JP2006167551A - Biological treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain high-quality treated water by solving a problem of a conventional fluidized bed carrier biological treatment method and a membrane separation activated sludge method to efficiently treat waste water containing a high-concentration organic substance by suppressing a required capacity of a treatment tank, without requiring a flocculent for removing excess sludge and preventing an immersed membrane from being clogged. <P>SOLUTION: Organic waste water is separated into floating sludge and separated water in a floatation/separation tank 2 after being treated in an aerobic biological tank 1 holding a fluidized carrier carrying a microbe. The separated water in the floatation/separation tank 2 is introduced into a separation membrane immersion tank 3, the sludge accompanying this separated water is separated, and water permeating through a separation membrane module 3A is discharged as treated water. The floating sludge of the floatation/separation tank 2, and separated sludge of the separation membrane immersion tank 3 are returned to the aerobic biological treatment tank 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a biological treatment apparatus for efficiently removing organic matter from wastewater containing high-concentration organic matter.

  Conventionally, as a method for removing organic matter from wastewater containing a high concentration of organic matter by biological treatment, there is known a fluidized bed carrier biological treatment method in which a carrier to which microorganisms are attached flows in treated water and the microorganisms consume or absorb the organic matter. It has been. This method can take a higher organic substance load per treatment tank volume than a general activated sludge method, and is excellent in treatment efficiency. As a specific method of such a fluidized bed carrier biological treatment method, for example, Japanese Patent Application Laid-Open No. 9-308992 discloses that the effluent of a biological treatment tank holding a fluid carrier carrying microorganisms is solid-liquid separated in a sedimentation tank. A method for obtaining treated water is disclosed.

  A membrane separation activated sludge method is also widely used in which water containing organic matter is mixed with activated sludge for biological treatment and then filtered using a separation membrane to separate the activated sludge from the treated water. As a method in which the separation activated sludge method is combined with a biofilm treatment tank in which a packed bed of a filter medium on which a biofilm has been formed, JP-A-6-47399 discloses that the effluent water from the biofilm treatment tank is submerged in a membrane membrane type. A method is disclosed in which membrane permeated water is extracted as treated water after being treated in a tempering treatment tank, and sludge in the treatment tank is returned to the preceding biofilm treatment tank.

Incidentally, JP 2002-34585 A discloses a method of filtering the treated water of a batch activated sludge treatment apparatus with a submerged membrane separator, but in the method of this JP 2002-34585 A, It is not assumed that the sludge separated and concentrated by the submerged membrane separator is returned to the batch biological treatment apparatus. That is, if sludge is returned by this method, it will be returned to one of a plurality of batch-type biological treatment devices, and even if returned alternately, it is difficult to maintain a uniform sludge concentration. Variation occurs and the quality of treated water becomes unstable.
JP-A-9-308892 JP-A-6-47399 JP 2002-34585 A

  However, in the fluidized bed biological treatment method, microorganisms grow and flow out as surplus sludge mixed with the treated water, but this surplus sludge is difficult to flock, so the sedimentation rate is slow, and this is completely removed in the sedimentation tank. It is necessary to provide a large sedimentation tank or forcibly settle using a large amount of aggregating agent.

  On the other hand, the membrane-separated activated sludge method has the advantages of increasing the decomposition rate of organic matter and obtaining clean treated water by maintaining the activated sludge at a high concentration when treating high concentrations of organic matter. Since sludge has adhesiveness, the separation membrane directly immersed in the activated sludge is likely to be clogged, and the cleaning strength and frequency of the separation membrane must be increased.

  The present invention solves the problems of the above-described conventional fluidized bed carrier biological treatment method and membrane separation activated sludge method, reduces wastewater containing high-concentration organic matter, reduces the required capacity of the treatment tank, and removes excess sludge. It is another object of the present invention to provide a biological treatment apparatus that does not require a flocculant and that can be efficiently treated by preventing clogging of the immersion membrane and obtaining high-quality treated water.

