JP7157285B2 - Sewage treatment method - Google Patents

Description

The present invention relates to a sewage treatment method. More specifically, the present invention relates to a sewage treatment method using an activated sludge process.

As described in Non-Patent Document 1, in a general activated sludge process, first, sewage and activated sludge are supplied to an aeration tank. Second, the mixture of sewage and activated sludge is aerated in an aeration tank. As a result, organic matter in the sewage is decomposed by the action of aerobic microorganisms contained in the activated sludge.

Third, the mixed liquid after aeration is supplied to the sedimentation tank. Fourthly, the mixture is allowed to stand still in the sedimentation tank. As a result, the mixture is separated into sediment and supernatant water. This supernatant water is discharged as treated water. A part of this sediment is reused as activated sludge in the aeration tank (hereinafter, the sediment supplied from the sedimentation tank to the aeration tank is referred to as "return sludge").

Patent Document 1 (Japanese Patent No. 3699570) describes an improved activated sludge process. In the activated sludge method described in Patent Document 1, after culturing return sludge in a culture tank, it is supplied to an aeration tank as activated sludge. When culturing the return sludge in the culture tank, the microbial preparation is added to the return sludge.

Japanese Patent No. 3699570

Toru Ikegami, "Activated sludge method using the action of aerobic microorganisms", Internet <URL: https://kcr. Kurita. co. jp/wtschool/016. html>

In a general activated sludge method, the returned sludge is reused as it is as activated sludge. Return sludge includes not only microorganisms but also organic matter released by the metabolism of microorganisms (Biomass Associated Products, hereinafter referred to as "BAP") and organic matter released with the death of microorganisms (Utilizing Associated Products, hereinafter “UAP”).

Since BAP and UAP are also sludged together with organic matter in sewage, a large amount of excess sludge is generated in a general activated sludge process. Also, as a result of the BAP and UAP being returned to the aeration tank, the sedimentation of the sludge is reduced.

According to the activated sludge method described in Patent Document 1, the sewage treatment capacity is relatively improved. However, in the activated sludge method described in Patent Document 1, the microbial preparation is added to the return sludge, which increases the environmental load.

The present invention has been made in view of the problems of the prior art as described above. More specifically, the present invention provides a sewage treatment method capable of improving sewage treatment capacity, improving sludge settling property, and reducing excess sludge without increasing the environmental load.

The sewage treatment method of the present invention comprises a first aeration step of supplying sewage and activated sludge to an aeration tank, aerating a first liquid containing sewage and activated sludge in the aeration tank; A separation step of separating the first liquid into supernatant water and sediment in the sedimentation tank, supplying the supernatant water and sediment to the culture tank, and supplying the second liquid containing the supernatant water and sediment in the culture tank It comprises a second aeration step of aerating the liquid and a supply step of supplying the second liquid as activated sludge to the aeration tank.

In the sewage treatment method of the present invention, the sewage treatment capacity is improved because the microorganisms in the sediment contained in the second liquid are cultured and used as activated sludge.

In addition, according to the findings of the present inventors, the precipitate separated in the separation step contains BAP and UAP, so by culturing the second liquid containing the precipitate in the second aeration step, Selection pressure is applied to microorganisms capable of degrading BAP and UAP (more specifically, microorganisms that generated BAP and UAP). As a result, in the second aeration step, microorganisms capable of degrading BAP and UAP are preferentially grown and evolved. Therefore, in the sewage treatment method of the present invention, the activated sludge contains a large amount of microorganisms capable of decomposing BAP and UAP, thereby suppressing the generation of excess sludge and deterioration of sedimentation properties caused by BAP and UAP.

Furthermore, in the sewage treatment method of the present invention, no microbial preparation is used in culturing the microorganisms in the sediment, so an increase in the environmental load associated with sewage treatment can be suppressed. According to the findings of the present inventors, the addition of the microbial preparation to the sediment also hinders the cultivation of microorganisms capable of degrading BAP and UAP in the culture tank.

