JP6934358B2 - Organic wastewater treatment equipment and treatment method - Google Patents

Description

The present invention relates to an organic wastewater treatment apparatus and a treatment method, and more particularly to an organic wastewater treatment apparatus and a treatment method suitable for treating sewerage, human waste, private factory wastewater and the like.

Conventionally, for example, in a sewage treatment plant, treated water that has been solid-liquid separated in a settling basin is first introduced into an aeration tank and treated with activated sludge, but the electricity cost for supplying oxygen to maintain aerobic microorganisms is high. It is enormous, and the development of energy-saving technology is an urgent issue. Furthermore, with the growth of activated sludge, excess sludge increases, and sludge disposal costs a great deal of money.

Further, in recent years, there have been an increasing number of cases in which sludge is anaerobic digested for the purpose of utilizing biomass to obtain methane and used for power generation. In order to obtain a large amount of energy, it is necessary to efficiently introduce organic matter into the anaerobic digestion tank, but most of the organic matter is aerobically processed in the aeration tank with great power and decomposed into water and carbon dioxide. Has been done. That is, recovering as much organic matter as possible leads to recovering energy.

As a method for treating organic wastewater using microorganisms, Japanese Patent No. 4474930 (Patent Document 1) has a two-tank type biological treatment step as a multi-stage activated sludge method utilizing the phagocytosis of microorganisms. In the first tank, dispersed cells are generated, and in the second tank, a technique for flocking and coexisting with microbes is described.

In Japanese Patent No. 5223219 (Patent Document 2), as a method for biologically treating organic wastewater in two stages, a drug-free floating separation type solid-liquid separation means is provided in the subsequent stage of the first biological treatment reaction tank. If the treated water has a fluidized bed type biological membrane carrier, it is treated in a second biological treatment reaction tank, treated in a second biological treatment reaction tank, an inorganic flocculant is added to the treated water, and floating separation is performed again. It is described that advanced processing is performed after this.

According to International Publication No. 2016/148806 (Patent Document 3), by mixing excess sludge with organic wastewater with a hydraulic residence time of 10 minutes or less, organic matter in the wastewater is adsorbed on the excess sludge, and this mixed liquid is used. An example of a water treatment method and an apparatus capable of recovering an organic substance and performing a highly efficient and stable treatment by solid-liquid separation is described.

Japanese Patent No. 4474930 Japanese Patent No. 5223219 International Publication No. 2016/148806

However, there is still room for consideration regarding the knowledge for achieving both the technique for reducing excess sludge and the technique for efficiently recovering energy in any of the methods and devices for treating organic wastewater described in the above-mentioned prior art.

For example, in Patent Document 1, although a certain effect is obtained in reducing the amount of excess sludge generated, no specific consideration is given to the point of recovering organic matter from organic wastewater with high efficiency. Patent Document 2 describes that the problem of increased organic matter load and precipitation of metal salts caused by the flocculant can be avoided when the flocculant is used, but the knowledge is limited to the addition of the flocculant and the improvement of water quality. .. Patent Document 3 describes that a part of organic substances can be adsorbed by adding excess sludge to organic wastewater and bringing it into contact with each other. However, as a result of the examination by the present inventors, the technique described in Patent Document 3 In some cases, organic matter cannot be fully recovered.

In view of the above problems, the present invention provides an organic wastewater treatment apparatus and a treatment method capable of both improving the energy recovery rate and reducing excess sludge.

As a result of diligent studies, the present inventor uses a multi-stage biological treatment device to suppress the generation of excess sludge, and in order to improve the recovery efficiency of organic matter, particularly disperse bacteria in the excess sludge are mainly used. We found that bacteria play an important role and came up with the present invention. That is, when the surplus sludge and the wastewater containing organic matter are brought into contact with each other, the dispersed bacteria in the surplus sludge have a high contribution rate to the adsorption of organic matter. Therefore, the efficiency of organic matter recovery can be improved by efficiently growing the dispersed bacteria. Further, in order to recover the dispersed bacteria that have adsorbed organic matter, it is desirable to add excess sludge containing protozoa that prey on the dispersed bacteria.

