JPWO2007088860A1 - Biological treatment method of organic wastewater - Google Patents

Abstract

Provided is a biological treatment method for organic wastewater that can stably obtain a sludge reduction effect due to the predatory action of micro-organisms and obtain treated water with good water quality. Organic wastewater is introduced into the aeration tank 21 and biologically treated with a high load to produce dispersible bacteria. The biological treatment liquid containing dispersible bacteria and flowing out from the aeration tank 21 is introduced into the micro-organism holding tank 31. The DO concentration in the aeration tank 21 is controlled, or the soluble BOD sludge load in the microbiological storage tank 31 is operated as 0.025 kg-BOD / kg-VSS / day or more and 0.05 kg-BOD / kg-VSS / day or less. In this way, micro organisms such as stag beetles are inhabited, and the amount of excess sludge generated is reduced by utilizing the predatory action of the micro organisms, and sludge flocs with good sedimentation are generated. [Selection] Figure 1

Description

  The present invention relates to a biological treatment method for organic wastewater that treats organic wastewater with activated sludge and the like, and particularly relates to a biological treatment method for organic wastewater that biologically reduces excess sludge generated by biological treatment of organic wastewater. .

Among the biological treatment methods that biologically treat organic wastewater containing organic matter, the activated sludge method has the advantage that treated water with good water quality is obtained and maintenance is easy, so various organic properties such as sewage and industrial wastewater are available. Widely used as a wastewater treatment method. However, the volumetric load of BOD (organic matter represented by biochemical oxygen consumption) to the biological treatment tank for performing activated sludge treatment is as low as about 0.5 to 0.8 kg / m ³ / day. For this reason, in order to cope with a high load, it is necessary to enlarge the aeration tank, and there is a problem that a large installation area is required.

On the other hand, a fluidized bed method is known as a biological treatment method capable of high load operation. In the fluidized bed method, the concentration of sludge retained in the aeration tank is increased by adding a carrier to the aeration tank and performing biological treatment, so that a high load operation with a BOD volumetric load of 3 kg / m ³ / day or more is possible. .

  By the way, when the wastewater is biologically treated, most of the BOD assimilated to the bacteria is used as a bacterial respiration substrate and decomposed into carbon dioxide and water, but a part is used for the growth of the bacteria. For example, in the activated sludge method, about 20 to 40% of BOD taken up by bacteria is used for cell synthesis. That is, there is a problem that about 20 to 40% of the BOD treated with activated sludge is converted into bacteria, and the bacteria grown using the BOD as a substrate are discharged as excess sludge. In particular, in the fluidized bed method, more surplus sludge is generated than in the normal activated sludge method, specifically, about 30 to 40% of surplus sludge is generated from the biodegraded BOD.

  Therefore, a second-stage biological treatment tank (hereinafter referred to as “micro-organisms”) that holds the adherent protozoa is provided at the subsequent stage of the first-stage biological treatment tank (hereinafter, sometimes referred to as “aeration tank” in particular). There is known a biological treatment method for organic wastewater provided with a “retaining tank” (for example, Patent Document 1). In the method disclosed in Patent Document 1, by applying a high BOD load to the first-stage biological treatment tank, the growth of protozoa is suppressed to prevent bacterial aggregation, and the first-stage biological treatment includes dispersible bacteria. The biological treatment liquid flowing out from the tank is introduced into the second stage biological treatment tank. Since the second stage biological treatment tank holds protozoa that prey on dispersible bacteria, preserving the dispersible bacteria by the protozoa reduces the amount of excess sludge and flocs of the biological community Progresses. For this reason, in the second stage biological treatment tank, a microbial assembly (sludge floc) with good sedimentation is formed, and the effluent from the second stage biological treatment tank is solid-liquid separated to obtain clear treated water. It is done.

  Thus, by combining the first-stage biological treatment tank operated at high load and the second-stage biological treatment tank holding the sticking protozoa, high load operation and reduction of excess sludge can be achieved. Treated water can also be obtained. For this reason, various improved methods have been proposed for the biological treatment method using the first-stage biological treatment tank and the second-stage biological treatment tank. For example, Patent Document 2 discloses a biological treatment apparatus in which a feed refinement tank is provided between a first-stage biological treatment tank and a second-stage biological treatment tank. In the apparatus disclosed in Patent Document 2, predation of bacteria by protozoa that is dispersed in flocked bacteria and held in the second-stage biological treatment tank in the subsequent stage by performing ultrasonic treatment or the like in a feed refinement tank Promote.

In addition, a method for reducing excess sludge by combining a fluidized bed method and an activated sludge method has been proposed (Patent Document 3). In the method disclosed in Patent Document 3, the biological treatment is performed by the fluidized bed method in the front-stage aeration tank, and then the BOD sludge load is 0.1 to 0.6 kg-BOD / kg-VSS / in the rear-stage biological treatment tank. Treated by activated sludge method as a day. In this method, high load treatment is possible by adding a carrier to the biological treatment tank on the front stage side, while self-digestion of activated sludge is promoted by lowering the BOD sludge load in the biological treatment tank on the rear stage side. And reduce the amount of excess sludge generated.
Japanese Patent Laid-Open No. 55-20649 JP-A-57-74082 Japanese Patent No. 3410699

  In the method described in Patent Document 3, sludge is reduced by utilizing self-digestion of activated sludge, but if the soluble BOD sludge load is lowered in order to promote self-digestion of activated sludge, the sedimentation property of sludge decreases. Therefore, there is a problem that the quality of treated water deteriorates.

  On the other hand, in the methods disclosed in Patent Document 1 and Patent Document 2, sludge is reduced by utilizing the predatory action of bacteria by a filtration predation type micro-organism that sucks and eats bacteria. In this method, sludge volume reduction and bacteria flocculation are promoted at the same time in the second-stage biological treatment tank that reduces sludge volume, thereby preventing sludge sedimentation from worsening. Can lose weight.

  However, in the methods disclosed in Patent Document 1 and Patent Document 2, it is difficult to adjust the processing conditions in the first-stage biological treatment tank and the second-stage biological treatment tank. In particular, when the treatment conditions in the first-stage biological treatment tank cannot be controlled within an appropriate range, not only the sludge reduction effect can be obtained but also the quality of the treated water may be deteriorated. For example, the biota retained in the second-stage biological treatment tank varies depending on the removal rate of soluble BOD in the first-stage biological treatment tank, and is constant in the micro-organism retention tank depending on the treatment conditions in the first-stage biological treatment tank. The amount of micro-organisms may not be maintained. Alternatively, when bacteria are larger than the diameter of the micro-organism, predation by the micro-organism does not proceed and the sludge reduction effect may be reduced.

