KR20020038409A - Aqua-composting BNR Device and Method for Clearing Wastewater Employing the Same - Google Patents

Abstract

PURPOSE: The purification method of sewage and waste water using underwater composting system and electric system is provided to improve the disposal efficiency of sewage/waste water and change generated sludge to compost by connecting the processes of water treatment and sludge treatment. CONSTITUTION: The purification method is as follows: settling floating materials of sewage/waste water in a first settling tank(1), where precipitates and supernatant are sent to composting tank and anaerobic tank, respectively; mixing the effluent, supernatant, and sludge from a final settling tank(6) in an anaerobic tank(2), where the effluent is kept for 1-2hrs. and the concentration of dissolved oxygen of the effluent is 0.01-0.2mg/L; supplying air to the effluent in an aerobic tank(3), where the concentration of dissolved oxygen of the effluent is 2-4mg/L; stirring the effluent in an anoxic tank(4), where the concentration of dissolved oxygen of the effluent is 0.01-0.5mg/L; settling the sludge contained in the effluent in a reaerobic tank(5), where the concentration of dissolved oxygen of the effluent is 3-4mg/L; exhausting supernatant to the outside of a final settling tank, and precipitated sludge in sent to a composting tank(7).

Description

Aqua-composting BNR Device and Method for Clearing Wastewater Employing the Same}

The present invention relates to an underwater composting device and a method for purifying wastewater using the same. More specifically, the present invention by composting the sludge generated in the water treatment process using a water composting device and an electric device, including sedimentation tank, anaerobic tank, aerobic tank, anaerobic tank, re-aeration tank and aquatic composting tank, the treatment process and sludge of sewage water The present invention relates to a method of treating sewage water in which a treatment process is linked.

At present, many processes are being researched or developed as advanced sewage water treatment process at home and abroad. While most of these processes do not go beyond the technical framework of combining anaerobic tanks, anaerobic tanks and aerobic tanks, it is true that these efforts have actually achieved some results. However, most of the developed water treatment processes focus only on the removal of organic substances, nitrogen and phosphorus in the influent, and the efficiency of the treatment process can be achieved because the plant is actually operated in conjunction with the sludge treatment process developed in a separate dimension. It can also be a major cause of deterioration. In particular, large domestic sewage treatment plants treat supernatant of high concentration sludge digestion process, which adversely affects overall process efficiency. As such, most of the processes developed in the prior art do not optimally link the main treatment process and the sludge treatment process in the development process, and thus problems or often fail when applying a laboratory or pilot scale development process to the actual treatment plant. There was a case.

Therefore, the necessity of effectively linking the main treatment process with the sludge treatment process and improving the efficiency of the wastewater treatment in the treatment plant has been continuously raised.

Therefore, the present inventors have made a thorough research to establish a sewage treatment method that effectively improves the efficiency of sewage treatment in the treatment plant by effectively linking the main treatment process with the sludge treatment process, and thus, sedimentation tank, anaerobic tank, aerobic tank, anaerobic tank, and ash. By using the water composting device including the aeration tank and the water composting tank, the sludge treatment and the main treatment process are perfectly connected to remove contaminants such as organic matter, nitrogen and phosphorus in the sewage water, and the sludge generated at this time as the compost material By converting to improve the efficiency of the sludge treatment, it was confirmed that the required cost can be reduced, and completed the present invention.

After all, the main object of the present invention is to provide an underwater composting apparatus including a sedimentation tank, anaerobic tank, aerobic tank, anoxic tank, reaeration tank, and underwater composting tank.

Another object of the present invention is to provide a method for purifying sewage water using an electric device.

1 is a schematic diagram of an underwater composting device according to an embodiment of the present invention.

Figure 2a is a cross-sectional view of a one-stage underwater composting tank according to an embodiment of the present invention.

Figure 2b is a cross-sectional view of a two-stage underwater composting tank according to an embodiment of the present invention.