In one aspect, the present invention completed based on the above findings is a water treatment apparatus in which a first aeration tank, a first separation tank, a second aeration tank, and a second aeration tank are arranged in this order. The process of obtaining treated water in the first aeration tank and returning at least a part of the sludge separated from the second separation tank by performing aerobic treatment while contacting the fluid bed carrier or fixed bed carrier carrying the above and the organic wastewater. Then, the step of contacting with the first aeration tank treated water, the solid-liquid separation of the first aeration tank treated water after contact in the first separation tank, and the first separation tank treated water from the first separation tank are first. 2. Provided is a method for treating organic wastewater, which comprises aerobically treating in an aeration tank and solid-liquid separating the treated water in the second aeration tank obtained in the second aeration tank in a second separation tank.

In one embodiment, the method for treating organic wastewater according to the present invention further includes returning a part of the sludge separated from the second separation tank to the first aeration tank.

In another embodiment of the method for treating organic wastewater according to the present invention, the fluidized bed carrier or fixed bed carrier carrying the biological film in the second aeration tank is brought into contact with the treated water in the first separation tank.

In another embodiment of the method for treating organic wastewater according to the present invention, a dividing wall is provided in the second aeration tank.

In still another embodiment, the method for treating organic wastewater according to the present invention is a solid-liquid separation method in a first separation tank and a second separation tank using any of a gravity precipitation type, a floating separation type, and a filtration separation type. do.

In still another embodiment, the method for treating organic wastewater according to the present invention anaerobic digests the sludge obtained in the first separation tank to obtain methane gas to generate electricity.

In another aspect, the present invention comprises a first aeration tank for obtaining treated water in the first aeration tank by performing aerobic treatment while contacting a fluid bed carrier or a fixed bed carrier carrying a biological film with organic wastewater. A first aeration tank that solid-liquid separates the treated water in the first aeration tank, a second aeration tank that aerobically treats the treated water in the first separation tank from the first aeration tank, and a second aeration tank from the second aeration tank. A second separation tank that separates the treated water into solid and liquid, and a return means that returns at least a part of the sludge separated from the second separation tank to the upstream side of the first separation tank and brings it into contact with the treated water in the first aeration tank. A equipped organic waste treatment device is provided.

According to the present invention, it is possible to provide an organic wastewater treatment apparatus and a treatment method capable of both improving the energy recovery rate and reducing excess sludge.

It is a schematic diagram explaining the organic wastewater treatment apparatus and treatment method which concerns on embodiment of this invention. It is a schematic diagram explaining the organic wastewater treatment apparatus and treatment method which concerns on 1st modification of embodiment of this invention. It is a schematic diagram explaining the organic wastewater treatment apparatus and the treatment method which concerns on the 2nd modification of the Embodiment of this invention. It is a schematic diagram explaining the organic wastewater treatment apparatus and the treatment method which concerns on the 3rd modification of the Embodiment of this invention. It is a schematic diagram explaining the organic wastewater treatment apparatus and treatment method which concerns on 4th modification of embodiment of this invention. It is the schematic which shows the processing flow of Examples 1 to 3 and Comparative Examples 1 to 3.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention specifies the structure, arrangement, etc. of components as follows. It's not something to do.

The method for treating organic wastewater according to the embodiment of the present invention is, for example, as shown in FIG. 1, in the order of the first aeration tank 1, the first separation tank 2, the second aeration tank 3, and the second separation tank 4. Organic wastewater can be treated using the arranged water treatment equipment.

The organic wastewater is not particularly limited, but organic wastewater containing at least a soluble organic substance or a pollutant such as a turbid substance is preferably used. Specifically, sewage, primary treated sewage, secondary treated sewage, human waste, livestock wastewater, wastewater from various manufacturing plants, and the like can be used as wastewater according to the present embodiment.

The organic wastewater is introduced into the first aeration tank 1. A carrier 11 having a fluidized bed or a fixed bed is arranged in the first aeration tank 1. When a fluidized bed carrier is arranged as the carrier 11, it is preferable to install a screen at the outlet of the first aeration tank 1 to prevent the carrier 11 from flowing out.

The filling rate of the carrier 11 is adjusted according to the BOD load of the organic wastewater to be treated, and is preferably in the range of 1 to 30% (volume ratio) of the tank capacity, for example. As the material of the carrier 11 of the first aeration tank 1, it is desirable that the carrier 11 is mainly composed of a polymer organic material such as polyurethane in addition to polyvinyl alcohol.

In the first aeration tank 1, air or oxygen is aerated in order to maintain an aerobic state. Dispersing bacteria adhere to the surface of the carrier 11, and organic substances in the organic wastewater are efficiently adsorbed and immobilized. The disperse grows on the nutrients of this organic matter, but the disperse that cannot be retained on the carrier 11 is released again into water. Therefore, the first aeration tank treated water, which is the treated water of the first aeration tank 1, contains liberated dispersed bacteria and residual organic matter.