1 is a schematic diagram of a sewage treatment system according to a first embodiment; FIG. It is process drawing which shows the sewage-treatment method which concerns on 1st Embodiment. It is a graph which shows the relationship between sewage treatment capacity and the elapsed months after the start of experiment. It is a graph which shows the relationship between sludge sedimentation and the number of months passed after the start of experiment. It is a graph which shows the relationship between the excess sludge amount and the number of months passed from the start of experiment. It is process drawing which shows the sewage-treatment method which concerns on 2nd Embodiment.

Embodiments of the present invention will be described with reference to the drawings. In the drawings below, the same or corresponding parts are denoted by the same reference numerals, and redundant description will not be repeated.

(Sewage treatment system according to the first embodiment)
The configuration of the sewage treatment system according to the first embodiment will be described below.

FIG. 1 is a schematic diagram of a sewage treatment system according to the first embodiment. The sewage treatment system according to the first embodiment includes a pretreatment tank 10, an aeration tank 20, a sedimentation tank 30, a culture tank 40, and a controller 50, as shown in FIG. A sewage treatment system according to the first embodiment is a system for treating sewage by an activated sludge method. The sewage W1 treated by the sewage treatment system according to the first embodiment contains organic substances. The sewage W1 is, for example, factory wastewater.

The pretreatment tank 10 stores sewage W1. In the pretreatment tank 10, sludge SL1 is separated from sewage W1. The sewage W1 after pretreatment in the pretreatment tank 10 is hereinafter referred to as post-pretreatment sewage W2.

The aeration tank 20 has a tank body 21 and an air supply section 22 . The tank main body 21 stores the post-pretreatment sewage W2 and the activated sludge SL2. Hereinafter, the liquid containing the post-pretreatment sewage W2 and the activated sludge SL2 is referred to as the first liquid L1. The air supply section 22 has an air diffuser 23 and a pump 24 . The diffuser pipe 23 is arranged inside the tank body 21 . A pump 24 is connected to the diffuser tube 23 . The pump 24 supplies air to the interior of the tank body 21 through the air diffusion pipe 23 .

The sedimentation tank 30 stores the first liquid L1 that has undergone aeration in the aeration tank 20 . In the aeration tank 20, the first liquid L1 is separated into supernatant water W3 and sediment SL3. Part of the sediment SL3 is supplied to the culture tank 40, another part of the sediment SL3 is supplied to the aeration tank 20 as activated sludge SL2, and the rest of the sediment SL3 is discarded.

The culture tank 40 has a tank body 41 and an air supply section 42 . A portion of the supernatant water W3 and a portion of the sediment SL3 are stored in the tank main body 41 . Hereinafter, the liquid containing the supernatant water W3 and the sediment SL3 will be referred to as the second liquid L2. The supernatant water W3 that is not stored in the tank body 41 is discharged as treated water.

The air supply unit 42 has an air diffuser 43 and a pump 44 . The diffuser pipe 43 is arranged inside the tank body 41 . A pump 44 is connected to the diffuser tube 43 . The pump 44 supplies air to the inside of the tank body 41 through the air diffusion pipe 43 . The water level sensor 45 is arranged inside the tank body 41 . The water level sensor 45 measures the water level of the second liquid L2 inside the tank body 41 and outputs a signal corresponding to the measurement result to the control device 50 . The second liquid L2 is supplied from the culture tank 40 to the aeration tank 20 by driving the pump 46 .

The control device 50 is composed of, for example, a control panel including a programmable controller, a microcontroller, and the like. The control device 50 receives an output signal from the water level sensor 45 . An output signal from controller 50 is input to pump 46 . More specifically, the controller 50 stops the pump 46 and stops the supply of the second liquid L2 to the aeration tank 20 when the water level of the second liquid L2 detected by the water level sensor 45 falls below a predetermined level. Stop.

(Sewage treatment method according to the first embodiment)
The sewage treatment method according to the first embodiment will be described below.

FIG. 2 is a process chart showing the sewage treatment method according to the first embodiment. As shown in FIG. 2, the sewage treatment method according to the first embodiment includes a pretreatment step S1, a first aeration step S2, a separation step S3, a second aeration step S4, and a supply step S5. is doing.

