Sewage treatment system

Abstract

The utility model belongs to the technical field of sewage treatment, and relates to a sewage treatment system which comprises a first-stage anoxic tank, a first-stage aerobic tank, a second-stage anoxic tank and a second-stage aerobic tank which are sequentially connected through pipelines, and sludge generated after reaction in the second-stage aerobic tank flows back to the first-stage aerobic tank. Sludge generated after nitrification in a secondary aerobic tank in a wastewater treatment process flows back to a primary aerobic tank for cyclic nitrification, so that the chemical oxygen demand and the total nitrogen load in the sludge are reduced, and the chemical oxygen demand and the total nitrogen in discharged water are reduced; meanwhile, by arranging two-stage anoxic denitrification and two-stage nitration reaction, the nitration and denitrification reaction time is prolonged, the removal rate of ammonia nitrogen and total nitrogen in sewage is increased, the content of ammonia nitrogen and total nitrogen in drained water is reduced, the content of ammonia nitrogen, total nitrogen, chemical oxygen demand and total phosphorus in sewage is further reduced through the synergistic effect, and the emission standard is met.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment and relates to a sewage treatment system. Background Art

[0002] The second phase of the existing sewage treatment plant has a designed capacity of 30,000 tons per day, with 75% of the influent being printing and dyeing wastewater and 25% being domestic sewage. The existing sewage treatment technology, which sequentially processes wastewater through a regulating tank, a primary sedimentation tank, an anoxic tank, an aerobic tank, and a secondary sedimentation tank, produces product water that meets the local environmental protection department's sewage treatment plant discharge standards, the "Class B Sewage Discharge Standard," which include COD ≤ 50 mg / l, TP ≤ 0.6 mg / l, TN ≤ 12 mg / l, and ammonia nitrogen ≤ 4 mg / l.

[0003] The existing process was at risk of exceeding discharge standards for ammonia nitrogen (NH3-N), total nitrogen (TN), chemical oxygen demand (COD), and total phosphorus (TP). These four water production indicators needed to be reduced by approximately 20% from their original levels, namely: COD ≤ 40mg / l, TP ≤ 0.5mg / l, TN ≤ 10mg / l, and ammonia nitrogen ≤ 3mg / l. This made the existing wastewater treatment method no longer meet the new emission standards, necessitating an upgrade of the existing process. However, due to site constraints, the wastewater treatment plant's footprint could not be expanded, and the upgrade had to be completed within the existing area. Utility Model Content

[0004] The utility model aims to provide a sewage treatment system, which returns the sludge produced after nitrification in the secondary aerobic tank in the wastewater treatment process to the primary aerobic tank for nitrification in a cycle, thereby increasing the content of activated sludge, reducing the chemical oxygen demand (COD) and total nitrogen (TN) load in the sludge, and thus reducing the chemical oxygen demand (COD) and total nitrogen (TN) in the drainage water; at the same time, by setting up two-stage anoxic denitrification and two-stage nitrification reactions, the nitrification and denitrification reaction times are prolonged, the removal rate of ammonia nitrogen (NH3-N) and total nitrogen (TN) in the sewage is increased, and the ammonia nitrogen (NH3-N) and total nitrogen (TN) contents in the drainage water are reduced. The synergistic effect further reduces the ammonia nitrogen (NH3-N), total nitrogen (TN), chemical oxygen demand (COD) and total phosphorus (TP) contents in the sewage to meet the discharge standards.

[0005] In a first aspect, the utility model provides a sewage treatment system, comprising a primary anoxic tank, a primary aerobic tank, a secondary anoxic tank and a secondary aerobic tank connected in sequence by pipes, wherein the sludge generated after the reaction in the secondary aerobic tank flows back into the primary aerobic tank.

[0006] In some embodiments, a filtering mechanism is provided in the secondary aerobic tank, and the sewage is filtered through the filtering mechanism after reacting in the secondary aerobic tank and then discharged.

[0007] In some embodiments, an aeration device is provided in the primary aerobic tank and the secondary aerobic tank.

[0008] In some embodiments, the volume ratio of the primary anoxic tank, the primary aerobic tank, the secondary anoxic tank, and the secondary aerobic tank is 1-3:2-4:0.5-1.5:2-4.

[0009] In some embodiments, the volume ratio of the primary anoxic tank, the primary aerobic tank, the secondary anoxic tank, and the secondary aerobic tank is 2:3:1:3.