Therefore, in the present embodiment, at least a part of the excess sludge separated from the second separation tank 4 is returned to the upstream side of the first separation tank 2 via the return means 5, and the returned sludge and the first aeration tank are returned. It has a step of contacting with treated water. The place of contact may be in the middle of the piping or water channel between the first aeration tank 1 and the first separation tank 2, or a separate mixing tank may be provided. The surplus sludge obtained from the second separation tank 4 contains not only bacteria but also protozoa that prey on them. The dispersed bacteria contained in the first aeration tank 1 and its treated water are positioned at the bottom of the food chain and are preyed on by protists and the like. By bringing the excess sludge from the second separation tank 4 into contact with the dispersed bacteria that have captured the organic matter, the organic matter in the first aeration tank treated water can be efficiently immobilized.

The first aeration tank treated water obtained by aerating organic wastewater contains a large amount of dispersed bacteria in which organic matter is immobilized in addition to soluble organic matter. More organic matter can be precipitated in the first separation tank 2 than in the example of Cited Document 3 in which sludge from the second separation tank 4 is directly contacted, and the organic matter in the organic wastewater can be more efficiently than in Cited Document 3. Can be recovered.

The excess sludge from the second separation tank 4 is returned to the second aeration tank 3 in the amount required to maintain the activated sludge amount (MLSS) of the second aeration tank 3, but all the rest is returned to the first aeration tank 3. It is desirable to return and add to the treated water. By doing so, the excess sludge will be separated and collected only in the first separation tank 1, which simplifies the system. For example, when it is necessary to treat and discharge excess sludge from the second separation tank 4, a pump is required to separately transfer it to the sludge treatment process. Therefore, a pump for discharging such excess sludge, etc. The number of devices can be reduced.

The first aeration tank treated water after contact with the excess sludge is solid-liquid separated in the first separation tank 2. In the first separation tank 2, solid-liquid separation can be performed by any of a gravity precipitation type, a levitation separation type, and a filtration separation type. The treated water obtained in the first separation tank 2 (treated water in the first separation tank) is sent to the second aeration tank 3.

In the second aeration tank 3, the treated water in the first separation tank from the first separation tank 2 is aerobically treated. In the first separation tank treated water according to the present embodiment, excess sludge from the second separation tank 4 is added to the first air exposure tank treated water from the first air exposure tank 1, and organic matter is immobilized on the excess sludge. Since the excess sludge on which the organic matter is immobilized is removed in the first separation tank 2, the load on the organic matter is reduced as compared with the case where the excess sludge is not added. As a result, the amount of oxygen required by the second aeration tank 3 can be reduced as compared with the conventional case, so that the aeration power of the second aeration tank 3 can be reduced and the device can be simplified.

The second aeration tank treated water treated in the second aeration tank 3 is sent to the second separation tank 4. In the second separation tank 4, solid-liquid separation can be performed by any of a gravity precipitation type, a levitation separation type, and a filtration separation type.

The excess sludge obtained in the second separation tank 4 may be returned to the second aeration tank 3 in order to maintain the amount of activated sludge (MLSS) in the second aeration tank 3, and the rest may be returned to the first aeration tank 2. It is returned to the upstream side. The excess sludge may be returned to the middle of the flow path as long as it is between the first aeration tank 1 and the first separation tank 2, or the mixing tank is between the first aeration tank 1 and the first separation tank 2. May be provided separately.

In a treatment device equipped with a multi-stage aeration tank that imitates the phenomenon of the food chain, which is mainly used for the purpose of reducing excess sludge as a method for preferentially culturing dispersed bacteria, the first stage part is the predator for dispersed bacteria. It is a comfortable environment with less organic matter. According to the organic wastewater treatment apparatus and treatment method according to the embodiment of the present invention, the organic wastewater is once biologically treated and the dispersed bacteria are brought into contact with the wastewater in which the dispersed bacteria have grown, so that the dispersed bacteria are brought into contact with the wastewater for a short time. It is possible to efficiently adsorb organic substances to the maximum extent.

If the dispersed bacteria that have adsorbed organic matter are preyed on and decomposed by protists in the subsequent stage, the organic matter may not be recovered. In the present embodiment, the excess sludge extracted from the second separation tank 4 is added to the treated water in the first aeration tank and brought into contact with the treated water. As a result, the dispersed bacteria that have taken in the organic matter floating in the water can be more efficiently adsorbed on the excess sludge, solid-liquid separated in the first separation tank 2 and extracted as sludge, and the sludge having a high organic matter concentration can be recovered.