In the pretreatment step S1, sewage W1 is supplied to the pretreatment tank 10 and stored therein. Sludge SL1 is separated from the wastewater W1 by allowing the wastewater W1 to stand still in the pretreatment tank 10, and the separated sludge SL1 accumulates at the bottom of the pretreatment tank 10. FIG. The sludge SL1 may be separated from the sewage W1 by supplying air to the sewage W1 stored in the pretreatment tank 10 to float the sewage W1.

In the first aeration step S2, first, the first liquid L1 containing the pretreated sewage W2 and the activated sludge SL2 is supplied to the aeration tank 20 (tank main body 21) and stored therein. Second, air is supplied to the inside of the aeration tank 20 by driving the air supply unit 22 while the first liquid L1 is stored in the aeration tank 20 . More specifically, by driving the pump 24 , air is supplied to the inside of the aeration tank 20 through the air diffusion pipe 23 . Thereby, the first liquid L1 is aerated inside the aeration tank 20 .

Activated sludge SL2 contains microorganisms. Microorganisms in the activated sludge SL2 include aerobic microorganisms. The organic matter contained in the first liquid L1 is oxidatively decomposed by the above-mentioned microorganisms to form massive flocs together with the above-mentioned microorganisms.

In the separation step S3, first, the first liquid L1 that has undergone the aeration in the first aeration step S2 is supplied to the sedimentation tank 30 and stored therein. Second, the first liquid L1 stored in the sedimentation tank 30 is allowed to stand still. As a result, flocs in the first liquid L1 precipitate as sediment SL3 at the bottom of the sedimentation tank 30, and the first liquid L1 is separated into supernatant water W3 and sediment SL3.

The sediment SL3 contains aerobic microorganisms. In addition, UAP and BAP are contained in the sediment SL3.

In the second aeration step S4, first, the second liquid L2 containing the supernatant water W3 and the sediment SL3 is supplied to and stored in the culture tank 40 (tank body 41). Second, air is supplied to the inside of the culture tank 40 by driving the air supply unit 42 while the second liquid L2 is stored in the culture tank 40 . More specifically, by driving the pump 44 , air is supplied to the inside of the culture tank 40 through the diffuser pipe 43 .

Thereby, the culture of the second liquid L2 is performed. That is, the microorganisms capable of degrading the BAP and UAP in the second liquid L2 (specifically, the microorganisms that generated the BAP and UAP) decompose the BAP and UAP in the second liquid L2 and activate them. be done.

No microbial preparation is added to the second liquid L2 in the second aeration step S4. A nutrient may be added to the second liquid L2 in the second aeration step S4. This nutrient may be, for example, sludge SL1.

In the supply step S5, the second liquid L2 cultured in the culture tank 40 is supplied to the aeration tank 20 as activated sludge SL2. Preferably, only part of the second liquid L2 cultured in the culture tank 40 is supplied to the aeration tank 20 as the activated sludge SL2. The second aeration step S4 and the supply step S5 are repeated after the culture tank 40 is replenished with the supernatant water W3 and the sediment SL3. When the water level of the second liquid L2 detected by the water level sensor 45 falls below a predetermined level, the control device 50 stops the operation of the pump 46, so that only part of the second liquid cultured in the culture tank 40 is It will be supplied to the aeration tank 20 .

<Details of the second aeration step S4>
The second aeration step S4 has a first step S41, a second step S42, and a third step S43. In the first step S41, the remaining portion of the second liquid L2 after the supply step S5 is performed is aerated. In the second step S42, after adding the supernatant water W3 to the remainder of the second liquid L2, aeration is performed. In the third step S43, the sediment SL3 is added to the remainder of the second liquid L2, and then aeration is performed.

The second step S42 and the third step S43 are performed after the first step S41. The third step S43 is performed after the second step S42. The third step S43 may be performed simultaneously with the second step S42. That is, both the supernatant water W3 and the sediment SL3 may be added to the remainder of the second liquid L2, and then the aeration may be performed.

Let VW3 be the volume of the supernatant water _W3 added in the second step S42, and VSL3 be the volume of the sediment _SL3 added in the third step S43. The value obtained by dividing _VW3 by _VSL3 is preferably decreased as the number of repetitions of the second aeration step S4 increases.