  The biological treatment apparatus of the present invention (Claim 1) receives an organic wastewater, holds an aerobic biological treatment tank holding a fluid carrier carrying microorganisms, receives the effluent from the aerobic biological treatment tank, and the effluent. A separation membrane immersion tank that separates sludge entrained by the separation water and discharges the treated water, A separation membrane immersion tank comprising a separation membrane module immersed in the tank and an air diffuser provided below the separation membrane module; and a flotation sludge of the floating separation tank is returned to the aerobic biological treatment tank. And a second sludge returning means for returning the sludge of the separation membrane immersion tank to the aerobic biological treatment tank.

  A biological treatment apparatus according to a second aspect is the biological treatment apparatus according to the first aspect, wherein the second sludge return means is constituted by a return pump and a return pipe, and the first sludge return means is jetted from a discharge port of the return pipe. The floating sludge is configured to be pushed into the aerobic biological treatment tank by the sludge.

The biological treatment apparatus according to claim 3 is the biological treatment apparatus according to claim 1 or 2, wherein the aerobic biological treatment tank includes a first aerobic biological treatment tank and a second aerobic biological treatment tank. The floating sludge and the sludge from the separation membrane immersion tank are returned to the first aerobic biological treatment tank, and the tank load of the first aerobic biological treatment tank is 0.8 to 8.0 kg-BOD / m ^3. -It is characterized by d.

  The biological treatment apparatus according to claim 4 is characterized in that, in claim 3, the effective capacity of the second aerobic biological treatment tank is 1 to 10 times the effective capacity of the first aerobic biological treatment tank. To do.

  The biological treatment apparatus according to claim 5 is the biological treatment apparatus according to any one of claims 1 to 4, wherein the sludge concentration in the separation membrane immersion tank is 1,000 to 6,000 mg / L, and the residence time is 1 to 18 hours. It is characterized by being.

  According to the biological treatment apparatus of the present invention, high-concentration organic wastewater can be efficiently treated by using a relatively small-capacity apparatus without requiring a flocculant and preventing clogging of the immersion film. As a result, high-quality treated water can be obtained.

  That is, in the biological treatment apparatus of the present invention, the fluidized bed carrier biological treatment is first performed on the organic wastewater with a high concentration, and the treated water is efficiently removed by flotation separation using fine bubbles, The excess sludge is further subjected to solid-liquid separation in a subsequent separation membrane immersion tank. In this separation membrane immersion tank, a relatively low concentration of sludge after removing most of the excess sludge in the floating separation tank flows in advance, so there is little problem of clogging in membrane filtration. Thus, it is possible to efficiently carry out the decomposition and removal of the remaining organic matter and the sludge membrane filtration using the immersion membrane.

  The treated water obtained as the permeated water of the submerged membrane in the separation membrane soaking tank is a high quality treated water that has permeated through a microfiltration (MF) membrane or the like.

  Then, by returning the separated sludge from the floating separation tank and the separated sludge from the separation membrane soaking tank to the aerobic biological treatment tank, in this aerobic biological treatment tank, the ability to remove organic substances with poor degradability in fluidized bed carrier biological treatment Can be improved, and this can be efficiently decomposed and removed.

  For this reason, according to the present invention, a relatively small water tank and a small separation membrane area, and the cleaning strength and frequency of the separation membrane are greatly reduced as compared with the prior art, and accordingly, the operation cost is reduced and a clean process is performed. It becomes possible to obtain water efficiently.

  Hereinafter, embodiments of a biological treatment apparatus of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of a biological treatment apparatus of the present invention.

  In FIG. 1, reference numeral 1 denotes an aerobic biological treatment tank, in which a fluid carrier carrying microorganisms is held, a screen 1a provided at the treated water outflow part, and an air diffuser provided at the lower part in the tank 1b. Reference numeral 2 denotes a levitation separation tank (pressure levitation tank) that floats floating substances such as excess sludge using fine bubbles. Reference numeral 3 denotes a separation membrane immersion tank, in which a separation membrane module 3A is immersed, and a diffuser 3B is provided below the separation membrane module 3A. 5 is a pump that mixes and pressurizes a part of the treated water in the separation membrane immersion tank 3 and the outside air, and the floating separation tank 2 generates pressurized water containing a large amount of fine bubbles, and 6 is sludge in the separation membrane immersion tank 3. This is a pump 6 for pushing back to the aerobic biological treatment tank 1 while preventing sticking of the levitated substance floating on the levitating separation tank 2 using a part of the aerobic biological treatment tank 1. 7 is a liquid level gauge, and 8 is a current plate.