  This invention is made in view of the said subject, and provides the biological treatment method of the organic wastewater which can obtain the treated water of favorable water quality, and also can obtain stably the sludge reduction effect by the predation action of a micro organism. For the purpose.

  The present inventors can grow dispersible bacteria in the aeration tank by controlling the concentration of dissolved oxygen (DO) in the aeration tank in the high load treatment process, and a predetermined amount of micro organisms can be added to the micro organism holding tank. It was found that the food necessary for holding can be stably supplied. In addition, the present inventors have found that a predetermined amount of micro organisms can be easily held in the micro organism holding tank by controlling so that the soluble BOD sludge load of the micro organism holding tank is within a certain range. .

  The present invention has been completed based on such knowledge, and the biological treatment tank is divided into a plurality of stages, and the DO concentration of the biological treatment tank (aeration tank) on the front stage is controlled, or the biological treatment tank on the rear stage (microorganism holding) By controlling the soluble BOD sludge load in the tank), the micro-organisms are stably grown in the micro-organism holding tank to reduce the excess sludge. More specifically, the present invention provides the following.

  (1) Introducing organic wastewater containing organic matter into an aeration tank and biologically treating it under aerobic conditions, and introducing a biological treatment liquid flowing out from the high load treatment process into a micro-organism holding tank A low-load treatment step for biological treatment, and either or both of the oxygen concentration of the aeration tank in the high-load treatment step and the soluble BOD sludge load on the micro-organism holding tank in the low-load treatment step An organic substance that generates dispersible bacteria using the organic substance as a substrate in the high-load treatment step, and that prey on the dispersible bacteria by the micro-organisms that inhabit the micro-organism holding tank in the low-load treatment step. Biological treatment method for effluent.

  In the low load treatment step, the soluble BOD sludge load on the micro organism holding tank is set to 0.025 kg-BOD / kg-VSS / day or more and 0.05 kg-BOD / kg-VSS / day or less (1). Biological treatment method for organic wastewater.

  (3) The biological treatment method for organic wastewater according to (1) or (2), wherein in the high-load treatment step, biological treatment is performed with a dissolved oxygen concentration in the aeration tank of 0.5 mg / L or less.

  (4) In the high load treatment step, the amount of the organic wastewater flowing into the aeration tank and the concentration of the organic matter contained in the organic wastewater are measured to obtain the amount of CODcr to be decomposed in the high load treatment step The biological treatment method for organic wastewater according to any one of (1) to (3), wherein an oxygen supply amount is controlled based on the amount of CODcr to be decomposed.

  (5) In any one of (1) to (4), in the high load treatment step, an oxygen deficiency period in which the dissolved oxygen concentration of the liquid in the aeration tank is 0 mg / L is provided by controlling an oxygen supply amount Biological treatment method of organic wastewater as described in 1.

  (6) In the high load treatment step, the oxygen depletion period is in a ratio of 0.25 or more and 1 or less to an aerobic period in which the dissolved oxygen concentration of the liquid in the aeration tank exceeds 0 mg / L. The biological treatment method for organic wastewater according to (5), wherein the supply amount is controlled.

  (7) The organic wastewater according to any one of (1) to (6), wherein the oxygen supply amount is controlled so that a difference between an oxygen consumption rate and an oxygen supply rate is 10% or less in the high load treatment step. Biological treatment method.

  (8) The biological treatment method for organic wastewater according to any one of (1) to (7), wherein the fine organisms are allowed to inhabit in the fine organism holding tank at a concentration of 5% or more of the sludge MLVSS.

  (9) The biological treatment method for organic wastewater according to any one of (1) to (8), wherein the organic wastewater bypassing the aeration tank is directly flowed into the microbiological tank.

  In the present invention, the effluent (biological treatment liquid) that is processed in the aeration tank and flows out from the high-load treatment step includes bacteria that have grown using organic substances contained in organic wastewater as substrates. In the present invention, such a biological treatment liquid is introduced into a micro organism holding tank, and sludge generation is reduced by predation of bacteria by micro organisms and self-digestion of bacteria. For this reason, the micro organism holding tank is operated under conditions suitable for holding a predetermined amount of micro organisms and allowing bacteria to aggregate.

  In order to hold a predetermined amount of micro-organisms in the micro-organism holding tank, the DO concentration of the aeration tank, which is the pre-stage biological treatment tank operated at high load, and the latter-stage bio-treatment tank operated at low load Control either or both of the soluble BOD loadings of the microbiological holding tank.

  When controlling the DO concentration in the aeration tank, the DO concentration is controlled so that dispersible bacteria dominate. The DO concentration of the liquid in the aeration tank can be controlled by adjusting the amount of oxygen supplied to the aeration tank. As a method of controlling the oxygen supply amount for predominating dispersible bacteria in the aeration tank, a DO meter is provided in the aeration tank, and the value of the DO meter is 0.5 mg / L or less, preferably 0.1 mg / L. Hereinafter, a method of adjusting the oxygen supply amount so as to be more preferably 0.05 mg / L or less can be mentioned.

  In addition, since oxygen supplied to the aeration tank is mainly used for organic matter decomposition and consumed, the amount of organic wastewater flowing into the aeration tank and the concentration of organic matter are measured, so the oxygen supply amount to the aeration tank is set. May be. That is, by obtaining the inflow amount of organic waste water and the concentration of organic matter, the amount of organic matter supplied to the aeration tank is obtained, and the amount of CODcr (organic matter expressed by chemical oxygen consumption) brought into the aeration tank can be grasped. Since 70 to 90% of soluble CODcr is mainly converted into dispersible bacteria in the aeration tank, 70 to 90% of soluble CODcr contained in the raw water (organic waste water) flowing into the aeration tank is a fungus. If the amount of oxygen required to oxidatively decompose CODcr obtained by subtracting the CODcr content of the bacterial cells when converted into the body is supplied to the aeration tank, the DO concentration in the aeration tank is kept at 0.5 mg / L or less. Dispersed bacteria can predominate. That is, if the yield of bacterial cells and the decomposability of the soluble CODcr of the target wastewater are obtained in advance, the optimum amount of oxygen to be supplied to the aeration tank can be determined even if the organic matter concentration of the organic wastewater that is the raw water changes. In addition, although the organic substance density | concentration contained in organic wastewater may be calculated | required as CODcr, calculating | requiring as BOD or total amount of organic substances (TOC) is not excluded.

  Or you may provide the period (oxygen deficiency period) which makes DO concentration of the liquid in the tank of an aeration tank substantially zero, such as temporarily stopping oxygen supply. By providing the oxygen-deficient period, it is possible to suppress the growth of bacteria whose length exceeds 5 μm and is in a form that is difficult to be preyed on by micro-organisms. The oxygen deficiency period can be set by means of intermittently supplying oxygen to the aeration tank (intermittent aeration) or temporarily reducing the oxygen supply amount. In particular, when the organic substance concentration fluctuation in organic wastewater is large (for example, when the fluctuation range is 50 to 150% or more), it is difficult to keep DO at a constant value, so the oxygen deficiency period It is preferable to suppress the growth of bacteria that are difficult to be preyed on by micro-organisms.

