KR20230156186A - Bio-filtering apparatus, waste water treatment system having the same and waste water treatment methode - Google Patents

Abstract

The biological filtration device according to the present invention includes a filter tube that has the shape of a hollow tube extending in the vertical direction and has an upper net and a lower net that are arranged to cross the internal space and are spaced apart from each other in the vertical direction; A plurality of floating filter media inserted between the upper and lower nets in the inner space of the filter pipe; a discharge pipe provided on an upper portion of a side wall of the filter pipe at a point where the upper net is installed; It is configured to include; a cleaning air supply pipe that supplies backwash gas between the upper and lower meshes in the internal space of the filter pipe. The sewage treatment facility according to the present invention includes a flow control tank provided with an inlet through which wastewater flows; A contact aeration tank in which a filter medium and a bubble injection unit are installed; A biological filtration device configured as described above is mounted therein, and includes a settling tank having an outlet connected to the outlet pipe; wherein the height of the top of the filtering pipe is located higher than the appropriate water level of the settling tank.

Description

Biological filtration apparatus, sewage treatment facility and waste water treatment method equipped with the same {Bio-filtering apparatus, waste water treatment system having the same and waste water treatment methode}

The present invention relates to a biological filtration device that treats sewage by biological methods, a sewage treatment facility equipped with the same, and a sewage treatment method using the same. More specifically, it relates to a biological filtration device that treats sewage by a biological method, and more specifically, to a sewage treatment method using the same. ) and a biological filtration device that can be cleaned without a separate backwash facility, a sewage treatment facility equipped with the same, and a sewage treatment method.

In general, if sewage and excrement generated from industrial sites or homes are buried in the soil, they can permeate into the soil, contaminating soil and groundwater, and destroying the natural environment, so the sewage is treated at a sewage treatment facility.

Hereinafter, a conventional sewage treatment facility will be described in detail with reference to the attached drawings.

Figure 1 is a cross-sectional view showing the internal structure of a conventional sewage treatment facility.

As shown in Figure 1, a conventional sewage treatment facility consists of tanks divided by a plurality of partitions within one main body, including a flow rate adjustment tank (10), a contact aeration tank (20), a sedimentation tank (30), and a discharge tank (40). It consists of, etc.

When wastewater flows in through the inlet 12 of the flow rate adjustment tank 10, the flow rate adjustment tank 10 adjusts the flow rate of the wastewater. The contact aeration tank 20 is composed of a first contact aeration tank 21, a second contact aeration tank 22, a third contact aeration tank 23, a fourth contact aeration tank 24, etc., and in the contact aeration tank 20, a flow rate adjustment tank. Organic substances in the wastewater that have passed through (10) come into contact with an appropriate amount of oxygen so that they can be decomposed by aerobic microorganisms.

A filter medium 50 to which microorganisms attach is installed inside the contact aeration tank 20 to remove various organic substances contained in sewage. At this time, in order to effectively remove organic substances contained in sewage, a sufficient supply of dissolved oxygen is essential, so a separate bubble injection unit 60 for supplying oxygen is installed on the lower side of the filter medium 50.

In the sedimentation tank 30, sediment contained in the wastewater that has passed through the contact aeration tank 20 is gradually deposited. The sedimentation tank 30 sediments the sludge decomposed in the contact aeration tank 20 and discharges only the supernatant water to the outlet while sending the sludge to the flow rate adjustment tank 10 on the upstream side. The wastewater discharged from the settling tank (30) is sent to the defoaming tank (not shown) to remove the bubbles in the contact aeration tank (20), and the wastewater that has passed through the defoaming tank (not shown) is sent to the outflow pipe (42) of the discharge tank (40). ) to exit the sewage treatment facility.

As mentioned above, the wastewater flowing into the flow rate adjustment tank 10 is filtered while passing through the contact aeration tank 20. A large amount of suspended solids may also be present in the wastewater passing through the contact aeration tank 20. Suspended matter filtration devices for filtering out substances once again have been proposed in various ways.

However, the suspended solids filtration devices proposed so far not only require separate installation space but also require various additional facilities for backwashing, so they have the disadvantage of being difficult to apply to currently commercialized FRP sewage treatment facilities.

In particular, filtration devices are most commonly used as a means to remove suspended solids, and the filtration devices or biological filtration devices proposed to date include backwash pumps, automatic control valves, backwash water tanks, air compressors, and backwash sludge collection devices. , backwash sludge drawing device, etc., there are many necessary devices, and the structure is not only complex, but also difficult to control accurately.