  There is no restriction | limiting in particular in the shape of the aerobic biological treatment tank 1, Any of cylindrical shape, a rectangular parallelepiped shape, etc. may be sufficient, and the baffle board etc. for preventing a stagnation inside may be provided.

  The carrier held in the aerobic biological treatment tank 1 is made of a material that immobilizes microorganisms and flows in water, and has a specific gravity equivalent to water and easily adheres to microorganisms. The size of the structure is preferably in the range of 0.5 to 200 mm as the maximum distance when sandwiched between two parallel plates. However, the carrier held in the tank may be uniform in shape, size, material, or the like, or different ones may be mixed. Further, the amount of carrier retained in the aerobic biological treatment tank 1 is 10 to 60 of the effective capacity of the aerobic biological treatment tank 1 when the carrier is randomly stacked on land with the same state as in the water in the tank. % Is preferable.

The screen 1a is for separating the carrier and the effluent water, as long as the opening is smaller than the size of the carrier and the effluent water can be separated from the flowing carrier, and its shape and material are particularly limited. However, for example, a stainless steel screen or a plastic mesh can be used. The surface area of water portion of the screen 1a is effluent ^{1 m} 3 / d per 0.5 m ² or more, for example, to such a 1～1.5M ² is preferred from the viewpoint of water outflow efficiency. Further, in order to prevent clogging by the carrier of the screen 1a, a water flow in a direction parallel to the surface of the screen 1a may be sufficiently applied by, for example, providing a diffuser tube or the like below the screen 1a.

  The air diffuser 1b provided in the lower part of the aerobic biological treatment tank 1 causes a necessary and sufficient flow throughout the inside of the aerobic biological treatment tank 1, and can distribute dissolved oxygen to microorganisms. There are no particular restrictions on the type or number of installations, but for example, a diffuser, an aerator, a perforated diffuser tube, or the like can be used.

The effective capacity (effective volume) of the aerobic biological treatment tank 1 may be designed so that the tank load is 0.8 to 8.0 kg-BOD / m ³ · d when the inflowing organic matter is represented by BOD. preferable. If the tank load is larger than this range, sufficient organic matter removal cannot be performed, and if it is smaller than this range, the capacity of the apparatus is undesirably increased.

  The floating separation tank 2 may have a cylindrical shape or a rectangular parallelepiped shape, and may have a baffle plate or the like for preventing the occurrence of stagnation inside, but is adjacent to the aerobic biological treatment tank 1 and is attached to the aerobic biological treatment tank. 1 is desirable. A discharge nozzle 5A for pressurized water containing fine bubbles produced by the pump 5 is provided in the lower part of the levitation separation tank 2 so that the pressurized water is discharged upward and mixed with inflow water in the tank. Yes.

  The pump 5 is a mechanism for generating pressurized water containing fine bubbles in the levitation separation tank 2, and sucks outside air together with water from the suction side using an ejector or the like, and the most fine bubbles are generated at about 0.5 MPa or less. By increasing the pressure to a greater pressure, bubbles are made finer. The discharge amount is preferably set to 1/50 to 1/5 of the amount of treated water in the floating separation tank 2 in a state including fine bubbles. If this amount is too large, the apparent volume of floating solids will increase, and if it is too small, sufficient floating separation will not be performed. Further, the pump 5 does not suck air from the inlet, but pushes and melts air pressurized by an air compressor or the like on the discharge side, and decompresses this in a pipe or a pressure vessel, thereby forming fine bubbles. You may do it.

  The type and type of the pump 5 are not particularly limited as long as the above discharge pressure is obtained and water containing bubbles can be continuously sent out even with some cavitation. As the pressurized raw water of the pump 5, it is desirable to use a part of the treated water of the separation membrane immersion tank 3 or introduce water such as well water that does not contain SS from the outside.

  The solids in the tank are captured by the microbubbles contained in the pressurized water discharged from the discharge nozzle 5A into the floating separation tank 2 by such a pump 5, and the captured solid content obtains buoyancy to obtain the floating separation tank. Only the relatively clean treated water that floats up inside 2 is sent to the subsequent process from the discharge port 2A. On the other hand, since the solid content that has floated accumulates in the upper part, the concentrated sludge in the separation membrane immersion tank 6 is pulled out by the pipe 6B and the pump 6 and pressurized, and periodically sprayed from the nozzle 6A, thereby aerobic biological treatment tank 1 Push back.

