A method for operating an oxidation ditch system at full load during sludge bulking periods

Abstract

The application discloses a method for full-load operation of an oxidation ditch system during a sludge expansion period, and the oxidation ditch system comprises a pretreatment zone, an oxidation ditch and a secondary sedimentation tank, and comprises the following steps: opening a water inlet valve of the oxidation ditch, and re-injecting sewage treated by the pretreatment zone; meanwhile, clear water in the upper layer of the oxidation ditch is discharged to the secondary sedimentation tank; the water inlet valve of the oxidation ditch is closed, all pushers in the oxidation ditch are opened, the newly-injected sewage is mixed with the original sludge-water mixture, and the mixture is circulated and flows in the oxidation ditch to perform an anaerobic reaction and release phosphates; then, an aeration system in the oxidation ditch is opened, and the sewage in the oxidation ditch is circulated to perform an aerobic-anoxic working condition; the aeration system and the pushers in the oxidation ditch are closed to perform static sedimentation; and the intermittent operation is repeated. The application controls the expanded sludge in the oxidation ditch, thereby reducing the influence of the expanded sludge on the secondary sedimentation, and enabling the oxidation ditch process to normally produce at full load during the sludge expansion period in winter.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for operating an oxidation ditch system at full load during the sludge expansion period. Background Technology

[0002] Oxidation ditch is a typical completely mixed plug-flow activated sludge treatment system, which has advantages such as simple process flow, convenient management, low infrastructure and operating costs, good sludge settling properties, resistance to shock loads, stable and reliable operation, and good treatment effect. Oxidation ditch technology has now become one of the mainstream wastewater treatment technologies in my country, with a huge number of completed and under-construction projects both domestically and internationally.

[0003] The Carrousel oxidation ditch process, also known as the circulating baffled oxidation ditch, is a type of activated sludge process. It consists of three parts: pretreatment, the oxidation ditch, and a secondary sedimentation tank. Wastewater first undergoes a pretreatment process to remove solid waste and pollutants through physical removal methods. Then, it enters the oxidation ditch and mixes with the sludge already present. The oxidation ditch is typically annular and contains aeration and flow-propelling equipment. Under the action of aeration and flow, the sludge-water mixture in the oxidation ditch continuously experiences aerobic-anoxic environments. In the aerobic aeration zone, aerobic biochemical and nitrification reactions occur between the wastewater and microorganisms in the sludge, removing COD, ammonia nitrogen, and total phosphorus from the wastewater. In the anoxic zone, denitrification reactions occur, removing total nitrogen from the water. The effluent from the oxidation ditch is a sludge-water mixture that flows to the secondary sedimentation tank for sludge-water separation. The separated water is discharged, while the remaining sludge-water mixture is partially returned to the oxidation ditch and partially transported to the sludge treatment system for dewatering.

[0004] During the operation of oxidation ditch processes, especially in winter, sludge is prone to bulking and loosening. This bulking reduces the sludge's settling properties, preventing effective sedimentation in the secondary settling tank and leading to deterioration of effluent quality, with increased suspended solids (SS) and turbidity. When sludge bulking is severe, it is necessary to reduce or stop the influent flow to avoid further impact on the treatment system. Therefore, to ensure the quality of the effluent from the secondary settling tank, the treatment system is forced to reduce its production volume, typically to only 60-85% of the treatment load. This results in the system not operating at full capacity, limiting and affecting the wastewater treatment capabilities and posing significant challenges to the operation and management of wastewater treatment projects.

[0005] Ensuring that oxidation ditch processes can operate at full capacity under sludge expansion conditions, especially in winter, and overcoming periods of poor operating conditions, is a pressing issue for the industry. To address this, the industry often employs methods such as adjusting the sludge return flow rate, increasing sludge dewatering, or adding disinfectants to the expanding sludge, but these methods have limited effectiveness and short-term results. Summary of the Invention

[0006] The purpose of this invention is to provide a method for an oxidation ditch system to operate at full load during the sludge expansion period, so that the oxidation ditch system can operate normally at full load under the condition of sludge expansion.

