Sewage treatment system based on pipe culvert dissolved oxygen gradient regulation and control

Abstract

The invention relates to a sewage treatment system and method based on pipe culvert dissolved oxygen gradient regulation and control, the sewage treatment system comprises an anaerobic section, an anoxic section and a stepped aerobic section which are communicated in sequence along the water flow direction of a drainage pipe culvert, dissolved oxygen gradients are formed in sequence through control of a fuzzy PID dynamic algorithm, and the tail end of the pipe culvert is provided with a catch basin communicated with the stepped aerobic section. A discharge water body is arranged at the downstream of the intercepting well, a gate is arranged in the intercepting well, so that mud-water mixed liquid is intercepted to the mud-water separation and backflow device on sunny days, or rainwater is discharged into the discharge water body on rainy days, the downstream of the mud-water separation and backflow device is communicated with a constructed wetland, and the constructed wetland is communicated with the discharge water body at the downstream. The sewage treatment function is embedded into an existing drainage pipe culvert, mud-water separation and sedimentation, mixed liquid backflow and sludge backflow are integrated in the mud-water separation and backflow device, the construction cost is greatly reduced, occupied land and investment are saved, the nitrogen and phosphorus removal efficiency is cooperatively improved, and the device is suitable for urban overflow pollution treatment and decentralized sewage treatment scenes.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment technology, and in particular to an integrated sewage treatment system that combines an improved activated sludge process with an artificial wetland, which is suitable for municipal drainage culverts, combined sewer overflow pollution and decentralized sewage treatment scenarios. Background Art

[0002] Traditional activated sludge processes (such as the AAO process) rely on large-scale sewage treatment plants, which pose challenges such as high capital investment and large land occupation. Urban drainage culverts, serving as wastewater transport systems, lack effective utilization of their internal space. In existing technologies, aeration within culverts is primarily used to prevent siltation, rather than systematically degrading pollutants. Furthermore, the outlet often lacks advanced treatment, leading to contamination of receiving water bodies. Therefore, there is an urgent need to develop a low-cost technology that leverages the existing culvert space to couple efficient biological treatment with ecological purification. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a sewage treatment system and method based on pipe culvert dissolved oxygen gradient regulation.

[0004] The technical solution of the present invention to solve the above technical problems is as follows: a sewage treatment system based on dissolved oxygen gradient regulation in a culvert, comprising an anaerobic section, an anoxic section and a stepped aerobic section arranged in sequence along the water flow direction of the drainage culvert, and a dissolved oxygen gradient is formed in sequence through fuzzy PID dynamic algorithm control, the end of the culvert is provided with an interception well connected to the stepped aerobic section, the downstream of the interception well is the discharge water body, a gate is provided in the interception well to intercept the mud and water mixture to the mud and water separation and reflux device on sunny days, or to discharge rainwater into the discharge water body on rainy days, an artificial wetland is provided downstream of the mud and water separation and reflux device, the mud and water separation and reflux device is also connected to the culvert inlet and the anoxic section respectively through a mud and water coordinated regulation module to return part of the sludge to the culvert inlet and return part of the mixed liquid to the anoxic section, and the artificial wetland is connected to the discharge water body downstream.

[0005] The beneficial effects of the present invention are: the sewage treatment system based on dissolved oxygen gradient regulation in the culvert of the present invention, by sequentially connecting and setting anaerobic sections, anoxic sections and stepped aerobic sections along the water flow direction of the drainage culvert, and adjusting the aeration volume in real time through the fuzzy PID dynamic algorithm to maintain the stability of the dissolved oxygen gradient, embeds the sewage treatment function into the existing drainage culvert, and integrates mud and water separation and sedimentation, mixed liquor return and sludge return into the mud and water separation and return device, greatly reducing construction costs, saving land and infrastructure investment, and synergistically improving the denitrification and phosphorus removal efficiency through gradient aeration and wetland ecological purification, which is suitable for urban combined sewer overflow pollution control and decentralized sewage treatment scenarios.

