JPH0780491A - Biological treatment of waste water or the like - Google Patents

Abstract

PURPOSE:To effectively utilize the whole volume of a reaction tank for treatment of waste water by utilizing magnetic force to concentrate activated sludge forcedly, and efficiently returning the concentrated activated sludge to the inlet side of the reaction tank. CONSTITUTION:Powdery magnetic substance 16 is added to activated sludge liquid in a reaction tank 2. The activated sludge is transferred to a separation tank 1 placed in the outlet 2a side of the reaction tank 2. Thereafter a magnetic field is impressed in the separation tank 1 by a magnetic generator 10. Thereby activated sludge 14 holding the powdery magnetic substance 16 is caught on the magnetic generator 10 and forcedly flocculated. Since activated sludge 14 flocculated in the separation tank 1 still has sufficient fluidity in the treated liquid, impression of the magnetic field is stopped for a time. In the meanwhile, the concentrated activated sludge liquid containing flocculated activated sludge 14 is returned to the inlet 2a side of the reaction tank 2 through a pipeline 13.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a technique for treating organic wastewater and the like by an activated sludge method, and more specifically, it concentrates activated sludge from a reaction tank using magnetic force and returns it to the reaction tank. The present invention relates to a biological treatment method of wastewater including a process.

[0002]

2. Description of the Related Art As a technique of this kind, as shown in FIG. 6, a magnetic substance powder 37 is added to and mixed with an activated sludge liquid in an aeration tank 35 which is a reaction tank to retain the magnetic substance powder 37 in the activated sludge 14. Then, the activated sludge liquid is guided by a pump 39 to a separation tank 38 provided on the outlet 35b side of the aeration tank 35, and the activated sludge 14 in which magnetic powder 37 is held on a rotating drum 40 magnetized in the separation tank 38. The activated sludge 14 is forcibly aggregated by adsorbing the activated sludge, and the activated sludge 14 adhering to the surface of the rotating drum 40 is scraped off by the scraping plate 41 and continuously returned to the aeration tank 35. A method of separating activated sludge and treated water as described above is known (Japanese Patent Publication No. 63-59759).

According to this method, the final settling tank, which required a vast space in the wastewater treatment system by the activated sludge method, can be downsized or omitted, and a large space saving can be realized. In addition, since the activated sludge concentration in the aeration tank 35 increases, it is possible to increase the inflowing organic substance capacity. Further, even when bulking (sludge expansion) occurs, activated sludge and treated water can be easily solid-liquid separated, so that sludge outflow can be prevented.

[0004]

However, in the above-mentioned conventional technique, the sludge collected by being attached to the rotary drum 40 has no fluidity.
There is a problem that the concentration cannot be returned to the a side, and in a large-scale reaction tank, the activated sludge concentration on the inlet 35a side is always low, and only the outlet 35b side has a high concentration, so that the reaction tank volume cannot be effectively used.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to efficiently return the activated sludge forcibly concentrated by using magnetic force to the inlet side of the reaction tank, and to make the entire volume of the reaction tank into waste water. An object of the present invention is to provide a biological treatment method for wastewater that can be effectively used for treatment.

[0006]

In order to achieve the above object, the biological treatment method for wastewater and the like according to the first invention is a first process for adding magnetic powder to activated sludge liquid in a reaction tank. And a second process of transferring the activated sludge liquid to a separation tank provided on the outlet side of the reaction tank, and applying a magnetic field in the separation tank to capture the activated sludge containing magnetic powder at a predetermined site. And forcibly agglomerating the liquid, and a fourth process of temporarily stopping the application of the magnetic field and returning the concentrated activated sludge liquid containing the agglomerated activated sludge to the inlet side of the reaction tank. It is characterized by being

The biological treatment method for wastewater and the like according to the second invention is the first process of adding magnetic powder to the activated sludge liquid in the reaction tank, and the activated sludge liquid at the outlet of the reaction tank. A second process of transferring to an ascending-flow type separation tank connected to the third process, and a third process of applying a magnetic field in the separation tank to capture the activated sludge containing the magnetic powder at a predetermined site to aggregate the sludge. A fourth process for temporarily stopping the application of the magnetic field and for returning the concentrated activated sludge liquid containing the flocculated activated sludge to the inlet side of the reaction tank while using the water flow from the reaction tank during that time. Is characterized by.