[0007] The specific technical solution is as follows:

[0008] A method for operating an oxidation ditch system at full capacity during the sludge bulking period, the oxidation ditch system comprising a pretreatment zone, an oxidation ditch, and a secondary sedimentation tank, comprising the following steps:

[0009] S1, Inlet and Drainage Stage:

[0010] Open the inlet valve of the oxidation ditch to re-inject the wastewater that has been treated in the pretreatment area; at the same time, the clear water in the upper layer of the oxidation ditch is discharged into the secondary sedimentation tank.

[0011] S2, Mixing and Aeration Stage:

[0012] Close the inlet valve of the oxidation ditch, turn on all the flow promoters in the oxidation ditch, mix the newly introduced sewage with the original mud-water mixture, and circulate it in the oxidation ditch to carry out anaerobic reaction and release phosphate; then turn on the aeration system in the oxidation ditch, and the sewage in the oxidation ditch will circulate in an aerobic-anoxic condition.

[0013] S3, Sedimentation Stage:

[0014] Turn off the aeration system and the flow booster in the oxidation ditch and allow it to settle.

[0015] S4. Repeat steps S1-S3 intermittently.

[0016] In a further embodiment, the water replacement volume of the oxidation ditch in step S1 is 40% to 60% of the capacity of a single oxidation ditch, and the water inlet time of the oxidation ditch is 2 to 4 hours.

[0017] In a further embodiment, the stirring time of the propeller in step S2 is 2-4 hours, wherein the aeration system is turned on only after the propeller has been working for at least 30 minutes; the number of cycles of the aerobic-anoxic condition is 20-40 times; and nitrification and denitrification processes are carried out simultaneously in the aerobic-anoxic condition.

[0018] In a further embodiment, the settling time in step S3 is 0.5 to 1 hour.

[0019] In a further embodiment, the oxidation ditch may include a single oxidation ditch or a dual oxidation ditch.

[0020] In a further embodiment, the oxidation ditch is a single oxidation ditch, and it operates intermittently;

[0021] The oxidation ditch is a dual oxidation ditch, with the two oxidation ditches operating intermittently and separately, allowing the oxidation ditch system to continuously receive and discharge water; or one oxidation ditch can operate normally and continuously receiving and discharging water, while the other oxidation ditch operates intermittently.

[0022] In a further embodiment, the sludge from the secondary sedimentation tank is directly discharged for treatment and is not returned to the oxidation ditch. That is, the sludge from the secondary sedimentation tank is pumped to a sludge treatment system for dewatering.

[0023] In a further proposed solution, during the sedimentation stage, the expanded sludge in the oxidation ditch is transported to the sludge treatment system through the drainage pipe at the bottom of the oxidation ditch for sludge dewatering treatment.

[0024] A further proposed method involves adding a settling agent to the aeration zone 1-2 hours after the aeration system is turned on, with the amount of settling agent added being 0.3-1 ppm based on the total volume of wastewater in a single oxidation ditch.

[0025] A further step involves detecting the phosphate concentration in the influent of the oxidation ditch. When the phosphate concentration is 1-2 mg / L, a phosphorus removal agent is added to the aeration zone of the oxidation ditch. The dosage of the phosphorus removal agent is 10-20 ppm based on the total volume of wastewater in a single oxidation ditch.

[0026] The method of the present invention is also applicable to oxidation ditch systems with high sludge concentrations.

[0027] In this invention, each stage can be flexibly controlled. The time for the influent and effluent stages is adjusted based on the production water load, generally 2 to 4 hours. The time for the mixing and aeration stages is adjusted based on the requirements of the oxidation ditch effluent for COD, ammonia nitrogen, total nitrogen, and total phosphorus, generally 2 to 4 hours. The time for the sedimentation stages is adjusted based on the amount of sludge carried by the effluent, generally 0.5 to 1 hour.