  The oxygen deficiency period is preferably set to be 0.25 to 1 times longer than the aerobic period (period in which the DO concentration exceeds 0 mg / L) in which the aeration tank is in an aerobic condition. The oxygen deficiency period is preferably 1 to 60 minutes, and particularly preferably within 2 minutes. The oxygen deficiency period and the aerobic period are preferably set alternately at intervals of several minutes, for example, at intervals of about 2 to 10 minutes. However, a time interval of 30 minutes or 1 hour is not excluded.

  In order to more precisely control the DO concentration, the oxygen supply amount may be controlled so that the difference between the oxygen consumption rate and the oxygen supply rate in the aeration tank is 10% or less, preferably 5% or less. Good. The oxygen consumption rate is calculated by temporarily stopping or reducing the oxygen supply amount after temporarily supplying excessive oxygen so that the DO concentration of the liquid in the aeration tank becomes 2 mg / L or more. Good. That is, the oxygen consumption rate can be calculated from the decrease rate of the DO concentration when oxygen is excessively supplied and when oxygen supply is suppressed. Since the oxygen consumption rate varies depending on the properties of organic wastewater, changes in processing conditions, and the like, it is preferable to calculate the oxygen consumption rate at least once per hour, specifically at intervals of 20 to 40 minutes.

  On the other hand, the reason for controlling the soluble BOD sludge load in the micro organism holding tank is as follows. If a large amount of organic matter is supplied to the micro organism holding tank, bacteria that grow using the organic matter as a substrate will proliferate in a form that avoids predation by micro organisms, and sufficient sludge reduction effect cannot be obtained, and if bacteria grow in filamentous form, There is also a risk of causing a bulking phenomenon. In addition, the number of micro-organisms that disassemble flocs increases, and the quality of treated water may deteriorate. On the other hand, if the amount of organic matter supplied to the micro-organism holding tank is insufficient, a predetermined amount of micro-organisms will not be retained in the micro-organism holding tank, and the sludge reduction effect will not be reduced. As a result of the decrease in sedimentation, the quality of treated water may be deteriorated.

  In order to prevent such a problem, in the present invention, the soluble BOD sludge load on the micro organism holding tank holding micro organisms is controlled, in particular 0.05 kg-BOD / kg-VSS / day or less, particularly 0.025 to 0.05 kg. -Control to be in the range of BOD / kg-VSS / day. In this invention, while controlling the soluble BOD sludge load of a micro organism holding tank, you may control DO density | concentration of an aeration tank as mentioned above.

  In addition, as a biological treatment system of the micro organism holding tank, an activated sludge method for returning the separated sludge by providing a solid-liquid separation device such as a sedimentation basin after the micro organism holding tank, and a separation membrane in the micro organism holding tank A membrane separation activated sludge method or the like can be used. Moreover, you may add the support | carrier suitable for hold | maintaining a micro organism and bacteria to a micro organism holding tank. As the carrier, various fluid fillers can be used, and the material and shape are not particularly limited. The filling rate of the carrier is preferably about 10 to 50% in bulk volume per tank.

  In addition, since micro-organisms have a slower growth rate than bacteria, the SRT (average sludge residence time) of the micro-organism holding tank is preferably 10 days or longer. However, if the SRT is too long, the micro organisms will be retained excessively in the micro organism holding tank, and a lot of micro organisms such as feces will accumulate. Therefore, if the SRT is 40 days or less, particularly 10 days or more and 30 days or less. Good. In addition, SRT is calculated | required by Numerical formula 1.

(Equation 1)
SRT (day) = amount of sludge in tank ÷ amount of extracted sludge

  Here, the amount of sludge in the tank is the existing amount of microorganisms (sludge) in the biological treatment tank, and is obtained from Equation 2. The amount of extracted sludge is the amount of microorganisms (sludge) discharged from the biological treatment tank, and is obtained from Equation 3.

(Equation 2)
Amount of sludge in tank = concentration of insoluble solid (SS) (mg / L) x tank volume (L)

(Equation 3)
Extracted sludge amount = insoluble solid (SS) concentration (mg / L) x sludge extracted amount (L / day)

  Further, in order to allow a predetermined amount of micro organisms to live in the micro organism holding tank, dispersible bacteria of 0.1% by weight or more, particularly about 5 to 20% by weight of the COD amount of the solid matter contained in the biological treatment liquid. Is preferably brought into the micro-organism holding tank. Furthermore, you may add the substance used as a nutrient of a micro organism to a micro organism holding tank. Substances containing lipids are particularly preferred as nutrients, and examples of lipids include phospholipids, free fatty acids, and sterols. Particularly, substances containing phospholipids such as lysophospholipids and lecithin can be suitably used. Specifically, rice bran, beer pomace, oil pomace, side dish, shellfish powder, eggshell, vegetable extract, fish extract, various amino acids, various vitamins, and the like can be used as nutrients. The addition amount is preferably 0.01 mg / L / day or more, particularly 0.1 to 10 mg / L / day per tank volume.

  It is preferable that the micro organisms inhabit the micro organism holding tank at a concentration of 5% or more of MLVSS. In the present specification, the term “microorganism” is a generic term for aquatic protozoa and metazoans that prey on bacteria, and protozoa include Paramecium and weevil, and metazoans include rotifers and nematodes. In particular, it is preferable to dominate micro organisms exhibiting predatory behavior of filtration and predation as micro organisms. Specifically, by controlling the soluble BOD sludge load on the micro organism holding tank as described above, the weevil and stag beetle are controlled. Is preferred. Moreover, MLVSS (Mixed Liquid Volatile Suspended Solid) means the concentration of sludge (organic matter) combusted at 600 ° C.

  According to the present invention, by controlling the DO concentration in the aeration tank, the dispersible bacteria that are easily preyed on by micro-organisms such as filtered predatory protozoa are prevalent, and the micro-organism retained in the micro-organism holding tank The amount of organisms can be stabilized. In the present invention, the biological treatment is performed at a high load in the aeration tank, while the soluble BOD sludge load on the microbiology holding tank holding the microbiology such as protozoa is reduced, thereby contributing to sludge reduction. The amount of micro-organisms can be stabilized. For this reason, according to this invention, the generation amount of excess sludge can be reduced stably and the treated water with low SS density | concentration can be obtained.

