Sewage treatment system

Abstract

The utility model discloses a sewage treatment system. The sewage treatment system comprises a pretreatment unit, a biological treatment unit and a chemical treatment unit, the biological treatment unit comprises a multi-stage biological tank, a secondary sedimentation tank and a carbon source dosing pipeline; the multi-stage biological tank is divided into an anaerobic zone, a first-stage anoxic zone, a first-stage aerobic zone, a second-stage anoxic zone and a second-stage aerobic zone from back to front; the anaerobic zone, the first-stage anoxic zone and the second-stage anoxic zone are respectively connected with a water outlet of the water inlet header pipe through a first water inlet branch pipe, a second water inlet branch pipe and a third water inlet branch pipe; the first-stage aerobic zone and the second-stage aerobic zone are respectively connected with the first-stage anoxic zone and the second-stage anoxic zone through a first sludge inner return pipe and a second sludge inner return pipe; a water inlet of the secondary sedimentation tank is connected with a water outlet of the secondary aerobic zone, and a sludge bin of the secondary sedimentation tank is respectively connected with the anaerobic zone and the secondary aerobic zone through two sludge return pipes; the carbon source dosing pipeline comprises a first dosing point arranged at the front end of the primary anoxic zone and a second dosing point arranged at the tail end of the primary aerobic zone. According to the utility model, the treatment efficiency can be improved and the cost can be reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to a sewage treatment system. BACKGROUND

[0002] At present, in the field of sewage treatment, AAO (anaerobic-anoxic-aerobic) treatment process as a classic and effective biological treatment process has been widely used. However, the traditional AAO treatment process often faces the problems of poor denitrification and phosphorus removal effect, high operating cost and large sludge production when treating low carbon-nitrogen ratio sewage. In the prior art, although there are many improvement methods, there are still the following shortcomings:

[0003] 1. When treating low carbon-nitrogen ratio sewage, due to insufficient carbon source, the activity of denitrifying bacteria that can achieve denitrification and polyphosphorus bacteria that can achieve phosphorus removal is limited, resulting in a significant decrease in denitrification and phosphorus removal effect. Not only does it affect the water quality, but also increases the difficulty and cost of subsequent treatment.

[0004] 2. When treating low carbon-nitrogen ratio sewage, a large amount of external carbon source needs to be added to meet the needs of denitrifying bacteria, which not only increases the operating cost, but also causes secondary pollution to the environment.

[0005] 3. Sludge treatment is an important link in the process of sewage treatment, but the traditional process often produces a large amount of sludge, which not only increases the difficulty and cost of subsequent treatment, but also may pose a potential threat to the environment.

[0006] 4. In the process of denitrification and phosphorus removal, a large amount of energy and chemical agents are often consumed, which not only increases the operating cost of the system, but also has adverse effects on the environment. INVENTION CONTENTS

[0007] The utility model aims at overcoming the defects of the prior art and providing a sewage treatment system which can greatly improve the efficiency of denitrification and phosphorus removal and reduce the cost of carbon source addition.

[0008] The utility model aims at overcoming the defects of the prior art and providing a sewage treatment system which can greatly improve the efficiency of denitrification and phosphorus removal and reduce the cost of carbon source addition.

[0009] The biological treatment unit comprises an AAO biological tank, a secondary sedimentation tank and a carbon source dosing pipeline; wherein,

