Pre-aerated wastewater treatment system and process

Abstract

The application provides a pre-aeration sewage treatment system and process, wherein the pre-aeration tank adopts a pre-aeration mode to simultaneously remove particulate pollutants in sewage and pre-oxygenate the sewage; the pre-anoxic tank controls DO of the pre-oxygenated sewage and controls FNA concentration of the pre-anoxic tank by adding reagents from a reagent adding tank arranged at the front end of the pre-anoxic tank; the sewage treated from the pre-anoxic tank enters an anaerobic tank to occur denitrification and anaerobic ammonia oxidation reaction; and the sewage treated from the anaerobic tank enters an aerobic tank to remove ammonia nitrogen and TP in the sewage. The application can realize total nitrogen removal effect of low carbon-nitrogen ratio sewage.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a pre-aeration wastewater treatment system and process. Background Technology

[0002] Urban wastewater treatment technology has evolved to include various efficient nitrogen and phosphorus removal processes, such as the AAO process, modified AAO process, oxidation ditch process, and biological filter process. These processes are suitable for different treatment requirements and meet corresponding discharge standards. However, in actual operation, some wastewater treatment plants may have excessive treatment capacity, leading to resource waste, such as land resources occupied in the design, construction costs of corresponding structures, energy consumption during operation, and labor costs. Therefore, process design is particularly critical in urban wastewater treatment. While meeting the corresponding discharge standards and withstanding load shocks, it is also necessary to save land resources and reduce energy consumption as much as possible. At the same time, existing processes are not ideal for nitrogen and phosphorus removal from low C / N ratio influent, and biological phosphorus removal is ineffective, leading to over-reliance on chemical phosphorus removal. This results in the need for additional carbon sources to achieve the desired nitrogen removal effect during actual operation.

[0003] Among existing wastewater treatment processes, the mainstream process is the AAO process, and the structures include pretreatment grit chambers, anaerobic, anoxic, and aerobic tanks in the biological stage, secondary sedimentation tanks for sludge-water separation, and high-efficiency sedimentation tanks and disinfection tanks for advanced treatment.

[0004] The existing biological treatment processes and their operation in wastewater treatment plants have the following problems:

[0005] 1. Existing biological treatment processes have excessive processing capacity in actual operation, with excessive aeration in the aerobic tank, and the pollutant removal effect of each process stage is not effectively utilized, resulting in waste of structures and increased operating costs; This invention helps to save operating costs by rationally arranging the process flow and reducing unnecessary stages.

[0006] 2. Due to large fluctuations in influent water quality, the sludge returned from external sources causes a large amount of nitrate nitrogen to be consumed by COD in the anaerobic tank, resulting in a low carbon source in the anaerobic tank and poor biological phosphorus removal efficiency, leading to over-reliance on chemical phosphorus removal. This invention improves biological phosphorus removal efficiency and reduces the use of chemical phosphorus removal agents by rationally controlling the conditions of the anaerobic and aerobic tanks and supplementing the carbon source.

[0007] 3. Under conditions of low C / N ratio influent, the denitrification effect in the anoxic tank is poor, requiring the addition of an additional carbon source to achieve the desired denitrification effect, which increases the daily operating costs of the wastewater treatment plant. This invention, through reasonable regulation, sets up fixed sponge packing at the front end of the anaerobic tank to promote the occurrence of short-cut nitrification in the pre-anoxic tank and anaerobic ammonia oxidation at the front end of the anaerobic tank, achieving efficient denitrification while reducing the consumption of carbon source in the anaerobic tank during the denitrification process, thus achieving efficient denitrification of wastewater with low C / N ratio. Summary of the Invention

[0008] In view of the deficiencies in the prior art, the purpose of this invention is to provide a pre-aeration wastewater treatment system and process.

[0009] A pre-aeration wastewater treatment system according to the present invention includes: a pre-aeration tank, a pre-anoxic tank, an anaerobic tank, and an aerobic tank, wherein:

[0010] From the direction of sewage flow, the pre-aeration tank, pre-anoxic tank, anaerobic tank and aerobic tank are connected in sequence.

[0011] The pre-aeration tank uses a pre-aeration method to simultaneously remove particulate pollutants from the wastewater and pre-oxygenate the wastewater.

[0012] The pre-anoxic tank controls DO in the pre-oxygenated wastewater, and controls the FNA concentration in the pre-anoxic tank by adding chemicals through a dosing tank located at the front end of the pre-anoxic tank.

