KR20090046794A - Method and apparatus for biological treatment of organic of organic wastewater - Google Patents

Abstract

An object of this invention is to stabilize the sludge loss effect in the multistage active sludge method using the feeding effect of a micro animal. The organic wastewater is introduced into the first biological treatment tank 1 equipped with aeration means, and survives in ordinary raw water, such as, for example, genus Alkogenes, Pseudomonas, Bacillus, Aerobacter, and Flavobacterium. At least 70%, preferably at least 80%, more preferably at least 90% of the organic components (soluble BOD) are oxidatively decomposed by the bacteria. The treated water of the first biological treatment tank 1 is introduced into the second biological treatment tank 2, where surpluses by oxidative decomposition of remaining organic components, self-decomposition of dispersible bacteria, and predation of micro-animals are carried out. The sludge is reduced. The second biological treatment tank 2 uses a fluidized bed in which a carrier (C) is added to increase the amount of oil in the tank of the micro-animal.

Description

METHOD AND APPARATUS FOR BIOLOGICAL TREATMENT OF ORGANIC OF ORGANIC WASTEWATER}

The present invention relates to a biological treatment method and apparatus for organic wastewater that can be used for organic wastewater treatment in a wide range of concentrations, including domestic wastewater, sewage, food factories and pulp mills, and in particular, treatment efficiency without deteriorating the treated water quality. In addition, the present invention relates to a biological treatment method and apparatus for organic wastewater capable of reducing the amount of surplus sludge generated.

The activated sludge method used in the case of organic treatment of organic wastewater has been widely used for sewage treatment, industrial wastewater treatment, and the like from the advantages of good treatment water quality and easy maintenance. However, since the BOD volume load used for operation is about 0.5 to 0.8 kg / m 3 / d, a large site area is required. In addition, since 20 to 40% of the decomposed BOD is converted into cells or sludge, a large amount of surplus sludge treatment also becomes a problem.

As for the high load treatment of organic wastewater, a fluidized bed method in which a carrier is added is known. When this method is used, it becomes possible to operate with BOD volume load of 3 kg / m <3> / d or more. However, the amount of sludge generated is about 30% of the decomposed BOD, and the disadvantage is that the amount of sludge generated is higher than that of the normal activated sludge method.

In Japanese Patent Publication No. 55-20649, organic wastewater is first treated with bacteria in a first treatment tank, and organic matter contained in the wastewater is oxidatively decomposed and converted into cells of non-aggregated bacteria, followed by sticking progeny in a second treatment tank. It is said that it is possible to reduce the surplus sludge by preserving and removing animals. In addition, in the above method, high load operation is possible, and the treatment efficiency of the activated sludge process is also improved. As described above, a number of wastewater treatment methods have been devised using the preservation of protozoa and welfare animals which are located at high levels of bacteria.

Japanese Patent Application Laid-Open No. 2000-210692 proposes a countermeasure against deterioration in treatment performance due to fluctuations in the water quality of raw water, which is a problem in the treatment method of Japanese Patent Publication No. 55-20649. As a specific method, "adjust the BOD fluctuation of the to-be-processed water within 50% from the median value of average concentration", "measure the quality of the water in the 1st treatment tank and the 1st treated water as time passes", or "the 1st At the time of deterioration of the water quality of a treated water, the method of adding a microbial agent or a sludge to a 1st treatment tank "is mentioned.

In Japanese Patent Application Laid-Open No. 60-23832, the above-mentioned foods are treated by ultrasonic treatment or mechanical agitation when feeding the first settled sludge or surplus sludge from the treatment of bacteria, yeast, actinomycetes, seaweeds, molds or wastewater to protozoa or welfare animal. It has been proposed to reduce the size of the flock to the mouth of the animal.

Patent 3410699 is a patent relating to the multi-stage treatment of fluidized bed and activated sludge process. In this method, the activated sludge method of the latter stage is operated by the low load of BOD sludge load 0.1 kg-BOD / kg-MLSS / d, and it can self-oxidize sludge, and can reduce a sludge discharge amount significantly.

Patent Document 1: Japanese Patent Laid-Open No. 55-20649

Patent Document 2: Japanese Patent Laid-Open No. 2000-210692

Patent Document 3: Japanese Patent Publication No. 55-20649

Patent Document 4: Japanese Patent Publication No. 60-23832

Patent Document 5: Japanese Patent No. 3410699

The multi-stage activated sludge method using the preservation action of micro-animals such as protozoa and welfare animals is actually used for organic wastewater treatment, and the treatment efficiency is improved and the amount of generated sludge is reduced by 50% depending on the target wastewater. Is possible. However, this sludge reduction effect is not stable at present. This is because a method of maintaining a stable animal is not established.