The value obtained by dividing _VW3 by _VSL3 may be decreased each time the number of repetitions of the second aeration step S4 increases, and is decreased each time the number of repetitions of the second aeration step S4 increases by a predetermined number of 2 or more times. may be After the number of repetitions of the second aeration step S4 reaches a predetermined number, the value obtained by dividing _VW3 by _VSL3 does not have to decrease as the number of repetitions of the second aeration step S4 increases. may be used).

The time when the first step _S41 is performed is TS41, the time when the second step _S42 is performed is TS42, and the time when the third step _S43 is performed is TS43. T _S41 , T _S42 and T _S43 are preferably decreased as the number of repetitions of the second aeration step S4 increases.

T _S41 , T _S42 and T _S43 may be decreased each time the number of repetitions of the second aeration step S4 increases, and is decreased each time the number of repetitions of the second aeration step S4 increases by two or more predetermined times. may After the number of repetitions of the second aeration step S4 reaches a predetermined number, T _S41 , T _S42 and T _S43 do not have to be decreased as the number of repetitions of the second aeration step S4 increases. can also be used).

Let V _air1 be the amount of air supplied to the inside of the culture tank 40 (tank body 41 ) in the first step S41. Also, the amount of air supplied to the inside of the culture tank 40 in the second step S42 is defined as V _air2 . Further, the amount of air supplied to the inside of the culture tank 40 in the third step S43 is defined as V _air3 .

V _air1 , V _air2 and V _air3 are maintained within a certain range. V _{air1 ,} V _{air1 ,} V _Air2 and V _air3 are maintained within a certain range.

(Effect of the sewage treatment method according to the first embodiment)
The effect of the sewage treatment method according to the first embodiment will be described below.

In a general activated sludge method, the sediment in the sedimentation tank 30 is returned to the aeration tank 20 as it is as activated sludge SL2. On the other hand, in the sewage treatment method according to the first embodiment, the sediment in the sedimentation tank 30 is cultured in the second aeration step S4 and then returned to the aeration tank 20 . Therefore, according to the sewage treatment method according to the first embodiment, the sewage treatment capacity is improved as compared with the general activated sludge method.

In a general activated sludge method, the sediment in the sedimentation tank 30 is returned to the aeration tank 20 as it is as activated sludge SL2. Since BAP and UAP are also sludged together with the organic matter in the wastewater, a large amount of excess sludge is generated in the general activated sludge process. Also, as a result of the BAP and UAP being returned to the aeration tank 20, the settling properties of the sludge are reduced.

According to the findings of the present inventors, BAP and UAP in sludge are decomposed only by the microorganisms that generated the BAP and UAP. Therefore, in the sewage treatment method according to the first embodiment, the second When the second liquid L2 is aerated in the aeration step S4, selective pressure is applied to the microorganisms capable of decomposing BAP and UAP in the second liquid L2.

Further, in the sewage treatment method according to the first embodiment, the aeration in the second aeration step S4 is performed with the supernatant water W3 added to the second liquid L2, so the oxygen environment in the second liquid L2 is improved. ing. Therefore, while the second aeration step S4 is being performed, microorganisms capable of decomposing BAP and UAP in the second liquid L2 are preferentially grown and evolved.

As a result, according to the sewage treatment method according to the first embodiment, the activated sludge SL2 containing many microorganisms capable of decomposing BAP and UAP is returned to the aeration tank 20, and excess sludge is generated due to BAP and UAP. and deterioration of sedimentation is suppressed.

When the microbial preparation is added to the second liquid L2, the environmental load increases (for example, the microbial species contained in the microbial preparation may destroy the ecosystem of the place where the sewage treatment method is being implemented. ). On the other hand, in the sewage treatment method according to the first embodiment, since no microbial preparation is added to the second liquid L2, an increase in environmental load is suppressed.

According to the findings of the present inventors, the addition of the microbial preparation reduces the selective pressure on microorganisms capable of degrading UAP and BAP, so that preferential growth and evolution of microorganisms capable of degrading UAP and BAP occur. will be suppressed.