KR 10-0824809 B1

The present invention was proposed to solve the above problems. It can filter suspended solids in the sedimentation tank without the need for separate installation space, can clean the flotation media without a separate backwash device, and has excellent usability due to its simple configuration. The purpose is to provide a biological filtration device, a sewage treatment facility equipped with the same, and a sewage treatment method using the same.

The biological filtration device according to the present invention for achieving the above object has the shape of a hollow tube extending in the vertical direction, and is provided with an upper and lower net arranged to cross the internal space and spaced apart from each other in the vertical direction. Yeo Jae-gwan, who does; A plurality of floating filter media inserted between the upper and lower nets in the inner space of the filter pipe; a discharge pipe provided on an upper portion of a side wall of the filter pipe at a point where the upper net is installed; It is configured to include; a cleaning air supply pipe that supplies backwash gas between the upper and lower meshes in the internal space of the filter pipe.

The cleaning air supply pipe is configured to supply air to a portion of the space between the upper and lower nets adjacent to the lower net.

The cleaning air supply pipe is formed so that the nozzle faces upward.

The cleaning air supply pipe is disposed so that the injection port is adjacent to one inner wall of the filter pipe.

A guide plate is provided on the inner wall of the filter pipe to spirally guide the flow direction of the air supplied from the cleaning air supply pipe.

It further includes a filtration filter covering the upper opening of the filter tube.

The sewage treatment facility according to the present invention includes a flow control tank provided with an inlet through which wastewater flows; A contact aeration tank in which a filter medium and a bubble injection unit are installed; A biological filtration device configured as described above is mounted therein, and includes a settling tank having an outlet connected to the outlet pipe; wherein the height of the top of the filtering pipe is located higher than the appropriate water level of the settling tank.

an air lift pipe that transports wastewater in the flow rate adjustment tank to the contact aeration tank; It further includes a return pipe for returning the sludge that has fallen to the bottom of the settling tank to the flow rate adjustment tank.

It further includes a water level gauge that measures the water level in the settling tank, and the air lift pipe is configured to stop operation when the water level in the settling tank exceeds a preset standard value.

The sewage treatment method according to the present invention is a method of purifying sewage wastewater using a sewage treatment facility configured as described above, comprising: a first step of determining whether the water level in the sedimentation tank is above the standard value; A second step of stopping the air lift operation of the flow rate adjustment tank if the water level in the sedimentation tank is higher than the standard value in the first step; a third step of returning the sludge in the sedimentation tank to the flow rate adjustment tank to lower the water level in the sedimentation tank; A fourth step of removing sludge attached to the flotation media by supplying cleaning air through a cleaning air supply pipe; A fifth step of stopping the supply of cleaning air; It includes a sixth step of resuming the air lift operation of the flow rate adjustment tank.

The third step is configured to stop supplying cleaning air when the supply of cleaning air continues for a preset time.

The third step is configured to stop supplying cleaning air when the water level in the sedimentation tank falls below a standard value.

The biological filtration device according to the present invention and the sewage treatment facility equipped with the same can filter suspended solids in the sedimentation tank without the need for a separate installation space, can wash the flotation media without a separate backwash device, and have a simple configuration, making them easy to use. It has the advantage of being excellent and highly usable.

In addition, by using the sewage treatment method according to the present invention, the wastewater discharged from the sedimentation tank can be filtered once again, thereby improving the wastewater filtration effect, and has the advantage that the flotation media is automatically backwashed according to the contamination level of the flotation media. there is.

Figure 1 is a cross-sectional view showing the internal structure of a conventional sewage treatment facility.
Figure 2 is a cross-sectional perspective view of the biological filtration device according to the present invention.
Figure 3 is a cross-sectional view of a sewage treatment facility according to the present invention.
Figure 4 is a flow chart of the sewage treatment method according to the present invention.
Figures 5 to 7 are diagrams showing the state of use of the sewage treatment facility according to the present invention.
Figure 8 is a cross-sectional perspective view of the second embodiment of the biological filtration device according to the present invention.

Hereinafter, with reference to the attached drawings, embodiments of the biological filtration device according to the present invention, the sewage treatment facility equipped with the same, and the sewage treatment method will be described in detail.