[0010] The AA0 biological tank is divided into an anaerobic zone, a first anoxic zone, a first aerobic zone, a second anoxic zone and a second aerobic zone from back to front by first to fourth partitions, the two ends of the first partition are not connected with the two side walls of the AA0 biological tank to form a flow water port, the two ends of the second partition are connected with the two side walls of the AA0 biological tank, but the middle part of the second partition is disconnected to form a flow water port; the two ends of the third partition are not connected with the two side walls of the AA0 biological tank to form a flow water port, the two ends of the fourth partition are connected with the two side walls of the AA0 biological tank, but the middle part of the fourth partition is disconnected to form a flow water port; the anaerobic zone is connected with the water outlet of a water inlet main pipe through a first water inlet branch pipe, the water inlet of the water inlet main pipe is connected with an aerated grit chamber of a pretreatment unit, a first gate valve and a first flow meter are installed on the water inlet main pipe; the first anoxic zone is connected with the water outlet of the water inlet main pipe through a second water inlet branch pipe, a second gate valve and a second flow meter are installed on the second water inlet branch pipe; the second anoxic zone is connected with the water inlet main pipe through a third water inlet branch pipe, a third gate valve and a third flow meter are installed on the third water inlet branch pipe; the first aerobic zone is connected with the first anoxic zone through a first sludge internal return pipe; the second aerobic zone is connected with the second anoxic zone through a second sludge internal return pipe;

[0011] The water inlet of the secondary sedimentation tank is connected with the overflow water outlet of the second aerobic zone, the sludge tank at the bottom of the secondary sedimentation tank is connected with the anaerobic zone and the second aerobic zone through two sludge return pipes respectively; the water outlet pipe of the secondary sedimentation tank is connected with the chemical treatment unit;

[0012] The carbon source dosing pipeline comprises a first dosing point arranged at the front end of the first anoxic zone and a second dosing point arranged at the end of the first aerobic zone.

[0013] The sewage treatment system, wherein the anaerobic zone, the first anoxic zone and the second anoxic zone are each provided with a submersible mixer.

[0014] The sewage treatment system, wherein the chemical treatment unit comprises a high-efficiency sedimentation tank, a denitrification deep-bed filter and a contact disinfection tank connected in sequence through a front water outlet pipe, the denitrification deep-bed filter is connected with the high-efficiency sedimentation tank through a backwashing water pipe;

[0015] The sludge concentration unit comprises a sludge concentration tank and a sludge dewatering workshop connected in sequence, the sludge concentration tank is connected with the residual sludge outlet of the secondary sedimentation tank and the chemical sludge outlet of the high-efficiency sedimentation tank through two concentration pipes respectively.

[0016] The sewage treatment system, wherein the high-efficiency sedimentation tank comprises a mixing tank and a flocculation tank; the mixing tank is provided with a mixing mixer; the flocculation tank is provided with a flocculation mixer.

[0017] The sewage treatment system, wherein the contact disinfection tank is provided with a plant area reuse pump station and a water outlet metering tank.

[0018] The sewage treatment system, wherein the aerated grit chamber is provided with a slope type grit chamber and a gas explosion device, and a grit suction pump on the grit chamber is installed on a grit suction bridge which is movable to cross between the top surfaces of the two side walls of the aerated grit chamber.

[0019] The sewage treatment system has the following characteristics:

[0020] 1. The sectional water inlet design is adopted to realize step-by-step treatment of sewage and step-by-step release of carbon source, effectively solve the problem of insufficient carbon source, and the added carbon source dosing pipeline can flexibly adjust the carbon source dosage according to the actual water quality, realize accurate dosing and efficient utilization of carbon source, ensure that phosphorus accumulating bacteria and denitrifying bacteria obtain sufficient carbon source, and significantly improve the denitrification and phosphorus removal efficiency; while ensuring the denitrification and phosphorus removal effect, the consumption of carbon source is greatly reduced, and the operation cost is effectively reduced.

[0021] 2. The sludge return system is optimized, a multi-stage return mode is adopted, the sludge activity is improved, and the sludge age is prolonged, which helps to reduce the amount of sludge generated, reduce the difficulty and cost of sludge treatment; at the same time, the multi-stage return mode also helps to improve the stability and anti-impact load capacity of the system.

[0022] 3. The sectional water inlet biological treatment unit has compact structure and simple operation, and is easy to realize automatic control and management, thereby further reducing the operation difficulty and cost. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a principle structure diagram of the sewage treatment system of the utility model;

[0024] Figure 2 is a principle structure diagram of a biological treatment unit in the sewage treatment system of the utility model. DETAILED DESCRIPTION

[0025] The utility model will be further described below with reference to the drawings.