By recovering the organic matter as sludge in the first separation tank 2, the load amount of the organic matter in the second aeration tank 3 is reduced, and the oxygen requirement is reduced. As a result, the aeration power required for the aeration of the second aeration tank 3 can be reduced. As a result, the energy used can be reduced. In addition, the second aeration tank 3 is provided with a multi-stage aeration tank that imitates the phenomenon of the food chain, so that water is passed in the order of bacteria, protists, and metazoans to suppress the increase of activated sludge due to the growth of bacteria. It becomes possible to reduce excess sludge.
That is, according to the present invention, it is possible to provide an organic wastewater treatment apparatus and a treatment method capable of both improving the energy recovery rate and reducing excess sludge.

(First modification)
In the organic wastewater treatment method and treatment apparatus according to the first modification of the present invention, as shown in FIG. 2, the return means 5 first aerates a part of the excess sludge separated in the second separation tank 4. It further includes returning to tank 1. According to the first modification, the dispersed bacteria released in the first aeration tank 1 can be effectively immobilized by the returned sludge. Others are substantially the same as the organic wastewater treatment method and treatment apparatus shown in FIG.

(Second modification)
As shown in FIG. 3, the organic wastewater treatment method and treatment apparatus according to the second modification of the present invention have a fluidized bed or fixed bed carrier 31 held in the second aeration tank 3. By installing the carrier 31 in the second aeration tank 3, the amount of excess sludge generated can be reduced by efficiently maintaining the protists that prey on the dispersed bacteria and the protists that prey on the protists in the aeration tank. Can be done. As the material of the carrier 31 of the second aeration tank, a carrier 31 mainly composed of a polymer organic material such as polyvinylidene chloride or vinylon is desirable in addition to polypropylene. Others are substantially the same as the organic wastewater treatment method and treatment apparatus shown in FIG.

(Third modification example)
As shown in FIG. 4, the method and apparatus for treating organic wastewater according to a third modification of the present invention include providing one or more divided walls 32 in the second aeration tank 3. By dividing the second aeration tank 3 into multiple stages by the dividing wall 32, the food chain by living organisms can be carried out in accordance with the flow path, and the amount of excess sludge generated can be further reduced. It is sufficient that one or more dividing walls 32 are arranged, but by arranging a plurality of dividing walls 32 and increasing the number of processing stages, organisms constituting the food chain such as bacteria, protists, and metazoans naturally establish segregation and each biota. It is possible to stabilize the operation while grasping the relationship of the food chain while managing. Others are substantially the same as the organic wastewater treatment method and treatment apparatus shown in FIG.

(Fourth modification)
As shown in FIG. 5, the method and apparatus for treating organic wastewater according to the fourth modification of the present invention describe a specific treatment mechanism for sludge obtained from the first separation tank 2. It is different from the processing method and processing apparatus shown in FIG. Others are substantially the same as the organic wastewater treatment method and treatment apparatus shown in FIG.

That is, the sludge obtained from the first separation tank 2 is supplied to the anaerobic digestion tank 6 for anaerobic digestion treatment. Anaerobic digestion of sludge produces digestive gas containing methane. This digestion gas is stored in the gas holder 7, and if necessary, the digestion gas is pretreated with hydrogen sulfide, siloxane, or the like in the gas pretreatment device 8. Then, power is generated by the generator 9 using the digested gas after the pretreatment.

The generated electricity may be sold to an electric power company or the like or used as electric power for an organic wastewater treatment device. In FIG. 5, the configuration of the second aeration tank 3 is described in the same manner as the configuration of FIG. 1, but the configuration shown in the second modification or the third modification may be adopted instead of FIG. Of course.

Examples of the present invention are shown below together with comparative examples, but these examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

As shown in FIG. 6, Comparative Examples 1 to 3 were operated in parallel with Examples 1 to 3 for the same organic wastewater (sewage). In Examples 1 to 3, a fluidized bed carrier made of polyvinyl alcohol was held in the first aeration tank at 20% of the tank capacity according to the BOD load of the target organic wastewater. In Examples 1 to 3 and Comparative Examples 1 to 3, gravity type settling basins were used for the first separation tanks 2 and 20 and the second separation tanks 4 and 40.