Disclosure of the Invention

An object of the present invention is to stabilize the sludge reduction effect in the multi-stage activated sludge method using the feeding action of a micro animal.

In the biological treatment method of the organic wastewater of the present invention, two or more biological treatment tanks are passed through the organic wastewater to the first biological treatment tank, and the biological treatment is performed by the bacteria, and the bacteria in the dispersed state from the first biological treatment tank are treated. A biological treatment method in which a first treatment water to be introduced is biologically treated by introducing into a second biological treatment tank and microanimals are present in the second biological treatment tank, wherein the dissolved oxygen concentration of the first biological treatment tank is 0.5 mg / l or less. The second biological treatment tank is used as a fluidized bed having a carrier, and the treated water of the second biological treatment tank is subjected to solid-liquid separation.

An organic wastewater treatment apparatus of the present invention comprises two or more biological treatment tanks, and passes organic wastewater to the first biological treatment tank, and biologically treats them with bacteria, and includes bacteria in a dispersed state from the first biological treatment tank. In the biological treatment apparatus which introduce | transduces the said 1st treated water into a 2nd biological treatment tank, and makes a micro animal exist in this 2nd biological treatment tank, The dissolved oxygen concentration of a 1st biological treatment tank is 0.5 mg / L or less And control means for controlling, means for forming a fluidized bed of carrier in the second biological treatment tank, and solid-liquid separation means for solid-liquid separation treatment of the second biological treatment tank treatment water.

1 is a flowchart of the first embodiment.

2 is a flowchart of the second embodiment.

3 is a flowchart of a third embodiment.

4 is a flowchart of a fourth embodiment.

5 is a flowchart of a comparative example.

In this invention, since the dissolved oxygen concentration of the 1st biological treatment tank was made into 0.5 mg / L or less, dispersion bacteria of about 1-5 micrometers are prioritized in a 1st biological treatment tank. This 1-5 micrometer dispersion bacterium is rapidly fed by a micro animal in a second biological treatment tank.

Moreover, in this invention, since the 2nd biological treatment tank was made into the fluidized bed which has a support | carrier, the holding amount in the tank of a micro animal can be raised. That is, since this carrier functions as the chief of the adherent filtration predatory micro-animals which preys on dispersed bacteria, this micro-animal can be stably maintained in a tank.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment is described with reference to FIGS.

1 is a schematic diagram of the basic flow of the invention. The organic wastewater is introduced into the first biological treatment tank 1 equipped with aeration means, and for example, ordinary genus such as alkali genus bacteria, Pseudomonas bacteria, Bacillus bacteria, aerobacter bacteria, and Flavobacterium bacteria. At least 70%, preferably at least 80%, more preferably at least 90% of the organic components (soluble BOD) are oxidatively degraded by the bacteria that survive in the wastewater.

The pH of the first biological treatment tank 1 is 6 or more, preferably 8 or less. However, when many oil components are contained in raw water, pH may be 8.0 or more.

In the present invention, 1 to 5 by controlling the dissolved oxygen (DO) concentration of the first biological treatment tank 1 to 0.5 mg / l or less, preferably 0.1 mg / l or less, more preferably 0.05 mg / l or less. Dispersed bacteria of μm dominate, and they are rapidly fed in the second biological treatment tank.

This DO concentration can be adjusted by controlling the amount of aeration.

By controlling the BOD volume load of the first biological treatment tank 1 to 1 kg / m 3 / d or more and the HRT to 24 hours or less, the predominance of the dispersible bacteria can be promoted. In addition, by shortening the HRT, the wastewater having a low BOD concentration can be treated at a high load.

Moreover, a part of sludge from the 2nd biological treatment tank 2 may be conveyed to this 1st biological treatment tank 1, or the 1st biological treatment tank 1 may be multistage 2 or more.