<Description of the reference numerals for the main parts of the drawings>

1: first settling tank 2: anaerobic tank

3: aerobic tank 4: anaerobic tank

5: reaeration tank 6: final precipitation tank

7: Underwater Composting Tank 7-1: Intermittent Aeration Tank

7-2: Solid-liquid Separation Tank 8: Sediment Delivery Line

9: outflow line 10: sludge delivery line

11: Sludge collection line 12: Underwater compost tank supernatant delivery line

13: sludge discharge line 14: stirrer

15: air supply 16: baffle

Underwater composting apparatus of the present invention is the first sewage tank is directly introduced into the wastewater, sedimentation of suspended solids contained in the introduced wastewater, and the first settling tank for sending out the supernatant to the anaerobic tank; An anaerobic tank communicated with the initial settling tank, inflow of effluent from the initial settling tank, sludge sent out from the final settling tank is added, and equipped with a stirrer; Adjacent to the side of the anaerobic tank, the outflow of the anaerobic tank flows into the natural flow type, an aerobic tank equipped with an air supply; Adjacent to the side of the aerobic tank, the outflow of the aerobic tank flows into the natural flow type, an anoxic tank equipped with a stirrer; Adjacent to the side of the anoxic tank, the outflow of the anoxic tank flows into the natural flow type, re-aeration tank equipped with an air supply; Adjacent to the side of the re-aeration tank, the outflow of the re-aeration tank flows into the natural flow type, the final sedimentation tank for sedimenting the sludge contained in the re-aeration tank, the discharge of the supernatant to the outside; Communication with the initial settling tank, the final settling tank and the anaerobic tank, and includes an underwater composting tank equipped with a slaw fat extraction line, a stirrer and an air supply.

The electric underwater composting tank communicates with the initial settling tank to store the material settled in the initial settling tank, communicates with the final settling tank and stores the sludge settled in the final settling tank, and communicates with the anaerobic tank to supply the sludge to the anaerobic tank, and excess sludge to the outside The sludge discharge line, the stirrer and the air supply to discharge may be in the form of a single stage water tank provided in one tank.

In addition, the electric underwater composting tank communicates with the initial settling tank, stores the material settled in the initial settling tank, sludges it, and communicates with the final settling tank to introduce the sludge settled in the final settling tank, intermittent aeration tank equipped with a stirrer and air supply ; And a solid-liquid separation tank having a sludge discharge line communicating with the intermittent aeration tank, in which sludge from the intermittent aeration tank is introduced, and communicating with the anaerobic tank, the sludge is sent to the anaerobic tank, and having a sludge discharge line for releasing excess sludge to the outside. It may be in the form.

The wastewater purification method, which is connected to the wastewater treatment process and sludge treatment process using the electric water composting device, flows the wastewater into the initial sedimentation tank, settles the suspended solids, and then sends the sediment into the underwater composting tank and the supernatant is sent to the anaerobic tank. step; The supernatant of the first settling tank and the sludge supernatant of the underwater composting tank were introduced into the anaerobic tank, and the concentration of the microorganisms contained in the inflow liquid introduced into the anaerobic tank by adding the sludge was maintained at 2,500 to 4,000 mg / L, and 0.01 to 0.2 mg / L. Stirring while maintaining the concentration of dissolved oxygen, and flowing out into the aerobic tank by the amount introduced; Supplying air so that the concentration of dissolved oxygen contained in the inlet of the aerobic tank is maintained at 2 to 4 mg / L, and flowing out into the anoxic tank by the amount of inflow; Stirring the concentration of dissolved oxygen contained in the inflow water of the anoxic tank while maintaining 0.01 to 0.5 mg / L, and distilling it into the reaeration tank by the amount introduced; Supplying air to maintain the concentration of dissolved oxygen contained in the inlet water of the reaeration tank at 3 to 4 mg / L, and flowing out the final settling tank by the amount introduced; After sedimenting the sludge contained in the effluent flowing into the final sedimentation tank, the sedimented sludge is discharged to the underwater composting tank, the supernatant is discharged to the outside of the underwater composting device; And supplying the supernatant of the underwater composting tank to the anaerobic tank, and transforming the sludge into the composting form and discharging the sludge to the outside of the underwater composting apparatus through the sludge discharge line.

Hereinafter, with reference to the accompanying drawings, it will be described in more detail the configuration of the underwater composting device of the present invention.