Figure 2 is a cross-sectional perspective view of a biological filtration device according to the present invention, and Figure 3 is a cross-sectional view of a sewage treatment facility according to the present invention.

The biological filtration device 100 according to the present invention is a type of biological filtration device for filtering suspended substances in the sedimentation tank 30. As shown in Figure 2, the biological filtration device 100 has the shape of a hollow tube extending in the vertical direction and has an internal space. A filter pipe 110 having an upper net 112 and a lower net 114 arranged to cross but spaced apart from each other in the vertical direction, and the upper net 112 and the lower net of the internal space of the filter tube 110. A plurality of floating filter media 120 inserted between the nets 114, a draw-out pipe 130 provided on the side wall of the filter pipe 110 above the point where the upper net 112 is installed, and the filter pipe ( It is configured to include a cleaning air supply pipe 140 that supplies backwashing gas between the upper net 112 and the lower net 114 in the internal space of 110).

The floating filter 120 is made of a material with a specific gravity less than 1, and as water rises inside the filter pipe 110, it floats upward and comes into close contact with the bottom of the upper net 112. In this way, when wastewater flows in through the lower opening of the filter pipe 110 with a plurality of floating filter media 120 in close contact with the bottom of the upper net 112, various suspended substances contained in the wastewater are transferred to the floating filter media. Since it is filtered through 120, only the filtered water is discharged to the outside through the outlet pipe 130. At this time, the flotation media 120 is made of synthetic resin balls or fiber balls with a plurality of pores formed on the surface so that suspended substances can be adsorbed. This flotation media 120 is commercialized in the conventional upflow filtration system. Therefore, detailed description of the characteristics of the floating media 120 will be omitted.

When filtration by the flotation media 120 continues for a certain period of time and a large amount of suspended matter is adsorbed to the flotation media 120, air is sprayed onto the flotation media 120 through the cleaning air supply pipe 140 to flotate the flotation media 120. Wash the filter medium (120). At this time, if a large amount of flotation media 120 is pressed against the bottom of the upper net 112, the flotation media 120 does not move significantly even if air is sprayed on the flotation media 120, so the flotation media 120 A problem arises in that suspended substances attached to the surface do not fall off.

Therefore, when cleaning the floating media 120, the level of water flowing into the filter pipe 110 is lowered and the plurality of floating media 120 are spaced downward from the upper net 112. In this way, when the plurality of floating filter media 120 are spaced downward from the bottom of the upper net 112, the adhesion between the floating filter media 120 is lowered, so that when washing air is sprayed toward the floating media 120, each floating media 120 They move more actively, and as a result, suspended substances attached to the surface of the flotation media 120 fall in the form of sludge (S).

In this way, the process in which the suspended solids attached to the flotation media 120 are separated and fall by the supply of washing air will be described in detail with reference to FIGS. 5 to 7 below.

The sewage treatment facility according to the present invention is a type of water treatment device equipped with the biological filtration device 100 shown in FIG. 2, and as shown in FIG. 3, the flow rate adjustment tank 10 is provided with an inlet 12 through which wastewater flows. ), a contact aeration tank 20 in which a filter medium 50 and a bubble injection unit 60 are installed, and a biological filtration device 100 configured as above is installed therein and connected to the outlet pipe 130. It is configured to include a settling tank (30) having an outlet (42).

At this time, since the top height of the filter pipe 110 is located slightly higher than the appropriate water level of the sedimentation tank 30, the wastewater in the sedimentation tank 30 flows into the filter pipe 110 through the lower opening of the filter pipe 110. After being introduced into the interior, suspended solids pass through the lower net 114 and pass between a plurality of floating filters 120, and are filtered by the floating filters 120. The wastewater with suspended solids filtered out while passing through the floating filter 120 passes through the upper net 112 and is then discharged to the outside of the sewage treatment facility through the outlet pipe 130 and the outlet 42.

Meanwhile, an air lift pipe 200 is installed inside the flow rate adjustment tank 10 to transfer the wastewater in the flow rate adjustment tank 10 to the contact aeration tank 20, and a lift pipe 200 is installed at the end of the air lift pipe 200 from the outside. A lift air supply pipe 210 through which air is supplied is connected. Therefore, when lift air is supplied to the air lift pipe 200 through the lift air supply pipe 210, the lift air rises along the inside of the air lift pipe 200, and the wastewater in the flow adjustment tank 10 is discharged from the lift air. Due to the rising air current, the air rises along the air lift pipe 200 and passes into the contact aeration tank 20.