The biological treatment method for wastewater and the like according to the third invention is the first process of adding magnetic powder to the activated sludge liquid in the reaction tank and the activated sludge liquid at the outlet of the reaction tank. The second process of transferring to the separation tank provided on the side, and energizing the electromagnets arranged around the separation tank to apply a magnetic field in the separation tank, and the activated sludge containing the magnetic powder is placed in the separation tank in a predetermined manner. And a fourth process of temporarily stopping the application of the magnetic field and returning the concentrated activated sludge liquid containing the flocculated activated sludge to the inlet side of the reaction tank. It is characterized by including.

The biological treatment method for wastewater and the like according to the fourth aspect of the present invention is the first process of adding magnetic powder to the activated sludge liquid in the reaction tank and the activated sludge liquid at the outlet side of the reaction tank. The second process of transferring to the upflow type separation tank provided in the above, and a magnetic field is applied to the inside of the separation tank by energizing the electromagnets arranged around the separation tank to activate the activated sludge containing the magnetic powder in a predetermined amount. The third process of trapping and aggregating at the site, and temporarily stopping the energization of the electromagnet, during which the water flow from the reaction tank is used to open the valve provided below the upper end of the separation tank And a fourth process for returning the concentrated activated sludge liquid containing the coagulated activated sludge to the inlet side of the reaction tank.

In the first to fourth inventions, a part or the whole of the reaction tank may have an oxygen-free structure.
The particle size of the magnetic powder is preferably 10 μm or less.

[0011]

According to the method of the first aspect of the present invention, the magnetic powder is incorporated into the activated sludge in the reaction tank by the first process, and the active sludge containing the magnetic powder is retained by the second process. The sludge liquid is introduced into the separation tank, and the activated sludge containing the magnetic powder is magnetically trapped at a predetermined portion in the separation tank by the third process and forcibly aggregated.
The activated sludge aggregated in the separation tank through the above process is
It is still in the treatment liquid and has sufficient fluidity. Therefore, in the subsequent fourth process, the application of the magnetic field is temporarily stopped to release the capture of the activated sludge, and during that time, the concentrated activated sludge liquid containing the flocculated activated sludge is returned to the inlet side of the reaction tank by the fluid transfer means. As a result, high-concentration activated sludge can be efficiently returned to the wastewater inlet side of the reaction tank.

According to the method of the second invention, in the fourth process, the concentrated activated sludge liquid containing the flocculated activated sludge is returned to the inlet side of the reaction tank by utilizing the water flow from the reaction tank. With this, high-concentration activated sludge can be efficiently returned to the wastewater inlet side of the reaction tank without using a dedicated transfer means such as a pump.

According to the method of the third aspect of the present invention, in the third process, the electromagnets arranged around the separation tank are energized to apply a magnetic field to the separation tank to retain the magnetic powder. The activated sludge thus obtained is captured at a predetermined site on the inner surface of the separation tank. Next, in the fourth process, the energization of the electromagnet is temporarily stopped to release the trapping of the activated sludge, and in the meantime, the activated sludge of high concentration is returned to the inlet side of the waste water of the reaction vessel. It can be returned efficiently. According to the method of the third aspect of the present invention, since the electromagnet arranged around the separation tank is used as the magnetic field generating means, no obstacle is provided in the separation tank, and the entire volume of the separation tank is effectively made. Available.

According to the method of the fourth aspect of the invention, in the fourth process, the energization of the electromagnet is temporarily stopped to release the trapping of the activated sludge, while the water flow from the reaction tank is utilized. By returning the concentrated activated sludge liquid containing the coagulated activated sludge to the inlet side of the reaction tank, the high-concentration activated sludge trapped on the inner surface of the separation tank can be efficiently returned to the wastewater inlet side of the reaction tank. . According to the method of the fourth aspect of the present invention, since the electromagnet arranged around the separation tank is used as the magnetic field generating means, it is not necessary to provide an obstacle in the separation tank, and the entire volume of the separation tank can be effectively used. It can be used and the flocculated activated sludge can be effectively conveyed by the water flow from the reaction tank.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment in which the biological treatment method according to the present invention is applied to the treatment of wastewater will be described below with reference to FIGS.