[0028] The present invention has the following advantages over the prior art:

[0029] (1) The method of the present invention can effectively control and regulate the amount of expanded sludge in the oxidation ditch transferred to the secondary sedimentation tank, which can significantly reduce the solid surface load of the secondary sedimentation tank and improve the water quality and stability of the effluent from the secondary sedimentation tank.

[0030] (2) In this invention, the wastewater in the oxidation ditch is operated intermittently, that is, intermittent inflow and outflow, anaerobic-aerobic-anoxic process and sedimentation treatment, and the sludge in the secondary sedimentation tank is not returned to the oxidation ditch, thereby reducing the hydraulic load of the secondary sedimentation tank and improving the effluent quality and stability of the secondary sedimentation tank.

[0031] (3) In the inlet and outlet stages of this application, the oxidation ditch discharges clear water, which basically does not carry sludge. When sludge expansion occurs in the oxidation ditch, the sludge in the oxidation ditch is controlled to remain in the oxidation ditch and does not flow to the secondary sedimentation tank, so there is basically no impact on the secondary sedimentation tank, thus effectively ensuring the water quality of the effluent from the secondary sedimentation tank.

[0032] (4) In this application, the oxidation ditch is a double oxidation ditch, and the two oxidation ditches operate intermittently and separately, so that the oxidation ditch system continuously receives and discharges water; that is, the expanded sludge from the two oxidation ditches does not flow to the secondary sedimentation tank, thus completely eliminating the influence of expanded sludge on the secondary sedimentation tank.

[0033] Alternatively, one oxidation ditch with a lower sludge concentration can be operated continuously with normal inflow and outflow, while the other oxidation ditch with a relatively higher sludge concentration can be operated intermittently. Since one of the oxidation ditches operates in an intermittent mode, the effluent is basically free of sludge, which can reduce the solid surface load of the secondary sedimentation tank, significantly reduce the negative impact of expanded sludge on the secondary sedimentation tank, and ensure the stability and quality of the effluent from the secondary sedimentation tank.

[0034] (5) By using the method of the present invention, during the winter sludge expansion period, the oxidation ditch system maintains full-load operation of the entire oxidation ditch system for a certain period of time (usually about 1 to 3 months), reducing the situation of passively reducing the sewage treatment load.

[0035] (6) In this invention, the oxidation ditch can adopt a combination and conversion of various operation modes, such as intermittent operation of a single oxidation ditch, intermittent operation of two oxidation ditches staggered, or intermittent operation of one oxidation ditch in two oxidation ditches, in order to meet the needs of sewage treatment. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments.

[0037] Example 1:

[0038] A method for operating an oxidation ditch system at full capacity during the sludge bulking period, the oxidation ditch system comprising a pretreatment zone, an oxidation ditch, and a secondary sedimentation tank, comprising the following steps:

[0039] S1, Inlet and Drainage Stage:

[0040] Open the inlet valve of the oxidation ditch to re-inject the wastewater that has been treated in the pretreatment area; at the same time, the clear water in the upper layer of the oxidation ditch is discharged into the secondary sedimentation tank.

[0041] The water replacement rate of the oxidation ditch is 40% to 60% of the capacity of a single oxidation ditch, and the water inlet time of the oxidation ditch is 2 to 4 hours.

[0042] S2, Mixing and Aeration Stage:

[0043] Close the inlet valve of the oxidation ditch, turn on all the flow promoters in the oxidation ditch, mix the newly introduced sewage with the original mud-water mixture, and circulate it in the oxidation ditch to carry out anaerobic reaction and release phosphate; then turn on the aeration system in the oxidation ditch, and the sewage in the oxidation ditch will circulate in an aerobic-anoxic condition.

[0044] The stirring and aeration stage lasts for 2-4 hours, with the aeration system only turned on after the flow booster has been working for at least 30 minutes; the aerobic-anoxic cycle number is 20-40 times; and nitrification and denitrification processes are carried out simultaneously in the aerobic-anoxic condition.

[0045] S3, Sedimentation Stage:

[0046] Turn off the aeration system and the flow booster in the oxidation ditch and allow it to settle.

[0047] The settling time is 0.5 to 1 hour.

