JP7537064B2 - Wastewater treatment methods - Google Patents

Description

The present invention relates to a wastewater treatment method, more specifically, to a wastewater treatment method using an activated sludge process.

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

Third, the mixed liquor after aeration is supplied to a settling tank. Fourth, the mixed liquor is allowed to stand in the settling tank. This separates the mixed liquor into a sediment and supernatant water. The supernatant water is discharged as treated water. A portion of the sediment is reused in the aeration tank as activated sludge (hereinafter, the sediment supplied from the settling tank to the aeration tank is referred to as "returned sludge").

Patent Document 1 (JP Patent Publication No. 3699570) describes an improved activated sludge process. In the activated sludge process described in Patent Document 1, the return sludge is cultured in a culture tank and then supplied to an aeration tank as activated sludge. When the return sludge is cultured in the culture tank, a microbial preparation is added to the return sludge.

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 typical activated sludge process, the return sludge is reused as it is as activated sludge. The return sludge contains not only microorganisms, but also organic matter released by the metabolism of the microorganisms (Biomass Associated Products, hereinafter referred to as "BAP") and organic matter released with the death of the microorganisms (Utilizing Associated Products, hereinafter referred to as "UAP").

Since BAP and UAP are also converted into sludge together with the organic matter in the wastewater, a large amount of excess sludge is generated in a typical activated sludge process. In addition, the settling property of the sludge is reduced as a result of the BAP and UAP being returned to the aeration tank.

The activated sludge process described in Patent Document 1 relatively improves the wastewater treatment capacity. However, in the activated sludge process described in Patent Document 1, a microbial preparation is added to the return sludge, which increases the environmental load.

The present invention has been made in consideration of the problems of the conventional techniques as described above. More specifically, the present invention provides a wastewater treatment method capable of improving wastewater treatment capacity, improving sludge settling properties, and reducing excess sludge without increasing the environmental load.

The wastewater treatment method of the present invention includes a first aeration step of supplying wastewater and activated sludge to an aeration tank and aerating a first liquid containing the wastewater and activated sludge in the aeration tank; a separation step of supplying the first liquid to a settling tank and separating the first liquid into supernatant water and sediment in the settling tank; a second aeration step of supplying the supernatant water and sediment to a culture tank and aerating a second liquid containing the supernatant water and sediment in the culture tank; and a supply step of supplying the second liquid to the aeration tank as activated sludge.

In the wastewater treatment method of the present invention, the microorganisms in the sediment contained in the second liquid are cultured and then used as activated sludge, thereby improving the wastewater treatment capacity.

Furthermore, according to the findings of the present inventors, since the precipitate separated in the separation step contains BAP and UAP, selective pressure is applied to microorganisms capable of decomposing BAP and UAP (more specifically, the microorganisms that generated BAP and UAP) by culturing the second liquid containing the precipitate in the second aeration step. As a result, in the second aeration step, microorganisms capable of decomposing BAP and UAP are preferentially grown and evolved. Therefore, in the wastewater treatment method of the present invention, the activated sludge contains a large amount of microorganisms capable of decomposing BAP and UAP, and the generation of excess sludge and deterioration of settling properties caused by BAP and UAP are suppressed.

Furthermore, in the wastewater treatment method of the present invention, since no microbial preparation is used for culturing the microorganisms in the sediment, it is possible to suppress an increase in the environmental load associated with wastewater treatment. According to the findings of the present inventors, the addition of a microbial preparation to the sediment also hinders the cultivation of microorganisms capable of decomposing BAP and UAP in the culture tank.

1 is a schematic diagram of a wastewater treatment system according to a first embodiment. FIG. FIG. 1 is a process diagram showing a wastewater treatment method according to a first embodiment. 1 is a graph showing the relationship between wastewater treatment capacity and the number of months elapsed since the start of the experiment. 1 is a graph showing the relationship between sludge settling property and the number of months elapsed since the start of the experiment. 1 is a graph showing the relationship between the amount of excess sludge and the number of months elapsed since the start of an experiment. FIG. 6 is a process diagram showing a wastewater treatment method according to a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to the accompanying drawings, in which the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated.