[0026] Please refer to Figure 1 and Figure 2 The sewage treatment system of the utility model comprises a pretreatment unit 1, a biological treatment unit 2, a chemical treatment unit 3 and a sludge concentration unit 4.

[0027] The core function of the pretreatment unit 1 is physical interception and preliminary treatment; the pretreatment unit includes an inlet gate well 10, an inlet pump house 12 and an aerated grit chamber 14 connected in sequence; wherein, the inlet gate well 10 is equipped with a coarse screen device 11; the inlet pump house 12 is equipped with a fine screen device 13; the aerated grit chamber 14 is equipped with a sloping grit hopper and an aeration device, and the grit suction pump on the grit hopper is installed on the grit suction bridge, which is movably connected between the tops of the two side walls of the aerated grit chamber 14.

[0028] Biological treatment unit 2 includes an AAO biological tank 20, a secondary sedimentation tank 21, and a carbon source dosing pipeline 22; wherein,

[0029] The AA0 biological tank 20 is divided from back to front into an anaerobic zone 201, a primary anoxic zone 202, a primary aerobic zone 203, a secondary anoxic zone 204, and a secondary aerobic zone 205 by a first to a fourth partition. The two ends of the first partition are not connected to the side walls of the AA0 biological tank 20, forming water outlets. The two ends of the second partition are connected to the side walls of the AA0 biological tank 20, but the middle of the second partition is broken, forming a water outlet. The two ends of the third partition are not connected to the side walls of the AA0 biological tank 20, forming water outlets. The two ends of the fourth partition are connected to the side walls of the AA0 biological tank 20, but the middle of the fourth partition is broken, forming a water outlet. The anaerobic zone 201 is connected to the outlet of the main inlet pipe 210 via a first inlet branch pipe 211. The inlet of the main inlet pipe 210 is connected to the aeration unit 1. The air-sedimentation sand tank 14 is connected, and a first gate valve 221 and a first flow meter 231 are installed on the main inlet pipe 210. The primary anoxic zone 202 is connected to the outlet of the main inlet pipe 210 through a second inlet branch pipe 212, and a second gate valve 222 and a second flow meter 232 are installed on the second inlet branch pipe 212. The secondary anoxic zone 204 is connected to the main inlet pipe 210 through a third inlet branch pipe 213, and a third gate valve 223 and a third flow meter 233 are installed on the third inlet branch pipe 213. The primary aerobic zone 203 is connected to the primary anoxic zone 202 through a first sludge internal return pipe 241. The secondary aerobic zone 205 is connected to the secondary anoxic zone 204 through a second sludge internal return pipe 242. Submersible mixers 250 are installed in the anaerobic zone 201, the primary anoxic zone 201, and the secondary anoxic zone 204.

[0030] The inlet of the secondary sedimentation tank 21 is connected to the overflow outlet of the secondary aerobic zone 205;

[0031] The sludge bin 210 at the bottom of the secondary sedimentation tank 21 is connected to the anaerobic zone 201 and the secondary aerobic zone 205 through two sludge return pipes 251 and 252, respectively; the effluent pipe of the secondary sedimentation tank 21 is connected to the chemical treatment unit.

[0032] The carbon source adding pipeline 22 comprises a first adding point arranged at the front end of the first anoxic zone 202 and a second adding point arranged at the end of the first aerobic zone 203.

[0033] The core function of the anaerobic zone 201 is to release phosphorus by phosphorus accumulating organisms and hydrolytic acidification; the core function of the first anoxic zone 202 is to remove nitrogen by main denitrification; the core function of the first aerobic zone 203 is to remove nitrogen by nitrification and phosphorus removal; the core function of the second anoxic zone 204 is to remove nitrogen by deep denitrification; and the core function of the second aerobic zone 205 is to stabilize and ensure water quality.