The schematic diagram of the biological treatment apparatus which concerns on the 1st embodiment for implementing this invention. The schematic diagram of the biological treatment apparatus which concerns on the 2nd embodiment for implementing this invention. The schematic diagram of the biological treatment apparatus which concerns on the 3rd embodiment for implementing this invention. The schematic diagram of the biological treatment apparatus which concerns on the 4th embodiment for implementing this invention. The schematic diagram of the biological treatment apparatus which concerns on the 5th embodiment for implementing this invention. 6 is a diagram illustrating a control pattern of an oxygen supply amount in Example 3. FIG. It is a figure which shows the result of the reference example 7.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Hereinafter, the same members are denoted by the same reference numerals, and description thereof is omitted or simplified. FIG. 1 is a schematic diagram of an organic wastewater biological treatment apparatus (hereinafter simply referred to as “treatment apparatus”) 11 used for carrying out the present invention. The processing apparatus 11 includes an aeration tank 21, a micro organism holding tank 31, and a sedimentation basin 41 as a solid-liquid separation means. In order to further promote sludge reduction, sludge floc separated from treated water in the sedimentation basin 41 is used. A sludge treatment tank 51 for biological treatment is further provided.

  The aeration tank 21 and the micro organism holding tank 31 are connected to each other in series by a first connection pipe 35, and the micro organism holding tank 31 and the sedimentation tank 41 are connected to each other in series by a second connection pipe 45. The sedimentation basin 41 and the micro-organism holding tank 31 are connected by a sludge return path 65 so that a part of the sludge separated in the sedimentation tank 41 is returned to the micro-organism holding tank 31 as return sludge. From the sludge return path 65, a sludge discharge path 56 and a treated sludge path 57 are branched, and a part of the sludge separated in the sedimentation basin 41 is sent from the treated sludge path 57 to the sludge treatment tank 51 and further reduced. The surplus is discharged from the sludge discharge channel 56 to the outside of the system.

  In this processing apparatus 11, first, organic wastewater such as sewage and industrial wastewater is introduced into the aeration tank 21 from the raw water channel 25 as treated water. In the aeration tank 21, the organic wastewater is mixed with the activated sludge retained in the tank, and a high load treatment process for biodegrading the organic matter contained in the organic wastewater is performed. In the aeration tank 21, biological treatment is performed while controlling the oxygen supply amount from the gas supply means (aeration pipe in this embodiment) 22 so that the DO concentration of the liquid in the tank is within a predetermined range, and the dispersible bacteria are favored. Fortune-telling. Although the control of the oxygen supply amount is as described in detail, it is preferable that the DO concentration of the liquid in the tank measured by the DO meter 23 is 0.5 mg / L or less.

  The aeration tank 21 controls the oxygen supply amount so that the ratio of dispersible bacteria to the cells is 50% or more, particularly 80 to 100%. In order to dominate dispersible bacteria precipitated by the filtered predation type micro-organism in the aeration tank 21, in addition to adjusting the DO concentration of the aeration tank 21, the HRT (hydraulic residence time of the aeration tank 21) ) Is preferably set short. Specifically, the HRT that can remove about 70 to 90% of the soluble organic matter contained in the organic wastewater that has flowed into the aeration tank 21 is an optimum value, and the HRT is within 0.75 to 1.5 times the optimum value. It is preferable to control so as to be within the range. Since the optimum value of HRT varies depending on the type of organic waste water, etc., it is preferable to obtain the optimum value of HRT in advance by a desktop test or the like. Generally, the HRT of the aeration tank 21 is preferably 24 hours or less, and particularly preferably 2 to 8 hours.

  As a method of maintaining the HRT within a certain range, when the amount of organic waste water flowing into the aeration tank 21 decreases, the amount of water entering the aeration tank 21 is returned by returning the treated water to the aeration tank 21. Examples thereof include a method and a method of changing the water level of the aeration tank 21 in accordance with the fluctuation of the amount of wastewater flowing into the aeration tank 21. HRT refers to the time from when the treated water flows into the biological treatment tank (aeration tank 21) until it flows out, and the volume (L) of the biological treatment tank (aeration tank 21) is defined as the treated water (organic). It is calculated by dividing by the flow rate (L / hour) of the waste water).

The aeration tank 21 performs biological treatment (high load treatment) with a higher organic load than the biological treatment (low load treatment) in the microorganism holding tank 31, and more specifically, the soluble BOD volume. The operation may be performed at a high load of 1 kg-BOD / m ³ / day or more, preferably 3 kg-BOD / m ³ / day or more and 20 kg-BOD / m ³ / day or less. This is because when the BOD volume load is increased, dispersive bacteria are likely to dominate by preventing flocculation of bacteria and dominance of filamentous bacteria, and the volume of the aeration tank 21 can be reduced.

  As a biological treatment system in the aeration tank 21, an arbitrary system such as a floating system or a fluidized bed system can be employed. The aeration tank 21 may be divided into two or more stages and may be a multistage type, or the sludge returned from the micro-organism holding tank 31 subsequent to the aeration tank 21 may be introduced. Further, a carrier may be added to the aeration tank 21.

  As the carrier, various fluid fillers can be used, and the material is not particularly limited. Specific examples of the carrier material include inorganic substances such as ash, sand, activated carbon, and ceramic, and synthetic substances and organic substances such as cellulose (including cellulose derivatives). Examples of synthetic resins include polyurethane, polyethylene, polypropylene, polystyrene, and polyvinyl alcohol. A foam obtained by appropriately mixing a foaming agent with these synthetic resins and foaming is suitably porous with a network structure. Can be used. Moreover, you may use the support | carrier which uses a gel-like substance as a raw material.

  The shape of the carrier is not limited, and examples thereof include a granular shape, a cylindrical shape, a honeycomb shape, a thread shape, and a corrugated shape. Examples of the granular carrier shape include a sphere, a pellet, and a rectangle. A carrier having a size of about 0.1 to 10 mm can be preferably used. In order to promote the production of dispersible bacteria, the filling rate of the carrier is preferably smaller than usual. Specifically, the bulk volume per aeration tank 21 is preferably 10% or less, particularly preferably 5% or less. .

  In the aeration tank 21, 70% or more, preferably 80% or more, more preferably 90% or more of the soluble BOD contained in the organic waste water is decomposed, and the pH is preferably 6 or more and 8 or less. However, the pH may exceed 8 when treating organic wastewater containing a large amount of oil (for example, 100 mg / L or more).

  In the aeration tank 21, a high-load treatment process for biodegrading most of the soluble BOD (for example, 70% or more) contained in the organic wastewater introduced as the treated water is performed. Since the aeration tank 21 is operated by adjusting the DO concentration by controlling the oxygen supply amount, a dispersive bacterium predominates, and a suspension (biological treatment liquid) containing unaggregated bacteria is present in the aeration tank 21. Spill from. The biological treatment liquid is introduced into the micro organism holding tank 31 via the first connection pipe 35.