  The pump 6 pressurizes and sends a part of the concentrated sludge in the separation membrane immersion tank 3 in order to push it back to the aerobic biological treatment tank 1 while preventing the floating solid matter in the floating separation tank 2 from sticking, and the separation membrane It is provided to keep the sludge concentration in the immersion tank 3 constant. The average discharge amount of the pump 6 is preferably in the range of 1/10 to 3 of the amount of treated water in the floating separation tank 2. If this amount is too large, the amount of treated water in the flotation separation tank will increase, and if it is too small, the floating solids will not be pushed back enough to the aerobic biological treatment tank 1, and the sludge concentration in the separation membrane immersion tank 3 will also increase. To do. It is desirable that the sludge return by the pump 6 is intermittently performed in order to keep the water surface height of the floating separation tank 2 and the separation membrane immersion tank 3 constant. The type of the pump 6 is not particularly limited as long as the pressure and flow rate required by the nozzle 6a can be obtained, and the structure is less likely to cause trouble such as clogging due to sludge.

  The nozzle 6 </ b> A is a nozzle that sprays a part of sludge in the separation membrane immersion tank 3 in order to prevent the floating solid matter in the floating separation tank 2 from sticking and send it to the aerobic biological treatment tank 1. One or more are provided on the water surface or directly below the water surface. The nozzle 6A is not particularly limited in type and structure as long as it is capable of obtaining the injection force necessary for sludge delivery without being clogged with sludge, and when two or more nozzles are provided, each is the same. It may be different or different.

  When the floating solids in the floating separation tank 2 are sent to the aerobic biological treatment tank 1 together with the concentrated sludge in the separation membrane immersion tank 3 by the nozzle 6A, when the floating solids are sent out from the water surface of the floating separation tank 2 It is good also as an aid of sending out by raising only.

  As shown in the figure, the surface area and depth of the water surface gradually narrow toward the aerobic biological treatment tank 1 so that the floating solids do not stay or stick, and the rectifying plate 8 that does not catch the floating solids floats. It is desirable to provide in the separation tank 2.

  Even if the BOD is about 300 mg / L, the separation water in the floating separation tank 2 does not cause any particular problem in the subsequent process. If the BOD is to be reduced, the volume of the aerobic biological treatment tank 1 needs to be increased. Therefore, the aerobic biological treatment tank 1 has a volume of the aerobic biological treatment tank 1 so that the BOD of the separated water in the floating separation tank 2 is about 150 to 600 mg / L in the range of the aforementioned tank load. It is preferable to define.

  There is no restriction | limiting in particular in the shape of the separation membrane immersion tank 3, Any, such as a cylindrical shape and a rectangular parallelepiped shape, may be provided, and the baffle plate etc. for preventing a stagnation inside may be provided. The effective volume of the separation membrane immersion tank 3 is 2 hours or more with respect to the amount of treated water (inflow water), for example, 5 to 10 hours, and the separation membrane portion of the separation membrane module 3A can be sufficiently immersed in water. Be larger than size. The sludge concentration (MLSS) in the tank is approximately 6000 mg / L or less, for example, 3,000 to 5,000 mg / L, so that the separation membrane module 3A can maintain a high membrane flux. Furthermore, it is preferable to adjust the amount of sludge drawn by the pump 6.

  The separation membrane of the separation membrane module 3A immersed in the separation membrane immersion tank 3 may have a pore diameter equal to or smaller than that of the MF membrane, and the shape thereof may be hollow or planar, and the material is not particularly defined. The separation membrane module 3A is arranged so that the part related to solid-liquid separation is completely immersed in the water in the tank. The separation membrane module 3A performs aeration from the aeration device 3B provided below as needed to vibrate the membrane surface to prevent microorganisms from sticking, and the cross-flow flow causes the membrane flux to flow. Improvements may be made. The membrane flux of the separation membrane module 3A is not particularly defined, but since the sludge concentration in the separation membrane immersion tank 3 can be determined so that it becomes the maximum, it should be higher than the flux in the original membrane activated sludge method. Can do. For example, in the case of a hollow fiber MF membrane made of polyethylene, what is used at a membrane flux of 0.25 m / d under the condition of a sludge concentration of 10,000 mg / L by a normal membrane-type activated sludge method is shown in the following examples. Thus, in the apparatus to which the present invention is applied, the treatment can be performed with a high membrane flux of about 0.4 m / d on the condition of the sludge concentration of 4500 mg / L.