[0048] S4. Repeat steps S1-S3 intermittently.

[0049] In a further embodiment, the oxidation ditch may include a single oxidation ditch or a dual oxidation ditch. When the oxidation ditch is a single ditch, it operates intermittently.

[0050] When the oxidation ditch is a dual oxidation ditch, the two oxidation ditches operate intermittently and separately, so that the oxidation ditch system can continuously receive and discharge water; or one oxidation ditch can operate normally and continuously receive and discharge water, while the other oxidation ditch operates intermittently.

[0051] In this application, the sludge from the secondary sedimentation tank is directly discharged for treatment and is not returned to the oxidation ditch. During the sedimentation stage, the expanded sludge in the oxidation ditch is transported to the sludge treatment system through the drain pipe at the bottom of the oxidation ditch for sludge dewatering treatment.

[0052] One to two hours after the aeration system is turned on, a settling agent is added to the aeration zone. The amount of settling agent added is 0.3-1 ppm based on the total volume of wastewater in a single oxidation ditch.

[0053] The phosphate concentration in the influent of the oxidation ditch is tested. When the phosphate concentration is 1-2 mg / L, a phosphorus removal agent is added to the aeration zone of the oxidation ditch. The dosage of the phosphorus removal agent is 10-20 ppm based on the total volume of sewage in a single oxidation ditch.

[0054] The phosphorus removal agent used in this application is a commonly used iron or aluminum salt, such as polyferric sulfate; the flocculant used in this application is polyacrylamide, a commonly used substance in the art.

[0055] Example 2:

[0056] A single-ditch Carrousel oxidation ditch system is designed to process 5000 tons per day.3 / d, the hydraulic retention time of the oxidation ditch is 12h. In winter, sludge bulking occurs, reaching as high as 7500mg / L, forcing a reduction in production.

[0057] The oxidation ditch system, using the method of this invention, achieves full-load operation. The specific processing procedure is as follows:

[0058] a) Influent and Drainage Stage: Open the influent valve of the oxidation ditch to re-inject the pre-treated wastewater. The supernatant clear water after sedimentation in the oxidation ditch is discharged into the secondary sedimentation tank. The influent and drainage stage is controlled within 2 hours, and the influent replacement volume of the oxidation ditch is 50% of the oxidation ditch capacity.

[0059] b) Mixing and Aeration Stage: Close the inlet valve of the oxidation ditch and turn on all the flow promoters in the oxidation ditch. The flow promoters mix the newly introduced wastewater with the existing mud-water mixture in the oxidation ditch, and the wastewater circulates within the ditch to undergo anaerobic reactions, releasing phosphates. After 30 minutes, turn on the aeration system in the oxidation ditch. The wastewater then circulates in an aerobic-anoxic cycle, repeating 20 times, simultaneously carrying out nitrification and denitrification biochemical processes.

[0060] 1.5 hours after the aeration system is turned on, add the settling agent polyacrylamide to the aeration zone at a dosage of 0.3 ppm based on the total volume of wastewater in a single oxidation ditch. Detect the phosphate concentration in the influent of the oxidation ditch system. When it reaches 1 mg / L, add the phosphorus removal agent polyferric sulfate to the aeration zone at a dosage of 10 ppm based on the total volume of wastewater in a single oxidation ditch.

[0061] The total time for the mixing and aeration stages should be controlled within 3 hours.

[0062] c) Sedimentation stage: Turn off all aeration and flow propulsion equipment in the oxidation ditch, and allow the wastewater in the oxidation ditch to settle for 1 hour.

[0063] The clarity of the effluent from the oxidation ditch is controlled by adjusting the sedimentation time. A longer sedimentation time results in clearer effluent, while a shorter time leads to more turbid effluent and a greater amount of sludge carried to the secondary sedimentation tank. In this embodiment, 1 hour is preferred.

[0064] d) Repeat step ac for intermittent operation.

[0065] In this embodiment, the sludge from the secondary sedimentation tank of the oxidation ditch system is directly discharged for treatment and is not returned to the oxidation ditch. That is, the sludge discharged from the secondary sedimentation tank is directly transported to the sludge treatment system for disposal.