  In the micro-organism holding tank 31, a low-load treatment process is performed in which oxygen-containing gas is supplied from the gas supply means 32 and biological treatment is performed under aerobic conditions. It is preferable that the pH of the liquid in the micro organism holding tank 31 is about 4 to 8. In the micro organism holding tank 31, the amount of sludge generated is reduced by predation of bacteria by the micro organisms and self-digestion of the bacteria, and the flocculation of dispersible bacteria is promoted. For this reason, the micro organism holding tank 31 is preferably operated under conditions suitable for holding a predetermined amount of micro organisms and allowing bacteria to aggregate.

  In particular, in the present invention, by supplying a biological treatment liquid containing dispersible bacteria predominated in the aeration tank 21, it is possible to inhabit the micro-organism holding tank 31 with micro-organisms at a concentration of 5% or more of the sludge MLVSS. it can.

  The microbiological storage tank 31 has a soluble BOD sludge load with respect to the microbiological storage tank 31 of 0.05 kg-BOD / kg-VSS / day or less, particularly in the range of 0.025-0.05 kg-BOD / kg-VSS / day. It is good to drive as. This is in order to prevent bacteria in the form of filaments and the like that are difficult to be preyed on by the micro-organisms in the micro-organism holding tank 31, and to preferentially inhabit the microbes of the filter predation type. Moreover, in order to retain the micro organisms whose growth rate is slower than that of the bacteria in the micro organism holding tank 31, the SRT is preferably set to 24 hours or more, particularly 10 days or more. However, if the SRT is too long, the micro organisms are excessively held in the micro organism holding tank 31 and a lot of micro organisms such as feces accumulate, so the SRT is 40 days or less, particularly 10 days or more and 30 days or less. Good.

  Furthermore, in order to secure the food of micro organisms that inhabit the micro organism holding tank 31, 0.1% by weight or more of the amount of solid CODcr (organic matter expressed by chemical oxygen consumption) contained in the biological treatment liquid, In particular, it is preferable that about 5 to 20% by weight of soluble CODcr is brought into the micro organism holding tank. Furthermore, you may add the substance used as a nutrient of a micro organism to the micro organism holding tank 31. FIG. Substances containing lipids are particularly preferred as nutrients, and examples of lipids include phospholipids, free fatty acids, and sterols. Particularly, substances containing phospholipids such as lysophospholipids and lecithin can be suitably used. Specifically, rice bran, beer pomace, oil pomace, side dish, shellfish powder, eggshell, vegetable extract, fish extract, various amino acids, various vitamins, and the like can be used as nutrients. The addition amount is preferably 0.01 mg / L / day or more, particularly preferably 0.1 to 10 mg / L day per tank volume.

  The biological treatment system of the micro organism holding tank 31 is other than the activated sludge method in which solid-liquid separation means such as a sedimentation basin 41 is provided at the subsequent stage of the micro organism holding tank 31 and the separated sludge is returned as in this embodiment. In addition, a membrane separation activated sludge method or the like in which a separation membrane is provided in a micro organism holding tank can be used. Furthermore, a carrier suitable for holding a micro organism in the micro organism holding tank can be added to the micro organism holding tank 31. A support | carrier is not specifically limited, The support | carrier mentioned above can be used, and it is preferable that a filling rate shall be about 10 to 40% by bulk volume per tank.

  In the micro-organism holding tank 31, the dispersible bacteria contained in the biological treatment liquid that has flowed out of the aeration tank 21 are reduced by predation and self-digestion by the micro-organisms. As a result, in the micro-organism holding tank 31, bacteria that become surplus sludge are consumed and the sludge is reduced, and sludge flocs are formed by agglomeration of the bacteria and flocking.

  The liquid containing the sludge floc flows out from the micro organism holding tank 31 and is introduced into the sedimentation basin 41 through the second connection pipe 45 and separated from the treated water. The treated water is taken out from the treated water passage 55 connected to the outlet side of the sedimentation basin 41, and a part of the separated sludge is returned from the sludge return passage 65 to the micro organism holding tank 31. In the processing apparatus 11 which concerns on this embodiment, a part of sludge isolate | separated by the sedimentation basin 41 is sent to the sludge processing tank 51 from the process sludge path 57, and sludge is reduced biologically. A part of the sludge separated in the sedimentation basin 41 may be returned to the aeration tank 21.

  The sludge treatment tank 51 may have the same configuration as the microorganism holding tank 31. Specifically, in the sludge treatment tank 51, an oxygen-containing gas such as air is supplied from a gas supply means 52 such as an air diffuser, the micro organisms are grown, and the amount of sludge generated is further reduced by utilizing the predation action of the micro organisms. To do. A carrier may be added to the sludge treatment tank 51 in the same manner as the microorganism holding tank 31, and a nutrient may be added to promote the growth of microorganisms.

  Of the sludge floc that could not be processed in the sludge treatment tank 51 and / or the sludge drawn out from the sedimentation basin 41, the remaining parts except for the part returned to the micro-organism holding tank 31 and the part sent to the sludge treatment tank 51 The sludge flock may be discharged out of the system from the sludge discharge path 56.

  The present invention promotes the growth of dispersible bacteria in the aeration tank 21 by controlling the amount of oxygen supplied to the aeration tank 21, and the above embodiment can be modified as appropriate. For example, as shown in FIG. 2, using the treatment device 12 provided with a flow meter 26 in the raw water channel 25, the aeration tank 21 uses the amount of organic wastewater flowing into the aeration tank 21 and the organic matter concentration of the organic wastewater. The oxygen supply amount may be controlled by obtaining the required oxygen amount.

  A carrier can be added to either one or both of the micro organism holding tanks 31. Preferred types and filling rates of carriers added to each tank are as described above. In FIG. 3, the schematic diagram of the processing apparatus 13 which added the support | carrier 58 to the aeration tank 21 is shown. Further, a nutrient or the like may be added in order to promote the growth of micro organisms in the micro organism holding tank 31. Furthermore, the sludge treatment tank 51 may be configured to chemically reduce sludge by blowing ozone or the like, or may be configured to physically reduce sludge by mechanical crushing or the like.

  Next, with reference to FIG. 4 and FIG. 5, the method of stabilizing the amount of micro-organisms by controlling the soluble BOD sludge load of the micro-organism holding tank 31 will be described. The processing apparatus 14 of FIG. 4 includes an aeration tank 21, a micro organism holding tank 31, and a sedimentation tank 41 as a solid-liquid separation unit. In this processing apparatus 14, instead of controlling the DO concentration in the aeration tank 21, by controlling the soluble BOD sludge load on the microorganism holding tank 31, the microorganism holding capacity in the microorganism holding tank 31 is stabilized. The DO concentration is not provided in the aeration tank 21 as the DO concentration in the aeration tank 21 is not particularly controlled. However, in order to promote the generation of dispersible bacteria in the aeration tank 21 as described above, the dissolved oxygen concentration in the aeration tank 21 should not be too high, and the DO in the aeration tank 21 in the processing apparatus 14 is 0.5 mg / L. The following is preferable.