[0013] Wastewater treated in the pre-anoxic tank enters the anaerobic tank, where denitrification and anaerobic ammonium oxidation reactions occur.

[0014] Wastewater treated in the anaerobic tank enters the aerobic tank to remove ammonia nitrogen and total phosphorus (TP).

[0015] Preferably, the pre-aeration tank is equipped with aeration pipes, perforated aerators, and sand removal equipment, wherein:

[0016] Wastewater is pre-aerated and oxygenated through the aeration pipe and perforated aerator, and then passes through the sand removal equipment to remove particulate pollutants from the wastewater.

[0017] Preferably, the pre-anoxic tank is equipped with a stirrer and a flow promoter, wherein:

[0018] The agitator is located at the water inlet, forming a mixing zone, and the reagent in the dosing tank enters the mixing zone through a dosing pump.

[0019] The flow pump directs wastewater from the bottom of the pre-anoxic tank through the water passage into the anaerobic tank.

[0020] Preferably, the anaerobic tank is divided into a first anaerobic zone and a second anaerobic zone. The first anaerobic zone is equipped with fixed sponge packing material, and the second anaerobic zone is an oxidation ditch type.

[0021] Preferably, the reagent used in the dosing tank at the front end of the anaerobic tank is a sodium nitrite solution.

[0022] Preferably, the pre-aeration tank is connected to a main inlet pipe on the inlet side, and the outlet side is connected to the pre-anoxic tank via the inlet pipe of the biochemical tank, and to the anaerobic tank via the inlet pipe of the anaerobic tank.

[0023] Preferably, the pre-anoxic tank and the secondary sedimentation tank are connected by an external reflux pipe.

[0024] Preferably, the aerobic tank is divided into two aeration zones, with the DO in the first aeration zone being 2.0–3.0 mg / L and the DO in the second aeration zone being 1.0–2.0 mg / L; the ORP in the aerobic tank is controlled to be above 40 mV.

[0025] Preferably, an online NH3-N detector is installed at the end of the first aeration zone of the aerobic tank, which is connected to the automatic aeration control system. The NH3-N warning value is set to 5 mg / L. If the warning value is exceeded, the aeration rate of the aeration zone is automatically increased to increase the DO of the aerobic tank.

[0026] A process for a wastewater treatment system based on the above-mentioned pre-aeration, according to the present invention, includes the following steps:

[0027] Step S1: Wastewater enters the pre-aeration tank from the main inlet pipe. After pre-aeration and oxygenation and removal of particulate matter in the pre-aeration tank, it enters the pre-anoxic tank.

[0028] Step S2: Wastewater enters the pre-anoxic tank. The influent to the pre-anoxic tank is mixed with the anaerobic return sludge from the external return pipe. The mixture is homogeneous under the action of the agitator to control the aerobic environment of DO in the pre-anoxic tank. The concentration of FNA in the pre-anoxic tank is controlled by adding sodium nitrite.

[0029] Step S3: Wastewater enters the anaerobic tank through the bottom water passage of the pre-anoxic tank and mixes with the influent from the anaerobic tank inlet pipe. In the anaerobic environment of the first anaerobic zone, anaerobic ammonia oxidation reaction occurs to remove nitrogen. In the second anaerobic zone, polyphosphate-accumulating bacteria undergo anaerobic phosphorus release.

[0030] Step 4: Wastewater enters the aerobic tank from the anaerobic tank. Under aerobic conditions, NH3-N in the wastewater undergoes nitrification under the action of nitrifying bacteria in the activated sludge; polyphosphate-accumulating bacteria in the activated sludge undergo aerobic phosphorus uptake under aerobic conditions, removing TP from the wastewater.

[0031] Step 5: The effluent from the aerobic tank enters the secondary sedimentation tank through the effluent pipe. After the sludge and water are separated in the secondary sedimentation tank, the clarified effluent is discharged. The remaining sludge containing NH3-N is returned to the pre-anoxic tank through the external return pipe.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. This invention strictly controls the operating conditions of each process section, giving full play to the operational functions of the pre-aeration tank, pre-anoxic tank, anaerobic tank, and aerobic tank, preventing the process from failing to function effectively, and reducing operating costs while efficiently treating wastewater.