  The air diffuser 3B provided below the separation membrane module 3A may be any device as long as it causes necessary and sufficient flow throughout the separation membrane immersion tank 3 and can distribute dissolved oxygen to microorganisms. There are no particular restrictions on the type or number of installations, but for example, a diffuser, an aerator, a perforated diffuser tube, or the like can be used. This aeration may be performed as an aeration for membrane vibration of the separation membrane module 3A described above, or may be performed separately.

  In the present invention, in order to keep the sludge concentration in the separation membrane immersion tank 3 low, a part of the liquid (concentrated sludge) in the separation membrane immersion tank 3 is returned to the aerobic biological treatment tank 1. In order to keep the operating pressure of the separation membrane module 3A constant, it is preferable that the water surface of the water surface is not changed as much as possible, and the return is preferably performed only while the discharged water from the floating separation tank 2 is flowing in. .

  Further, the separation membrane module 3A needs to be periodically washed with a chemical such as 0.1 wt% sodium hypochlorite in order to maintain the permeation flux. Since the sludge concentration is low, the frequency of chemical cleaning can be kept low even if the permeation flux is increased. For example, as shown in the examples described later, the conventional method is 10,000 mg / L, and the permeation flux of the membrane is 0.25 m. In the same manner as when operating at / d, according to the present invention, even when operating at a sludge concentration of 4500 mg / L and a membrane permeation flux of 0.4 m / d, the chemical cleaning frequency with 0.1% sodium hypochlorite is Both can be done every 3 months, and the permeation flux of the membrane can be maintained for a long time.

  In such a biological treatment apparatus, raw water (organic waste water) is introduced into the aerobic biological treatment tank 1 and subjected to fluidized bed carrier biological treatment, and then is floated and separated by pressure in the floating separation tank 2. Is pushed back into the aerobic biological treatment tank 1 by the concentrated sludge in the separation membrane immersion tank 3 from A part of the floating sludge in the floating separation tank 2 may be discharged out of the system as necessary. The separated water in the levitation separation tank 2 is then introduced into the separation membrane immersion tank 3, subjected to aerobic biological treatment with microorganisms in the tank, and then subjected to membrane filtration with the separation membrane module 3 </ b> A, and the membrane permeated water is discharged out of the system as treated water. Is done. The sludge in the separation membrane immersion tank 3 is returned to the aerobic biological treatment tank 1 together with the floating sludge in the floating separation tank 2 by the pump 6. This return sludge may also be partially discharged outside the system as necessary.

  According to the biological treatment apparatus of FIG. 1 (a), a large amount of excess sludge generated in the fluidized bed carrier biological treatment by floating and separating the fluidized bed carrier biologically treated water that has passed through the aerobic biological treatment tank 1 in the floating separation tank 2. The parts can be separated without using a flocculant. Then, a slight excess sludge contained in the separated water of the floating separation tank 2 is separated by membrane filtration in the separation membrane immersion tank 3. In this separation membrane immersion tank 3, sludge with a relatively low concentration after removing most of the excess sludge in the floating separation tank 2 flows in advance, so there is little problem of clogging in membrane filtration. Decomposition and removal of the organic matter remaining in the tank 3 and sludge membrane filtration with an immersion membrane can be performed efficiently. The treated water obtained as the permeated water of the separation membrane module 3A of the separation membrane immersion tank 3 is a high-quality treated water that has permeated the MF membrane or the like. In addition, in the present invention, the floating sludge in the flotation separation tank 2 and the separation sludge in the separation membrane immersion tank 3 are returned to the aerobic biological treatment tank 1 to remove organic substances having poor degradability in the aerobic biological treatment tank 1. Ability can be improved. For this reason, the effective capacity of the aerobic biological treatment tank 1 is sufficient, and as a result, the overall apparatus capacity can be reduced.