[0034] The effluent path of the biological treatment unit 2 is: the second aerobic zone 205→ the secondary sedimentation tank 21 + sludge tank 210 (solid-liquid separation)→ the high-efficiency sedimentation tank 31.

[0035] The chemical treatment unit 3 comprises the high-efficiency sedimentation tank 31, the denitrification deep bed filter 32 and the contact disinfection tank 33 which are sequentially connected through a front effluent pipe, wherein the high-efficiency sedimentation tank 31 is internally provided with a mixing tank and a flocculation tank; the mixing tank is internally provided with a mixing agitator; the flocculation tank is internally provided with a flocculation agitator; the denitrification deep bed filter 32 is connected with the high-efficiency sedimentation tank 31 through a backwashing water pipe 320; and the contact disinfection tank 33 is internally provided with a plant area reuse pump station 331 and an effluent metering tank 332.

[0036] The sludge concentration unit 4 comprises the sludge concentration tank 41 and the sludge dewatering workshop 42 which are sequentially connected, wherein the sludge concentration tank 41 is correspondingly connected with the residual sludge outlet of the secondary sedimentation tank 21 and the chemical sludge outlet of the high-efficiency sedimentation tank 31 through two concentration pipes.

[0037] The sewage treatment system of the utility model, the whole treatment process is as follows:

[0038] The sewage enters the water inlet gate well 10 through the water inlet main pipe, first passes through the coarse grid device 11 to carry out the first interception and blockage of floating coarse sundries or heavy sediments such as sand, small stone blocks and the like, the sewage passing through the coarse grid device 11 flows into the water inlet pump house 12, when the water level of the water inlet pump house 12 reaches 4.55 meters, flows into the fine grid device 13 through the overflow hole of the water inlet pump house 12 to carry out the second interception, separates the smaller diameter suspended solids and particulate impurities in the sewage through the fine grid device 13, the grid residue intercepted by the fine grid device 13 is conveyed to the screw press through the shaftless screw conveyor and is pressed, and finally the pressed residue is discharged into a small trolley and is transported out. The sewage filtered through the fine grid device 13 enters the aeration grit chamber 14, the air blower in the aeration grit chamber 14 forms a cyclone by aeration to separate inorganic sand particles (such as silt), the sand particles are gathered along the inclined sand collecting hopper, and the sand water mixture is pumped to the sand water separator by the sand suction pump on the movable sand suction bridge, the sand residue is transported out, and the clear water is returned. The aeration reduces the deposition of organic matters at the same time, and the pretreatment is completed.

[0039] The sewage from the aerated grit chamber 14 enters the AA0 biological tank 20. The first gate valve 221 is always open; when the flow ratio of the sewage reaches more than 80% of the design flow ratio, the opening of the second gate valve 222 is opened to 50%-70% (trigger condition: nitrate nitrogen NO3-N at the end of the first anoxic zone 202 > 3 mg / L). If the nitrate nitrogen NO3-N at the end of the second anoxic zone 204 > 2 mg / L, the opening of the third gate valve 223 is opened to 30%-50%, and the sludge internal return ratio is increased to 250%-300%, and the chemical oxygen demand COD of the anaerobic zone 201 is monitored simultaneously > 150 mg / L; when the flow ratio of the sewage reaches 50%-80% of the design flow ratio, the opening of the second gate valve 222 is opened to 30%-50% (trigger condition: nitrate nitrogen NO3-N at the end of the first anoxic zone 202 > 2 mg / L), and if the total nitrogen TN of the effluent > 10 mg / L, the opening of the third gate valve 223 is opened to 10%-20%, and the opening degree and the flow change rate ratio are dynamically adjusted to 1:1.2; when the flow ratio of the sewage is less than 50% of the design flow ratio, the second gate valve 222 and the third gate valve 223 are closed, and the chemical oxygen demand COD of the anaerobic zone 201 is forced to be > 200 mg / L, and if the total nitrogen TN of the effluent > 12 mg / L, the opening of the second gate valve 222 is adjusted to ≤20%, the sludge internal return ratio is reduced to below 150%, and the interference of dissolved oxygen is reduced.