1 is a schematic view showing an embodiment of the underwater composting device of the present invention. As shown in Figure 1, the underwater composting device of the present invention is the first settling tank (1), anaerobic tank (2), aerobic tank (3), anoxic tank (4), re-aeration tank (5), final sedimentation tank (6) and underwater composting tank ( 7). The bottom of the initial sedimentation tank (1) is a sediment discharge line (8) in communication with the water composting tank (7), one side of the initial sedimentation tank (1) is provided with the inflow of sewage water, the other side of the anaerobic tank (2) It is provided with the effluent discharge line (9) in communication with. The anaerobic tank (2) is provided with a stirrer (14), on one side of the outflow water discharge line (9) communicated with the initial settling tank (1), the underwater composting tank supernatant liquid delivery line (12) in communication with the underwater compost tank (7) And a sludge discharge line 10 in communication with the final settling tank 6, the other side of the anaerobic tank 2, the outflow of the anaerobic tank 2 can flow into the adjacent aerobic tank 3, anaerobic tank (2) The residence time of the influent water is configured to be 1 to 2 hours. The aerobic tank (3) is provided with an air supply (15), one side adjacent to the anaerobic tank (2) can be the inflow of the anaerobic tank (2) flows into the natural flow type, the other side is the outflow of the aerobic tank (3) It can be introduced into the natural oxygen flow into the adjacent anoxic tank (4), the residence time of the influent water in the aerobic tank (3) is configured to be 3 to 4 hours. The oxygen-free tank 4 is provided with a stirrer 14, one side adjacent to the aerobic tank 3 can be the inflow water of the aerobic tank 3 flows into the natural flow type, the other side is the outflow of the anoxic tank 4 It may be introduced into the natural reflow tank 5 adjacent to the reaeration tank 5, and the residence time of the inflow water in the anaerobic tank 4 is configured to be 3 to 4 hours. Reaeration tank (5) is provided with an air supply (15), one side adjacent to the anoxic tank (4), the outflow of the anoxic tank (4) can be introduced into the natural flow type, the other side of the reaeration tank (5) Effluent can be introduced into the adjacent final sedimentation tank (6), the retention time of the influent in the reaeration tank (5) is configured to be 10 to 20 minutes. At the bottom of the final settling tank (6), a sludge discharge line (10) communicating with the anaerobic tank (2) is provided, and the electric sludge discharge line (10) is branched in the middle to collect the sludge connected with the water composting tank (7). The line 11 is provided, and one side is comprised so that the outflow water of the reaeration tank 5 may flow in. One side of the underwater composting tank (7) is provided with a sediment discharge line (8) in communication with the initial settling tank (1) and a sludge collection line (11) in communication with the sludge discharge line (10), the other side of the anaerobic tank An underwater composting tank supernatant dispensing line 12 communicating with (2) is provided, and a sludge discharge line 13 for discharging composted sludge to the outside of the underwater composting apparatus is provided at the bottom, and an agitator 14 is provided therein. ) And an air supply 15.

Figure 2a is a cross-sectional view of a one-stage underwater composting tank according to an embodiment of the present invention. As shown in Figure 2a, the air supply unit 15 is provided in the center of the bottom portion of the underwater composting tank to supply air intermittently, the stirrer 14 is provided on the upper end of the air supply 15, the first settling tank in one side The sediment discharge line 8 and the sludge collection line 11 branched from the sludge discharge line 10 communicated with (1) are provided, and the upper end of the other side prevents the flow of sludge by the stirrer 17. The baffle 16 is provided, and the part where the baffle is installed is provided with an underwater composting tank supernatant dispensing line 12 communicating with the anaerobic tank 2, and at the bottom to discharge the composted sludge to the outside of the underwater composting device. Sludge discharge line 13 is provided.

Figure 2b is a cross-sectional view of a two-stage underwater composting tank according to an embodiment of the present invention. As shown in Fig. 2B, the two-stage water composting tank is composed of an intermittent aeration tank 7-1 and a solid-liquid separation tank 7-2 adjacent to each other. The air supply unit 15 is provided at the center of the bottom of the intermittent aeration tank 7-1, and the stirrer 14 is provided at the upper end of the air supply unit 15, and on one side, the air supply unit 15 is in communication with the initial settling tank 1. A sludge collection line 11 branched from the sediment discharge line 8 and the sludge discharge line 10 is provided, and the other side is a solid-liquid separation tank 7-2 adjacent to the effluent of the intermittent aeration tank 7-1. It is configured to be introduced into natural flow type. In addition, the solid-liquid separation tank (7-2) is one side adjacent to the intermittent aeration tank (7-1) is configured so that the effluent of the intermittent aeration tank (7-1) can flow into the natural flow type, the top of the other side It is provided with an underwater composting tank supernatant sending line 12 in communication with the anaerobic tank (2), the bottom is provided with a sludge discharge line 13 for discharging the composted sludge to the outside of the underwater composting device.

Hereinafter, a method of purifying sewage water in which the sewage treatment process and the sludge treatment process are connected using the underwater composting apparatus of the present invention will be described in more detail, and the effects of using the electric apparatus will be described.