[Embodiment 1] FIG. 1 is a schematic configuration diagram showing a first embodiment of an apparatus for treating wastewater by the method of the present invention. As shown in the figure, the inlet 2 a of the reaction tank 2 is connected to a wastewater introduction pipe 3, the outlet 2 b is connected to an outflow pipe 4, and the outflow pipe 4 is connected to a final settling tank 5. To the final settling tank 5, a treated water outflow pipe 6 for flowing out the overflowed supernatant water and a return sludge pipe 7 for returning the precipitate to the reaction tank 2 are connected. A sludge return pump 33 is provided in the middle of the return sludge pipe 7. An air diffusing plate 19 is installed at the bottom of the reaction tank 2, and air is supplied to the air diffusing plate 19 through the air pipe 20 so that the air diffusing plate 1
Bubbles are discharged from 9 and the inside of the reaction tank 2 is aerated. A transfer pump 8 is installed near the bottom of the reaction tank 2, and its discharge port is connected to the separation tank 1 via a transfer pipe 9. Inside the separation tank 1, a comb-shaped or parallel plate-shaped magnetic generator 10 for generating a magnetic field is provided. The magnetic generator 10 is made of a magnetic material such as iron and is connected to an exciting means such as an electromagnet (not shown) provided outside the separation tank 1. Separation tank 1
A magnetic separation water pipe 11 for sending the overflow water to the final settling tank 5 is connected to the upper part of the. Separation tank 1
A magnetic separation sludge pump 12 is provided in the vicinity of the bottom of the inside, and its discharge port is connected to a wastewater introduction pipe 3 at an inlet 2a of the reaction tank 2 via a return pipe 13. A magnetic powder supplying device 15 is provided near the upper part of the reaction tank 2, and from this, the magnetic powder 16 is provided in the reaction tank 2 if necessary.
Are being put in.

In the apparatus of this embodiment configured as described above, the inflowing wastewater is introduced into the reaction tank 2 through the wastewater introducing pipe 3, and is normally sent from the outflow pipe 4 to the final settling tank 5, and the supernatant water is treated. It is discharged through the water outflow pipe 6. At this time, the activated sludge 14 in the reaction tank 2 is subjected to wastewater treatment, and then settled and separated in the final settling tank 5, and is returned to the reaction tank 2 through the return sludge pipe 7 by driving the sludge return pump 33. When the sedimentation of the organisms 14 in the final sedimentation tank 5 is poor,
The magnetic powder supply device 15 is operated to put the magnetic powder 16 into the reaction tank 2, and after a predetermined time has elapsed, the transfer pump 8 is driven to transfer the activated sludge liquid in the reaction tank 2 to the separation tank 1. At the same time, the magnetic generator 10 is excited. Separation tank 1
Most of the activated sludge 14 sent to is held in a state in which the magnetic powder 16 is taken inside, and is captured on the surface of the magnetic generator 10 by the magnetic force. As a result, the separation tank 1
Most of the activated sludge 14 sent to is sent to the final settling tank 5 via the magnetic separation water pipe 11 where the liquid having a low biological concentration is sent to the final settling tank 5, where the supernatant liquid is subjected to settling separation operation and the supernatant liquid is treated water. The activated sludge 14 that has flowed out through the outflow pipe 6 and leaked from the separation tank 1 passes through the return sludge pipe 7 and again into the reaction tank 2
Returned to.

On the other hand, the transfer pump 8 and the magnetic generator 10
Is intermittently stopped, and the magnetic separation sludge pump 12 is driven during this stop time. Then, the activated sludge 14 attached to the magnetic field generator 10 is separated from the surface of the magnetic field generator 10 and returned to the reaction tank 2 through the return pipe 13. Since the activated sludge 14 collected in the separation tank 1 can be returned to the inlet 2a side of the reaction tank 2, the activated sludge concentration in the reaction tank 2 can be uniformly increased, and the entire volume of the reaction tank 2 can be effectively used. The wastewater treatment can be carried out. Moreover, since most of the activated sludge 14 sent to the separation tank 1 is collected and returned to the reaction tank 2, the load on the final settling tank 5 is significantly reduced,
The washout of the activated sludge 14 to the treated water is eliminated, and the problem of bulking is solved. If the separation tank 1 is always movable, the activated sludge 1 with a higher concentration can be obtained.
Since 4 can be returned to the reaction tank 2, the concentration of activated sludge in the reaction tank 2 is improved and it becomes possible to receive waste water with a higher load.