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

Fig. 1 is a schematic diagram of a sewage treatment system according to a first embodiment. As shown in Fig. 1, the sewage treatment system according to the first embodiment has a pretreatment tank 10, an aeration tank 20, a sedimentation tank 30, a culture tank 40, and a control device 50. The sewage treatment system according to the first embodiment is a system for treating sewage by an activated sludge method. Sewage W1 treated by the sewage treatment system according to the first embodiment contains organic matter. The sewage W1 is, for example, factory wastewater.

Wastewater W1 is stored in the pretreatment tank 10. Sludge SL1 is separated from the wastewater W1 in the pretreatment tank 10. Hereinafter, the wastewater W1 after the pretreatment in the pretreatment tank 10 is referred to as pretreated wastewater W2.

The aeration tank 20 has a tank body 21 and an air supply unit 22. Pretreated wastewater W2 and activated sludge SL2 are stored in the tank body 21. Hereinafter, the liquid containing the pretreated wastewater W2 and the activated sludge SL2 is referred to as a first liquid L1. The air supply unit 22 has an air diffuser pipe 23 and a pump 24. The air diffuser pipe 23 is disposed inside the tank body 21. The pump 24 is connected to the air diffuser pipe 23. The pump 24 supplies air into the tank body 21 via the air diffuser pipe 23.

The settling tank 30 stores the first liquid L1 that has been aerated in the aeration tank 20. In the aeration tank 20, the first liquid L1 is separated into a supernatant water W3 and a sediment SL3. A 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 remainder of the sediment SL3 is discarded.

The culture tank 40 has a tank body 41 and an air supply unit 42. A part of the supernatant water W3 and a part of the sediment SL3 are stored in the tank body 41. Hereinafter, the liquid containing the supernatant water W3 and the sediment SL3 is referred to as a 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 aeration pipe 43 and a pump 44. The aeration pipe 43 is disposed inside the tank body 41. The pump 44 is connected to the aeration pipe 43. The pump 44 supplies air to the inside of the tank body 41 through the aeration pipe 43. The water level sensor 45 is disposed 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 configured with a control panel including, for example, a programmable controller, a microcontroller, etc. An output signal from the water level sensor 45 is input to the control device 50. The output signal from the control device 50 is input to the pump 46. More specifically, the control device 50 stops the pump 46 when the water level of the second liquid L2 detected by the water level sensor 45 falls below a predetermined level, and stops the supply of the second liquid L2 to the aeration tank 20.

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

Fig. 2 is a process diagram showing the wastewater treatment method according to the first embodiment. As shown in Fig. 2, the wastewater 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.

In the pretreatment step S1, wastewater W1 is supplied to and stored in the pretreatment tank 10. By leaving the wastewater W1 stationary in the pretreatment tank 10, sludge SL1 is separated from the wastewater W1, and the separated sludge SL1 accumulates at the bottom of the pretreatment tank 10. Note that the sludge SL1 may be separated from the wastewater W1 by, for example, supplying air to the wastewater W1 stored in the pretreatment tank 10 to cause it to float up.

In the first aeration step S2, first, a first liquid L1 containing pretreated wastewater W2 and activated sludge SL2 is supplied to and stored in the aeration tank 20 (tank body 21). Second, with the first liquid L1 stored in the aeration tank 20, the air supply unit 22 is driven to supply air into the aeration tank 20. More specifically, the pump 24 is driven to supply air into the aeration tank 20 via the air diffuser 23. As a result, the first liquid L1 is aerated in the aeration tank 20.

The activated sludge SL2 contains microorganisms. The microorganisms in the activated sludge SL2 include aerobic microorganisms. The organic matter contained in the first liquid L1 is oxidized and decomposed by the microorganisms, and becomes aggregated flocs together with the microorganisms.

In the separation step S3, first, the first liquid L1 that has been aerated in the first aeration step S2 is supplied to and stored in the settling tank 30. Second, the first liquid L1 stored in the settling tank 30 is allowed to stand. As a result, the flocs in the first liquid L1 settle to the bottom of the settling tank 30 as a precipitate SL3, and the first liquid L1 is separated into a supernatant water W3 and the precipitate SL3.

The sediment SL3 contains aerobic microorganisms. The sediment SL3 also contains UAP and BAP.