[0066] During the sedimentation stage, the expanded sludge in the oxidation ditch is pumped to the sludge treatment system through the drainage pipe at the bottom of the oxidation ditch for sludge dewatering treatment, thereby continuously reducing the sludge concentration in the oxidation ditch system.

[0067] Comparative Example 1:

[0068] After pretreatment, the wastewater enters the oxidation ditch. Under the action of aeration and flow, the mud-water mixture in the oxidation ditch continuously experiences aerobic-anoxic conditions. The effluent from the oxidation ditch is a mud-water mixture that flows to the secondary sedimentation tank for mud-water separation. The separated water is discharged externally, while the remaining mud-water mixture is partially returned to the oxidation ditch and partially transported to the sludge treatment system for sludge dewatering.

[0069] Add a settling aid, polyacrylamide, to the aeration zone at a dosage of 0.3 ppm based on the total volume of wastewater in a single oxidation ditch. Detect the phosphate concentration in the influent of the oxidation ditch system. When the phosphate concentration reaches 1 mg / L, add a phosphorus removal agent, polyferric sulfate, to the aeration zone at a dosage of 10 ppm based on the total volume of wastewater in a single oxidation ditch.

[0070] The effluent flow and water quality of the oxidation ditch systems in Example 2 and Comparative Example 1 were tested as follows:

[0071]

[0072] As can be seen from the table above, the treatment method of the present invention can significantly improve the treatment load of the oxidation ditch system, enabling it to operate at full capacity even during the sludge expansion period.

[0073] Example 3:

[0074] A certain dual-ditch Carrousel oxidation ditch system is designed to process 40,000 tons per day. 3 / d, the hydraulic retention time of the oxidation ditch is 14h. In winter, sludge bulking occurs, and the sludge concentration is high, reaching 7000mg / L, forcing a significant reduction in production.

[0075] This oxidation ditch system, employing the method of this invention, gradually achieved full-load operation. The two oxidation ditches operate at staggered intervals, ensuring continuous water inflow and outflow. The specific treatment process is as follows:

[0076] a) Influent and Drainage Stage: Open one influent valve of the oxidation ditch to re-inject the pretreated wastewater from the pretreatment zone. The supernatant clear water after sedimentation in the oxidation ditch is discharged into the secondary sedimentation tank. The influent and drainage stage is controlled within 4 hours, and the influent replacement volume of the oxidation ditch is approximately 60% of the oxidation ditch's capacity.

[0077] b) Mixing and Aeration Stage: The influent to the oxidation ditch is shut off, and all flow promoters are turned on. The flow promoters mix the newly introduced wastewater with the existing mud-water mixture within the oxidation ditch, allowing the wastewater to circulate and undergo anaerobic reactions, releasing phosphates. After 30 minutes, the aeration system in the oxidation ditch is activated, and the wastewater circulates in an aerobic-anoxic cycle, simultaneously undergoing nitrification and denitrification. The aerobic-anoxic cycle is repeated 40 times, and the mixing and aeration time is controlled to 3 hours.

[0078] 1.5 hours after the aeration system is turned on, add the settling agent polyacrylamide to the aeration zone at a dosage of 1 ppm based on the total volume of wastewater in a single oxidation ditch. Detect the phosphate concentration in the influent of the oxidation ditch system. When it reaches 2 mg / L, add the phosphorus removal agent polyferric sulfate to the aeration zone at a dosage of 20 ppm based on the total volume of wastewater in a single oxidation ditch.

[0079] c) Sedimentation stage: All aeration and flow-generating equipment in the oxidation ditch are shut down, and the wastewater in the oxidation ditch is in a static sedimentation stage. The sedimentation time is controlled at 0.5 hours.

[0080] d) Repeat step ac to complete the intermittent operation of a single oxidation ditch.

[0081] The time for both steps a and b+c is 4 hours. By simply swapping the time order of steps a and b+c, the two oxidation ditches can be combined to form a system with continuous water inflow and continuous water outflow.