  In the processing apparatus 14, it controls so that the soluble BOD sludge load of the micro organism holding tank 31 may be in a predetermined range, specifically, the soluble BOD sludge load is 0.05 kg-BOD / kg-VSS / day or less. To do. Moreover, it is preferable that the micro-organism holding tank 31 is operated at an aerobic condition by supplying an oxygen-containing gas from the gas supply means 32 at a pH of 5 to 8. In the processing apparatus 14, the micro-organism holding tank 31 is operated for 12 hours or more and 40 days or less, preferably 30 days or less, more preferably about 10 to 30 days in order to grow micro-organisms with a slow growth rate. . In the micro-organism holding tank 31, it is preferable to circulate a part of the solid content (sludge) separated from the liquid in the subsequent sedimentation basin 41 as return sludge. Or it is good also as a membrane separation system which hold | maintains sludge in a tank by providing a separation membrane in the micro-organism holding tank 31. Moreover, the micro organism holding tank 31 may be a fluidized bed type by filling the carrier. In this case, the carrier filled in the micro organism holding tank 31 is not particularly limited, and the above-described carrier can be used.

  A biological treatment liquid mainly containing dispersible bacteria flows out from the aeration tank 21 and flows into the micro-organism holding tank 31. The micro-organism holding tank 31 holds micro-organisms, and dispersible bacteria contained in the biological treatment liquid flowing out from the aeration tank 21 are reduced by predation and self-digestion by the micro-organisms. Further, in the micro organism holding tank 31, bacteria also grow using the remaining organic substances contained in the biological treatment liquid as a substrate. However, since the soluble BOD sludge load on the micro organism holding tank 31 is low, the growth of bacteria in the micro organism holding tank 31. It remains to the extent that it is consumed as a bait necessary to maintain the number of micro-organisms retained.

  As a result, a predetermined amount of micro-organisms is held in the micro-organism holding tank 31, and bacteria that become surplus sludge are consumed to reduce sludge, and sludge flocs are formed by agglomeration of flocs and aggregation of bacteria. The sludge floc has an SVI (sedimentation volume ml per gram of sludge) of about 150 or less, and is easily separated from the liquid in the sedimentation basin 41.

  The liquid containing the sludge floc flows out from the micro organism holding tank 31 and is introduced into the sedimentation basin 41 through the second connection pipe 45 and separated from the treated water. The treated water is taken out from the treated water passage 55 connected to the outlet side of the sedimentation basin 41, and at least a part of the separated sludge is returned to the micro-organism holding tank 31 from the sludge return passage 65. Part of the sludge separated in the sedimentation basin 41 may be discharged out of the system as excess sludge from the sludge discharge path 56 branched from the sludge return path 65. Further, a part of the returned sludge may be returned to the aeration tank 21. A sludge treatment tank (not shown) for introducing excess sludge and reducing the sludge by a biological, chemical, or physical method is provided. You may provide in the processing apparatus 14, and may further reduce the excess sludge generation amount.

  The present invention introduces a biological treatment liquid containing dispersible bacteria generated by performing biological treatment under a high load into the microbiological holding tank 31, and sets the soluble BOD sludge load within a predetermined range to produce microbiologicals. The sludge is flocculated and reduced in weight through the predatory action of the above, and the above embodiment can be modified as appropriate. For example, a carrier can be added to one or both of the aeration tank 21 and the microorganism holding tank 31. Preferred types and filling rates of carriers added to each tank are as described above. Further, a nutrient or the like may be added in order to promote the growth of micro organisms in the micro organism holding tank 31.

  Furthermore, as shown in FIG. 5, the raw water channel 25 may be branched, and a part of the raw water may be directly flowed into the micro organism holding tank 31. Thus, by setting it as the apparatus structure which supplies a part of raw | natural water to the micro-organism holding tank 31 not via the aeration tank 21, the decomposition rate of the soluble BOD contained in the raw water introduced into the aeration tank 21 is increased. The amount of raw water to be bypassed to the micro organism holding tank 31 can be adjusted in consideration. For this reason, in the processing apparatus 15 shown in FIG. 5, it becomes easy to adjust the operating conditions of the micro organism holding tank 31 so as to be suitable for holding micro organisms and flocking.

[Example 1]
Hereinafter, the present invention will be described in more detail based on examples. As Example 1, artificial wastewater (COD _cr concentration 1,200 mg / L, soluble BOD concentration 600 mg / L, soluble CODcr concentration 1,100 mg / L) was used as the water to be treated using the treatment device 11 shown in FIG. Experimented. The aeration tank 21 had a capacity of 3.6 L, pH 7.0, HRT 4 hours, and was operated without returning sludge. In the aeration tank 21, since 80% of the soluble CODcr contained in the water to be treated and the total CODcr concentration are reduced by 30%, the oxygen supply amount is controlled based on the total CODcr amount decomposed in the aeration tank 21, and the liquid in the tank The DO concentration was 0.01 mg / L.

  The micro-organism holding tank 31 was operated with a capacity of 15 L, an MLVSS concentration of 3,900 mg / L, pH 7, a soluble BOD sludge load of 0.044 kg-BOD / kg-VSS / day, and an HRT of 17 hours. Oxygen was supplied to the micro-organism holding tank 31 so that the DO in the tank was 2 to 3 mg / L. A part of the sludge floc separated in the sedimentation basin 41 was returned to the micro-organism holding tank 31 through the sludge return path 55. In the first embodiment, the sludge treatment tank 51 is not used, and the remaining part of the sludge floc separated in the sedimentation basin 41 excluding the part returned to the micro-organism holding tank 31 is taken as surplus sludge from the sludge discharge passage 55 to the outside of the system. Discharged.

  As a result of the treatment under the above conditions, in the aeration tank 21, the proportion of the dispersed bacteria having a length of about 1 to 5 μm with respect to the bacterial cell SS is about 80%, and the dispersive bacteria are proliferated preferentially. I was able to. In addition, the living organism 31 is predominantly inhabited at a concentration of 100,000 to 130,000 pieces / ml (10 to 13% of MLVSS), and the conversion rate of BOD sludge contained in the treated water Was 0.15 kg-MLSS / kg-BOD, and the SS concentration of treated water taken out from the sedimentation basin 41 was kept at about 20 mg / L or less.