[0006] On the basis of the above technical solution, the present invention can also be improved as follows:

[0007] Furthermore: a cyclone aerator is provided in the anoxic section, and the cyclone aerator operates intermittently; a microporous aeration tube is provided in the stepped aerobic section, and the microporous aeration tube operates continuously.

[0008] Furthermore: the stepped aerobic section includes at least three levels, and the dissolved oxygen concentration of each level is 2.8-3.5 mg / L, 1.8-2.5 mg / L, and 1.0-1.5 mg / L, respectively, and the length of each level accounts for 20%-40% of the total length of the stepped aerobic section.

[0009] Further: the mud-water separation and reflux device is equipped with an intercepting pipe, a mud-water separator, a water collecting tank, a mixed liquid reflux pump and a sludge reflux pump. One end of the intercepting pipe extends out of the mud-water separation and reflux device and is connected to the intercepting well. The mud-water separator is arranged in the middle of the mud-water separation and reflux device, and the water collecting tank is arranged on the upper part of the outer wall of the mud-water separation and reflux device, and the water collecting tank is connected to the artificial wetland.

[0010] Furthermore: a plurality of water distribution holes connected to the artificial wetland are provided on the outer wall of the water collecting tank.

[0011] Further: the mud and water coordinated control module includes a mixed liquid return pump and a sludge return pump. The mixed liquid return pump is arranged at the bottom of the mud and water separation and reflux device close to the intercepting pipe, and the output end of the mixed liquid return pump is connected to the anoxic section through a pipeline. The sludge return pump is arranged at the bottom outside the mud and water separation and reflux device, and the output end of the sludge return pump is connected to the culvert inlet.

[0012] Further: The specific implementation of sequentially forming the dissolved oxygen gradient by fuzzy PID dynamic algorithm control is:

[0013] The aeration rate correction coefficient is calculated based on the membership function using the water inlet flow, chemical oxygen demand (COD), and NH3-N concentration of the pipe culvert intersection as feedforward inputs and the measured values ​​of the dissolved oxygen sensors in each section as feedback inputs;

[0014] The cyclone aerator in the anoxic section and the microporous aeration pipe in the stepped aerobic section are respectively controlled according to the aeration amount correction coefficient to dynamically adjust the aeration amount.

[0015] The present invention also provides a sewage treatment method based on pipe culvert dissolved oxygen gradient regulation, which adopts the sewage treatment system based on pipe culvert dissolved oxygen gradient regulation and includes the following steps:

[0016] The sewage enters the anaerobic section through the culvert inlet and stays in the anaerobic section for 40-60 minutes, controlling the dissolved oxygen concentration DO ≤ 0.2 mg / L to release phosphorus and hydrolyze organic matter;

[0017] The sewage enters the anoxic section through the anaerobic section and stays in the anoxic section for 60-120 minutes. The dissolved oxygen concentration DO is controlled by the fuzzy PID dynamic algorithm to be ≤= 0.2-0.5 mg / L to perform denitrification treatment;

[0018] The sewage enters the stepped aerobic section through the anoxic section and is treated in three stages with a total residence time of 4-5 hours. The dissolved oxygen concentration (DO) is controlled step by step to 3.5-1.0 mg / L through a fuzzy PID dynamic algorithm, and nitrification, carbon oxidation and phosphorus absorption are completed simultaneously.

[0019] The sewage enters the interception well through the stepped aerobic section and, on sunny days, is diverted to the mud-water separation and return flow device by controlling the gate in the interception well. The sewage then enters the downstream artificial wetland for treatment for 1-3 days before being discharged. The hydraulic load of the artificial wetland is less than 0.5m³ / (㎡·d).