In addition, when the residence time (HRT) is longer than the optimum value, it leads to the predominance of filamentous bacteria and the formation of flocs, and in the second biological treatment tank 2, bacteria that are hard to be preyed by micro animals are generated. Throw it away. Therefore, it is preferable to control the HRT of the 1st biological treatment tank 1 uniformly. Since the optimum HRT varies depending on the drainage, it is preferable to obtain an HRT capable of removing 70 to 90% of the organic component from the desk test or the like. As a method of maintaining the HRT at an optimum value, a part of the treated water is returned when the amount of water is reduced to make the quantity of water flowing into the first biological treatment tank 1 constant, and the HRT of the first biological treatment tank 1 is stabilized. There is a method of varying the water level of the first biological treatment tank in accordance with the fluctuation of the method and the discharge amount. The width to stabilize is preferably within 0.75 to 1.5 times the optimum HRT determined by the desk test.

In the present invention, when a large amount of organic matter remains in the treated water from the first biological tank 1 introduced into the second biological treatment tank 2, the oxidative decomposition of the second biological treatment tank 2 is performed. Will be done at.

When oxidative degradation of organic matter by bacteria occurs in the second biological treatment tank 2 in which a large amount of micro-animals are present, it is known that microorganisms multiply in a form that is difficult to be fed as a countermeasure for escaping from micro-animals. The bacterial group propagated in this form is not fed by a micro animal, and their decomposition depends only on self-extinguishing, so that the effect of reducing the amount of production is reduced.

Therefore, in the present invention, it is preferable that the first treatment tank 1 decomposes most of the organic matter, that is, 70% or more, preferably 80% or more of the wastewater BOD, and converts the cells into stable cells. Therefore, as shown in FIG. 2, it is preferable that the first biological treatment tank 1 also be a fluidized bed having a carrier. In addition, when the filling rate of the carrier in the first biological treatment tank 1 is excessively high, dispersed bacteria are not produced, and bacteria adhere to the carrier, or filamentous bacteria grow, so that the filling rate of the carrier of the first biological treatment tank is increased. It is preferable to set it as 10% or less, Preferably it is 2 to 10% especially 2 to 5%, and it is possible to produce | generate the dispersion bacteria which are easy to prey, without affecting concentration fluctuation.

The carrier may have any shape such as a spherical shape, a pellet shape, a hollow cylinder shape, a thread shape, or the like, and may have a diameter of about 0.1 to 10 mm. The material may be any material such as a natural material, an inorganic material or a polymer material, and a gel material may be used.

Next, the treated water of the first biological treatment tank 1 is introduced into the aerobic second biological treatment tank 2 provided with an aeration means, where the oxidative decomposition of the remaining organic components and the magnetism of the dispersible bacteria Reduction of excess sludge by decomposing and feeding on small animals is performed.

As this microanimal, a sticking microanimal is suitable. These sticking micro-animals are protozoa, which have a tendency to stick to solid particles or solid substances, or protozoa, which have a tendency to adhere and agglomerate with each other. In addition to the disease-fixing ciliated worms, such as Bortisella, Epistillis, Opcularia, Carcassium, and Juthamium, apidesca and euprotes that crawl on the solid surface are accompanied by sludge. Because it is easy to settle, it can use.

Since the second biological treatment tank 2 utilizes the action of micro-animals and the autolysis of bacteria, which are slower in propagation rate than bacteria, it is necessary to use the operating conditions and the processing apparatus in which micro-animals and bacteria stay in the system. Thus, in the second biological treatment tank 2, the carrier C is added to form a fluidized bed in which the holding amount in the tank of the microanimals can be increased. The carrier to be added may be any shape, such as spherical shape, pellet shape, hollow cylinder shape, and thread shape, and the size may be a diameter of about 0.1 to 10 mm. The material may be any material such as a natural material, an inorganic material or a polymer material, and a gel material may be used. The carrier C also flows by aeration.

In the second biological treatment tank 2, since a large amount of chiefs is required to hold the micro-animals, the filling rate of the carrier to be added is preferably 10% or more, preferably 10 to 50%, particularly 20 to 40%. Do.

The treated water from the second biological treatment tank 2 is separated into solid-liquid separation in the sedimentation basin 3, and sedimented excess sludge and supernatant water (treated water).

By using the solid-liquid separation means as a coagulation sedimentation method or a pressure flotation method (not shown) consisting of the coagulation tank 4 and the precipitation tank 5 as shown in FIG.

In addition, as shown in FIG. 4, part or all of the sludge separated from the treated water from the second biological treatment tank 2 is added to the third biological treatment tank 6 equipped with aeration means to reduce the sludge. May be further promoted.