In the sewage treatment method according to the first embodiment, only a part of the second liquid L2 that has undergone the second aeration step S4 is returned to the aeration tank 20 as the activated sludge SL2, and the supernatant water W3 and the sediment SL3 are added. When the second aeration step S4 is repeatedly performed in the second aeration step S4, the remainder of the second liquid L2 that has not been returned to the aeration tank 20 acts as an inoculum, so that the activity of microorganisms capable of degrading UAP and BAP in the second aeration step S4 can be made smoothly.

In the first step S41, activation of microorganisms capable of degrading UAP and BAP proceeds. In the second step S42, since the supernatant water W3 is added and aeration is performed, the oxygen environment is improved and the activation of the microorganisms capable of degrading UAP and BAP is further promoted. In the third step S43, the precipitate SL3 is added, so that the UAP and BAP are supplied to the second liquid L2 in a state in which the activation of the microorganisms capable of degrading the UAP and BAP has progressed.

Therefore, when the second aeration step S4 includes the first step S41, the second step S42, and the third step S43, the selective pressure against microorganisms capable of degrading UAP and BAP increases, and in the second aeration step S4 Activation of microorganisms capable of degrading UAP and BAP can be performed more smoothly.

As the number of repetitions of the second aeration step S4 increases, the activation of microorganisms capable of degrading _UAP and _BAP progresses. Even if the oxygen environment in the second liquid L2 is deteriorated), the activation of microorganisms capable of degrading UAP and BAP can be promoted. Then, the value obtained by dividing _VW3 by _VSL3 is decreased (that is, the amount and concentration of UAP and BAP supplied to the second liquid L2 are increased). The selection pressure for degradable microorganisms is even higher.

As the number of repetitions of the second aeration step _S4 increases, the activation of the microorganisms capable of degrading _UAP and _BAP progresses. activation can proceed. As a result, the amount of activated sludge SL2 that can be supplied from the culture tank 40 per unit time can be increased.

As the second aeration step S4 progresses in the order of the first step S41, the second step S42 and the third step S43, the ratio of the volume of the second liquid L2 to the volume of the culture tank 40 increases. When V _air1 , V _air2 and V _air3 are maintained within a certain range, the second liquid L2 air supply per volume is reduced. As a result, the selective pressure against microorganisms capable of degrading UAP and BAP in the second liquid L2 is further increased.

When a nutrient such as sludge SL1 is added to the second liquid L2 in the second aeration step S4, the organic matter in the nutrient becomes a nutrient source for the microorganisms in the second liquid L2. Activation of microorganisms can be further advanced.

<Experimental example>
A sewage treatment experiment conducted to confirm the effect of the sewage treatment method according to the first embodiment will be described below.

FIG. 3 is a graph showing the relationship between the sewage treatment capacity and the number of months elapsed after the start of the experiment. In FIG. 3, sewage treatment capacity is evaluated by BOD (Biochemical Oxygen Demand) load capacity. The higher the BOD load capacity value, the higher the sewage treatment capacity. As shown in FIG. 3, when sewage is treated according to the sewage treatment method according to the first embodiment, the BOD load capacity is in the range of 1.8 kg/m ³ to 3.8 kg/m ³ . , the average BOD load capacity was 2.7 kg/m ³ .

On the other hand, when wastewater is treated according to the general activated sludge method, the BOD capacity is about 0.5 kg/m ³ to 1.0 kg/m ³ . From this comparison, the sewage treatment method according to the first embodiment has about three times the sewage treatment capacity as compared with the general activated sludge method.

FIG. 4 is a graph showing the relationship between sludge sedimentation and the number of months elapsed after the start of the experiment. In FIG. 4, the sludge settling property is evaluated by SVI (Sludge Volume Index). The smaller the SVI value, the better the sludge settling property. As shown in FIG. 4, when sewage was treated according to the sewage treatment method according to the first embodiment, the SVI value was continuously It was less than 100 (SVI value considered good). Also, in this case, the SVI value was continuously less than 200 (the SVI value considered unsatisfactory) for 39 months out of the 40-month experimental period.

On the other hand, when wastewater was treated according to the general activated sludge method, the SVI value did not fall below 100 continuously for four months or more. In this case, the period during which the SVI value was continuously less than 200 was 18 months at the maximum.