[0020] On the basis of the above technical solution, the present invention can also be improved as follows:

[0021] Furthermore, the mud-water separation and reflux device performs mud-water separation and sedimentation, mixed liquid reflux and sludge reflux treatment on sewage, which specifically includes the following steps:

[0022] Under the guidance of the mud-water separator, the lighter supernatant and gas move upward, and the supernatant flows into the water collection tank, and then flows out from the water distribution holes outside the water collection tank into the artificial wetland. Through substrate adsorption, plant absorption and microbial degradation, the residual nitrogen, phosphorus and trace organic matter in the supernatant are removed, and then it meets the standards and enters the discharge water body;

[0023] The gas from sewage overflows directly to the outside;

[0024] The heavier sludge in the sewage moves downward and settles at the bottom of the mud-water separation and return device to achieve mud-water separation;

[0025] The sludge return pump returns part of the sludge to the culvert inlet, and the mixed liquid return pump returns part of the mixed liquid to the combined well in front of the anoxic section, realizing the coordinated regulation function of mud and water.

[0026] Further: The sewage treatment method based on pipe culvert dissolved oxygen gradient control also includes the excess sludge control step:

[0027] Regularly check the MLSS concentration of the sewage mixed liquor at the end of the culvert. When the MLSS concentration of the mixed liquor is > 4500 mg / L, start the sludge return pump to discharge part of the remaining sludge to the municipal sludge treatment system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the overall layout structure of a sewage treatment system based on pipe culvert dissolved oxygen gradient control according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic structural diagram of a sewage treatment system based on pipe culvert dissolved oxygen gradient control according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic structural diagram of a mud-water separation and return flow device according to an embodiment of the present invention.

[0031] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0032] 1. Culvert inlet, 2. Anaerobic section, 3. Anoxic section, 4. Stepped aerobic section, 5. Interceptor well, 6. Discharge water body, 7. Mud-water separation and return device, 8. Constructed wetland, 9. Interceptor pipe, 10. Mud-water separator, 11. Collection tank, 12. Water distribution hole, 13. Mixed liquor return pump, 14. Sludge return pump, 15. Combined well. DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0034] like Figure 1 As shown, a sewage treatment system based on dissolved oxygen gradient regulation in a culvert comprises an anaerobic section 2, an anoxic section 3 and a stepped aerobic section 4 which are sequentially connected through a combining well 15 along the flow direction of the drainage culvert, and a dissolved oxygen gradient is sequentially formed through fuzzy PID dynamic algorithm control. An interception well 5 connected to the stepped aerobic section 4 is provided at the end of the culvert, and a discharge water body 6 is downstream of the interception well 5. A gate is provided in the interception well 5 to intercept the mud-water mixture and divert it to a mud-water separation and return flow device 7 on sunny days, or to discharge rainwater into the discharge water body 6 on rainy days. An artificial wetland 8 is provided downstream of the mud-water separation and return flow device 7. The mud-water separation and return flow device 7 is further connected to the culvert inlet 1 and the anoxic section 3 respectively through a mud-water coordinated control module to return part of the sludge to the culvert inlet 1 and return part of the mixed liquid to the anoxic section 3. The artificial wetland 8 is connected to the discharge water body 6 downstream.

[0035] The beneficial effects of the present invention are as follows: the sewage treatment system based on dissolved oxygen gradient regulation in the culvert of the present invention, by sequentially connecting an anaerobic section 2, an anoxic section 3 and a stepped aerobic section 4 along the water flow direction of the drainage culvert, and adjusting the aeration volume in real time through a fuzzy PID dynamic algorithm to maintain a stable dissolved oxygen gradient, embeds the sewage treatment function into the existing drainage culvert, and integrates mud and water separation and sedimentation, mixed liquor return and sludge return into the mud and water separation and return device, greatly reducing construction costs, saving land and infrastructure investment, and synergistically improving the denitrification and phosphorus removal efficiency through gradient aeration and wetland ecological purification, which is suitable for urban combined sewer overflow pollution control and decentralized sewage treatment scenarios.