In the above structure, the transfer pump 8
The transfer pipe 9 is omitted, and a U-shaped water channel 17 is provided in the flow path (outflow pipe 4) connecting the reaction tank 2 and the final settling tank 5 as shown in FIGS. The magnetic generator 10 may be provided for use in No. 1 and a comb-shaped or parallel plate-shaped magnetic generator 10 is provided at the upstream side portion or the downstream side portion of the water channel 17. When the magnetic generator 10 is provided in the downstream side portion of the water channel 17, the magnetic generator 1 is attached as the activated sludge 14 is attached.
The 0 portion is clogged, the flow path is blocked, and the water level on the upstream side rises. Therefore, as shown in FIG. 3, a level switch 18 is provided on the upstream side of the water channel 17 so that the excitation of the magnetic generator 10 is temporarily released when the water level rises. In this configuration, the activated sludge 14 accumulates at the bottom of the U-shaped water channel 17, so the return pipe 13 for returning the recovered activated sludge 14 to the reaction tank 2 is connected to the bottom of the water channel 17. Preferably.

[Embodiment 2] FIG. 4 is a schematic configuration diagram showing a second embodiment of an apparatus for treating wastewater by the method of the present invention. In this embodiment, a transfer pump 8 is provided near the outlet 2b in the reaction tank 2, and two separation tanks 2 are provided at a position higher than the reaction tank 2 from the discharge port of the transfer pump 8.
A pipe 23 is connected to the bottoms of 1 and 22. Separation tank 2
Both 1 and 22 are formed in a bottomed cylindrical shape, and annular electromagnets 24 and 25 are provided so as to surround the periphery. The overflow water in the separation tanks 21 and 22 is sent to the final settling tank 5 via the magnetic separation water pipe 29, respectively. A return pipe 30 is connected to the side walls of the separation tanks 21 and 22 at a position lower than the connection position of the magnetic separation water pipe 29. Solenoid valves 26 and 27 are provided in the middle of the return pipe 30. The other components designated by the same reference numerals as those in FIG. 1 are the same as those in the first embodiment.

In the apparatus of this embodiment constructed as described above, the normal operation, that is, the operation when the separation tanks 21 and 22 are not operated, is the same as in the first embodiment. Then, when the settling property of the activated sludge 14 in the final settling tank 5 deteriorates, the magnetic powder supplying device 15 is operated to introduce the magnetic powder 16 into the reaction tank 2, and after a predetermined time elapses, the transfer pump 8 Is driven to transfer the activated sludge liquid in the reaction tank 2 to the separation tanks 21 and 22, and the electromagnet 24,
Energize 25. As a result, the activated sludge 14 is captured on the inner surfaces of the separation tanks 21 and 22, and the liquid having a low biological concentration is sent to the final settling tank 5 through the magnetic separation water pipe 29. When the operation is continued, the activated sludge 14 is accumulated in the separation tanks 21 and 22, and is in a concentrated state. In that case, the electromagnets 24, 2
The energization of 5 is temporarily stopped while the solenoid valves 26, 27
By opening, the activated sludge 14 is returned to the reaction tank 2 through the return pipe 30 by the rising water flow sent from the reaction tank 2 by the transfer pump 8. The solenoid valves 26, 27 are opened for a certain period of time and then closed again. That is,
The deenergization of the electromagnets 24 and 25 and the opening operation of the solenoid valves 26 and 27 are synchronized in the separation tanks 21 and 22. Separation tank 2
1, 22 are formed in the shape of a bottomed cylinder, and there are no obstacles such as the magnetic generator 10 inside, so that the total volume of the separation tanks 21 and 22 can be effectively used and the water flow from the reaction tank 2 The activated sludge 14 can be effectively conveyed.
When a larger number of separation tanks are provided, it is preferable to use a timer to shift the operation timing of the electromagnets and electromagnetic valves of each separation tank.