[Example 2]
The test was performed under the same conditions as in Example 1 except that the oxygen supply to the aeration tank 21 was intermittently performed. That is, in Example 1, the oxygen supply to the aeration tank 21 was continuously performed, whereas in Example 2, the oxygen supply to the aeration tank 21 was intermittently performed, and the DO in the liquid in the aeration tank 21 was reduced. The aerobic period of 2 mg / L was 1 minute, the oxygen depletion period of 0 mg / L of DO in the tank was 1 minute, and the period of DO between 0 and 2 mg / L (referred to as the transition period) was 2 minutes .

  As a result, in the aeration tank 21, the proportion of the dispersed bacteria having a length of about 1 to 5 μm with respect to the bacterial cells SS was about 70%, and the dispersible bacteria could be proliferated predominately. In addition, worms predominately in the micro organism holding tank 31 at a concentration of about 100,000 / ml, and the sludge conversion rate of BOD contained in the treated water is 0.20 kg-MLSS / kg-BOD, The SS concentration of treated water taken out from the sedimentation basin 41 changed at about 20 mg / L or less.

[Example 3]
Since the oxygen consumption rate in the aeration tank 21 was calculated, the test was performed under the same conditions as in Example 1 except that the required oxygen amount required for biological treatment from the aeration tank 21 was determined and the oxygen supply amount was controlled. Specifically, once the oxygen supply amount to the aeration tank 21 is increased once in an hour so that the DO concentration of the liquid in the aeration tank 21 temporarily exceeds 2 mg / L (for 2 minutes), oxygen The supply rate was temporarily reduced (or stopped), and the oxygen consumption rate was determined from the rate of decrease in the DO concentration of the liquid in the tank. FIG. 6 shows an oxygen supply amount control pattern in the third embodiment. In this example, based on the oxygen consumption rate thus obtained, the oxygen supply rate was controlled so that the DO concentration in the aeration tank 21 was 0.01 mg / L.

  As a result, in the aeration tank 21, the proportion of the dispersed bacteria having a length of about 1 to 5 μm with respect to the bacterial cell SS was about 90%, and the dispersible bacteria could be proliferated preferentially. In addition, worms predominately live in the micro-organism holding tank 31 at a concentration of about 100,000 to 130,000 / ml, and the sludge conversion rate of BOD contained in the treated water is 0.15 kg-MLSS / The SS concentration of the treated water taken out from the kg-BOD and the sedimentation basin 41 changed at about 20 mg / L or less.

[Reference Example 1]
In Reference Example 1, the DO concentration control in the aeration tank 21 was examined. Specifically, the DO concentration of the liquid in the tank of the aeration tank 21 was the same value as that of the microorganism holding tank 31, that is, 2 to 3 mg / L. In the aeration tank 21, filamentous bacteria having a length of about 10 to 50 μm grew more dominant than dispersed bacteria having a diameter of about 1 to 5 μm, and predation by micro-organisms became difficult. As a result, the concentration of micro-organisms in the micro-organism holding tank 31 is reduced to a concentration of 10,000 to 20,000 / ml (1-2% of MLVSS), and the sludge conversion rate of BOD contained in the treated water is The SS concentration of the treated water taken out from 0.30 kg-MLSS / kg-BOD and sedimentation basin 41 was about 30 mg / L.

[Example 4]
The aeration tank 21 was filled with a 5 mm square sponge carrier 58 at a bulk volume ratio of 5% with respect to the aeration tank 21, and the test was performed using the processing apparatus 13 of FIG. In Example 4, the conditions were the same as in Example 1 except that the aeration tank 21 was filled with the carrier 58, and the oxygen concentration was controlled to control the DO concentration in the aeration tank 21 to be 0.01 mg / L. . As a result, in the aeration tank 21, the proportion of dispersed bacteria having a length of about 1 to 5 μm with respect to the bacterial cell SS was about 80%, and the dispersible bacteria could be predominately grown. In addition, worms predominately live in the micro-organism holding tank 31 at a concentration of 100,000 to 130,000 / ml, and the sludge conversion rate of BOD contained in the treated water is 0.15 kg-MLSS / The SS concentration of treated water taken out from the kg-BOD and sedimentation basin 41 changed at about 20 mg / L or less.

  In Example 4, the flow rate of the organic waste water that flows into the aeration tank 21 after one month from the start of the test is halved, the BOD volumetric load on the aeration tank 21 is halved, and the sedimentation basin is passed through the treated water return path 42. In 41, the treated water separated from the sludge floc was returned to the aeration tank 21. The amount of treated water returned was the same as the decrease in organic wastewater. Thus, after continuing the process which reduced the to-be-processed water flow rate for 12 hours, it returned to the to-be-processed water flow rate, and repeated repeating the process to stop the return of treated water for 12 hours. During this time, the HRT of the aeration tank 21 was maintained substantially constant by returning the treated water when the treated water flow rate decreased. During this time, the dominant state of the dispersible bacteria is maintained in the aeration tank 21, the sludge conversion rate can be maintained at the above-mentioned value, and the concentration of the worm beetles in the microorganism holding tank 31 is about 100,000 to 130,000 / ml. Value was maintained.

[Reference Example 2]
In Reference Example 2, the test was performed under the same conditions as in Example 4 except that the treated water was not returned when the treated water flow rate was reduced in Example 4. In Reference Example 1, as a result of continuing the test of repeating the process of reducing the treated water flow rate for 12 hours and returning the flow rate for the next 12 hours for 3 days, the dispersion state that predominately existed in the aeration tank 21 Instead of bacteria, filamentous bacteria having a length of about 20 to 1,000 μm became dominant. Moreover, in the micro organism holding tank 31, the beetle decreased to about 12,000 pieces / mL, and the sludge conversion rate increased to 0.40 kg-MLSS / kg-BOD. Moreover, the SS concentration of the treated water taken out from the sedimentation basin 41 was about 40 mg / L.

  The results of Examples 1 to 4 and Reference Examples 1 and 2 are shown in Table 1.

  As described above, according to the present invention, dispersible bacteria are dominant in the aeration tank 21, and the amount of surplus sludge generated using the predatory action of the micro-organisms in the micro-organism holding tank 31 provided downstream of the aeration tank 21. Could be reduced.

[Reference Example 3]
Next, Reference Example 3 for controlling the soluble BOD sludge load on the micro-organism holding tank 31 will be described. In Reference Example 3, an experiment was conducted using artificial waste water (COD _cr concentration of 1,000 mg / L, soluble BOD concentration of 640 mg / L) as the water to be treated, using the treatment device 15 shown in FIG. The aeration tank 21 was operated with a capacity of 3.6 L, pH 7, HRT 4 hours, DO concentration of about 1.0 mg / L and no return sludge. The micro-organism holding tank 31 has a capacity of 15 L and was operated at pH 7, MLVSS 3,700 mg / L, and HRT 17 hours. The decomposition rate of the soluble BOD in the aeration tank 21 is about 95%, and a part of the raw water is directly introduced from the bypass 26 to the micro-organism holding tank 31, so that the amount of sludge in the micro-organism holding tank 31 is reduced. The soluble BOD sludge load was 0.03 kg-BOD / kg-VSS / day. In Reference Example 3, the soluble BOD volumetric load in the entire biological treatment tank including the aeration tank 21 and the microbiological holding tank 31 was 0.75 kg / m ³ / day, and HRT was 21 hours.