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, with the second liquid L2 stored in the culture tank 40, the air supply unit 42 is driven to supply air into the culture tank 40. More specifically, the pump 44 is driven to supply air into the culture tank 40 via the air diffuser 43.

This allows the second liquid L2 to be cultured. That is, the microorganisms capable of decomposing 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 are activated.

In the second aeration step S4, 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. 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 as activated sludge SL2 to the aeration tank 20. Preferably, only a portion of the second liquid L2 cultured in the culture tank 40 is supplied as activated sludge SL2 to the aeration tank 20. The second aeration step S4 and the supply step S5 are repeatedly performed after refilling the culture tank 40 with supernatant water W3 and 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, whereby only a portion of the second liquid cultured in the culture tank 40 is supplied to the aeration tank 20.

<Details of the second aeration step S4>
The second aeration step S4 includes a first step S41, a second step S42, and a third step S43. In the first step S41, aeration is performed on the remaining part of the second liquid L2 after the supply step S5 is performed. In the second step S42, supernatant water W3 is added to the remaining part of the second liquid L2, and then aeration is performed. In the third step S43, a precipitate SL3 is added to the remaining part 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 aeration may be performed.

The volume of the supernatant water W3 added in the second step S42 is designated as _VW3 , and the volume of the sediment SL3 added in the third step S43 is designated as _VSL3 . It is preferable that the value obtained by dividing _VW3 by _VSL3 decreases 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, or may be decreased each time the number of repetitions of the second aeration step S4 increases by a predetermined number of times that is equal to or greater than 2. 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 be decreased (it may be kept constant) as the number of repetitions of the second aeration step S4 increases.

The time when the first step S41 is performed is designated as _Ts41 , the time when the second step S42 is performed is designated as _Ts42 , and the time when the third step S43 is performed is designated as _Ts43 . It is preferable that _Ts41 , _Ts42 , and _Ts43 decrease as the number of repetitions of the second aeration step S4 increases.

_Ts41 , _Ts42 , and _Ts43 may be decreased every time the number of repetitions of the second aeration step S4 increases, or may be decreased every time the number of repetitions of the second aeration step S4 increases a predetermined number of times that is equal to or greater than 2. After the number of repetitions of the second aeration step S4 reaches a predetermined number, _Ts41 , _Ts42 , and _Ts43 do not have to be decreased (they may be constant) as the number of repetitions of the second aeration step S4 increases.

The amount of air supplied to the inside of the culture tank 40 (tank body 41) in the first step S41 is defined as V _air1 . The amount of air supplied to the inside of the culture tank 40 in the second step S42 is defined as V _air2 . 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. Even if V _air1 , V _air2 and V _air3 fluctuate, when the upper limit value and the lower limit value are within a predetermined range (for example, within ±10 percent of the control target value), V _air1 , V _air2 and V _air3 are maintained within the certain range.

(Effects of the wastewater treatment method according to the first embodiment)
The effects of the wastewater treatment method according to the first embodiment will be described below.

In a typical activated sludge process, the sediment in the settling tank 30 is returned as it is to the aeration tank 20 as activated sludge SL2. On the other hand, in the wastewater treatment method according to the first embodiment, the sediment in the settling tank 30 is cultured in the second aeration step S4 and then returned to the aeration tank 20. Therefore, the wastewater treatment method according to the first embodiment has an improved wastewater treatment capacity compared to a typical activated sludge process.

In a typical activated sludge process, the sediment in the settling tank 30 is returned as it is to the aeration tank 20 as activated sludge SL2. Since BAP and UAP are also converted into sludge together with the organic matter in the wastewater, a large amount of excess sludge is generated in a typical activated sludge process. In addition, the return of BAP and UAP to the aeration tank 20 reduces the settling property of the sludge.

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

In the wastewater treatment method according to the first embodiment, the aeration in the second aeration step S4 is performed in a state in which the supernatant water W3 is added to the second liquid L2, and therefore the oxygen environment in the second liquid L2 is improved. 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 of the first embodiment, activated sludge SL2 containing a large number of microorganisms capable of decomposing BAP and UAP is returned to the aeration tank 20, thereby suppressing the generation of excess sludge and deterioration of settling properties caused by BAP and UAP.