[0010] In some embodiments, the primary anoxic tank, the primary aerobic tank, and the secondary anoxic tank contain biological fillers.

[0011] In some embodiments, the nitrified liquid produced in the primary aerobic tank is returned to the primary anoxic tank.

[0012] In some embodiments, a stirring device is provided in the primary anoxic tank and the secondary anoxic tank.

[0013] In some embodiments, the primary anoxic tank is connected to a primary sedimentation tank for pre-treating sewage via a pipeline, and the primary sedimentation tank is arranged at the water inlet end of the primary anoxic tank.

[0014] In some embodiments, the side walls of the primary anoxic tank, the primary aerobic tank, the secondary anoxic tank, and the secondary aerobic tank are made of corrugated carbon steel plates.

[0015] In summary, this application includes at least one of the following beneficial technical effects:

[0016] By returning the sludge produced after nitrification in the secondary aerobic tank to the primary aerobic tank for nitrification, the activated sludge content is increased, the chemical oxygen demand (COD) and total nitrogen (TN) load in the sludge are reduced, thereby reducing the chemical oxygen demand (COD) and total nitrogen (TN) in the drainage. At the same time, by setting up two-stage anoxic denitrification and two-stage nitrification reactions, the nitrification and denitrification reaction times are extended, the removal rates of ammonia nitrogen (NH3-N) and total nitrogen (TN) in the sewage are increased, and the ammonia nitrogen (NH3-N) and total nitrogen (TN) contents in the drainage are reduced. The combined effect further reduces the ammonia nitrogen (NH3-N), total nitrogen (TN), chemical oxygen demand (COD) and total phosphorus (TP) contents in the sewage to meet the discharge standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of a sewage treatment system in an embodiment of the present utility model;

[0018] Figure 2 It is a structural diagram of the sewage treatment system in an embodiment of the present utility model.

[0019] Figure numerals: 1, primary sedimentation tank; 2, primary anoxic tank; 3, primary aerobic tank; 4, secondary anoxic tank; 5, secondary aerobic tank; 6, water inlet pipe; 61, submersible pump; 7, air supply equipment; 8, aeration stirring pipe; 9, microporous aeration disk; 10, primary nitrification pipe; 11, primary denitrification pipe; 12, secondary nitrification pipe; 13, nitrification liquid return pipe; 131, nitrification liquid return pump; 14, tap water pipe; 15, mixing tank; 16, feeding pipe; 161, metering pump; 17, MBR membrane bioreactor; 18, outlet pipe; 181, water production pump; 182, clean water barrel; 183, drain pipe; 19, sludge return pipe; 191, sludge return pump; 192, sludge discharge pipe. DETAILED DESCRIPTION

[0020] The following is a detailed description of the technical solution of the present invention, which does not limit the scope of protection of the present invention. Non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the scope of protection of the present invention.

[0021] The existing sewage treatment plant's second phase is designed to produce 30,000 tons per day. 75% of the influent is printing and dyeing wastewater, and 25% is domestic sewage. The existing sewage treatment technology sequentially processes wastewater through a regulating tank, a primary sedimentation tank, an anoxic tank, an aerobic tank, and a secondary sedimentation tank. After nitrification in the aerobic tank, 200% of the sludge is returned to the anoxic tank via a reflux pump. This technology meets the current effluent standards of the local environmental protection department's existing sewage treatment plant, as shown in Table 1 below.

[0022] However, due to stricter discharge standards imposed by the local environmental protection department, the existing process's water output, including ammonia nitrogen (NH3-N), total nitrogen (TN), chemical oxygen demand (COD), and total phosphorus (TP), could no longer meet the effluent standards set by the environmental protection department (see Table 1 below), posing the risk of exceeding these standards. These four water output indicators needed to be reduced by approximately 20% from their original levels, and the existing wastewater treatment method was no longer able to meet the new discharge standards.

[0023] Table 1 Pollutant content and emission standards

[0024]

[0025] The removal of ammonia nitrogen NH3-N and total nitrogen TN is mainly the result of nitrification and denitrification in activated sludge:

[0026] Nitrification under aerobic conditions: NH3-N (electron donor) → NO2- / NO3-

[0027] Denitrification under anoxic conditions: NO 2- / NO 3- (Electron acceptor) → N2

[0028] Therefore, NH3-N in wastewater needs to be converted into NO under aerobic conditions first. 2- / NO 3- , and then converted into harmless N2 under anoxic conditions to achieve the purpose of meeting emission standards.