  The biological treatment apparatus shown in FIG. 1 (a) performs one-stage fluidized-bed carrier biological treatment in one aerobic biological treatment tank, but the biological treatment apparatus of the present invention is as shown in FIG. 1 (b). Alternatively, two aerobic biological treatment tanks may be provided, and the effluent of the first aerobic biological treatment tank 1A may be introduced into the second aerobic biological treatment tank 1B to perform the two-stage fluidized bed carrier biological treatment.

  In FIG.1 (b), 1A is a 1st aerobic biological treatment tank, the fluid support | carrier which carry | supported the microorganisms is hold | maintained inside, Screen 1Aa provided in the treated water outflow part, and the lower part in a tank inside A provided air diffuser 1Ab. 1B is a second aerobic biological treatment tank, in which a fluid carrier carrying microorganisms and suspended activated sludge are held, and is provided in a screen 1Ba provided in the treated water outflow part and in the lower part in the tank. A diffuser 1Bb. Other configurations are the same as those of the biological treatment apparatus shown in FIG. 1A, and members having the same functions are denoted by the same reference numerals.

  About the shape of 1st, 2nd aerobic biological treatment tank 1A, 1B, the kind and holding | maintenance amount of the support | carrier hold | maintained in a tank, the structure of screen 1Aa, 1Ba, and the structure of diffuser 1Ab, 1Bb, FIG. It is the same as the aerobic biological treatment tank 1 of a).

  The first and second aerobic biological treatment tanks 1A and 1B basically have the same specifications, but different configurations may be adopted for both. Sludge from the subsequent floating separation tank 2 and separation membrane immersion tank 3 is returned to the first aerobic biological treatment tank 1A.

Regarding the effective capacity (effective volume) of the first and second aerobic biological treatment tanks 1A and 1B, the effective capacity of the first aerobic biological treatment tank 1A is the tank load when the inflowing organic matter is represented by BOD. It is preferable to design so that it may become 0.8-8.0kg-BOD / m < ³ > * d. If the tank load is larger than this range, sufficient organic matter removal cannot be performed, and if it is smaller than this range, the capacity of the apparatus is undesirably increased. The effective capacity of the second aerobic biological treatment tank 1B is preferably larger than the effective capacity of the first aerobic biological treatment tank 1A, for example, 5 of the effective capacity of the first aerobic biological treatment tank 1A. It is preferably ˜8 times. When the effective capacity of the second aerobic biological treatment tank 1B is smaller than this range, it is not possible to sufficiently remove the hardly decomposable organic matter.

  In addition, about the structure and conditions, such as the floating separation tank 2, the separation membrane immersion tank 3, and the pumps 5 and 6, it is the same as that of the biological treatment apparatus of Fig.1 (a).

  Also in the biological treatment apparatus of FIG. 1 (b), raw water (organic waste water) is sequentially introduced into the first aerobic biological treatment tank 1A and the second aerobic biological treatment tank 1B, and the two-stage fluidized bed carrier. After being biologically treated, it is floated under pressure in the flotation separation tank 2, and the floating sludge is pushed back into the first aerobic biological treatment tank 1 </ b> A by the concentrated concentration of the separation membrane immersion tank 3 from the pump 6. A part of the floating sludge in the floating separation tank 2 may be discharged out of the system as necessary. The separated water in the levitation separation tank 2 is then introduced into the separation membrane immersion tank 3, subjected to aerobic biological treatment with microorganisms in the tank, and then subjected to membrane filtration with the separation membrane module 3 </ b> A, and the membrane permeated water is discharged out of the system as treated water. Is done. The sludge in the separation membrane immersion tank 3 is returned to the first aerobic biological treatment tank 1A together with the floating sludge of the floating separation tank 2 by the pump 6. This return sludge may also be partially discharged outside the system as necessary.