In addition, the settling tank 30 is provided with a return pipe 300 that returns the sludge S that has fallen to the bottom of the settling tank 30 to the flow rate adjustment tank 10. At this time, the return pipe 300, like the air lift pipe 200, may be configured to transfer the sludge (S) in the sedimentation tank 30 using the rising air current of air supplied from the outside, and may be configured to transfer the sludge (S) in the sedimentation tank 30, and may be used as a separate pump ( It may be configured to transport the sludge (S) by (not shown).

The air lift pipe 200 and return pipe 300 as described above are applied in substantially the same way to conventional sewage treatment facilities such as FRP sewage treatment facilities, and the air lift pipe 200 and return pipe 300 Detailed description is omitted.

Figure 4 is a flow chart of the sewage treatment method according to the present invention, and Figures 5 to 7 are diagrams of the use state of the sewage treatment facility according to the present invention.

The sewage treatment method according to the present invention is a method of purifying sewage and wastewater using the sewage treatment facility shown in FIG. 3. The wastewater flowing into the flow adjustment tank (10) through the inlet (12) is discharged through the air lift pipe (200). After passing to the contact aeration tank 20, organic matter in the wastewater is removed by the filter medium 50 installed in the contact aeration tank 20. The wastewater from which organic matter has been removed while passing through the contact aeration tank 20 is transferred to the settling tank 30, undergoes a process of settling sludge (S), and then flows into the inside of the filter pipe 110 through the lower opening of the filter pipe 110. flows into. As shown in FIG. 5, the wastewater flowing into the filter pipe 110 passes through a space where the flotation filter medium 120 is dense, removing various suspended substances, and then flows out to the outside through the discharge pipe 130 and the outlet 42. is discharged as

At this time, when the amount of suspended solids filtered by the flotation media 120 increases and aggregates to form sludge (S), the pores between the flotation media 120 are clogged by the sludge (S), so the wastewater in the sedimentation tank 30 It cannot be discharged to the outside smoothly, and as a result, the water level in the sedimentation tank 30 gradually rises.

In this way, when the water level of the sedimentation tank 30 is detected and the water level of the sedimentation tank 30 becomes more than the standard value (S10), it is determined that it is time to wash the floating media 120, and the washing process of the floating media 120 is performed. It will proceed. At this time, whether the water level in the settling tank 30 rises above the standard value can be determined by the operator directly with the naked eye, or may be configured to be automatically measured by a water level gauge (not shown) installed in the settling tank 30. It may be possible.

As shown in FIG. 5, in a state where a plurality of floating media 120 are pressed against the bottom of the upper net 112, even if air is supplied to the floating media 120, the plurality of floating media 120 do not move actively. Since it is not maintained and remains in a fixed state, the cleaning efficiency of the flotation media 120 is reduced. Therefore, when cleaning the flotation filter 120, the sludge (S) and wastewater that fell on the bottom of the settling tank 30 are returned to the flow rate adjustment tank 10 through the return pipe 300 to lower the water level in the settling tank 30. , it is desirable to lower the density of the floating media 120.

At this time, if the operation of the air lift pipe 200, which transfers the wastewater in the flow rate adjustment tank 10 to the contact aeration tank 20, continues, the wastewater in the contact aeration tank 20 is continuously transferred to the settling tank 30, so the settling tank 30 Even if the sludge (S) and wastewater are returned to the flow adjustment tank (10), the water level in the sedimentation tank (30) does not decrease.

Therefore, when the water level in the settling tank 30 becomes higher than the standard value and the floating media 120 is to be washed, first stop the operation of the air lift pipe 200 (S20) and then use the return pipe 300 to wash the floating media 120. 30) The water level in the sedimentation tank 30 is lowered by returning the sludge (S) to the flow rate adjustment tank (10) (S30). As shown in FIG. 6, when the water level in the settling tank 30 decreases and the adhesion between the flotation media 120 decreases, cleaning air is supplied through the cleaning air supply pipe 140 to remove the sludge (S) attached to the flotation media 120. ) is removed (S40).

At this time, if the cleaning air supply pipe 140 is configured to supply air to the floating media 120 located on the upper side, the floating media 120 located on the lower side cannot move actively, so cleaning may not be performed normally. . Therefore, the cleaning air supply pipe 140 supplies air to the area adjacent to the lower net 114 in the space between the upper net 112 and the lower net 114, and the sprayed air is not directly directed to the flotation media 120. It is preferable that the injection port 142 of the cleaning air supply pipe 140 is formed to face upward so that it can be contacted.