In addition, in this invention, it may be preferable not to convey the outflow sludge from the 2nd biological treatment tank 2 to neither the 1st biological treatment tank 1 nor the 2nd biological treatment tank 2. This is because when the sludge from the 2nd biological treatment tank 2 is returned to the 1st biological treatment tank 1, the disperse bacteria in the 1st biological treatment tank 1 will be preyed by a micro animal. In addition, when the sludge is returned to the second biological treatment tank 2, when the returned micro animal is settled on the floc instead of the carrier and the floc is dismantled due to load fluctuation or temperature fluctuation, the micro animal flows out of the system. Because there are cases.

In the present invention, however, a part of the treated sludge from the third biological treatment tank 6 is transferred to the second biological treatment tank 2 in order to replenish the microanimals with the second biological treatment tank in addition to reducing the sludge. You may return. In this case, if the micro animal is excessively replenished, it is difficult to maintain the cell mass to remove the organic matter. In addition, since bacteria that are difficult to prey may also multiply and lose sludge in the second biological treatment tank, the second animal treatment tank 2 may not be able to carry out weight loss. It is preferable to control so that it may not be 20% or more.

In addition, without using the third biological treatment tank (6), the surplus sludge was killed by using any one or a combination of anaerobic treatment, physical treatment, and chemical treatment, and after that, the animal was killed as it is, or separated into solid and liquid. You may return to a 1st or 2nd biological treatment tank. In addition, the third biological treatment tank 6 may be provided, and the above treatment may be performed on the surplus sludge from the third biological treatment tank.

In addition, a sedimentation basin into which the treated water of the third biological treatment tank 6 is introduced may be provided, and at least a portion of the precipitated sludge may be returned to the biological treatment tank 3. Further, the third biological treatment tank 6 may be a fluidized bed or membrane separation type aerobic treatment method to which a carrier is added, so that the residence time may be increased. Moreover, solid-liquid separation may send a treated water to the 1st biological treatment tank 1 or the 2nd biological treatment tank 2, and solid content may be returned to the 3rd biological treatment tank 6. Moreover, you may discharge | emit as excess sludge without conveying solid content.

In order to promote predation by micro-animals, the pH of the second biological treatment tank 2 or the third biological treatment tank 6 may be 7.0 or less, for example, 5.0 to 7.0.

In addition, even if the operating conditions are set to be suitable for the growth of the micro-animals in this manner, if the components essential for the growth of the micro-animals are not contained in the drainage, the micro-animals do not proliferate, and the sludge reduction effect is not improved. Therefore, by adding the nutrient to the second biological treatment tank 2, the microanimals may be kept stable, so that the effect of sludge reduction may be stabilized. In addition, the weight loss effect may be stabilized by adding a nutrient to the third biological treatment tank 6.

These nutrients include phospholipids, free fatty acids, lysolipids, sterols and lecithins containing them, others, liquid sugars, rice bran, rice squeezed with beer, rice squeezed with vegetable oil, and soy-derived products (liquid soy milk, powdered soy milk, bean curd, dry busy , Tofu, kina powder, soybean-derived feed, etc.), sugar beet zest, shell powder, eggshell, vegetable extract, fish extract, various amino acids, vitamins, etc. Use nutrients alone or in combination.

Example 1

Raw water (fish meat extract, vegetable extract, liquid sugar was mixed in a 2: 2: 1 weight ratio and BOD was adjusted to 650 mg / l) according to the flow shown in FIG. 3. The capacity of the first biological treatment tank 1 is 2.5 L, the capacity of the second biological treatment tank 2 is 4.4 L raw water supply amount is 21 L / day, and only 0.01 mg of DO of the first biological treatment tank 1 is used. It was set to / l, and the DO of the 2nd biological treatment tank 2 was operated by aeration so that it might be 2-3 mg / l.

A sponge having a filling rate of 5% and a filling rate of 40% and an average particle diameter of 3 mm (square) as a carrier was added to the first biological treatment tank 1.

The BOD volume load for the first biological treatment tank was operated under conditions of 5.5 kg-BOD / m ³ / d, HRT 3.5 hours, total BOD volume load 2.0 kg-BOD / m ³ / d, HRT 9.6 hours. The results are shown in Table 1. Sludge conversion averaged 0.30 kg-MLSS / kg-BOD. The BOD of the treated water was 10 mg / l or less.