[0029] After investigation and analysis, the reasons why existing technologies cannot meet water production standards are as follows:

[0030] 1. In the existing process section, sewage passes through the anoxic tank and aerobic tank in sequence for nitrification and denitrification. The volume ratio of the anoxic tank and the aerobic tank is 1:2, the anoxic tank has 3 compartments and the aerobic tank has 6 compartments. The sewage retention time is short, and the nitrification and denitrification reactions are not sufficient, resulting in a small amount of nitrate nitrogen flowing back to the anoxic stage. The nitrate nitrogen supply of denitrifying bacteria in the anoxic stage is insufficient, and ultimately the total nitrogen and ammonia nitrogen cannot be removed more thoroughly, ultimately resulting in excessive emissions of NH3-N and total nitrogen (TN).

[0031] 2. Chemical oxygen demand COD and total phosphorus TP are due to insufficient activated sludge concentration and excessive chemical oxygen demand COD and total nitrogen TN load in the sludge, resulting in excessive effluent.

[0032] Based on this, and taking into account site limitations, the sewage treatment plant's floor area cannot be expanded, and new sewage treatment sites cannot be added. The present invention upgrades the existing process on the original site, and the upgrade needs to be completed on the original area.

[0033] The nitrification liquid described in the present invention refers to sewage after primary nitrification.

[0034] Activated sludge, as used herein, refers to sludge that has undergone two-stage nitrification and denitrification, resulting in high microbial activity and a rich variety and quantity. It is a general term for microbial communities and the organic and inorganic substances they adhere to. Activated sludge also includes dewatered sludge and dried sludge. The activity of microorganisms, particularly bacteria, in these sludges decreases, requiring 3-7 days of acclimatization to restore activity.

[0035] Example

[0036] A sewage treatment system, such as Figure 1 and Figure 2As shown, the system comprises a primary sedimentation tank 1, a primary anoxic tank 2, a primary aerobic tank 3, a secondary anoxic tank 4, and a secondary aerobic tank 5, which are sequentially connected by pipes. The volume ratio of the primary anoxic tank 2, the primary aerobic tank 3, the secondary anoxic tank 4, and the secondary aerobic tank 5 is 2:3:1:3. The primary anoxic tank 2, the primary aerobic tank 3, the secondary anoxic tank 4, and the secondary aerobic tank 5 are assembled into a container-like rectangular box with dimensions of 6m × 2.2m × 2.3m. The surrounding area is clad with corrugated carbon steel plates with a thickness of 6mm, and the inner bottom plate is a patterned plate with a thickness of ≥8mm, which has excellent corrosion resistance. By setting up two-stage anoxic denitrification and two-stage nitrification reactions, the nitrification and denitrification reaction times are prolonged. At the same time, by returning the sludge, the ammonia nitrogen (NH3-N), total nitrogen (TN), chemical oxygen demand (COD), and total phosphorus (TP) contents in the wastewater are further reduced.

[0037] The sewage to be treated includes 75% printing and dyeing wastewater and 25% domestic sewage. The specific pollutant content is shown in Table 2. The sewage is introduced into the primary sedimentation tank 1 through the water inlet pump as an on-site biochemical water intake point. 500 mg / L of citric acid is continuously added through a dosing metering pump as the water inlet pump runs, and the pH is adjusted to between 5.5-6.5. A filtering device is provided in the primary sedimentation tank 1. In this embodiment, the filtering device is a filter screen arranged at the bottom of the primary sedimentation tank 1 to filter out larger solid pollutants such as suspended matter, and then the sewage is introduced into the primary anoxic tank 2 through the water inlet pipe 6. The water inlet pipe 6 is a DN25 steel wire hose with an inner diameter of 25 mm. A submersible pump 61 is installed at one end of the water inlet pipe 6 close to the primary sedimentation tank 1. The submersible pump 61 is 15 meters away from the bottom of the primary sedimentation tank 1, and the flow rate of the submersible pump 61 is 1m 3 / h.

[0038] like Figure 2 As shown, the sewage treatment system of the present invention also includes an aeration structure, which includes an air supply device 7, an aeration stirring pipe 8 and a microporous aeration disk 9 connected to the air supply device 7. The first-level anoxic tank 2 and the second-level anoxic tank 4 are each provided with an aeration stirring pipe 8, each having multiple air outlet holes with a diameter of 5 mm and arranged at a downward angle of 45 degrees. The first-level aerobic tank 3 and the second-level aerobic tank 5 are each provided with a microporous aeration disk 9. The aeration stirring pipe 8 and the microporous aeration disk 9 are connected to the air supply device 7 via a pipeline. The air supply device 7 is an air pump or fan for providing gas.