[0034] 2. This invention achieves nitrogen removal at the front end of the anaerobic tank, controls the nitrate nitrogen concentration and dissolved oxygen in the anaerobic tank, prevents excessive denitrification, causes denitrifying bacteria to compete with polyphosphate-accumulating bacteria for carbon sources, affecting the function of polyphosphate-accumulating bacteria, and replenishes the carbon source in the anaerobic tank by diverting raw water to the anaerobic tank, promoting the anaerobic phosphorus release of polyphosphate-accumulating bacteria, and controls DO in the aerobic tank, preventing over-aeration in the aerobic tank while enhancing the biological phosphorus removal effect.

[0035] 3. This invention controls the dissolved oxygen (DO) in the effluent from the pre-aeration tank and the pre-anoxic tank, and effectively controls the fluorinated ammonia (FNA) concentration in the pre-anoxic tank by adding chemicals. Furthermore, a fixed sponge packing material is installed at the front end of the anaerobic tank to promote short-cut nitrification in the pre-anoxic tank and anaerobic ammonia oxidation at the front end of the anaerobic tank. This achieves efficient denitrification while reducing carbon source consumption in the anaerobic tank during the denitrification process, thus realizing efficient denitrification of wastewater with a low carbon-to-nitrogen ratio.

[0036] 4. This invention achieves short-cut nitrification and anaerobic ammonia oxidation by controlling the operating conditions of the pre-anoxic tank and the anaerobic tank. Furthermore, by diverting the influent to supplement the carbon source for the anaerobic tank, it can effectively remove nitrogen and phosphorus from urban domestic sewage with a low carbon-to-nitrogen ratio, while saving land resources, saving energy and reducing consumption, and facilitating operation and management. Attached Figure Description

[0037] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0038] Figure 1 This is a schematic diagram of a pre-aeration biological wastewater treatment process.

[0039] In the picture:

[0040] 1. Main inlet pipe; 2. Pre-aeration tank; 3. Inlet pipe for biological treatment tank; 4. Inlet pipe for anaerobic tank; 5. Pre-anoxic tank; 6. Anaerobic tank; 601 First anaerobic zone; 602 Second anaerobic zone; 7. Online ammonia nitrogen detection and automatic aeration control module; 8. Aerobic tank; 801 First aeration zone; 802 Second aeration zone; 9. Outlet pipe for biological treatment tank; 10. Secondary sedimentation tank; 11. External return pipe; 12. Chemical dosing tank; 13. Outlet pipe for secondary sedimentation tank. Detailed Implementation

[0041] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0042] like Figure 1 As shown, this invention provides a pre-aeration wastewater treatment system and process capable of removing total nitrogen from wastewater with a low carbon-to-nitrogen ratio. Wastewater first undergoes pre-aeration, providing a foundation for short-cut nitrification in a pre-anoxic tank. By adding sodium nitrite to the front end of the pre-anoxic tank, the DO conditions and FNA concentration are controlled, acclimating the activated sludge and enriching nitrifying bacteria. This removes some NH3-N while simultaneously reducing NO2. - The accumulation of -N leads to the accumulation of a large amount of NO2. - Wastewater with nitrogen (TN) undergoes anaerobic ammonia oxidation in the anaerobic tank, effectively removing total nitrogen (TN). Simultaneously, the influent through the anaerobic tank's diversion pipe provides ample carbon source, enhancing the anaerobic phosphorus release by polyphosphate-accumulating bacteria. The aerobic tank is divided into two aeration zones and employs online ammonia nitrogen monitoring, PLC, and automatic aeration control. This effectively controls dissolved oxygen (DO) in the aerobic tank while preventing over-aeration and excessive NH3-N levels in the effluent. This process achieves enhanced nitrogen and phosphorus removal from low-carbon-to-nitrogen influent without the need for external carbon sources.