In addition, the cleaning air supply pipe 140 has the injection port 142 so that the floating media 120 can be mixed in the vertical direction as shown in FIG. 6 by the air sprayed through the cleaning air supply pipe 140. It is preferable that it is placed adjacent to one inner wall of the filter pipe 110. In this way, when the injection port 142 of the cleaning air supply pipe 140 is disposed adjacent to one inner wall of the filter pipe 110, the floating filter media 120 rises on the side where the injection port 142 is located and then rises from the injection port 140. Since a descending convection phenomenon occurs on the opposite side where (142) is located, all floating media (120) are evenly mixed and can be effectively washed.

When the washing of the flotation media 120 progresses to a certain level, the supply of the washing air is stopped (S50), and then the air lift operation of the flow adjustment tank 10 is resumed to restore the water level of the sedimentation tank 30 to the normal level ( S60).

At this time, the cleaning air may be set to be automatically stopped when the supply to the inside of the filter pipe 110 continues for a preset time, and the flotation filter may be stopped when the water level in the sedimentation tank 30 falls below the standard value. It may be set to stop supply when it is determined that the cleaning of (120) has progressed to a certain level.

In this way, by using the sewage treatment facility and sewage treatment method according to the present invention, suspended solids in the sewage water filled in the sedimentation tank 30 can be removed even without providing a separate space outside the sewage treatment facility, and the backwash pump and automatic Even without separate backwashing facilities such as control valves, backwashing tanks, air compressors, backwashing sludge collection devices, and backwashing sludge drawing devices, the flotation media 120 can be effectively washed, thereby maximizing sewage treatment efficiency. There is an advantage.

Figure 8 is a cross-sectional perspective view of the second embodiment of the biological filtration device 100 according to the present invention.

When the pores between the flotation media 120 are filled with sludge (S) and the water level in the sedimentation tank 30 increases, the water level in the sedimentation tank 30 must be lowered so that the flotation media 120 can be washed. The water level gauge in the sedimentation tank 30 is If there is a breakdown or the return pipe 300 does not operate normally, the water level in the sedimentation tank 30 continues to rise.

In this way, when the water level in the settling tank 30 rises excessively beyond the standard value, the wastewater in the settling tank 30 flows back into the contact aeration tank 20 and the flow rate adjustment tank 10, causing a problem of overflowing the sewage treatment facility. It can be.

The biological filtration device 100 according to the present invention is designed to solve the above problems, that is, when the water level in the sedimentation tank 30 becomes excessively high, the wastewater in the sedimentation tank 30 does not flow back into the contact aeration tank 20. Another feature of the configuration is that it is configured to be bypassed through the outlet 42. That is, the filter pipe 110 is formed in the shape of a hollow tube with the top open. When the water level in the sedimentation tank 30 becomes excessively high, the wastewater in the sedimentation tank 30 flows into the upper opening of the filter pipe 110. It can be discharged to the outside through the discharge pipe 130 and the outlet 42.

At this time, if the wastewater in the sedimentation tank 30 is discharged directly to the outside without passing through the flotation filter 120, contamination of soil and rivers may occur. Therefore, the biological filtration device 100 according to the present invention is designed to use the filter pipe 110. ) can be configured to filter wastewater flowing in through the upper opening.

That is, the biological filtration device 100 according to the present invention may be additionally provided with a filtration filter 150 that covers the upper opening of the filter pipe 110, as shown in FIG. 8. In this way, when the filtration filter 150 is additionally provided at the upper opening of the filter pipe 110, the wastewater flows into the inside of the filter pipe 110 through the upper opening of the filter pipe 110 without passing through the floating filter medium 120. Even if it is, it is additionally filtered by the filtration filter 150 and then discharged to the outside, so there is an advantage in that soil and river pollution problems can be prevented. At this time, the filtration filter 150 can be applied as any type of filter as long as it can filter out suspended solids contained in wastewater.

In addition, when the cleaning air is supplied to the flotation media 120 through the cleaning air supply pipe 140, the more actively the flotation media 120 moves, that is, the longer the moving distance of the flotation media 120, the more the flotation media 120 moves. (120) The cleaning efficiency is improved.