  As a result of the treatment under the above conditions, stag beetles predominately live at a concentration of 50,000 / ml (15% of MLVSS) in the micro organism holding tank 31 and convert BOD sludge contained in the treated water. The rate was 0.20 kg-MLSS / kg-BOD. Moreover, the SS concentration of the treated water taken out from the sedimentation basin 41 changed at about 10 mg / L.

[Reference Example 4]
Tested under the same conditions as in Reference Example 3 except that the direct introduction of raw water into the micro-organism holding tank 31 was stopped and the soluble BOD sludge load on the micro-organism holding tank 31 was changed to 0.01 kg-BOD / kg-VSS / day. Went. As a result, the number of micro-organisms in the micro-organism holding tank 31 was 1,000 / mL (1% of MLVSS) or less, and sludge reduction and flocking due to the predation of micro-organisms did not proceed. For this reason, in Reference Example 4, the sludge conversion rate of BOD contained in the water to be treated was 0.30 kg-MLSS / kg-BOD as BOD, and the SS concentration of treated water was 30 mg / L.

[Reference Example 5]
The test was performed under the same conditions as in Reference Example 3 except that the amount of raw water inflow into the micro-organism holding tank 31 was increased and the soluble BOD sludge load for the micro-organism holding tank 31 was set to 0.1 kg-BOD / kg-VSS / day. It was. As a result, bacteria grew in the form of filaments in the micro-organism holding tank 31 and became difficult to be preyed on by the micro-organisms, and the number of micro-organisms became 1,000 or less / mL. For this reason, sludge reduction and flocification due to the predatory action of micro-organisms did not proceed, and in Reference Example 5, the sludge conversion rate of BOD contained in the water to be treated was 0.40 kg-MLSS / kg-BOD as BOD. In Reference Example 5, the SS concentration of treated water was 10 mg / L, but due to the growth of filamentous bacteria, the compactness of the sludge decreased and the SVI was 220.

[Reference Example 6]
The test was performed under the same conditions as in Reference Example 3 except that the amount of raw water inflow into the micro-organism holding tank 31 was increased and the soluble BOD sludge load on the micro-organism holding tank 31 was set to 0.08 kg-BOD / kg-VSS / day. It was. As a result, the number of micro organisms in the micro organism holding tank 31 was also 30,000 / mL (7% of MLVSS). For this reason, the sludge conversion rate of BOD contained in to-be-processed water became 0.20kg-MLSS / kg-BOD as BOD. However, the dominant micro-organism was a floc predatory type worm that feeds like flocs, so flocs were swollen and the SS concentration of treated water was 120 mg / L.

  The results of Reference Examples 3 to 6 are shown in Table 2.

  As shown in Table 2, by controlling the soluble BOD sludge load in the micro-organism holding tank 31, it was possible to reduce the amount of surplus sludge generated using the predation action of micro-organisms. Moreover, since the flocification of bacteria was accelerated | stimulated in the micro-organism holding tank 31, and the sludge floc with favorable sedimentation was able to be produced | generated, the treated water of favorable water quality was obtained.

[Reference Example 7]
As Reference Example 7, the number of micro organisms in the micro organism holding tank 31 when the soluble BOD sludge load on the micro organism holding tank 31 was varied was examined. The results are shown in FIG.

  As shown in FIG. 7, a filtration predation type micro inhaling and precipitating dispersible bacteria by setting the soluble BOD sludge load to the micro organism holding tank 31 to about 0.05 kg-BOD / kg-VSS / day or less. We were able to dominate the creatures. For this reason, disintegration of sludge floc can be prevented and treated water with good water quality can be obtained by setting the soluble BOD sludge load to the micro organism holding tank 31 to 0.05 kg-BOD / kg-VSS / day or less. It has been shown.

  The present invention can be used for biological treatment of organic wastewater such as sewage.

Claims (9)

A high-load treatment process in which organic wastewater containing organic matter is introduced into an aeration tank and biologically treated under aerobic conditions;
A low-load treatment step of introducing a biological treatment liquid flowing out from the high-load treatment step into a micro-organism holding tank and biologically treating it,
Controlling one or both of the oxygen concentration of the aeration tank in the high load treatment step and the soluble BOD sludge load on the microorganism holding tank in the low load treatment step;
Organic wastewater organisms that produce dispersible bacteria using the organic matter as a substrate in the high-load treatment step, and that prey on the dispersible bacteria by micro-organisms that inhabit the micro-organism holding tank in the low-load treatment step Processing method.   The soluble BOD sludge load with respect to the micro organism holding tank is 0.025 kg-BOD / kg-VSS / day or more and 0.05 kg-BOD / kg-VSS / day or less in the low load treatment step. Biological treatment method for organic wastewater.   The biological treatment method for organic wastewater according to claim 1 or 2, wherein in the high load treatment step, biological treatment is performed with a dissolved oxygen concentration in the aeration tank being 0.5 mg / L or less. In the high load treatment step, the amount of the organic waste water flowing into the aeration tank and the concentration of the organic matter contained in the organic waste water are measured to determine the amount of CODcr to be decomposed in the high load treatment step. The biological treatment method for organic wastewater according to any one of claims 1 to 3, wherein the oxygen supply amount is controlled based on the amount of CODcr to be produced.   5. The organic substance according to claim 1, wherein, in the high-load treatment step, an oxygen deficiency period in which the dissolved oxygen concentration of the liquid in the aeration tank is 0 mg / L is provided by controlling an oxygen supply amount. Biological treatment method of wastewater.   In the high load treatment step, the oxygen supply amount is adjusted so that the ratio of the oxygen deficiency period to the aerobic period in which the dissolved oxygen concentration of the liquid in the aeration tank exceeds 0 mg / L is 0.25 or more and 1 or less. The biological treatment method for organic wastewater according to claim 5 to be controlled.   The biological treatment method for organic wastewater according to any one of claims 1 to 6, wherein the oxygen supply amount is controlled so that a difference between an oxygen consumption rate and an oxygen supply rate is 10% or less in the high load treatment step.   The biological treatment method of organic wastewater according to any one of claims 1 to 7, wherein the micro organisms are allowed to inhabit in the micro organism holding tank at a concentration of 5% or more of sludge MLVSS.   The biological treatment method for organic wastewater according to any one of claims 1 to 8, wherein the organic wastewater that has bypassed the aeration tank directly flows into the microbiological tank.