[0036] In one or more embodiments of the present invention, a cyclone aerator is provided in the anoxic section 3 and operates intermittently, and a microporous aeration tube is provided in the stepped aerobic section 4 and operates continuously.

[0037] In one or more embodiments of the present invention, the stepped aerobic section 4 includes at least three stages, and the dissolved oxygen concentration of each stage is 2.8-3.5 mg / L, 1.8-2.5 mg / L, and 1.0-1.5 mg / L, respectively, and the length of each stage accounts for 20%-40% of the total length of the stepped aerobic section.

[0038] In one or more embodiments of the present invention, the mud-water separation and reflux device 7 is provided with an intercepting pipe 9, a mud-water separator 10, a water collecting tank 11, a mixed liquor reflux pump 13 and a sludge reflux pump 14. One end of the intercepting pipe 9 extends out of the mud-water separation and reflux device 7 and is connected to the intercepting well 5. The mud-water separator 10 is arranged in the middle of the mud-water separation and reflux device 7. The water collecting tank 11 is arranged on the upper part of the outer wall of the mud-water separation and reflux device 7, and the water collecting tank 11 is connected to the artificial wetland 8.

[0039] In one or more embodiments of the present invention, a plurality of water distribution holes 12 communicating with the artificial wetland 8 are provided on the outer wall of the water collecting tank 11 .

[0040] In one or more embodiments of the present invention, the mud and water coordinated control module includes a mixed liquor return pump 13 and a sludge return pump 14. The mixed liquor return pump 13 is arranged at the bottom of the mud and water separation and reflux device 7 close to the intercepting pipe 9, and the output end of the mixed liquor return pump 13 is connected to the anoxic section 3 through a pipeline. The sludge return pump 14 is arranged at the bottom outside the mud and water separation and reflux device 7, and the output end of the sludge return pump 14 is connected to the culvert inlet 1.

[0041] In one or more embodiments of the present invention, the specific implementation of sequentially forming the dissolved oxygen gradient by fuzzy PID dynamic algorithm control is as follows:

[0042] The aeration rate correction coefficient is calculated based on the membership function using the water inlet flow, chemical oxygen demand (COD), and NH3-N concentration of the pipe culvert intersection 1 as feedforward inputs and the measured values ​​of the dissolved oxygen sensors of each section as feedback inputs;

[0043] The cyclone aerator in the anoxic section 3 and the microporous aeration tube in the stepped aerobic section 4 are controlled respectively to dynamically adjust the aeration volume according to the aeration volume correction coefficient.

[0044] The specific process of the sewage treatment system based on pipe culvert dissolved oxygen gradient regulation of the present invention is as follows:

[0045] On sunny days, the gate in the intercepting well 5 is closed, and the sewage is treated in sequence by the anaerobic section 2, the anoxic section 3 and the stepped aerobic section 4, so as to achieve the step-by-step removal of pollutants such as chemical oxygen demand (COD), nitrogen and phosphorus, and then intercepted by the intercepting well 5 to the mud-water separation and reflux device 7. Under the guidance of the mud-water separator 10, the lighter supernatant and gas of the mud-water mixture move upward, and the supernatant flows into the water collection tank 11, and then flows out from the water distribution hole 12 outside the water collection tank 11 into the artificial wetland 8. Through matrix adsorption, plant absorption and microbial degradation, the residual nitrogen, phosphorus and trace organic matter in the supernatant are removed, and then meet the standards and enter the discharge water body 6; the gas in the mud-water mixture overflows outward; the heavier sludge in the mud-water mixture moves downward and settles at the bottom, so as to achieve mud-water separation. Part of the sludge is returned to the culvert inlet 1 through the sludge return pump 14, and part of the mixed liquid is returned to the combination well 15 in front of the anoxic section 3 through the mixed liquid return pump 13, thereby realizing the sludge-water coordinated regulation function.