[0039] The bottoms of the primary anoxic tank 2 and the primary aerobic tank 3 are connected by a primary nitrification pipe 10 with an inner diameter of 40 mm. The tops of the primary aerobic tank 3 and the secondary anoxic tank 4 are connected by a primary denitrification pipe 11, and the bottoms of the secondary anoxic tank 4 and the secondary aerobic tank 5 are connected by a secondary nitrification pipe 12. This allows the wastewater to flow through the primary anoxic tank 2, primary aerobic tank 3, secondary anoxic tank 4, and secondary aerobic tank 5 at once, undergoing two-stage nitrification and denitrification.

[0040] The primary anoxic tank 2 contains biological filler, which is composed of a PE core rope and a aldehyded vinylon yarn bouquet. The wastewater remains in the tank for approximately six hours, undergoing a primary denitrification reaction under anoxic conditions, using the COD in the influent as the carbon source. After the reaction, the wastewater continues through the primary nitrification pipe 10 and enters the primary aerobic tank 3. If the wastewater remains in the primary denitrification tank for less than five hours, the conversion of nitrate nitrogen (NO₃) to nitrogen gas (N₂) may be incomplete, potentially causing the effluent total nitrogen (TN) to exceed the standard. If the wastewater remains in the primary denitrification tank for more than seven hours, the tank volume increases, increasing costs and providing little improvement in water treatment efficiency.

[0041] The first-level aerobic pool 3 contains biological fillers, according to 50m 3 / h aeration rate, the sewage stays in the primary aerobic tank 3 for about 11 hours and undergoes primary nitrification reaction under aerobic conditions. When the sewage stays in the primary nitrification time for less than 10 hours, it will lead to incomplete conversion of ammonia nitrogen into nitrate nitrogen NO3-, which may cause the total nitrogen TN in the effluent to exceed the standard; when the sewage stays in the primary nitrification time for more than 12 hours, it will also increase the tank volume and cost, but will not improve the water treatment effect much.

[0042] A nitrification liquid return pipe 13 is also connected between the bottom of the first aerobic tank 3 and the top of the first anoxic tank 2. The nitrification liquid return pipe 13 is a UPVC pipe with an inner diameter of 25 mm. A nitrification liquid return pump 131 is installed on the nitrification liquid return pipe 13. The flow rate of the nitrification liquid return pump 131 is 2m 3 / h, after the reaction in the primary aerobic tank 3 is completed, 50% of the nitrified liquid in the primary aerobic tank 3 is refluxed to the primary anoxic tank 2. Under the premise of ensuring sufficient nitrified liquid, the anaerobic environment of the denitrifying bacteria is not affected, the nitrate concentration in the primary anoxic tank 2 is guaranteed, and a substrate is provided for the denitrifying bacteria. The nitrate is converted into nitrogen gas and discharged into the atmosphere to achieve harmless treatment. The remaining sewage is introduced into the secondary anoxic tank 4 through the primary denitrification pipe 11.

[0043] The secondary anoxic tank 4 contains biological fillers. The sewage stays in the secondary anoxic tank 4 for about 3 hours and undergoes secondary denitrification reaction under anoxic conditions. When the sewage stays in the secondary denitrification tank for less than 2 hours, it will also lead to incomplete conversion of nitrate nitrogen NO3- into nitrogen gas N2; when the sewage stays in the secondary denitrification tank for more than 4 hours, the tank volume will also increase, which will not greatly improve the water treatment effect.

[0044] like Figure 2As shown, the sewage treatment system of this embodiment also includes a carbon source addition structure, which includes a tap water pipe 14, a mixing tank 15, a feeding pipe 16 and a metering pump 161. One end of the tap water pipe 14 is connected to a water source, and the other end is connected to the mixing tank 15. Glucose is added to the mixing tank 15, and then tap water is added through the tap water pipe 14 to mix to obtain a glucose solution. The mixing tank 15 is connected to two feeding pipes 16, and the two feeding pipes 16 are connected to the first-level anoxic tank 2 and the second-level anoxic tank 4 at one end away from the mixing tank 15. Metering pumps 161 are respectively installed on the two feeding pipes 16 for adding glucose as a carbon source for the reaction to the second-level anoxic tank 4. The amount of glucose added is 5 mg / L in the final concentration of the sewage in the second-level denitrification step. When the carbon source (COD carbon content) of the sewage itself in the first-level anoxic tank 2 is insufficient, the carbon source can also be supplemented by the carbon source addition structure. After the reaction is completed, the sewage continues to enter the second-level aerobic tank 5 through the pipeline.