[0082] In this embodiment, the expanded sludge in the oxidation ditch is pumped to the sludge treatment system through the drainage pipe at the bottom of the oxidation ditch during the settling stage, so as to continuously reduce the sludge concentration in the system.

[0083] In this embodiment, the sludge from the secondary sedimentation tank of the oxidation ditch system is directly discharged for treatment and is not returned to the oxidation ditch. That is, the sludge discharged from the secondary sedimentation tank is directly transported to the sludge treatment system for disposal.

[0084] Comparative Example 2:

[0085] Similar to Comparative Example 1, both oxidation ditches were treated using a conventional continuous inlet and outlet water method.

[0086] Add flocculant and phosphorus remover as in Example 3.

[0087] The effluent flow and water quality of the oxidation ditch systems in Example 3 and Comparative Example 2 were tested as follows:

[0088]

[0089] As can be seen from the table above, the treatment method of the present invention can significantly improve the treatment load of the oxidation ditch system, enabling it to operate at full capacity even during the sludge expansion period.

[0090] Example 4:

[0091] A certain dual-ditch Carrousel oxidation ditch system is designed to process 20,000 tons per day. 3 / d, the hydraulic retention time of the oxidation ditch is 10h. Sludge bulking occurs in winter, with the sludge concentration in one oxidation ditch being particularly high, reaching 8000mg / L, while the sludge concentration in the other oxidation ditch is about 5000mg / L, forcing the system to operate at a significant reduction in production.

[0092] This oxidation ditch system employs the method of this invention, implementing intermittent operation for oxidation ditches with high sludge concentrations, while maintaining the original continuous influent and continuous effluent operation mode for oxidation ditches with relatively low sludge concentrations. This gradually achieves full-load operation of the system. The specific treatment process for intermittent operation of a single oxidation ditch with high sludge concentration is as follows:

[0093] a) Influent and Drainage Stage: Open the influent valve of the oxidation ditch to re-inject the pre-treated wastewater. The supernatant clear water after sedimentation in the oxidation ditch is discharged into the secondary sedimentation tank. The influent and drainage stage is controlled within 3.5 hours, and the influent replacement rate of the oxidation ditch is 40% of the capacity of a single oxidation ditch.

[0094] b) Mixing and Aeration Stage: Close the inlet water to the oxidation ditch and turn on all flow promoters. Utilize the flow promoters' mixing action to mix the newly introduced wastewater with the existing mud-water mixture within the oxidation ditch, allowing it to circulate. This initiates anaerobic reactions in the wastewater, releasing phosphates. After 30 minutes, turn on the aeration system within the oxidation ditch. The wastewater will then continuously undergo aerobic-anoxic conditions, simultaneously carrying out nitrification and denitrification processes. The mixing and aeration time should be controlled to 3.5 hours.

[0095] 1.5 hours after the aeration system is turned on, add the settling agent polyacrylamide to the aeration zone at a dosage of 0.6 ppm based on the total volume of wastewater in a single oxidation ditch. Detect the phosphate concentration in the influent of the oxidation ditch system. When it reaches 1.5 mg / L, add the phosphorus removal agent polyferric sulfate to the aeration zone at a dosage of 150 ppm based on the total volume of wastewater in a single oxidation ditch.

[0096] c) Sedimentation stage: All aeration and flow-generating equipment in the oxidation ditch are shut off, and the wastewater in the oxidation ditch is in a static sedimentation stage. The sedimentation time is controlled within 1 hour.

[0097] d) Repeating steps a to c will complete the intermittent operation of a single oxidation ditch.

[0098] In an oxidation ditch system, one oxidation ditch operates continuously while the other operates intermittently, which can lead to periodic high-load operation in the continuously operating ditch. However, the Carrousel oxidation ditch process exhibits particularly strong resistance to shock and high loads, especially under high sludge concentrations, enabling it to adapt to such periodic high-load operation.