If a microbial preparation is added to the second liquid L2, the environmental load will be increased (for example, the microbial species contained in the microbial preparation may destroy the ecosystem of the place where the wastewater treatment method is carried out). On the other hand, in the wastewater treatment method according to the first embodiment, a microbial preparation is not added to the second liquid L2, so that the increase in the environmental load is suppressed.

Furthermore, according to the findings of the present inventors, the addition of a microbial preparation reduces the selective pressure against microorganisms capable of decomposing UAP and BAP, thereby suppressing the preferential proliferation and evolution of microorganisms capable of decomposing UAP and BAP.

In the wastewater treatment method of the first embodiment, only a portion of the second liquid L2 that has undergone the second aeration step S4 is returned to the aeration tank 20 as activated sludge SL2, and when the second aeration step S4 is repeatedly performed after adding supernatant water W3 and sediment SL3, the remainder of the second liquid L2 that has not been returned to the aeration tank 20 acts as seed bacteria, thereby smoothly activating microorganisms capable of decomposing UAP and BAP in the second aeration step S4.

In the first step S41, activation of microorganisms capable of decomposing UAP and BAP is promoted. In the second step S42, supernatant water W3 is added and aeration is performed, improving the oxygen environment and further promoting activation of microorganisms capable of decomposing UAP and BAP. In the third step S43, precipitate SL3 is added, so that UAP and BAP are supplied to the second liquid L2 in a state in which the microorganisms capable of decomposing UAP and BAP have been activated.

Therefore, when the second aeration step S4 has a first step S41, a second step S42 and a third step S43, the selective pressure on microorganisms capable of decomposing UAP and BAP is increased, and activation of microorganisms capable of decomposing UAP and BAP in the second aeration step S4 can be carried out more smoothly.

Since activation of microorganisms capable of decomposing UAP and BAP advances as the number of repetitions of the second aeration step S4 increases, even if the value obtained by dividing _VW3 by _VSL3 is reduced (i.e., even if the oxygen environment in the second liquid L2 stored in the culture tank 40 is deteriorated), activation of microorganisms capable of decomposing UAP and BAP can be promoted. As a result of reducing the value obtained by dividing _VW3 by _VSL3 (i.e., increasing the amount and concentration of UAP and BAP supplied to the second liquid L2), the selection pressure on microorganisms capable of decomposing UAP and BAP in the second liquid L2 becomes even higher.

As the number of repetitions of the second aeration step S4 increases, the activation of the microorganisms capable of decomposing UAP and BAP advances, so that even if _Ts41 , _Ts42 , and _Ts43 are reduced, the activation of the microorganisms capable of decomposing UAP and BAP can be advanced. 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 proceeds 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. If V _air1 , V _air2 , and V _air3 are maintained within a certain range, the amount of air supplied per volume of the second liquid L2 is reduced as the second aeration step S4 proceeds in the order of the first step S41, the second step S42, and the third step S43. As a result, the selection pressure on microorganisms capable of decomposing 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 serves as a nutrient source for the microorganisms in the second liquid L2, thereby further activating the microorganisms in the second liquid L2.

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

3 is a graph showing the relationship between the sewage treatment capacity and the number of months elapsed since the start of the experiment. In FIG. 3, the sewage treatment capacity is evaluated by the 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 the sewage treatment was performed according to the sewage treatment method of the first embodiment, the BOD load capacity was in the range of 1.8 kg/m ³ to 3.8 kg/m ³ , and the average value of the BOD load capacity was 2.7 kg/m ³ .

On the other hand, when wastewater is treated according to a general activated sludge method, the BOD capacity is about 0.5 kg/ ^m3 to 1.0 kg/ ^m3 . From this comparison, the wastewater treatment method according to the first embodiment has about three times the wastewater treatment capacity compared to the general activated sludge method.

FIG. 4 is a graph showing the relationship between sludge settling property and the number of months elapsed since 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 the sewage treatment method according to the first embodiment was used, the SVI value was continuously less than 100 (a value of SVI considered to be good) for 19 months out of the 40-month experimental period. In this case, the SVI value was continuously less than 200 (a value of SVI considered to be poor) for 39 months out of the 40-month experimental period.