Reference Example 1

In FIG. 3, 50% of the surplus sludge settled in the settling tank 5 was returned to the 2nd biological treatment tank 2, and the other thing which extended the sludge residence time was operated on the same conditions as Example 1. FIG.

As a result, the propagated fixed microanimals settled not on the carrier but on the return sludge flocs, and when the flocs were dismantled due to load fluctuations or temperature changes, they flowed out of the system. Table 1 shows the results of other operations. As shown in Table 1, the sludge conversion rate averaged 0.42 kg-MLSS / kg-BOD. From the above result, it became clear that Example 1 which does not return sludge to a 2nd biological treatment tank compared with this 1st reference example turns low sludge conversion rate.

Example 2

The same raw water as in Example 1 was treated according to the flow shown in FIG. In Example 1, the fourth biological treatment tank 6 having a capacity of 4 L is connected to the precipitation tank 5 in Example 1. DO of the 3rd biological treatment tank 6 was 2-3 mg / L. As in Example 1, the same carrier was added to the first biological treatment tank 1 at a filling rate of 5% and the second biological treatment tank 2 at a filling rate of 40%. As in Example 1, the BOD volume load for the first biological treatment tank was operated under the conditions of 5.5 kg-BOD / m 3 / d, HRT 3.5 hours, total BOD volume load 2.0 kg-BOD / m 3 / d and HRT 9.6 hours. It was.

0.4 L / d was discharged | emitted from the 3rd biological treatment tank 6 as excess sludge, and 0.4 L / d of excess sludge from the settling tank 5 was added to the 3rd biological treatment tank 6. Furthermore, it added once a day so that the density | concentration in the tank immediately after adding lecithin as a nutrient to the 3rd biological treatment tank 6 may be 1 mg / L. As a result, the sludge conversion rate became 0.15 kg-MLSS / kg-BOD. The BOD of the treated water was 10 mg / l or less.

Comparative Example 1

As shown in FIG. 5, raw water was treated in the same manner as in Example 1 in accordance with a flow connecting the biological treatment tank 10 with a width pipe having a capacity of 6.9 L and the sedimentation basin 11. The carrier was not added to the biological treatment tank 10. The DO of the biological treatment tank 10 was operated so that it might be 2-3 mg / l. The raw water supply amount was the same as in Example 1, and the whole amount of sludge was returned from the settling basin 11 to the biological treatment tank 10, and a part of the returned sludge was intermittently discharged so that the concentration of sludge in the tank was constant. . As a result of operating under a condition of 2.0 kg-BOD / m 3 / d of BOD volume load in total and 9.6 hours of HRT, filamentous bacteria occurred on the fifth day after the start of operation, and sludge did not settle in the sedimentation basin, resulting in treatment failure.

Comparative Example 2

In Comparative Example 1, a carrier similar to the above Example was added to the biological treatment tank at a filling rate of 40%. Sludge from the settling basin 11 was not returned at all. The others were operated under the same conditions as in Comparative Example 2. As a result, the sludge conversion was 0.55 kg-MLSS / kg-BOD. In addition, the quantity of the flocculant added when solid-liquid separation of biologically treated water became about twice as much as Example 1. FIG.

Comparative Example 3

In Example 1, operation was performed on the same conditions except having made DO of the 1st biological treatment tank 1 into 1 mg / L. The results are shown in Table 1. As shown in Table 1, when the DO is higher than 0.5 mg / L, the dispersion bacterium has a length of 10 µm or more, and it is not possible to feed a small animal, and it can be confirmed that the sludge conversion rate increases.

<Consideration>

From the above results, the following items were confirmed.

(1) By making DO of a 1st biological treatment tank into 0.5 mg / L or less, it can process efficiently.

(2) In Example 1 and Example 2 which added the support | carrier to the 2nd biological treatment tank, the amount of sludge generation | occurrence | production was low.

(3) In the standard activated sludge method, stable organic matter removal was possible even with a load falling into treatment failure by bulking or the like.

(4) Compared with the usual fluidized bed method of Comparative Example 2, the amount of sludge generation was small, and the amount of flocculant added in the flocculation tank was reduced to about 50%.

(5) According to the present invention, efficient biological treatment of organic wastewater becomes possible, and a significant reduction in sludge generated at the time of drainage treatment; Improvement of processing efficiency by high load operation; The effect of maintaining the stable treated water quality can be obtained.