The wastewater purification method, which combines the treatment process of sludge with sludge treatment process and sludge treatment process, enters the final sedimentation tank through the anaerobic tank, the aerobic tank, the anaerobic tank and the reaeration tank, and the symbolic liquid is sent to the outside. The discharged, precipitated sludge is sent to an underwater composting tank, composted, and then released to the outside.

After sewage water flowing into the water composting device is stored in the initial sedimentation tank (1), the suspended solids contained in the sewage water are sedimented first, and the sediment is sent to the water composting tank through the sediment discharge line (8), and the supernatant is discharged to the effluent discharge line. (9) is sent to the anaerobic tank (2). In the anaerobic tank (2), the final sedimentation tank through the supernatant of the first sedimentation tank introduced through the outflow water discharge line (9), the sludge supernatant and the sludge discharge line of the underwater composting tank introduced through the underwater compost tank discharge line (12) (10) The sludge sent out from 6) is mixed, and the concentration of microorganisms in the wastewater is maintained at 2,500 to 4,000 mg / L, and the dissolved oxygen is stirred at 0.01 to 0.2 mg / L. In the anaerobic tank (2), microorganisms are used to decompose organic matter in water under anaerobic conditions. Phosphorus accumulated in microorganisms is released into the wastewater under optimal anaerobic conditions without the inhibition of dissolved oxygen and nitrates. This removes organic matter in the influent. The sewage water stays in the anaerobic tank 2 for 1 to 2 hours and then flows into the aerobic tank 3 by natural flow. In the aerobic tank (3), air is supplied to maintain the dissolved oxygen concentration at 2 to 4 mg / L, and the organic matter in the water is decomposed using microorganisms under aerobic conditions. Nitrogen in the influent is nitrified, and phosphorus in the wastewater is It is reintroduced into microorganisms, in which the remaining organics are removed. The sewage water stays in the aerobic tank 3 for 3 to 4 hours, and then flows into the anaerobic tank 4 by natural flow. In the anoxic tank (4), the dissolved oxygen in the wastewater is maintained at 0.01 to 0.5 mg / L and stirred to decompose contaminants in the water using microorganisms under anaerobic conditions, especially organic matter and sludge derived from microorganisms in an electric aerobic tank. The nitrate is denitrogenated by reaction with the oxidized organic material of, thus producing gaseous nitrogen, and part of the gaseous nitrogen generated is released into the atmosphere, and part is mixed with sludge and left in the sewage water. In addition, the release of phosphorus accumulated in the microorganisms due to the lack of nitrates and organics is suppressed, thereby maintaining a low concentration of phosphorus in the wastewater. The sewage water stays in the anaerobic tank 4 for 3 to 4 hours and then flows into the reaeration tank 5 by natural flow. In the reaeration tank (5), air is supplied to maintain the concentration of dissolved oxygen in the wastewater at 2 to 4 mg / L, and the bubbles generated therein are mixed with the sludge and are not released into the atmosphere. Emissions to the atmosphere. The sewage water stays in the reaeration tank 5 for 10 to 20 minutes and then flows into the final settling tank 6. The sewage water in the final sedimentation tank 6 is settled for a certain time, and the sludge in the sewage is sedimented, and the supernatant liquid in which the sludge is settled is discharged to the outside of the underwater composting device. Since the pollutant removal rate of the water composting apparatus of the present invention is 95% or more of BOD ₅ of the introduced wastewater, 75 to 85% of nitrogen and 80 to 85% of phosphorus, the discharged water is polluted compared to the wastewater introduced to the water composting apparatus. It was found that the content of the material was low, especially the content of phosphorus and nitrogen in the water.

In addition, the sludge settled in the final settling tank (6) is sent to the anaerobic tank (2) through the sludge discharge line 10, excess sludge is sent through the sludge collection line (11) branched from the electric sludge delivery line (10). It is sent out to the water composting tank 7. Underwater composting tank (7) collects a small amount of sediment settled in the initial settling tank (1) through the sediment discharge line (8) communicated with the initial settling tank (1), and the final settling tank (11) through the sludge collection line (11) Collect the excess sludge settled in 6), supply the collected sludge with air and mix it for a long time to produce composted sludge. At this time, the air is supplied to the intermittent aeration method in which aeration and aeration are repeated by using the air supply unit 15 provided in the water composting tank. During aeration, the concentration of dissolved oxygen is maintained at 2 to 4 mg / L. At the time of aeration, the dissolved oxygen concentration is maintained at 0.01 to 0.5 mg / L, and the time ratio of aeration to aeration is preferably 1: 1 to 1: 2. The composted sludge produced is discharged out of the water composting device through the sludge discharge line 13. At this time, in order to remove the discharged water of the composted sludge, it is preferable to provide a supernatant from the composted sludge with a device such as the baffle 16 of Figure 2a or the solid-liquid separation tank of Figure 2b. That is, the supernatant collected by stagnating the composted sludge by obstructing the flow of the stirrer in the first stage water composting tank, or the supernatant collected in the solid-liquid separation tank in the second stage water composting tank through the supernatant composting tank supernatant sending line 12 It is sent to the anaerobic tank (2). Therefore, the composted sludge of the underwater composting tank 8 is discharged to the outside while maintaining a low water content.