[0099] Oxidation ditches operating intermittently do not distribute sludge back to the secondary sedimentation tank. During the settling phase, the expanded sludge in the oxidation ditch is pumped to the sludge treatment system through the drain pipe at the bottom of the oxidation ditch for sludge dewatering treatment, thereby continuously reducing the sludge concentration in the system.

[0100] Comparative Example 3:

[0101] Similar to Comparative Example 1, both oxidation ditches were treated using a conventional continuous inlet and outlet water method.

[0102] Add flocculant and phosphorus remover as in Example 4.

[0103] The effluent flow and water quality of the oxidation ditch systems in Example 4 and Comparative Example 3 were tested as follows:

[0104]

[0105] As can be seen from the table above, the treatment method of the present invention can significantly improve the treatment load of the oxidation ditch system, enabling it to operate at full capacity even during the sludge expansion period.

[0106] The above embodiments are merely examples of the method of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical and methodological essence of the present invention shall still fall within the scope of the technical and methodological solutions of the present invention.

Claims

1. A method for operating an oxidation ditch system at full load during the sludge bulking period, the oxidation ditch system comprising a pretreatment zone, an oxidation ditch, and a secondary sedimentation tank, characterized in that: Includes the following steps: S1, Inlet and Drainage Stage: Open the inlet valve of the oxidation ditch to re-inject the wastewater that has been treated in the pretreatment area; at the same time, the clear water in the upper layer of the oxidation ditch is discharged into the secondary sedimentation tank. S2, Mixing and Aeration Stage: Close the inlet valve of the oxidation ditch, turn on all the flow promoters in the oxidation ditch, mix the newly introduced sewage with the original mud-water mixture, and circulate it in the oxidation ditch to carry out anaerobic reaction and release phosphate; then turn on the aeration system in the oxidation ditch, and the sewage in the oxidation ditch will circulate in an aerobic-anoxic condition. S3, Sedimentation Stage: Turn off the aeration system and the flow booster in the oxidation ditch and allow it to settle. S4. Repeat steps S1-S3 intermittently.

2. The method according to claim 1, characterized in that: In step S1, the water replacement rate of the oxidation ditch is 40% to 60% of the capacity of a single oxidation ditch, and the water inlet time of the oxidation ditch is 2 to 4 hours.

3. The method according to claim 1, characterized in that: The stirring and aeration stage in step S2 lasts for 2 to 4 hours, during which the aeration system is turned on only after the flow booster has been working for at least 30 minutes; the aerobic-anoxic cycle number is 20 to 40 times; and nitrification and denitrification processes are carried out simultaneously in the aerobic-anoxic condition.

4. The method according to claim 1, characterized in that: The settling time in step S3 is 0.5 to 1 hour.

5. The method according to claim 1, characterized in that: The oxidation ditch may be a single oxidation ditch or a dual oxidation ditch.

6. The method according to claim 5, characterized in that: The oxidation ditch is a single oxidation ditch and operates intermittently; The oxidation ditch is a dual oxidation ditch, with the two oxidation ditches operating intermittently and separately, allowing the oxidation ditch system to continuously receive and discharge water; or one oxidation ditch can operate normally and continuously receiving and discharging water, while the other oxidation ditch operates intermittently.

7. The method according to claim 1, characterized in that: The sludge from the secondary sedimentation tank is discharged directly for treatment and is not returned to the oxidation ditch.

8. The method according to claim 1, characterized in that: During the sedimentation stage, the expanded sludge in the oxidation ditch is transported to the sludge treatment system through the drain pipe at the bottom of the oxidation ditch for sludge dewatering treatment.

9. The method according to claim 1, characterized in that: One to two hours after the aeration system is turned on, a settling agent is added to the aeration zone. The amount of settling agent added is 0.3-1 ppm based on the total volume of wastewater in a single oxidation ditch.

10. The method according to claim 1, characterized in that: The phosphate concentration in the influent of the oxidation ditch is tested. When the phosphate concentration is 1-2 mg / L, a phosphorus removal agent is added to the aeration zone of the oxidation ditch. The dosage of the phosphorus removal agent is 10-20 ppm based on the total volume of sewage in a single oxidation ditch.

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