also provided with an open / close valve 25a.

  In addition, each branch conduit 22a that connects each membrane filtration unit 5 and the suction conduit 22 is provided with a flow rate adjusting valve 23 as in the above embodiment. The adjustment mechanism and operation are substantially the same as in the above embodiment. In order to perform membrane cleaning of the membrane elements of a number of membrane filtration units 5 by backwashing in a state where the flow rate adjusting valve 23 is adjusted, the suction pump Pv is first stopped and then provided in the suction line 22. The on-off valve 22b is closed and the suction of filtered water by the suction pump Pv is stopped. Next, the drive of the reverse feed pump Pr is started and the open / close valve 25a provided in the backwash pipe 25 between the reverse feed pump Pr and the suction pipe 22 is opened and stored in the treated water tank 8. The treated water being pumped up is pumped through the suction pipe line 22 and the respective branch pipe lines 22a and sent through the hollow to the porous hollow fiber membrane 10a of the hollow fiber membrane element 10 of each membrane filtration unit 5. Using the transmembrane pressure difference, the treated water is pushed out from the hollow of the porous hollow fiber membrane 10a into the sludge. The solid matter adhering to the film surface is peeled off by the pushing force at this time. At this time, there is almost no difference in the amount of treated water supplied to the branch pipe 22a farthest from the reverse pump Pr and the branch pipe 22a closest to the reverse feed pump Pr, and cleaning in the treatment direction is performed uniformly.

  FIG. 7 shows a modified example of the backwashing device suitably applied to the backwashing method similar to the second embodiment. According to the figure, a three-port two-way switching valve Vc is provided in the suction pipe 22 between the suction pump Pv and the branch pipe 22a closest to the pump Pv. The suction line 22 is connected to two of the ports, and the backwash line 25 is connected to the remaining one port. Therefore, in this modified example, the suction line 22 and the backwash line 25 are not provided with opening / closing valves, respectively, as in the second embodiment, and the junction between the backwash line 25 and the suction line 22 is provided. Is provided with a three-port two-way switching valve Vc to reduce the number of parts. Other configurations and effects are not substantially different from those of the second embodiment, but in this modification, the switching operation of the three-port two-way switching valve Vc uses an electromagnetic switching valve that is operated by an electric signal. To do.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows roughly an example of the membrane separation sludge processing apparatus suitable in order to implement the processing method which concerns on Embodiment 1 of this invention. FIG. 3 is a three-dimensional view showing the entire configuration of a normal membrane filtration unit with a part broken away. It is a perspective view which shows typically the structural example of the membrane element which is a structural member of a hollow fiber membrane module. It is a three-dimensional view of an air diffuser that is one of the constituent members of the membrane filtration unit. It is explanatory drawing of the washing | cleaning procedure which shows an example of the washing | cleaning method of the hollow fiber membrane module by scrubbing washing | cleaning. It is a block diagram of the aeration process which shows the back washing | cleaning method of the hollow fiber membrane module which is Embodiment 2 of this invention. It is a block diagram of the aeration process which shows the back washing | cleaning method of the hollow fiber membrane module which is a modification of Embodiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fine screen 2 Raw water adjustment tank 3 Anoxic tank 4 Aeration tank 5 Membrane filtration units 5a-5d 1st-4th membrane filtration unit 6 Circulating fluid extraction part 7 Sludge storage tank 8 Treated water tank 9 Hollow fiber membrane module 10 Membrane element 10a Hollow fiber membrane 11 Membrane sheet 11a Potting material 12 Filtration water outlet tube 12a Filtration water outlet 12b L-type joint 13 Lower frame 14 Spiral fume 15 Aeration generators 15a-15d First to fourth aeration generators 16 Air introduction pipe (branch pipe)
17 Aeration pipe 18 Air main pipe 19 Flow rate adjusting valve 20 Upper wall material 21 Water collecting header pipe 21a Water collecting port 21b L-shaped joint 21c Water inlet 22 Suction pipe 22a Branch pipe 22b Open / close valve 23 Flow rate adjusting valves 23a-23d Fourth flow rate adjusting valve 24 Lower wall member 24a Post 25 Backwash conduit 25a Open / close valve P1 First liquid pump P2 Second liquid pump Pv Suction pump Pr Reverse pump Vc Three-port two-way switching valve B Aeration blower

Claims (2)

An anaerobic tank or an anaerobic tank and an aeration tank, and a membrane filtration unit is immersed in the anaerobic tank, and the wastewater is biologically processed sequentially from the anaerobic tank side to separate activated sludge into solid and liquid. An activated sludge treatment method,
The membrane filtration unit includes a hollow fiber membrane module in which a membrane surface of a sheet-like membrane element composed of a plurality of porous hollow fiber membranes is vertically arranged in parallel at a predetermined interval, and a lower portion of the yarn membrane module And a diffuser generating device that emits microbubbles and generates a gas-liquid mixed flow that rises toward the hollow fiber membrane module,
Immersing and arranging eight or more membrane filtration units in series in the aeration tank at a required interval;
Fluids for all the membrane filtration units and aeration generators arranged in the aeration tank are sucked or supplied all at once by a fluid suction source or supply source connected to each filtration unit via a branch pipe. Maintaining and managing the suction amount or supply amount of the gas so as to be substantially uniform with a flow rate adjusting valve arranged for each branch pipe ,
The fluid is separated into solid and liquid by the membrane filtration unit, and is connected through filtered water sucked by a suction source through each branch line and main suction line, and an air supply source and a branch line. The air discharged from each diffuser and the suction flow rate of filtered water sucked from each membrane filtration unit and the amount of air sent to each diffuser are arranged in each branch pipe. Individually adjusting with the flow rate adjusting valve, and maintaining and managing the processing suction amount from the entire membrane filtration unit and the amount of air discharged toward each membrane filtration unit substantially uniformly,
A membrane separation activated sludge treatment method characterized by that . The fluid is filtered water sucked by the suction source, and is fed back from the supply source of the filtered water to each membrane filtration unit via the branch pipe to each porous hollow fiber membrane of the membrane element. each supply flow rate of filtered water when cleaning the modules from the inside, to adjust with a flow regulating valve disposed in each branch conduit, substantially uniformly the feed rate of filtrate water supplied to each membrane filter unit The membrane separation activated sludge treatment method according to claim 1, which is maintained and managed.

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