(Example 1)
In Example 1 ((a) of FIG. 6), a part of the excess sludge obtained from the second separation tank 4 is placed at the inlet of the second aeration tank 3 in order to adjust the amount of activated sludge in the second aeration tank 3. The rest was returned by the return means 5, added to the treated water in the first aeration tank, mixed, and introduced into the first separation tank 2.

(Example 2)
In Example 2 ((b) of FIG. 6), a fixed bed carrier was installed in the second aeration tank 3. As the material of the carrier, a polypropylene carrier was installed so as to be 20% of the tank capacity. The entire amount of excess sludge was added to the treated water in the first aeration tank via the return means 5, mixed, and introduced into the first separation tank 2.

(Example 3)
In Example 3 ((c) of FIG. 6), the second aeration tank 3 is divided into five chambers by alternately installing partition walls 32 having the lower part and the upper part cut out so that water flows in a rain flow manner. Was given to. The same polypropylene fixed-floor carrier as in Example 2 was installed in each room so as to be 20% of the capacity of each room. The entire amount of excess sludge was added to the treated water in the first aeration tank, mixed, and introduced into the first separation tank 2.

(Comparative Example 1)
In Comparative Example 1 ((d) of FIG. 6), the treated water in the first separation tank 20 was introduced into the aeration tank 30 for treatment, and solid-liquid separation was performed again in the second separation tank 40. A part of the surplus sludge in the second separation tank 40 was returned to the aeration tank 30 in order to adjust the amount of activated sludge in the aeration tank 30, but the rest was discharged as surplus sludge.

(Comparative Example 2)
In Comparative Example 2 ((e) of FIG. 6), a part of the excess sludge in the second separation tank 40 was returned to the aeration tank 30 in order to adjust the amount of activated sludge in the aeration tank 30, but the rest was separated in the first separation tank 30. It was returned to the front of the tank 20 and brought into contact with the organic wastewater.

(Comparative Example 3)
In Comparative Example 3 ((f) of FIG. 6), the organic wastewater was directly introduced into the aeration tank 30, but the aeration tank 30 was divided into 5 chambers by alternately installing partition walls 32 having the lower part and the upper part cut out. The water flow was applied in a rain flow manner, and the same polypropylene fixed-floor carrier as in Examples 2 and 3 was installed in each room so as to be 20% of the capacity of each room.

(evaluation)
Regarding Examples 1 to 3 and Comparative Examples 1 to 3, the amount of organic matter recovered and the sludge of the first separation tank sludge obtained in the first separation tanks 2 and 20 and the surplus sludge discharged in the second separation tanks 4 and 40. It was evaluated by comparing the amount generated. The amount of organic matter recovered was indexed by the CODcr of sludge. The CODcr of sludge was measured according to the thermal decomposition method according to JIS K 0102. Regarding the amount of sludge generated and the amount of CODcr of sludge, the total amount of sludge generated in the first separation tank and excess sludge discharged was evaluated based on each treatment method.

The treatment amount in each treatment method was ^{constant at 5 m 3} / day, and the residence time HRT of water in the aeration tank and the separation tank was the same. The conditions are shown in Table 1. It was operated continuously for 90 days. Table 2 shows the results of sludge generation and CODcr amount per day on average for 90 days.

In Example 1, the amount of sludge generated was 1081 g / day and the amount of CODcr of sludge was 1864 g / day, and the amount of sludge generated increased 1.1 times as compared with Comparative Example 1, but the total amount of sludge CODcr was 1.3. It was possible to double the amount and improve the organic matter recovery rate. In Examples 2 and 3, by installing the carrier in the second aeration tank 3, the sludge generated in Examples 2 and 3 was 874 g / day and 769 g / day, respectively, and excess sludge was generated in Examples. It was possible to reduce it to about 81% and 71% as compared with 1. On the other hand, the total amount of sludge CODcr was 1719 g / day and 1623 g / day in Examples 2 and 3, respectively, and the organic matter recovery rate could be improved as compared with Comparative Examples 1 to 3.

From the results of Examples 1 to 3, the aspects of Examples 1 to 3 may be appropriately selected according to each application. For example, when it is desired to recover as much organic matter as possible, Example 1 in which excess sludge is not reduced is used. It can be seen that the embodiment of Example 2 or Example 3 is desirable when it is desirable to adopt the method and it is desired to recover a large amount of organic matter but to further reduce the generation of excess sludge.

Comparing Example 1 and Comparative Example 2, both are flows for the purpose of recovering more organic matter, but the total amount of CODcr of sludge is 1864 g / day in Example 1 depending on the presence or absence of the first aeration tank 1, and Comparative Example 2 The amount was 1567 g / day, which was 1.2 times higher in Example 1.