[0046] On rainy days, the water flow in the culvert is large, the gate in the intercepting well 5 is opened, the sludge return pump 14, the mixed liquid return pump 13 and the aeration device stop running, and the rainwater in the culvert is discharged into the discharge water body 6 through the intercepting well 5.

[0047] The present invention also provides a sewage treatment method based on pipe culvert dissolved oxygen gradient regulation, which adopts the sewage treatment system based on pipe culvert dissolved oxygen gradient regulation and includes the following steps:

[0048] S1: Sewage enters the anaerobic section 2 through the culvert inlet 1 and stays in the anaerobic section 2 for 40-60 minutes, controlling the dissolved oxygen concentration DO ≤ 0.2 mg / L to release phosphorus and hydrolyze organic matter;

[0049] Here, sewage flows into the anaerobic section 2 by gravity, and its dissolved oxygen concentration is lower than that of the incoming raw water, generally less than 0.2 mg / L, and no additional aerator is required.

[0050] S2: The sewage enters the anoxic section 3 through the anaerobic section 2 and stays in the anoxic section 3 for 60-120 minutes. The dissolved oxygen concentration DO is controlled by the fuzzy PID dynamic algorithm to be ≤= 0.2-0.5 mg / L to perform denitrification treatment;

[0051] Here, the power of the cyclone aerator provided in the anoxic section 3 is controlled by a fuzzy PID dynamic algorithm, thereby adjusting its aeration volume. The dissolved oxygen concentration DO is controlled within 0.2-0.5 mg / L through dynamic algorithm feedback control.

[0052] S3: The sewage enters the stepped aerobic section 4 through the anoxic section 3 and is treated in three stages with a total residence time of 4-5 hours. The dissolved oxygen concentration (DO) is controlled step by step to 3.5-1.0 mg / L by a fuzzy PID dynamic algorithm, and nitrification, carbon oxidation and phosphorus absorption are completed simultaneously.

[0053] At the same time, the power of the microporous aeration tubes in the stepped aerobic section 4 is controlled by the fuzzy PID dynamic algorithm to adjust the aeration volume. The dissolved oxygen concentration DO is controlled to 3.5-1.0 mg / L through dynamic algorithm feedback control.

[0054] S4: The sewage enters the interception well 5 through the stepped aerobic section 4 and, on sunny days, is diverted to the mud-water separation and reflux device 7 by controlling the gate in the interception well 5. The mud-water separation and reflux device 7 performs mud-water separation and sedimentation, mixed liquor reflux, and sludge reflux on the sewage. The lighter supernatant enters the downstream artificial wetland 8 for treatment for 1-3 days before being discharged. The hydraulic load of the artificial wetland 8 is less than 0.5m³ / (㎡·d).

[0055] In one or more embodiments of the present invention, the mud-water separation and reflux device 7 performs mud-water separation and sedimentation, mixed liquid reflux, and sludge reflux treatment on sewage, specifically including the following steps:

[0056] Under the guidance of the mud-water separator 10, the lighter supernatant and gas move upward, and the supernatant flows into the water collection tank 11, and then flows out from the water distribution holes 12 outside the water collection tank 11 into the artificial wetland 8. Through substrate adsorption, plant absorption and microbial degradation, the residual nitrogen, phosphorus and trace organic matter in the supernatant are removed, and then it meets the standards and enters the discharge water body 6;

[0057] Sewage gas leaks out;

[0058] The heavier sludge in the sewage moves downward and settles at the bottom of the mud-water separation and reflux device 7, achieving mud-water separation;

[0059] The sludge return pump 14 returns part of the sludge to the culvert inlet 1, and the mixed liquid return pump 13 returns part of the mixed liquid to the combination well 15 in front of the anoxic section 3, realizing the sludge and water coordinated control function.