On the other hand, when wastewater was treated using a general activated sludge process, the SVI value never remained below 100 for more than four consecutive months. In this case, the maximum period during which the SVI value remained below 200 was 18 months.

Fig. 5 is a graph showing the relationship between the amount of excess sludge and the number of months elapsed since the start of the experiment. In Fig. 5, the amount of excess sludge is evaluated by the 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 the wastewater. The lower the value of the COD unit sludge amount, the smaller the amount of excess sludge. As shown in Fig. 5, when wastewater was treated according to the wastewater treatment method of the first embodiment, the average value of the COD unit sludge amount was 6.2.

On the other hand, when wastewater was treated according to a general activated sludge process, the average COD unit sludge volume was 11.5. From this comparison, it was found that the wastewater treatment method according to the first embodiment reduced the volume of excess sludge by about 40 percent compared to the general activated sludge process.

From the results of the above wastewater treatment experiments, it has been experimentally demonstrated that the wastewater treatment method according to the first embodiment makes it possible to improve wastewater treatment capacity, improve sludge settling properties, and reduce excess sludge.

(Sewage treatment system according to the second embodiment)
The configuration of the wastewater treatment system according to the second embodiment is common to the configuration of the first wastewater treatment system, and therefore, a description of the configuration of the wastewater treatment system according to the second embodiment will be omitted here.

(Sewage treatment method according to the second embodiment)
The wastewater treatment method according to the second embodiment will be described below. Here, the differences from the wastewater treatment method according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

Fig. 6 is a process diagram showing a wastewater treatment method according to a second embodiment. As shown in Fig. 6, the wastewater treatment method according to the second embodiment has a pretreatment step S1, a first aeration step S2, a separation step S3, a second aeration step S4, and a supply step S5. In this respect, the wastewater treatment method according to the second embodiment is common to the wastewater treatment method according to the first embodiment. However, the wastewater treatment method according to the second embodiment is different from the wastewater treatment method according to the first embodiment in terms of the details of the second aeration step S4.

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

The volume of the supernatant water W3 added per unit time in the second aeration step S4 is designated as _QW3 . Also, the volume of the sediment SL3 added per unit time in the second aeration step S4 is designated as _QSL3 . It is preferable that the value obtained by dividing _QW3 by _QSL3 decreases as the number of repetitions of the second aeration step S4 increases.

The value obtained by dividing _QW3 by _QSL3 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 a predetermined number of times or more. After the number of repetitions of the second aeration step S4 reaches a predetermined number, the value obtained by dividing _QW3 by _QSL3 does not have to be decreased (it may be constant) as the number of repetitions of the second aeration step S4 increases.

The time during which the second aeration step S4 is performed is designated as T _S4 . It is preferable that T _S4 is decreased as the number of repetitions of the second aeration step S4 increases. T _S4 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 a predetermined number of times or more. After the number of repetitions of the second aeration step S4 reaches a predetermined number, T _S4 does not have to be decreased (it may be constant) as the number of repetitions of the second aeration step S4 increases.

(Effects of the wastewater treatment method according to the second embodiment)
The effects of the wastewater treatment method according to the second embodiment will be described below. Here, differences from the effects of the wastewater treatment method according to the first embodiment will be mainly described, and overlapping descriptions will not be repeated.

The wastewater treatment method according to the second embodiment has a second aeration step S4 and a supply step S5, similar to the wastewater treatment method according to the first embodiment. Therefore, similar to the wastewater treatment method according to the first embodiment, the wastewater treatment method according to the second embodiment also makes it possible to improve the wastewater treatment capacity, improve the sludge settling property, and reduce excess sludge without increasing the environmental load.

As the number of repetitions of the second aeration step S4 increases, the activation of microorganisms capable of decomposing UAP and BAP advances, so even if the value obtained by dividing _QW3 by _QSL3 is reduced (i.e., even if the oxygen environment in the second liquid L2 stored in the culture tank 40 is deteriorated), the activation of microorganisms capable of decomposing UAP and BAP can be promoted. As a result of reducing the value obtained by dividing _QW3 by _QSL3 (i.e., increasing the amount and concentration of UAP and BAP supplied to the second liquid L2), the selection pressure on microorganisms capable of decomposing UAP and BAP in the second liquid L2 becomes even higher.