[0040] The carbon source adding pipeline 22 includes a first adding point arranged at the front end of the first anoxic zone 202 and a second adding point arranged at the end of the first aerobic zone 203. The first adding point is used to strengthen the denitrification reaction and preferentially supplement easily degradable organic matter (chemical oxygen demand COD) required by denitrifying bacteria, so as to ensure that the denitrification rate is maximized. By controlling the adding amount (COD / TN = 4-6), the uptake of carbon source by polyphosphorus bacteria (PAOs) in the first anoxic zone 202 is limited, and the interference of the polyphosphorus bacteria (PAOs) on the denitrification reaction is reduced. Furthermore, the denitrification rate is increased by 30%-50%, and the nitrogen content TN (Total Nitrogen) of the effluent is stably ≤10 mg / L. The competition for carbon source between the denitrifying bacteria and the polyphosphorus bacteria (PAOs) is avoided, the phosphorus release amount in the anaerobic zone 201 is increased by 20%-30%, the second adding point is used to assist phosphorus removal, the carbon source is supplemented at the end of the first aerobic zone 203, the polyphosphorus bacteria (PAOs) are stimulated to excessively absorb phosphorus in the first aerobic zone 202, the synthesis of internal carbon source (PHB) is promoted, and the residual nitrate is inhibited. The supplemented carbon source can consume the dissolved oxygen DO (Dissolved Oxygen) in the first aerobic zone 203, reduce the concentration of nitrate entering the first anoxic zone 202 with the internal sludge return (control the nitrate nitrogen NO3-N ≤5 mg / L), improve the total phosphorus TP (Total Phosphorus) removal rate, and reduce the interference of the internal sludge return.

[0041] The submersible mixers 250 are arranged at the front end of the anaerobic zone 201, the first anoxic zone 202 and the second anoxic zone 204. The submersible mixer 250 in the anaerobic zone 201 ensures that the sludge and the influent are fully mixed, prevents the formation of a VFA (volatile fatty acid) concentration gradient, promotes the efficient phosphorus release of the polyphosphorus bacteria (PAOs), avoids local dead zones caused by sludge deposition, and maintains a strict anaerobic environment with an oxidation-reduction potential ORP (Oxidation-Reduction Potential) ≤-100 mV. The submersible mixers 250 in the first anoxic zone 202 and the second anoxic zone 204 can strengthen the contact efficiency of the denitrifying bacteria with the nitrate and the carbon source, shorten the denitrification reaction time by 30%, and further improve the phosphorus release rate and enhance the stability of the sludge.

[0042] The sludge return in the secondary sedimentation tank 21 is distributed in zones, and is returned to the anaerobic zone 201 (50%-80%) to supplement the PAOs bacterial population and maintain the mixed liquid suspended solids MLSS (Mixed Liquid Suspended Solids) concentration in the anaerobic zone 201 ≥3000 mg / L. The sludge is returned to the second anoxic zone 204 (30%-50%) to carry the nitrate in the nitrated liquid and strengthen the deep denitrification.

[0043] The sludge in the primary aerobic zone 203 is internally refluxed to the primary anoxic zone 202 (150% to 200%), and high-concentration nitrate is preferentially migrated to the primary anoxic zone 202; the internal reflux of the secondary aerobic zone 205 is to the secondary anoxic zone 204 (100% to 150%), and the dissolved oxygen (DO) carrying is reduced (the DO is controlled to be less than or equal to 0.3 mg / L), so that the reaction environment of the secondary anoxic zone 204 is ensured. The nitrification-denitrification coupling efficiency is improved, the total nitrogen (TN) removal rate is greater than or equal to 90%, and the sludge age is optimized.