In the second embodiment, the separation tank 21,
Although the case where the electromagnets 24 and 25 are arranged outside 22 has been described, the separation tank 1 of FIG. 1 may be used instead of the separation tanks 21 and 22 of FIG. 4, and the electromagnets may be provided inside thereof. In that case, the pipe 23 of the transfer pump 8 provided in the reaction tank 2 is connected to the bottom of the separation tank 1 so that the rising water flow sent from the reaction tank 2 by the transfer pump 8 is utilized. The activated sludge in the inside can be returned to the reaction tank 2.

[Embodiment 3] FIG. 5 is a schematic configuration diagram showing a third embodiment of an apparatus for treating wastewater by the method of the present invention. In this embodiment, the activated sludge liquid is transferred to the separation tanks 21 and 22 using the water flow from the reaction tank 2. However, the transfer pump 8 of FIG. 4 is not provided, the separation tanks 21 and 22 are arranged at the same height as the reaction tank 2, and the outlet 2b of the reaction tank 2 and the bottoms of the separation tanks 21 and 22 are piped. It is tied with 28. In addition, the separation tank 21,
22 is connected to a return sludge tank 31 provided separately, and the bottom of the return sludge tank 31 is connected to the wastewater introduction pipe 3 of the reaction tank 2 via the return sludge pipe 32. A sludge return pump 33 is provided in the return sludge pipe 32.

In the apparatus of this embodiment, the magnetic powder supplying device 15 is operated by a timer or the like so that the magnetic powder 16 is charged into the reaction tank 2 at a constant time interval, whereby the reaction is performed. The activated sludge liquid in the tank 2 is always mixed with the magnetic powder 16 having a constant concentration. Further, the electromagnets 24 and 25 of the separation tanks 21 and 22 are normally energized and kept in an energized state so that energization is intermittently stopped by a timer or the like and the solenoid valves 26 and 27 are opened only during that time. Leave. Therefore, in the apparatus of this embodiment, the activated sludge liquid from the reaction tank 2 always flows into the separation tanks 21 and 22 to separate them.
The activated sludge 14 is captured on the inner surface of 2, and a clear treatment liquid having a low biological concentration is discharged through the magnetic separation water pipe 29.
When the operation is continued, the activated sludge 14 is accumulated and concentrated in the separation tanks 21 and 22, but the energization of the electromagnets 24 and 25 is intermittently stopped, and the solenoid valves 26 and 27 are opened during that time. The activated sludge 14 accumulated on the inner surfaces of the separation tanks 21 and 22 is flowed by the water flow from the reaction tank 2 to the return sludge tank 31 through the return pipe 30. And
The activated sludge 14 accumulated in the return sludge tank 31 is returned to the reaction tank 2 through the return sludge pipe 7 by driving the sludge return pump 33. In this embodiment, the returned sludge tank 3
Although the final sedimentation tank 5 was omitted by installing 1 separately,
The returned sludge tank 31 and the final settling tank 5 may be used together.

In the above examples, the magnetic powder 1
The particle size of 6 is 10 μm or less. Iron powder is typically used as the magnetic powder 16, but other powder may be used as long as it has a property of being attracted to a magnetic field. For reference, the data when a simulated experiment in which iron powder having a particle size of 10 μm or less is added to the activated sludge liquid and a magnetic field is applied by a permanent magnet is shown below.

MLVSS concentration of activated sludge 2880 2880 2880 mg / l Iron powder addition concentration 900 1900 3050 mg / l MLVSS concentration after magnetic field separation 2300 1150 160 mg / l Further, in the above examples, a part of the reaction tank 2 was an oxygen-free structure. If so, the reaction tank 2 can be provided with a biological nitrogen or phosphorus removal function, and further, if the entire reaction tank 2 has an oxygen-free structure, anaerobic activated sludge treatment can be realized.
Further, the method of the present invention can be applied to a fermentation treatment facility for the purpose of producing useful substances, in addition to the purpose of treating wastewater.

[0027]

In summary, according to the present invention, the following excellent effects can be exhibited.

(1) According to the method described in claim 1, the activated sludge is captured in the separation tank by the magnetic field, and then the application of the magnetic field is temporarily stopped, and the concentrated activated sludge liquid containing the flocculated activated sludge in the meantime. The activated sludge can be efficiently returned to the inlet side of the reaction tank because the activated sludge is returned to the inlet side of the reaction tank. Therefore, the concentration of activated sludge in the reaction tank can be uniformly increased, and the entire volume in the reaction tank can be effectively used for wastewater treatment.