As the number of repetitions of the second aeration step S4 increases, the activation of microorganisms capable of decomposing UAP and BAP advances, so that even if T _S4 is reduced, the activation of microorganisms capable of decomposing UAP and BAP can be advanced, and 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 embodiment of the present invention has been described above, the above-mentioned embodiment can be modified in various ways. The scope of the present invention is not limited to the above-mentioned embodiment. The scope of the present invention is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

Each of the above-described embodiments is particularly advantageously applied to the treatment of wastewater containing organic matter.

10 Pretreatment tank, 20 Aeration tank, 21 Tank body, 22 Air supply unit, 23 Aeration pipe, 24 Pump, 30 Sedimentation tank, 40 Culture tank, 41 Tank body, 42 Air supply unit, 43 Aeration pipe, 44 Pump, 45 Water level sensor, 50 Control device, L1 First liquid, L2 Second liquid, S1 Pretreatment process, S2 First aeration process, S3 Separation process, S4 Second aeration process, S5 Supply process, S41 First process, S42 Second process, S43 Third process, SL1 Sludge, SL2 Activated sludge, SL3 Sediment, W1 Wastewater, W2 Pretreated wastewater, W3 Supernatant.

Claims (7)

A pretreatment process for performing pretreatment on the wastewater;
a first aeration step of supplying the pretreated wastewater and the activated sludge after the pretreatment in the pretreatment step to an aeration tank, and aerating a first liquid containing the pretreated wastewater and the activated sludge in the aeration tank;
a separation step of supplying the first liquid to a settling tank and separating the first liquid into a supernatant and a sediment in the settling 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;
and a supply step of supplying the second liquid to the aeration tank as the activated sludge,
The second aeration step is carried out after nutrients are added,
The nutrient is sludge contained in the wastewater to be pretreated,
In the supplying step, only a portion of the second liquid is supplied to the aeration tank as the activated sludge,
The second aeration step and the supply step are repeatedly performed after adding the supernatant water and the precipitate to the culture tank,
The second aeration step after only a portion 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, a second step of adding the supernatant water and then aerating, and a third step of adding the sediment and then aerating,
The wastewater treatment method , wherein the third step is carried out after the second step or simultaneously with the second step . 2. The wastewater treatment method according to claim 1, wherein a 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 decreased as the number of repetitions of the second aeration step increases. 2. The wastewater treatment method according to claim 1 , wherein the time for which the first step is performed, the time for which the second step is performed, and the time for which the third step is performed are decreased as the number of repetitions of the second aeration step increases. The wastewater treatment method according to any one of claims 1 to 3, wherein an amount of air supplied to the culture tank in the first step, an amount of air supplied to the culture tank in the second step, and an amount of air supplied to the culture tank in the third step are maintained within a certain range. 2. The wastewater treatment method according to claim 1 , wherein the addition of the supernatant water and the sediment is carried out continuously while aeration is being carried out. A pretreatment process for performing pretreatment on the wastewater;
a first aeration step of supplying the pretreated wastewater and the activated sludge after the pretreatment in the pretreatment step to an aeration tank, and aerating a first liquid containing the pretreated wastewater and the activated sludge in the aeration tank;
a separation step of supplying the first liquid to a settling tank and separating the first liquid into a supernatant and a sediment in the settling 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;
and a supply step of supplying the second liquid to the aeration tank as the activated sludge,
The second aeration step is carried out after nutrients are added,
The nutrient is sludge contained in the wastewater to be pretreated,
In the supplying step, only a portion of the second liquid is supplied to the aeration tank as the activated sludge,
The second aeration step and the supply step are repeatedly performed after adding the supernatant water and the precipitate to the culture tank,
The addition of the supernatant water and the sediment is carried out continuously while aeration is being carried out;
A wastewater treatment method, wherein a value obtained by dividing the volume of the added supernatant water by the volume of the added sediment decreases as the number of repetitions of the second aeration step increases. 7. The wastewater treatment method according to claim 5 , wherein the time during which the second aeration step is performed is decreased as the number of times the second aeration step is repeated increases.

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