As described and demonstrated in detail in the above, the present invention by composting sludge generated in the water treatment process using an underwater composting device and an electric device, including sedimentation tank, anaerobic tank, aerobic tank, anaerobic tank, reaeration tank and underwater composting tank, treatment of sewage water Provides a method for the purification of sewage water in which the process and the sludge treatment process are linked. Underwater composting device of the present invention includes a first settling tank, anaerobic tank, aerobic tank, anoxic tank, re-aeration tank, final sedimentation tank, and aquatic composting tank, the sewage treatment method and the sludge treatment process associated with the wastewater treatment using the electric water composting device is connected The sewage water introduced into the initial sedimentation tank is introduced into the final sedimentation tank through anaerobic tank, aerobic tank, anaerobic tank, and reaeration tank, and its supernatant is discharged to the outside, and the precipitated sludge is sent to the underwater composting tank and discharged to the outside. Steps. According to the present invention, by repeatedly applying the anaerobic and aerobic state can be composted sludge generated in the water treatment process in the wastewater, can recycle the composted sludge, it is possible to improve the treatment efficiency of the wastewater.

Claims (9)

First sedimentation tank which directly enters sewage water, sediments suspended matter contained in the introduced sewage water, and discharges supernatant into anaerobic tank; An anaerobic tank communicated with the initial settling tank, inflow of effluent from the initial settling tank, sludge sent out from the final settling tank is added, and equipped with a stirrer; Adjacent to the side of the anaerobic tank, the outflow of the anaerobic tank flows into the natural flow type, an aerobic tank equipped with an air supply; Adjacent to the side of the aerobic tank, the outflow of the aerobic tank flows into the natural flow type, an anoxic tank equipped with a stirrer; Adjacent to the side of the anoxic tank, the outflow of the anoxic tank flows into the natural flow type, re-aeration tank equipped with an air supply; Adjacent to the side of the re-aeration tank, the outflow of the re-aeration tank flows into the natural flow type, the final sedimentation tank for sedimenting the sludge contained in the re-aeration tank, the discharge of the supernatant to the outside; And, an underwater composting tank communicating with the initial settling tank, the final settling tank and the anaerobic tank, and equipped with a slaw fat extraction line, an agitator, and an air supply. The method of claim 1, Anaerobic tank has a residence time of influent 1 to 2 hours and dissolved oxygen of influent Characterized by maintaining the concentration of 0.01 to 0.2mg / L Underwater composting device. The method of claim 1, The aerobic tank has a residence time of influent 3 to 4 hours and dissolved oxygen in the influent. Characterized by maintaining the concentration of 2 to 4mg / L Underwater composting device. The method of claim 1, Anaerobic baths have a residence time of influent 3 to 4 hours and dissolved insoluble acid Characterized in that the concentration of the cow is maintained at 0.01 to 0.5mg / L Underwater composting device. The method of claim 1, The re-aeration tank has a residence time of influent of 10 to 20 minutes and dissolved acid of influent Characterized in that the concentration of the cow is maintained at 3 to 4 mg / L Underwater composting device. First sedimentation tank which directly enters sewage water, precipitates suspended solids contained in the introduced sewage water, and discharges the supernatant into the anaerobic tank; An anaerobic tank communicated with the initial settling tank, inflow of effluent from the initial settling tank, sludge sent out from the final settling tank is added, and equipped with a stirrer; Adjacent to the side of the anaerobic tank, the outflow of the anaerobic tank flows into the natural flow type, an aerobic tank equipped with an air supply; Adjacent to the side of the aerobic tank, the outflow of the aerobic tank flows into the natural flow type, an anoxic tank equipped with a stirrer; Adjacent to the side of the anoxic tank, the outflow of the anoxic tank flows into the natural flow type, re-aeration tank equipped with an air supply; Adjacent to the side of the re-aeration tank, the outflow of the re-aeration tank flows into the natural flow type, the final sedimentation tank for sedimenting the sludge contained in the re-aeration tank, the discharge of the supernatant to the outside; And, the air supply is provided in the center of the bottom portion, the stirrer is provided on the top of the air supply, one side is provided with a sludge collection line branched from the sediment discharge line and