FIG. 5 is a graph showing the relationship between the amount of excess sludge and the number of months elapsed from the start of the experiment. In FIG. 5, the surplus sludge amount is evaluated by COD (Chemical Oxygen Demand) unit sludge amount. The COD unit sludge amount is a value obtained by dividing the weight of sludge by the weight of organic matter contained in sewage. The lower the value of the COD unit sludge amount, the smaller the amount of surplus sludge. As shown in FIG. 5, when sewage was treated according to the sewage treatment method according to the first embodiment, the average COD unit sludge amount was 6.2.

On the other hand, when wastewater was treated according to the general activated sludge method, the average COD unit sludge amount was 11.5. From this comparison, according to the sewage treatment method according to the first embodiment, the excess sludge volume was reduced by about 40% compared to the general activated sludge method.

From the results of the above sewage treatment experiments, it has been experimentally clarified that the sewage treatment method according to the first embodiment can improve sewage treatment capacity, improve sludge settling property, and reduce excess sludge. rice field.

(Sewage treatment system according to the second embodiment)
The configuration of the sewage treatment system according to the second embodiment is common to the configuration of the first sewage treatment system. Therefore, the description of the configuration of the sewage treatment system according to the second embodiment is omitted here.

(Sewage treatment method according to the second embodiment)
A sewage treatment method according to the second embodiment will be described below. Here, differences from the sewage treatment method according to the first embodiment will be mainly described, and redundant description will not be repeated.

FIG. 6 is a process chart showing the sewage treatment method according to the second embodiment. As shown in FIG. 6, the sewage treatment method according to the second embodiment includes a pretreatment step S1, a first aeration step S2, a separation step S3, a second aeration step S4, and a supply step S5. is doing. Regarding this point, the sewage treatment method according to the second embodiment is in common with the sewage treatment method according to the first embodiment. However, the sewage treatment method according to the second embodiment differs from the sewage treatment method according to the first embodiment with respect to the details of the second aeration step S4.

More specifically, the second aeration step S4 of the sewage treatment method according to the second embodiment is not divided into the first step S41, the second step S42 and the third step S43. The second aeration step S4 of the sewage treatment method according to the second embodiment is repeated while the supernatant water W3 and the sediment SL3 are continuously added while the second aeration step S4 is being performed.

The volume of supernatant water W3 per unit time added in the second aeration step S4 is defined as _QW3 . Also, the volume of the sediment SL3 added per unit time in the second aeration step S4 is defined as Q _SL3 . The value obtained by dividing _QW3 by _QSL3 is preferably decreased as the number of repetitions of the second aeration step S4 increases.

The value obtained by dividing Q _W3 by Q _SL3 may be decreased each time the number of repetitions of the second aeration step S4 increases, and is decreased each time the number of repetitions of the second aeration step S4 increases by a predetermined number of times of 2 or more. may be After the number of repetitions of the second aeration step S4 reaches a predetermined number, the value obtained by dividing _QW3 by _QSL3 may not decrease as the number of repetitions of the second aeration step S4 increases. may be used).

The time during which the second aeration step _S4 is performed is TS4. TS4 is preferably decreased as the number of repetitions of the second aeration step _S4 increases. TS4 may be decreased each time the number of repetitions of the second aeration step _S4 increases, or may be decreased each time the number of repetitions of the second aeration step S4 increases by two or more predetermined times. After the number of repetitions of the second aeration step _S4 reaches a predetermined number, TS4 does not have to decrease (it may be constant) as the number of repetitions of the second aeration step S4 increases.

(Effect of the sewage treatment method according to the second embodiment)
Below, the effect of the sewage treatment method according to the second embodiment will be described. Here, differences from the effects of the sewage treatment method according to the first embodiment will be mainly described, and redundant description will not be repeated.

The sewage treatment method according to the second embodiment has a second aeration step S4 and a supply step S5, like the sewage treatment method according to the first embodiment. Therefore, like the sewage treatment method according to the first embodiment, the sewage treatment method according to the second embodiment also improves the sewage treatment capacity, improves the sludge settling property, and reduces the excess sludge without increasing the environmental load. is possible.