Comparative Example 3 is a flow for the purpose of reducing excess sludge without aiming at recovery of organic matter, but the amount of excess sludge was significantly reduced as compared with other methods, while the amount of organic matter was also reduced. This is basically the generation of excess sludge suppressed by the food chain in the aeration tank.

As described above, according to Examples 1 to 3, more methane gas can be obtained by treating sludge by anaerobic digestion by increasing the amount of organic matter recovered from the organic wastewater treatment process. I understand. It is also possible to reduce the amount of sludge generated.

1 ... 1st aeration tank 2 ... 1st separation tank 3 ... 2nd aeration tank 4 ... 2nd separation tank 5 ... Return means 6 ... Anaerobic digestion tank 7 ... Gas holder 8 ... Gas pretreatment device 9 ... Generator 11 ... Carrier 20 ... First separation tank 30 ... Aeration tank 31 ... Carrier 32 ... Partition wall (split wall)
40 ... Second separation tank

Claims (8)

In the water treatment device in which the first aeration tank, the first separation tank, the second aeration tank, and the second separation tank are arranged in this order.
In the first aeration tank, a fluidized bed carrier or a fixed bed carrier made of a high molecular weight organic material carrying a biological film is housed in an amount of 1 to 30% of the tank capacity, and the first aeration tank is brought into contact with the organic wastewater. The process of obtaining the first aeration tank treated water by performing aerobic treatment for growing dispersed bacteria in the aeration tank, and
At least a part of the sludge containing the protist separated from the second separation tank is returned to the first separation tank and brought into contact with the treated water in the first aeration tank to prey on the protist. The step of immobilizing the organic matter in the first aeration tank treated water on the sludge, and
The treated water in the first aeration tank after the contact is solid-liquid separated in the first separation tank, and the sludge on which the organic matter is immobilized is extracted for energy recovery.
The first separation tank treated water from the first separation tank is aerobically treated in the second aeration tank, and
A method for treating organic wastewater, which comprises solid-liquid separation of the second aeration tank treated water obtained in the second aeration tank in the second separation tank. The method for treating organic wastewater according to claim 1, further comprising returning a part of the sludge separated from the second separation tank to the first aeration tank. The method for treating organic wastewater according to claim 1 or 2, wherein the fluidized bed carrier or fixed bed carrier carrying the biofilm in the second aeration tank is brought into contact with the treated water in the first separation tank. The method for treating organic wastewater according to any one of claims 1 to 3, wherein a dividing wall is provided in the second aeration tank. The present invention according to any one of claims 1 to 4, wherein in the first separation tank and the second separation tank, solid-liquid separation is performed by using any of a gravity precipitation type, a levitation separation type, and a filtration separation type. The method for treating organic wastewater described. The method for treating organic wastewater according to any one of claims 1 to 5, wherein the sludge obtained in the first separation tank is anaerobic digested to obtain methane gas to generate electricity. Returning at least a part of the sludge containing the protozoa separated from the second separation tank to the first separation tank returns the sludge separated from the second separation tank to the second aeration tank. for the remainder of the sludge on the total amount of the first separation tank, or the first aeration tank and the first inner pipe or waterway between the separation tank, or the first aeration tank and the first separation tank The method for treating organic wastewater according to claim 1, which comprises returning the water to the mixing tank provided in the first aeration tank and bringing it into contact with the treated water in the first aeration tank. Aerobic for growing dispersed bacteria while accommodating 1 to 30% of the tank capacity of a fluidized bed carrier or fixed bed carrier made of a polymer organic material supporting a biological film and bringing the carrier into contact with organic wastewater. The first aeration tank, which is treated to obtain the treated water in the first aeration tank,
The first aeration tank The first separation tank for solid-liquid separation of the treated water and the first aeration tank
The second aeration tank for aerobically treating the treated water in the first separation tank from the first separation tank,
The second aeration tank for solid-liquid separation of the second aeration tank treated water from the second aeration tank, and the second aeration tank.
The sludge containing the protozoa separated from the second separation tank is returned to the second aeration tank, and the total amount of the remaining sludge separated from the second separation tank is put into the first separation tank or the first aeration. It is returned to the pipe or water channel between the tank and the first separation tank, or into the mixing tank provided between the first aeration tank and the first separation tank, and comes into contact with the treated water in the first aeration tank. An organic wastewater treatment apparatus characterized in that it is provided with a means of returning the wastewater.

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