Claims (19)

With 2 or more biological treatment tanks, organic wastewater is passed to a 1st biological treatment tank, biologically processed by a bacterium, and the 1st biological water which contains the bacteria of the dispersed state from a 1st biological treatment tank is a 2nd biological treatment In the biological treatment method which introduce | transduces into a tank and biologically processes and makes a micro animal exist in this 2nd biological treatment tank, The dissolved oxygen concentration of the first biological treatment tank is controlled to 0.5 mg / l or less, The biological treatment method of organic wastewater characterized by solid-liquid separation treatment of the treated water of a 2nd biological treatment tank using the said 2nd biological treatment tank as a fluidized bed with a support | carrier. The method according to claim 1, wherein the carrier is present in the first and second biological treatment tanks respectively, wherein the carrier filling rate of the first biological treatment tank is 10% or less, and the carrier filling rate of the second biological treatment tank is 10% or more. The biological treatment method of organic wastewater characterized by the fluidized bed. 2. The biological treatment method for organic wastewater according to claim 1, wherein the solid-liquid separation treatment is performed by coagulation precipitation or pressure flotation separation. The biological treatment method for organic wastewater according to claim 1, wherein sludge separated by the solid-liquid separation treatment is introduced into and reduced in the third biological treatment tank. The biological treatment method for organic wastewater according to claim 4, wherein at least one pH of the second biological treatment tank and the third biological treatment tank is set to 5.0 to 7.0. The biological treatment method for organic wastewater according to claim 4, wherein the nutrient for the organism is added to at least one of the second biological treatment tank and the third biological treatment tank. The biological treatment method for organic wastewater according to claim 1, wherein a part of raw water is added to the second biological treatment tank. The biological treatment method for organic wastewater according to claim 4, wherein a part of raw water is added to at least one of the second biological treatment tank and the third biological treatment tank. The method of claim 1, wherein the bacterium is at least one selected from the group consisting of genus Alkogen genus, Pseudomonas, Bacillus, Aerobacter spp. And Flavobacterium spp. The biological treatment method for organic wastewater according to claim 1, wherein in the first biological treatment tank, at least 70% of the soluble BOD is decomposed by the bacteria. The biological treatment method for organic wastewater according to claim 1, wherein the pH of the first biological treatment tank is 6 to 8. The biological treatment method for organic wastewater according to claim 1, wherein the dissolved oxygen concentration of the first biological treatment tank is 0.1 mg / l or less. The biological treatment method for organic wastewater according to claim 1, wherein the BOD volume load of the first biological treatment tank is 1 kg / m 3 / d or more, and the HRT is 24 hours or less. The biological treatment method for organic wastewater according to claim 2, wherein the carrier has a diameter of 0.1 to 10 mm. The method of claim 1, wherein the aeration is carried out in a second biological treatment tank to make aerobic, and the reduction of surplus sludge by oxidative decomposition of organic components introduced into the second biological treatment tank, self-decomposition of dispersible bacteria, and feeding of a micro animal is carried out. The biological treatment method of organic wastewater characterized by the above-mentioned. The method of claim 1, wherein the micro-animal is a fixed micro-animal. 17. The organic drainage of claim 16 wherein the sticking microanimal is at least one of vaginal bark, vorticella, epistilis, opcularia, carcassium, juthamium, apidesca and euprotes. Biological treatment method. The nutrient of claim 6, wherein the nutrient is phospholipids, free fatty acids, lysolin lipids, sterols, lecithin, liquid sugar, rice bran, beer squeezed rice, vegetable oil squeezed rice, liquid soy milk, powdered soy milk, bean curd, dried bean curd, tofu, kina At least one selected from the group consisting of flour, soybean-derived feed, sugar beet forage, shell powder, eggshell, vegetable extract, fish meat extract, amino acids and vitamins. With 2 or more biological treatment tanks, organic wastewater is passed to a 1st biological treatment tank, biologically processed by a bacterium, and the 1st biological water which contains the bacteria of the dispersed state from a 1st biological treatment tank is a 2nd biological treatment In the biological processing apparatus which introduces into a tank and carries out a biological process and makes a micro animal exist in this 2nd biological processing tank, A control device for controlling the dissolved oxygen concentration of the first biological treatment tank to 0.5 mg / l or less, An apparatus for forming a fluidized bed of a carrier in the second biological treatment tank, And a solid-liquid separation device for solid-liquid separation treatment of the second biological treatment tank treated water.

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