(2) According to the method of the second aspect, the concentrated activated sludge liquid containing the coagulated activated sludge is returned to the inlet side of the reaction tank by utilizing the water flow from the reaction tank, so that a dedicated pump or the like is used. High-concentration activated sludge can be efficiently returned to the wastewater inlet side of the reaction tank without using a transfer means.

(3) According to the method of claim 3, since the electromagnet arranged around the separation tank is used as the magnetic field generating means, it is not necessary to provide an obstacle in the separation tank, and the whole separation tank is provided. Volume can be used effectively.

(4) According to the method of claim 4, since the electromagnet arranged around the separation tank is used as the magnetic field generating means, no obstacle is provided in the separation tank, and the total volume of the separation tank is large. Can be effectively used, and the flocculated activated sludge can be effectively conveyed by the water flow from the reaction tank.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an apparatus for treating wastewater by the method of the present invention.

FIG. 2 is a partial schematic view showing a modified example of the device of FIG.

FIG. 3 is a partial schematic view showing a modified example of the apparatus of FIG.

FIG. 4 is a schematic configuration diagram showing a second embodiment of an apparatus for performing wastewater treatment by the method of the present invention.

FIG. 5 is a schematic configuration diagram showing a third embodiment of the apparatus for performing wastewater treatment by the method of the present invention.

FIG. 6 is a schematic configuration diagram showing an example of an apparatus for performing wastewater treatment by a conventional method.

[Explanation of symbols]

 1 Separation tank 2 Reaction tank (aeration tank) 2a Inlet 3 Wastewater introduction pipe 2b Outlet 4 Outflow pipe 5 Final settling tank 6 Treated water outflow pipe 10 Magnetic generator 13 Return pipe 15 Magnetic powder supply device 16 Magnetic powder 21 Separation Tank 22 Separation tank 24 Electromagnet 25 Electromagnet 26 Electromagnetic valve 27 Solenoid valve 30 Return pipe 31 Return sludge tank

Claims (4)

[Claims] 1. A process for adding magnetic powder to the activated sludge liquid in the reaction tank, a process for transferring the activated sludge liquid to a separation tank provided on the outlet side of the reaction tank, and a magnetic field applied in the separation tank. Then, the process of trapping the activated sludge containing the magnetic powder at a predetermined site in the separation tank to forcibly agglomerate it, and temporarily stopping the application of the magnetic field, during which the concentrated activated sludge containing the agglomerated activated sludge A process for returning the liquid to the reaction tank, and a biological treatment method for wastewater and the like. 2. A process for adding magnetic powder to the activated sludge liquid in the reaction tank, a process for transferring the activated sludge liquid to a separation tank provided on the outlet side of the reaction tank, and a magnetic field applied in the separation tank. Then, the process of trapping the activated sludge containing the magnetic powder at a predetermined site in the separation tank to agglomerate, and temporarily stopping the application of the magnetic field, while using the water flow from the reaction tank to agglomerate And a process of returning concentrated activated sludge liquid containing sludge to a reaction tank. 3. A process of adding magnetic powder to the activated sludge liquid in the reaction tank, a process of transferring the activated sludge liquid to a separation tank provided on the outlet side of the reaction tank, and a process arranged around the separation tank. The process of energizing the electromagnet to apply a magnetic field in the separation tank to capture and agglomerate the activated sludge containing the magnetic powder at a predetermined site in the separation tank, and temporarily stop the application of the magnetic field, And a process of returning concentrated activated sludge liquid containing coagulated activated sludge to a reaction tank. 4. A process for adding magnetic powder to the activated sludge liquid in the reaction tank, a process for transferring the activated sludge liquid to a separation tank provided on the outlet side of the reaction tank, and a process arranged around the separation tank. The process of energizing the electromagnet to apply a magnetic field in the separation tank to trap the activated sludge containing the magnetic powder at a predetermined site in the separation tank to agglomerate and temporarily stop the application of the magnetic field Of the biological treatment of wastewater, etc. characterized by including a process of temporarily stopping the energization of the wastewater and returning the concentrated activated sludge liquid containing the coagulated activated sludge to the reaction tank by using the water flow from the reaction tank during that time. Processing method.