[0043] Further explanation: According to the present invention, a pre-aeration wastewater treatment system is provided, including a pre-aeration tank 2, a pre-anoxic tank 5, an anaerobic tank 6, and an aerobic tank 8. The pre-aeration tank 2 is equipped with aeration pipes, perforated aerators, and a sand removal device. The aeration pipes are connected to the perforated aerators to pre-aerate and oxygenate the wastewater and remove particulate matter, preventing inorganic matter and particulate matter in the wastewater from affecting subsequent treatment and process operation. The perforated aerators are installed on one side of the pre-aeration tank wall for pre-aeration and to generate a swirling effect to remove particulate pollutants. The sand removal device is used to discharge particulate pollutants from the bottom of the pre-aeration tank. This is because larger particles will sink to the bottom under gravity, and some small particles will also be thrown to the bottom under the aeration swirling effect, thus requiring bottom sand removal. The inlet pipe 3 of the biological treatment tank connects to the outlet of the pre-aeration tank 2; the pre-anoxic tank 5 is equipped with an external return pipe 11; the external return pipe 11 connects the secondary sedimentation tank 10 and the pre-anoxic tank 5; the pre-anoxic tank 5 is equipped with a stirrer and a flow promoter, the stirrer is located at the inlet to form a mixing zone, and a dosing tank 12 is installed at the inlet of the pre-anoxic tank 5. The chemicals in the dosing tank 12 are pumped into the mixing zone of the pre-anoxic tank to control the FNA concentration in the pre-anoxic tank section, acclimate the activated sludge, and make nitrifying bacteria dominate in the activated sludge; the anaerobic tank 6 is equipped with a stirrer and a flow promoter, the stirrer in the anaerobic tank is used for mixing The uniform distribution of wastewater in the anaerobic tank helps to achieve effective removal of pollutants from the entire anaerobic tank. The flow promoter is used to propel the wastewater into the aerobic tank. The anaerobic tank is divided into two anaerobic zones. The first anaerobic zone 601 is equipped with fixed sponge packing, and the second anaerobic zone 602 is an oxidation ditch type. The aerobic tank 8 is equipped with an aeration main pipe and gill aerators, as well as an online ammonia nitrogen detection and automatic aeration control module 7. The aeration main pipe is connected to the gill aerators to provide aeration and oxygenation for the aerobic tank. The online ammonia nitrogen detection and automatic aeration control module is used to monitor the ammonia nitrogen concentration in the aerobic tank, thereby controlling the aeration rate and saving aeration energy consumption.

[0044] The hydraulic retention time of the pre-aeration tank 2 is 5-7 minutes, preferably 7 minutes; the DO concentration in the pre-aeration tank is controlled at 6-8 mg / L; the anaerobic tank inlet pipe 4 discharges 20-30% of the effluent from the pre-aeration tank into the front end of the anaerobic tank 6, preferably 25%; the hydraulic retention time of the pre-anoxic tank 5 is 0.3-0.8 hours, preferably 0.8 hours; the DO concentration in the pre-anoxic tank 5 is controlled at 0.5-1.0 mg / L; the FNA concentration in the pre-anoxic tank 5 is controlled at greater than 0.2 mg / L, mainly used for acclimating activated sludge and enriching nitrifying bacteria; the hydraulic retention time of the anaerobic tank 6 is 1-2 hours, preferably 2 hours; the DO concentration in the anaerobic tank 6 is controlled below 0.2 mg / L, and the ORP is controlled between -120 and -240 mV; the aerobic tank 8... The retention time is 4-5 hours, preferably 4 hours. The aerobic tank is equipped with a flow guide wall and an online ammonia nitrogen detector, PLC, and automatic aeration control module 7, dividing the aerobic tank 8 into a first aeration zone 801 and a second aeration zone 802, with the aeration rate controlled independently. The DO in the two aeration zones is controlled at 2.0-3.0 mg / L and 1.0-2.0 mg / L, respectively. The overall ORP of the aerobic tank 8 is controlled above 40 mV. An online NH3-N detector is installed at the end of the first aeration zone 801 of the aerobic tank 8. The online ammonia nitrogen detector is electrically connected to the PLC and automatic aeration control module to form a module control. The NH3-N warning value is set at 5 mg / L. If the warning value is exceeded, the aeration rate of the second aeration zone 802 is automatically increased to increase DO and enhance the NH3-N removal effect.

[0045] This invention provides a pre-aeration wastewater treatment process, and the steps to achieve the desired process effect are as follows:

[0046] Step 1: Pretreated wastewater enters the pre-aeration tank 2 through the main inlet pipe 1. In the pre-aeration tank 2, the wastewater undergoes pre-aeration and oxygenation through perforated aerators. Aeration can effectively remove soluble organic matter from particulate pollutants in the wastewater. At the same time, the swirling effect during the aeration process can cause particulate pollutants to settle. The sand removal equipment removes particulate pollutants from the wastewater, reducing the impact of particulate matter on subsequent treatment processes and equipment. Aeration can also increase the dissolved oxygen (DO) concentration in the wastewater. Wastewater with a high DO concentration enters the pre-anoxic tank 5, which provides preconditions for the short-cut nitrification reaction in the pre-anoxic tank 5, promoting the removal efficiency of pollutants in the pre-anoxic tank 5.