  Even in the biological treatment apparatus of FIG. 1B, the two-stage fluidized bed carrier biological treatment water that has passed through the first and second aerobic biological treatment tanks 1A and 1B is floated and separated in the floating separation tank 2. Most of the excess sludge generated by the bed carrier biological treatment can be separated without using a flocculant. Then, a slight excess sludge contained in the separated water of the floating separation tank 2 is separated by membrane filtration in the separation membrane immersion tank 3. In this separation membrane immersion tank 3, sludge with a relatively low concentration after removing most of the excess sludge in the floating separation tank 2 flows in advance, so there is little problem of clogging in membrane filtration. Decomposition and removal of the organic matter remaining in the tank 3 and sludge membrane filtration with an immersion membrane can be performed efficiently. The treated water obtained as the permeated water of the separation membrane module 3A of the separation membrane immersion tank 3 is a high-quality treated water that has permeated the MF membrane or the like. Moreover, in the present invention, the floating sludge is returned to the first aerobic biological treatment tank 1A by returning the floating sludge of the floating separation tank 2 and the separation sludge of the separation membrane immersion tank 3 to the second aerobic biological treatment tank. It is possible to improve the ability to remove organic substances with poor degradability in the second aerobic biological treatment tank 1B. For this reason, the effective capacity of the second aerobic biological treatment tank 1B is sufficient, and as a result, the overall apparatus capacity can be reduced. And if it is this biological treatment apparatus, the treated water of much better water quality can be obtained by performing a two-stage fluidized bed carrier biological treatment.

  Therefore, according to the present invention, a biological treatment apparatus for removing organic matter from water containing a high concentration of organic matter does not require a large sedimentation tank or flocculant for separation of sludge and treated water. And the washing | cleaning intensity | strength and frequency of a separation membrane are reduced significantly, and reduction of an operating cost can be aimed at.

  Such a biological treatment apparatus of the present invention is effective for biological treatment of organic wastewater such as food wastewater and liquor production wastewater such as cooking waste, and particularly among such organic wastewater. It is effective for biological treatment of high-concentration organic wastewater whose organic matter concentration is 2,000 mg-BOD / L or more.

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

Example 1
Using the biological treatment apparatus of the present invention shown in FIG. 1 (a), the tofu production waste water having a BOD concentration of 2,000 mg / L was treated at a flow rate of 100 L / d. The specifications of each tank are as follows.
Aerobic biological treatment tank 1: Effective capacity = 100L
BOD load = 2kg-BOD / m ³ · d
Carrier type = square shape with particle size of 3-10 mm
Material: Polyurethane foam
Carrier holding amount = 50% of tank effective capacity
Flotation separation tank 2: Effective capacity = 20L
Rectification plate: Ascending toward the aerobic biological treatment tank 1 and the water surface area and water depth gradually
Narrow shape.
Separation membrane immersion tank 3: Effective capacity = 30L
Residence time = 7.2 hours
Membrane type of separation membrane module = hollow fiber type polyethylene membrane

  The floating sludge in the floating separation tank 2 was returned to the aerobic biological treatment tank 1 at a flow rate of 80 L / d, and 160 L / d of separated water was introduced into the separation membrane immersion tank 3. In the separation membrane immersion tank 3, sludge in the tank was returned to the aerobic biological treatment tank 1 through the floating separation tank 2 at a flow rate of 60 L / d, and 100 L / d of membrane filtrate was taken out as treated water. The sludge concentration in the separation membrane immersion tank 3 was maintained at about 4500 mg / L.

  As a result, BOD concentration of 10 mg / L or less and high-quality treated water not containing SS could be stably obtained with a high membrane flux of 0.4 m / d without causing clogging of the separation membrane module.

  In the conventional membrane activated sludge method, the sludge concentration (MLSS) of the separation membrane immersion tank when the chemical cleaning frequency of the hollow fiber type separation membrane with a pore diameter of 0.4 μm is equal every three months, and the separation membrane module The relationship with the permeation flux is as shown in FIG. As is apparent from this figure, according to the biological treatment apparatus of the present invention, it is possible to set the sludge concentration in the separation membrane immersion tank to about 4500 mg / L, even though the organic wastewater with high concentration is treated. Therefore, the permeation flux of the separation membrane can be 0.4 m / d or more at the chemical cleaning frequency every three months. Therefore, it can be seen that the area of the separation membrane can be reduced by that amount compared to the conventional method, and the chemical cleaning frequency at that time can be equal to or less than that of the conventional method.