the sludge discharge line in communication with the initial settling tank, the other day A baffle is provided at the top of the side, and a part of the baffle is provided with an underwater composting tank supernatant discharge line communicating with the anaerobic tank, and a sludge discharge line for discharging the composted sludge to the outside of the underwater composting device. Underwater composting device comprising a one-stage composting tank. First sedimentation tank which directly enters sewage water, sediments suspended matter contained in the introduced sewage water, and discharges supernatant into anaerobic tank; An anaerobic tank in communication with the initial settling tank, inflow of the effluent from the initial settling tank, inflow of sludge sent out from the final settling tank, and equipped with a stirrer; Adjacent to the side of the anaerobic tank, the outflow of the anaerobic tank flows into the natural flow type, an aerobic tank equipped with an air supply; Adjacent to the side of the aerobic tank, the outflow of the aerobic tank flows into the natural flow type, an anoxic tank equipped with a stirrer; Adjacent to the side of the anoxic tank, the outflow of the anoxic tank flows into the natural flow type, re-aeration tank equipped with an air supply; Adjacent to the side of the re-aeration tank, the outflow of the re-aeration tank flows into the natural flow type, the final sedimentation tank for sedimenting the sludge contained in the re-aeration tank, the discharge of the supernatant to the outside; And, the air supply is provided in the center of the bottom portion, the stirrer is provided on the top of the air supply, one side is provided with a sludge collection line branched from the sediment discharge line and the sludge discharge line in communication with the initial settling tank, the other day The side is intermittent aeration tank configured to allow the outflow of the intermittent aeration tank to flow into the adjacent solid-liquid separation tank, and one side adjacent to the intermittent aeration tank is configured to allow the outflow of the intermittent aeration tank to flow into the natural flow. At the top of the side, there is a supercondensing tank supernatant dispensing line communicating with the anaerobic tank, and the bottom includes a two-stage aquatic composting tank consisting of a solid-liquid separator with a sludge discharging line for discharging composted sludge to the outside of the underwater composting device. Underwater composting device. (Iii) infiltrating sewage into the initial settling tank, allowing the suspended solids to settle, and then sending the sediment into an underwater composting tank and sending the supernatant to an anaerobic tank; (Ii) The supernatant of the first settling tank, the supernatant of the sludge of the underwater compost tank, and the precipitated sludge of the final settling tank were introduced into the anaerobic tank to maintain the concentration of microorganisms in the anaerobic tank at 2,500 to 4,000 mg / L, and dissolved at 0.01 to 0.2 mg / L. Stirring while maintaining the concentration of oxygen, and flowing out into the aerobic tank by the amount introduced; (Iii) supplying air so that the concentration of dissolved oxygen contained in the inlet water of the aerobic tank is maintained at 2 to 4 mg / L, and flowing it into the anoxic tank by the amount introduced; (Iv) stirring the concentration of dissolved oxygen contained in the inflow water of the anoxic tank while maintaining 0.01 to 0.5 mg / L, and distilling it into the reaeration tank by the amount introduced; (Iii) supplying air to maintain the concentration of dissolved oxygen contained in the inlet water of the reaeration tank at 3 to 4 mg / L, and draining the final settling tank by the amount introduced; (Iii) After the sludge contained in the effluent flowing into the final sedimentation tank is settled, the sedimented sludge is returned to the anaerobic tank, and the excess sludge is sent to the submerged tank, and the supernatant is discharged to the outside of the underwater composting device. Making a step; And, (Iii) The excess sludge sent to the aquatic composting tank is agitated for a long time under the condition of intermittent aeration, and the supernatant of the composted sludge is sent to the anaerobic tank, and the composted sludge from which the supernatant is removed is composted. A method of purifying sewage water using the water composting device of claim 1 comprising the step of discharging to the outside of the device. The method of claim 8, In the intermittent aeration air supply method of step (iii), the concentration of dissolved oxygen is 2 to Repeat the aeration of 4 mg / L and the aeration of 0.01 to 0.5 mg / L. Supply the group, and the ratio of time between aeration and aeration is 1: 1 to 1: 2. Characterized by A method for purifying sewage water using the underwater composting device of claim 1.