[0060] In one or more embodiments of the present invention, the sewage treatment method based on culvert dissolved oxygen gradient control further includes the following steps:

[0061] Regularly check the MLSS concentration of the sewage mixed liquor at the end of the culvert. When the MLSS concentration of the mixed liquor is greater than 4500 mg / L, start the sludge return pump 14 to discharge part of the remaining sludge to the municipal sludge treatment system.

[0062] The sewage treatment system and method based on dissolved oxygen gradient regulation in the culvert of the present invention embeds the sewage treatment function into the drainage culvert, and integrates mud-water separation and sedimentation, mixed liquor return and sludge return into the mud-water separation and return device, greatly reducing construction costs. At the same time, through the synergy of gradient aeration and wetland ecological purification, the efficiency of nitrogen and phosphorus removal is significantly improved.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sewage treatment system based on dissolved oxygen gradient regulation in a pipe culvert, characterized by: The invention comprises an anaerobic section (2), an anoxic section (3) and a stepped aerobic section (4) which are sequentially connected along the flow direction of the drainage culvert, and a dissolved oxygen gradient is formed by fuzzy PID dynamic algorithm control. The end of the culvert is provided with an interception well (5) connected to the stepped aerobic section (4). The downstream of the interception well (5) is a discharge water body (6). A gate is provided in the interception well (5) to intercept the mud-water mixture to the mud-water separation and return device (7) on sunny days, or to discharge rainwater into the discharge water body (6) on rainy days. An artificial wetland (8) is provided downstream of the mud-water separation and return device (7). The mud-water separation and return device (7) is further connected to the culvert inlet (1) and the anoxic section (3) respectively through a mud-water coordinated control module to return part of the sludge to the culvert inlet (1) and return part of the mixed liquid to the anoxic section (3). The artificial wetland (8) is connected to the discharge water body (6) downstream.

2. The sewage treatment system based on pipe culvert dissolved oxygen gradient regulation according to claim 1 is characterized in that: A cyclone aerator is provided in the anoxic section (3), and the cyclone aerator operates intermittently. A microporous aeration tube is provided in the stepped aerobic section (4), and the microporous aeration tube operates continuously.

3. The sewage treatment system based on pipe culvert dissolved oxygen gradient control according to claim 1 is characterized in that: The stepped aerobic section (4) includes at least three stages, and the dissolved oxygen concentrations of each stage are 2.8-3.5 mg / L, 1.8-2.5 mg / L, and 1.0-1.5 mg / L, respectively, and the length of each stage accounts for 20%-40% of the total length of the stepped aerobic section.

4. The sewage treatment system based on pipe culvert dissolved oxygen gradient regulation according to claim 1 is characterized in that: The mud-water separation and reflux device (7) is provided with an intercepting pipe (9), a mud-water separator (10), a water collecting tank (11), a mixed liquid reflux pump (13) and a sludge reflux pump (14). One end of the intercepting pipe (9) extends out of the mud-water separation and reflux device (7) and is connected to the intercepting well (5). The mud-water separator (10) is arranged in the middle of the mud-water separation and reflux device (7). The water collecting tank (11) is arranged on the upper part of the side wall of one side of the mud-water separation and reflux device (7), and the water collecting tank (11) is connected to the artificial wetland (8).

5. The sewage treatment system based on pipe culvert dissolved oxygen gradient regulation according to claim 4 is characterized in that: A plurality of water distribution holes (12) communicating with the artificial wetland (8) are provided on the outer side wall of the water collecting tank (11).

6. The sewage treatment system based on pipe culvert dissolved oxygen gradient regulation according to claim 1, characterized in that: The mud-water coordinated control module comprises a mixed liquor return pump (13) and a sludge return pump (14); the mixed liquor return pump (13) is arranged at the bottom of the mud-water separation and return device (7) near the intercepting pipe (9), and the output end of the mixed liquor return pump (13) is connected to the anoxic section (3) through a pipeline; the sludge return pump (14) is arranged at the bottom outside the mud-water separation and return device (7), and the output end of the sludge return pump (14) is connected to the culvert inlet (1).