[0047] Step 2: After pre-aeration, wastewater containing high concentrations of DO enters the pre-anoxic tank 5 through the inlet pipe 3 of the biological treatment tank. The wastewater containing DO enters the pre-anoxic tank 5, where it mixes with the anaerobic return sludge from the external return pipe 11. Under the action of a stirrer, the mixture is homogenized, maintaining an aerobic environment with DO concentrations of 0.5–1.0 mg / L in the pre-anoxic tank 5. Since nitrifying bacteria have a higher affinity for low concentrations of DO than nitrifying bacteria, an aerobic environment with DO concentrations of 0.5–1.0 mg / L can enhance the activity of nitrifying bacteria in the return sludge. Furthermore, by adding sodium nitrite, the FNA concentration in the pre-anoxic tank 5 is controlled to be above 0.2 mg / L, inhibiting the activity of nitrifying bacteria. This results in nitrifying bacteria dominating the activated sludge, causing short-cut nitrification of the wastewater, with some NH3-N being converted to NO2. - -N; After long-term controlled sludge acclimation, the nitrifying bacteria in the activated sludge maintain high activity, thus reducing or eliminating the need for chemical dosing. Controlling the DO at the end of the pre-anoxic tank to below 0.5 mg / L ensures that the functional microorganisms in the wastewater are primarily nitrifying bacteria. Therefore, at the end of the pre-anoxic tank 5, NH3-N flowing through the external return pipe 11 to the pre-anoxic tank 5 undergoes denitrification under low DO conditions, converting NH3-N into NO2. - -N, and consume some COD to achieve NO2 - -N accumulation;

[0048] Step 3: Under the action of the flow promoter, the wastewater enters the anaerobic tank 6 from the bottom water passage of the pre-anoxic tank 5, and mixes with the influent from the anaerobic tank inlet pipe 4; in the anaerobic environment of the first anaerobic zone 601, the NO2 in the wastewater... - -N reacts with NH3-N in wastewater through anaerobic ammonia oxidation under the action of anaerobic ammonia-oxidizing bacteria in activated sludge to remove nitrogen, and also removes NH3-N and NO2 from the wastewater. - -N, while the fixed sponge packing achieves biofilm enrichment of anaerobic ammonia oxidizing bacteria, enhancing the occurrence of anaerobic ammonia oxidation; in the second anaerobic zone 602, the water inlet pipe 4 of the anaerobic tank can provide sufficient carbon source for polyphosphate-accumulating bacteria in the anaerobic tank 6. Under the conditions of anaerobic environment and sufficient carbon source, polyphosphate-accumulating bacteria carry out anaerobic phosphorus release, creating conditions for the next step of excessive phosphorus uptake in the aerobic tank 8, while removing COD in the anaerobic tank 6;

[0049] Step 4: Wastewater enters the aerobic tank 8 from the anaerobic tank 6. Under aerobic conditions, NH3-N in the wastewater undergoes nitrification under the action of nitrifying bacteria in the activated sludge, converting NH3-N into NO3. - -N, removes NH3-N from wastewater; polyphosphate-accumulating bacteria in activated sludge undergo aerobic phosphorus uptake under aerobic conditions, absorbing large amounts of phosphorus from wastewater and storing it in their bodies, thus removing TP from the wastewater;

[0050] Step 5: The effluent from aerobic tank 8 enters secondary sedimentation tank 10 through effluent pipe 9. After sludge-water separation in secondary sedimentation tank 10, the clarified effluent is discharged. An external reflux ratio of 100%–150% is used to remove NO3-containing wastewater. - The remaining sludge from -N is returned to the pre-anoxic tank 5 via the external return pipe.