Comparative Example 1
In Example 1, the floating separation tank was omitted, and the treatment was performed in the same manner except that the effluent water from the aerobic biological treatment tank 1 was directly introduced into the separation membrane immersion tank 3. As a result, the BOD concentration of the obtained treated water was 10 to 20 mg / L and SS was not included, and the water quality was relatively high, but the sludge concentration in the separation membrane immersion tank 3 was 25,000 mg / L for 3 days. Due to the clogging of the separation membrane module, the membrane flux decreased to 0.1 m / d or less, making it difficult to continue the operation.

Comparative Example 2
In Example 1, when it processed similarly except having omitted the separation membrane in a separation membrane immersion tank, the BOD density | concentration of the obtained treated water is 200-500 mg / L, SS is 500-5000 mg / L. It was not possible to obtain high quality treated water.

Example 2
In Example 1, as shown in FIG. 1 (b), the following first and second aerobic biological treatment tanks 1A and 1B were provided as the aerobic biological treatment tanks to perform the two-stage fluidized bed carrier biological treatment. The process was performed in the same manner except that.
First aerobic biological treatment tank 1A: Effective capacity = 10L
BOD load = 3kg-BOD / m ³ · d (second
Together with aerobic biological treatment tanks)
Carrier type = square shape with particle size of 3-10 mm
Material: Polyurethane foam
Carrier holding amount = 50% of tank effective capacity
Second aerobic biological treatment tank 1B: Effective capacity = 57L
Carrier type = square shape with particle size of 3-10 mm
Material: Polyurethane foam
Carrier holding amount = 50% of tank effective capacity

  As a result, as in Example 1, the sludge concentration in the separation membrane immersion tank 3 is maintained at about 4500 mg / L, and stable operation with a high membrane flux of 0.4 m / d without causing clogging of the separation membrane module. It was possible to obtain a very high quality treated water containing no SS and having a BOD concentration of 5 mg / L or less.

It is a systematic diagram which shows embodiment of the biological treatment apparatus of this invention. In the membrane activated sludge method, the sludge concentration (MLSS) of the separation membrane immersion tank and the permeation flux of the separation membrane module when the chemical cleaning frequency of the hollow fiber type separation membrane with a pore diameter of 0.4 μm is equal every three months, It is a graph which shows the relationship.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aerobic biological treatment tank 1A 1st aerobic biological treatment tank 1B 2nd aerobic biological treatment tank 2 Floating separation tank 3 Separation membrane immersion tank 3A Separation membrane module 3B Air diffuser

Claims (5)

An aerobic biological treatment tank holding a fluid carrier carrying microorganisms and receiving organic waste water;
A floating separation tank that receives the effluent of the aerobic biological treatment tank and separates the effluent into floating sludge and separated water;
A separation membrane immersion tank that receives separation water from the floating separation tank and separates sludge entrained in the separation water and discharges treated water, the separation membrane module immersed in the tank, and the separation membrane module A separation membrane immersion tank comprising a diffuser provided below;
First sludge return means for returning the floating sludge of the floating separation tank to the aerobic biological treatment tank;
A second sludge return means for returning the sludge of the separation membrane immersion tank to the aerobic biological treatment tank;
A biological treatment apparatus comprising:   In Claim 1, the said 2nd sludge return means is comprised with a return pump and return piping, and the said 1st sludge return means makes the said sludge sludge by the sludge injected from the discharge port of this return piping. A biological treatment apparatus configured to be pushed into an aerobic biological treatment tank. 3. The aerobic biological treatment tank according to claim 1, wherein the aerobic biological treatment tank includes a first aerobic biological treatment tank and a second aerobic biological treatment tank. The floating sludge of the floating separation tank and the separation membrane immersion tank The sludge is returned to the first aerobic biological treatment tank, and the tank load of the first aerobic biological treatment tank is 0.8 to 8.0 kg-BOD / m ³ · d. Biological treatment equipment.   4. The biological treatment apparatus according to claim 3, wherein the effective capacity of the second aerobic biological treatment tank is 1 to 10 times the effective capacity of the first aerobic biological treatment tank.   5. The biological treatment apparatus according to claim 1, wherein the sludge concentration in the separation membrane immersion tank is 1,000 to 6,000 mg / L and the residence time is 1 to 18 hours. .

Images