[0044] After the sewage is subjected to biochemical treatment by the multi-stage biological tank 20, the sewage mixture flows into the secondary sedimentation tank 21 for sludge-water separation and sludge reflux, and the sludge that is not refluxed is discharged to the sludge thickening tank 41 by a submersible sewage pump, and is discharged to the sludge dewatering workshop 42 after thickening treatment, so that sludge dewatering and external transportation for centralized treatment are realized. The sewage separated from the sludge in the secondary sedimentation tank 21 continues to flow into the high-efficiency sedimentation tank 31, so that the synergistic effect of coagulation, flocculation and inclined plate sedimentation is realized to strengthen solid-liquid separation, and the residual sludge continues to be discharged to the sludge thickening tank 41 for treatment after thickening. The sewage continues to flow into the denitrification deep-bed filter tank 32, and deep denitrification and suspended matter interception are realized by the synergistic effect of biological denitrification and physical filtration. After the denitrification reaction, the sewage flows into the contact disinfection tank 33, so that water quality disinfection is realized to block the risk of disease transmission in the water body. After disinfection treatment, the water body flows to the effluent metering tank 332 to realize water quality inspection, and after the water quality indexes are inspected to meet the surface water class IV water standard, the water body flows into a river through an effluent pipe, or is sent to a factory as factory reclaimed water through a factory reuse pump station 331.

[0045] The sewage treatment system of the utility model, set up multiple water inlets before multi-stage biological tank 20, connect first water inlet branch pipe 211, second water inlet branch pipe 212 and third water inlet branch pipe 213 respectively. According to the sewage treatment demand, control the opening degree and the flow size of different water inlets through first gate valve 221 and first electromagnetic flowmeter 231, second gate valve 222 and second flowmeter 232, third gate valve 223 and third flowmeter 233, realize segmented water inlet.

[0046] The sewage treatment system of the utility model, set up submersible agitator in anaerobic zone 201, primary anoxic zone 202 and secondary anoxic zone 204, ensure that sludge and water contact fully, prevent sludge from depositing.

[0047] The sewage treatment system of the utility model, set up carbon source dosing point in primary anoxic zone 202 and primary aerobic zone 203 respectively. According to the water quality monitoring result and process demand, automatically adjust the flow and dosing time of dosing pump through control system, ensure that carbon source dosage is accurate and flexible.

[0048] The sewage treatment system of the utility model carries out the transformation to sludge backflow pipeline, adopts multistage backflow mode, sets up multiple backflow ports at the outlet of sludge bin 210 connected with secondary sedimentation tank 21, each backflow port is connected to anaerobic zone 201 and secondary anoxic zone 204 through sludge backflow pipeline, meanwhile, sets up sludge internal backflow pipe at the lower end of primary aerobic zone 203 and the lower end of secondary aerobic zone 205, correspondingly backflows part of sludge after sufficient aeration to primary anoxic zone 202 and secondary anoxic zone 204, realizes balanced flora and strengthens deep denitrification.

[0049] The sewage treatment system of the utility model, through intelligent water control system, monitors sludge concentration and treatment effect of each anoxic zone in real time, dynamically adjusts sludge backflow proportion and backflow path of each backflow port, ensures that sludge concentration gradient in each anoxic zone is reasonable, meets the demand of denitrification to sludge concentration, and avoids excessive accumulation of sludge in a certain area, which leads to the decline of treatment efficiency.

[0050] The sewage treatment system of the utility model, through the combination of multistage backflow and internal backflow, improves the overall activity of sludge, meanwhile, due to the reasonable distribution and recycling of sludge in each anoxic zone, unnecessary sludge discharge is reduced, sludge reduction is realized, the optimized sludge backflow system reduces energy consumption loss in the backflow process, such as pumping energy consumption and pipeline resistance loss, meanwhile, due to the realization of sludge reduction, the cost of subsequent sludge treatment (such as dewatering, drying, etc.) is reduced, thereby the operation cost of the system is reduced as a whole.

[0051] The above embodiments are only for illustrating the utility model, and are not limited to the utility model, and those skilled in the art can make various transformations or modifications without departing from the spirit and scope of the utility model, therefore, all equivalent technical solutions should belong to the scope of the utility model, and should be limited by each claim.