As the number of repetitions of the second aeration step S4 increases, the activation of microorganisms capable of degrading _UAP and _BAP progresses. Even if the oxygen environment in the second liquid L2 is deteriorated), the activation of microorganisms capable of degrading UAP and BAP can be promoted. Then, the value obtained by dividing _QW3 by _QSL3 is decreased (that is, the amount and concentration of UAP and BAP supplied to the second liquid L2 are increased). The selection pressure for degradable microorganisms is even higher.

As the number of repetitions of the second aeration step _S4 increases, the activation of the microorganisms capable of degrading UAP and BAP progresses. can be done. As a result, the amount of activated sludge SL2 that can be supplied from the culture tank 40 per unit time can be increased.

Although the embodiments of the present invention have been described as above, it is also possible to modify the above-described embodiments in various ways. Also, the scope of the present invention is not limited to the embodiments described above. The scope of the present invention is indicated by the claims, and is intended to include all changes within the meaning and range of equivalents to the claims.

Each of the above embodiments is particularly advantageously applied to the treatment of waste water containing organic matter.

REFERENCE SIGNS LIST 10 pretreatment tank 20 aeration tank 21 tank main body 22 air supply unit 23 air diffusion pipe 24 pump 30 sedimentation tank 40 culture tank 41 tank main body 42 air supply unit 43 air diffusion pipe 44 pump 45 water level sensor 50 control device L1 first liquid L2 second liquid S1 pretreatment step S2 first aeration step S3 separation step S4 second aeration step S5 supply step S41 first step S42 second Process, S43 Third process, SL1 sludge, SL2 activated sludge, SL3 sediment, W1 sewage, W2 sewage after pretreatment, W3 supernatant water.

Claims (9)

A pretreatment step for pretreatment of sewage;
The pretreated sewage and activated sludge after the pretreatment has been performed in the pretreatment step are supplied to an aeration tank, and the first liquid containing the pretreated sewage and the activated sludge is supplied to the aeration tank. A first aeration step of performing aeration;
A separation step of supplying the first liquid to a sedimentation tank and separating the first liquid into supernatant water and sediment in the sedimentation tank;
a second aeration step of supplying the supernatant water and the precipitate to a culture tank and aerating a second liquid containing the supernatant water and the precipitate in the culture tank;
A supply step of supplying the second liquid to the aeration tank as the activated sludge,
The second aeration step is performed after adding a nutrient,
The sewage treatment method, wherein the nutrient is sludge separated from the sewage by the pretreatment. In the supply step, only part of the second liquid is supplied to the aeration tank as the activated sludge,
2. The sewage treatment method according to claim 1, wherein said second aeration step and said supply step are repeated after adding said supernatant water and said sediment to said culture tank. The second aeration step after only part of the second liquid is supplied to the aeration tank as the activated sludge includes a first step of aerating the remainder of the second liquid, and A second step of adding and then aerating, and a third step of adding and aerating the precipitate,
3. The sewage treatment method according to claim 2, wherein said third step is performed after said second step or simultaneously with said second step. The value obtained by dividing the volume of the supernatant water added in the second step by the volume of the sediment added in the third step is reduced as the number of repetitions of the second aeration step increases. 4. The sewage treatment method according to claim 3. 4. The time for performing the first step, the time for performing the second step, and the time for performing the third step are reduced as the number of repetitions of the second aeration step increases. The sewage treatment method according to claim 4. The amount of air supplied to the culture tank in the first step, the amount of air supplied to the culture tank in the second step, and the amount of air supplied to the culture tank in the third step are within a certain range. The wastewater treatment method according to any one of claims 3 to 5, which is maintained. 3. The sewage treatment method according to claim 2, wherein the addition of said supernatant water and said sediment is performed continuously while aeration is taking place. 8. The sewage treatment method according to claim 7, wherein the value obtained by dividing the volume of the added supernatant water by the volume of the added sediment is reduced as the number of repetitions of the second aeration step increases. . The sewage treatment method according to claim 7 or 8, wherein the time during which said second aeration step is performed is reduced as the number of repetitions of said second aeration step increases.

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