The biological filtration device 100 according to the present invention is equipped with air supplied from the cleaning air supply pipe 140 on the inner wall of the filter pipe 110 so that the moving distance of the floating filter medium 120 can be increased as much as possible within a limited space. A guide plate 116 may be provided to guide the flow direction in a spiral manner. In this way, when the guide plate 116 is provided on the inner wall of the filter pipe 110, the air supplied from the cleaning air supply pipe 140 flows in a spiral shape, so the floating filter medium 120 also flows in a spiral shape along the cleaning air. As a result, the cleaning efficiency of the flotation media 120 is improved.

At this time, in this embodiment, only the case where the guide plate 116 guides the flow direction of the cleaning air in a spiral shape is shown. However, the shape of the guide plate 116 can be replaced by any shape if it can improve the cleaning effect. You can.

Above, the present invention has been described in detail using preferred embodiments, but the scope of the present invention is not limited to the specific embodiments and should be interpreted in accordance with the appended claims. Additionally, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

10: flow adjustment tank 12: inlet
20: contact aeration tank 30: sedimentation tank
42: outlet 50: filter medium
60: Bubble injection unit 100: Biological filtration device
110: Yeojae pipe 112: Upper net
114: lower net 116: guide plate
120: floating media 130: withdrawal pipe
140: cleaning air supply pipe 142: nozzle
150: Filtration filter 200: Air lift pipe
210: lift air supply pipe 300: return pipe
S: Sludge

Claims (12)

A filter tube that has the shape of a hollow tube extending in the vertical direction and has an upper network and a lower network that are arranged to cross the internal space and are spaced apart from each other in the vertical direction;
A plurality of floating filter media inserted between the upper and lower nets in the inner space of the filter pipe;
a discharge pipe provided on an upper portion of a side wall of the filter pipe at a point where the upper net is installed;
a cleaning air supply pipe that supplies backwash gas between the upper and lower meshes in the inner space of the filter pipe;
A biological filtration device comprising: In claim 1,
The cleaning air supply pipe is a biological filtration device characterized in that it is configured to supply air to a portion of the space between the upper and lower nets adjacent to the lower net. In claim 2,
A biological filtration device characterized in that the cleaning air supply pipe is formed so that the nozzle faces upward. In claim 3,
A biological filtration device, wherein the cleaning air supply pipe is disposed so that an injection port is adjacent to one inner wall of the filter pipe. In claim 1,
A biological filtration device characterized in that the inner wall of the filter pipe is provided with a guide plate that spirally guides the flow direction of the air supplied from the cleaning air supply pipe. In claim 1,
A biological filtration device further comprising a filtration filter covering the upper opening of the filter tube. A flow adjustment tank provided with an inlet through which wastewater flows;
A contact aeration tank in which a filter medium and a bubble injection unit are installed;
A sedimentation tank in which the biological filtration device according to any one of claims 1 to 6 is installed, and which has an outlet connected to the outlet pipe;
Includes,
A sewage treatment facility, characterized in that the height of the top of the filter pipe is located higher than the appropriate water level of the sedimentation tank. In claim 7,
an air lift pipe that transports wastewater in the flow rate adjustment tank to the contact aeration tank;
a return pipe that returns the sludge that falls to the bottom of the settling tank to the flow rate adjustment tank;
A sewage treatment facility further comprising: In claim 8,
Further comprising a water level gauge for measuring the water level of the sedimentation tank,
The air lift pipe is a sewage treatment facility characterized in that it is configured to stop operation when the water level in the sedimentation tank exceeds a preset standard value. As a method of purifying wastewater using the sewage treatment facility according to claim 8,
A first step of determining whether the sediment tank water level is above the standard value;
A second step of stopping the air lift operation of the flow rate adjustment tank if the water level in the sedimentation tank is higher than the standard value in the first step;
a third step of returning the sludge in the sedimentation tank to the flow rate adjustment tank to lower the water level in the sedimentation tank;
A fourth step of removing sludge attached to the flotation media by supplying cleaning air through a cleaning air supply pipe;
A fifth step of stopping the supply of cleaning air;
A sixth step of resuming the air lift operation of the flow adjustment tank;
A sewage treatment method comprising: In claim 10,
The third step is a sewage treatment method characterized in that it is configured to stop supplying cleaning air when the supply of cleaning air continues for a preset time. In claim 10,
The third step is a sewage treatment method characterized in that the supply of washing air is stopped when the water level in the sedimentation tank falls below the standard value.

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