[0045] The secondary aerobic tank 5 is provided with an MBR membrane bioreactor 17. The sewage stays in the secondary anoxic tank for about 11 hours. 3 / h aeration rate, allowing for secondary nitrification under aerobic conditions. Wastewater from the secondary nitrification reaction is filtered through the MBR membrane bioreactor 17 by a self-priming or centrifugal pump before being discharged. This achieves mud-water separation, clarifies the effluent, and removes suspended solids (SS). If the wastewater's secondary nitrification residence time is less than 10 hours, the conversion of ammonia nitrogen into nitrate nitrogen (NO3-) will also be incomplete. If the wastewater's secondary nitrification residence time is greater than 12 hours, the tank volume will also increase, with little improvement in water treatment efficiency.

[0046] The secondary aerobic tank 5 is connected to an outlet pipe 18 and a sludge return pipe 19. A water production pump 181 is installed on the outlet pipe 18. The outlet pipe 18 is connected to a clean water bucket 182 at one end away from the secondary aerobic tank 5 for temporarily storing the water discharged from the secondary aerobic tank 5. The clean water bucket 182 is connected to a drain pipe 183 for draining the water in the clean water bucket 182. One end of the sludge return pipe 19 is connected to the secondary aerobic tank 5, and the other end is connected to the primary aerobic tank 3. A sludge return pump 191 is installed on the sludge return pipe 19. After the reaction is completed, 150% (the amount of water produced is 100%), the reflux amount 150% means that 1.5 times the amount of water produced is refluxed, such as the water production is 1m 3 / h, the return flow is 1.5m 3Sludge at a rate of 100 / h (approximately 200 sludge tons / hour) is returned to the primary aerobic tank 3 via the sludge return pipe 19 and sludge return pump 191. This increases the activated sludge concentration in the primary aerobic tank 3 to 10,000 mg / L, enhancing microbial biochemical activity and reducing effluent COD and total phosphorus levels. A sludge return rate exceeding 160% results in excessive sludge content in the wastewater, prolonging wastewater retention time and overloading the equipment. A sludge return rate less than 110% shortens wastewater retention time, resulting in a low activated sludge content in the returned wastewater and poor removal of chemical oxygen demand (COD) and total phosphorus (TP).

[0047] Since the sludge in the secondary aerobic tank 5 has a high oxygen content, if it were to return directly to the primary anoxic tank 2 or the secondary anoxic tank 4, the anaerobic environment in both tanks would be destroyed, affecting the microbial survival environment of the primary anoxic tank 2 or the secondary anoxic tank 4. However, if it were to return to the primary aerobic tank 3, after consuming a large amount of oxygen in the primary aerobic tank 3, neither the sludge entering the secondary anoxic tank 4 nor the nitrification solution entering the primary anoxic tank 2 would have a significant impact on the microorganisms in the primary anoxic tank 2 or the secondary anoxic tank 4. The secondary aerobic tank 5 also serves as a membrane tank, and its aeration volume is approximately 2-4 times higher than that of the primary aerobic tank 3. Therefore, the return point is selected to be in the primary aerobic tank 3. The sludge return pipe 19 is connected to the sludge discharge pipe 192 for discharging excess sludge.

[0048] In this embodiment, the original three-grid space occupied by the anoxic tank and the six-grid space occupied by the aerobic tank are changed to a first-level anoxic tank 2 occupying two grids, a first-level aerobic tank 3 occupying three grids, a second-level anoxic tank 4 occupying one grid, and a second-level aerobic tank 5 occupying three grids. In other words, the original volume ratio of the anoxic and aerobic tanks, which was 1:2, is re-divided into a volume ratio of 2:3:1:3 for the first-level anoxic tank 2, the first-level aerobic tank 3, the second-level anoxic tank 4, and the second-level aerobic tank 5. This prolongs the nitrification and denitrification reaction time without adding new reaction tanks, thereby adjusting the wastewater residence time during the nitrification and denitrification reactions while maintaining the original footprint. Simultaneously, the activated sludge concentration is increased by specifying the sludge return rate and return flow nodes, and the nitrification and denitrification reactions are enhanced by adjusting the aeration rate and the specific return rate and return flow nodes of the nitrification solution. Combined with the use of MBR membranes, the combined effects further reduce the COD, TP, TN, and ammonia nitrogen contents in the wastewater, meeting the new emission standards.