7. The sewage treatment system based on pipe culvert dissolved oxygen gradient regulation according to claim 1, characterized in that: The specific implementation of sequentially forming the dissolved oxygen gradient by fuzzy PID dynamic algorithm control is as follows: Based on the water inlet flow rate, chemical oxygen demand COD, and NH3-N concentration of the pipe culvert intersection (1) as feedforward inputs, and the measured values ​​of the dissolved oxygen sensors in each section as feedback inputs, the aeration rate correction coefficient is calculated according to the membership function; The cyclone aerator in the anoxic section (3) and the microporous aeration tube in the stepped aerobic section (4) are controlled respectively according to the aeration volume correction coefficient to dynamically adjust the aeration volume.

8. A sewage treatment method based on pipe culvert dissolved oxygen gradient regulation, which adopts the sewage treatment system based on pipe culvert dissolved oxygen gradient regulation according to any one of claims 1 to 7, characterized in that: The steps include: The sewage enters the anaerobic section (2) through the culvert inlet (1) and stays in the anaerobic section (2) for 40-60 minutes, controlling the dissolved oxygen concentration DO ≤ 0.2 mg / L to release phosphorus and hydrolyze organic matter; The sewage enters the anoxic section (3) through the anaerobic section (2) and stays in the anoxic section (3) for 60-120 minutes. The dissolved oxygen concentration DO is controlled to 0.2-0.5 mg / L or less by a fuzzy PID dynamic algorithm to perform denitrification treatment; The sewage enters the stepped aerobic section (4) through the anoxic section (3) and is treated in three stages with a total residence time of 4-5 hours. The dissolved oxygen concentration (DO) is controlled step by step to 3.5-1.0 mg / L by a fuzzy PID dynamic algorithm, and nitrification, carbon oxidation and phosphorus absorption are completed simultaneously. The sewage enters the interception well (5) through the stepped aerobic section (4), and on sunny days, the gate in the interception well (5) is controlled to intercept the sewage to the mud-water separation and return flow device (7). The mud-water separation and return flow device (7) performs mud-water separation and sedimentation, mixed liquid return and sludge return treatment on the sewage. The lighter supernatant enters the downstream artificial wetland (8) for treatment for 1-3 days before being discharged. The hydraulic load of the artificial wetland (8) is less than 0.5m³ / (㎡·d).

9. The sewage treatment method based on pipe culvert dissolved oxygen gradient regulation according to claim 8, characterized in that: The mud-water separation and reflux device (7) performs mud-water separation and sedimentation, mixed liquid reflux and sludge reflux treatment on sewage, which specifically includes the following steps: Under the guidance of the mud-water separator (10), the lighter supernatant and gas move upward, and the supernatant flows into the water collection tank (11), and then flows out from the water distribution hole (12) outside the water collection tank (11) into the artificial wetland (8). Through matrix adsorption, plant absorption and microbial degradation, the residual nitrogen, phosphorus and trace organic matter in the supernatant are removed, and then it meets the standards and enters the discharge water body (6); The gas from sewage overflows directly to the outside; The heavier sludge in the sewage moves downward and settles at the bottom of the mud-water separation and return device (7), achieving mud-water separation; The sludge return pump (14) returns part of the sludge to the culvert inlet (1), and the mixed liquid return pump (13) returns part of the mixed liquid to the combined well (15) in front of the anoxic section (3), thereby realizing the sludge and water coordinated control function.

10. The sewage treatment method based on pipe culvert dissolved oxygen gradient regulation according to claim 8 or 9, characterized in that: It also includes the excess sludge control steps: The MLSS concentration of the sewage mixed liquor at the end of the culvert is regularly tested. When the MLSS concentration of the mixed liquor is greater than 4500 mg / L, the sludge return pump (14) is started to discharge part of the remaining sludge to the municipal sludge treatment system.

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