Claims

1. A sewage treatment system comprising a pretreatment unit, a biological treatment unit, a chemical treatment unit and a sludge concentration unit; the pretreatment unit comprises a water inlet gate well, a water inlet pump house and an aerated grit chamber connected in sequence; the water inlet gate well is provided with a coarse grid device; the water inlet pump house is provided with a sewage pump and a fine grid washing device; characterized in that, the biological treatment unit comprises an AA0 biological tank, a secondary sedimentation tank and a carbon source dosing pipeline; wherein, the AA0 biological tank is divided into an anaerobic zone, a first-stage anoxic zone, a first-stage aerobic zone, a second-stage anoxic zone and a second-stage aerobic zone from back to front by first to fourth partitions, the two ends of the first partition are not connected with the two side walls of the AA0 biological tank to form a water flow port, the two ends of the second partition are connected with the two side walls of the AA0 biological tank, but the middle part of the second partition is disconnected to form a water flow port; the two ends of the third partition are not connected with the two side walls of the AA0 biological tank to form a water flow port, the two ends of the fourth partition are connected with the two side walls of the AA0 biological tank, but the middle part of the fourth partition is disconnected to form a water flow port; the anaerobic zone is connected with the water outlet of a water inlet main pipe through a first water inlet branch pipe, the water inlet of the water inlet main pipe is connected with the aerated grit chamber of the pretreatment unit, and a first gate valve and a first flow meter are installed on the water inlet main pipe; the first-stage anoxic zone is connected with the water outlet of the water inlet main pipe through a second water inlet branch pipe, a second gate valve and a second flow meter are installed on the second water inlet branch pipe; the second-stage anoxic zone is connected with the water inlet main pipe through a third water inlet branch pipe, a third gate valve and a third flow meter are installed on the third water inlet branch pipe; the first-stage aerobic zone is connected with the first-stage anoxic zone through a first sludge internal return pipe; the second-stage aerobic zone is connected with the second-stage anoxic zone through a second sludge internal return pipe; the water inlet of the secondary sedimentation tank is connected with the overflow water outlet of the second-stage aerobic zone, the sludge bin at the bottom of the secondary sedimentation tank is connected with the anaerobic zone and the second-stage aerobic zone in a one-to-one correspondence through two sludge return pipes; the water outlet pipe of the secondary sedimentation tank is connected with the chemical treatment unit; the carbon source dosing pipeline comprises a first dosing point arranged at the front end of the first-stage anoxic zone and a second dosing point arranged at the end of the first-stage aerobic zone.

2. The sewage treatment system of claim 1, wherein, a submersible mixer is arranged in each of the anaerobic zone, the first-stage anoxic zone and the second-stage anoxic zone.

3. The sewage treatment system of claim 1, wherein, the chemical treatment unit comprises a high-efficiency sedimentation tank, a denitrification deep-bed filter and a contact disinfection tank connected in sequence through a front water outlet pipe, the denitrification deep-bed filter is connected with the high-efficiency sedimentation tank through a backwashing water pipe; the sludge concentration unit comprises a sludge concentration tank and a sludge dewatering workshop connected in sequence, the sludge concentration tank is connected with the residual sludge outlet of the secondary sedimentation tank and the chemical sludge outlet of the high-efficiency sedimentation tank in a one-to-one correspondence through two concentration pipes.

4. The sewage treatment system of claim 3, wherein, the high-efficiency sedimentation tank comprises a mixing tank and a flocculation tank; a mixing mixer is arranged in the mixing tank; a flocculation mixer is arranged in the flocculation tank.

5. The sewage treatment system of claim 3, wherein, a plant area reuse pump station and a water outlet metering tank are arranged in the contact disinfection tank.

6. The sewage treatment system of claim 1, wherein, a slope-type grit bucket and a gas explosion device are arranged in the aerated grit chamber, a grit suction pump on the grit bucket is installed on a grit suction bridge, and the grit suction bridge can be movably bridged between the top surfaces of the two side walls of the aerated grit chamber.

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