[0049] Technical Effects

[0050] The sewage was treated by the system of the embodiment, and the specific content of pollutants in the treated sewage is shown in Table 2 below. In Table 2, the various indicators of the influent are a mixture of two wastewaters, so the influent content of each indicator is between the content of the printing and dyeing wastewater and the domestic wastewater in Table 1.

[0051] Table 2 Pollutant content before and after sewage treatment

[0052]

[0053]

[0054] It can be seen that the ammonia nitrogen (NH3-N), total nitrogen (TN), chemical oxygen demand (COD), and total phosphorus (TP) contents of the sewage treated by the system of the present invention are greatly reduced, and can meet the effluent standards required by the environmental protection department. The BOD / COD ratio is 0.5, and a BOD / COD ratio of ≥0.45 indicates good biodegradability and can be used to treat sewage by biochemical methods, indicating that the method of the present invention has a good sewage treatment effect. A BOD / TN ratio of ≥2.5 indicates that TN can be removed by biochemical methods. The BOD / TN ratio of the present invention is 3, indicating that the method of treating sewage of the present invention is reasonably designed.

[0055] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A sewage treatment system, characterized in that: It comprises a primary anoxic pool, a primary aerobic pool, a secondary anoxic pool and a secondary aerobic pool which are sequentially connected by pipelines, wherein the secondary aerobic pool is provided with a filtering mechanism; The volume ratio of the first anoxic tank, the first aerobic tank, the second anoxic tank and the second aerobic tank is 2:3:1:3; The sewage treatment system further comprises a carbon source adding structure for adding a carbon source into the secondary anoxic tank; The pipeline includes a sludge return pipe and a nitrification liquid return pipe, wherein, The secondary aerobic tank is connected to one end of the sludge return pipe, and the other end of the sludge return pipe is connected to the primary aerobic tank, so that the sludge generated after the reaction in the secondary aerobic tank is returned to the primary aerobic tank through the sludge return pipe; The nitrification liquid reflux pipe is connected between the primary aerobic tank and the primary anoxic tank, and the nitrification liquid generated in the primary aerobic tank flows back into the primary anoxic tank through the nitrification liquid reflux pipe.

2. The sewage treatment system according to claim 1, characterized in that: The filtering mechanism is an MBR membrane bioreactor. After the sewage reacts in the secondary aerobic tank, it is filtered through the MBR membrane bioreactor and then discharged.

3. The sewage treatment system according to claim 1, wherein: The primary aerobic tank and the secondary aerobic tank are provided with an aeration device, and the aeration device comprises a microporous aeration disk respectively provided in the primary aerobic tank and the secondary aerobic tank.

4. The sewage treatment system according to claim 3, characterized in that: The first-level anoxic tank and the second-level anoxic tank are also provided with an aeration device, and the aeration device further includes an aeration stirring pipe respectively provided in the first-level anoxic tank and the second-level anoxic tank.

5. The sewage treatment system according to claim 4, characterized in that: The aeration device further includes an air supply device, and the aeration stirring pipe and the microporous aeration disk are respectively connected to the air supply device.

6. The sewage treatment system according to claim 1, wherein: The first-level anoxic pool, the first-level aerobic pool and the second-level anoxic pool all contain biological fillers.

7. The sewage treatment system according to claim 1, wherein: The carbon source addition structure includes a tap water pipe, a mixing tank and a feeding pipe. One end of the tap water pipe is connected to the water source, and the other end is connected to the mixing tank. The mixing tank is filled with the carbon source. One end of the feeding pipe is connected to the mixing tank, and the other end is connected to the secondary anoxic tank.

8. The sewage treatment system according to claim 7, characterized in that: There are two feeding pipes, the mixing tank is connected to the two feeding pipes, and the ends of the two feeding pipes away from the mixing tank are respectively connected to the primary anoxic tank and the secondary anoxic tank.

9. The sewage treatment system according to claim 1, wherein: The first-level anoxic tank is connected to a primary sedimentation tank for pre-treating sewage through a pipeline, and the primary sedimentation tank is arranged at the water inlet end of the first-level anoxic tank.

10. The sewage treatment system according to any one of claims 1 to 9, characterized in that: The side walls of the first-level anoxic pool, the first-level aerobic pool, the second-level anoxic pool and the second-level aerobic pool are made of corrugated carbon steel plates.

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