[0051] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0052] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A pre-aeration wastewater treatment system, characterized in that, include: The tanks consist of a pre-aeration tank, a pre-anoxic tank, an anaerobic tank, and an aerobic tank, among which: From the direction of sewage flow, the pre-aeration tank, pre-anoxic tank, anaerobic tank and aerobic tank are connected in sequence. The pre-aeration tank uses a pre-aeration method to simultaneously remove particulate pollutants from the wastewater and pre-oxygenate the wastewater. The pre-anoxic tank controls DO in the pre-oxygenated wastewater, and controls the FNA concentration in the pre-anoxic tank by adding chemicals through a dosing tank located at the front end of the pre-anoxic tank. Wastewater treated in the pre-anoxic tank enters the anaerobic tank, where denitrification and anaerobic ammonium oxidation reactions occur. Wastewater treated in the anaerobic tank enters the aerobic tank to remove ammonia nitrogen and total phosphorus (TP). The effluent from the aerobic tank flows through an outlet pipe into the secondary sedimentation tank. After sludge-water separation in the secondary sedimentation tank, the clarified effluent is discharged. The effluent containing NO3... - The remaining sludge from -N is returned to the pre-anoxic tank via an external return pipe; The pre-aeration tank is connected to a main inlet pipe on the inlet side, and the outlet side is connected to the pre-anoxic tank through the inlet pipe of the biological tank and to the anaerobic tank through the inlet pipe of the anaerobic tank. The pre-anoxic tank is equipped with a stirrer and a flow promoter, wherein: The agitator is located at the water inlet, forming a mixing zone, and the reagent in the dosing tank enters the mixing zone through a dosing pump. The flow pump directs wastewater from the bottom of the pre-anoxic tank through the water passage hole into the anaerobic tank. The dosing tank dispenses sodium nitrite solution. The anaerobic tank is divided into a first anaerobic zone and a second anaerobic zone. The first anaerobic zone is equipped with fixed sponge packing material, and the second anaerobic zone is an oxidation ditch type. The aerobic tank is divided into a first aeration zone and a second aeration zone. The DO in the first aeration zone is 2.0-3.0 mg / L, and the DO in the second aeration zone is 1.0-2.0 mg / L. The ORP in the aerobic tank is controlled to be above 40 mV.

2. The pre-aeration wastewater treatment system according to claim 1, characterized in that, The pre-aeration tank is equipped with aeration pipes, perforated aerators, and sand removal equipment, wherein: Wastewater is pre-aerated and oxygenated through the aeration pipe and perforated aerator, and then passes through the sand removal equipment to remove particulate pollutants from the wastewater.

3. The pre-aeration wastewater treatment system according to claim 1, characterized in that, An online NH3-N detector is installed at the end of the first aeration zone of the aerobic tank and is connected to the automatic aeration control system. The NH3-N warning value is set at 5 mg / L. If the warning value is exceeded, the aeration rate of the second aeration zone is automatically increased to increase the DO of the aerobic tank.

4. A process for a wastewater treatment system based on the pre-aeration method according to any one of claims 1-3, characterized in that, Includes the following steps: Step S1: Wastewater enters the pre-aeration tank from the main inlet pipe. After pre-aeration and oxygenation to remove particulate pollutants, it enters the pre-anoxic tank. Step S2: Wastewater enters the pre-anoxic tank. The influent to the pre-anoxic tank is mixed with the anaerobic return sludge from the external return pipe. The mixture is homogeneous under the action of a stirrer. The DO in the pre-anoxic tank is controlled to be 0.5-1.0 mg / L for an aerobic environment. Sodium nitrite is added to control the FNA concentration in the pre-anoxic tank to be greater than 0.2 mg / L for acclimation and enrichment of nitrifying bacteria. Step S3: Wastewater enters the anaerobic tank through the bottom water passage of the pre-anoxic tank and mixes with the influent from the anaerobic tank inlet pipe. In the anaerobic environment of the first anaerobic zone, anaerobic ammonia oxidation reaction occurs to remove nitrogen. In the second anaerobic zone, polyphosphate-accumulating bacteria undergo anaerobic phosphorus release. Step S4: Wastewater enters the aerobic tank from the anaerobic tank. Under aerobic conditions, NH3-N in the wastewater undergoes nitrification under the action of nitrifying bacteria in the activated sludge; polyphosphate-accumulating bacteria in the activated sludge undergo aerobic phosphorus uptake under aerobic conditions, removing TP from the wastewater. Step S5: The effluent from the aerobic tank enters the secondary sedimentation tank through the effluent pipe. After sludge-water separation in the secondary sedimentation tank, the clarified effluent is discharged; the effluent containing NO3 is removed. - The remaining sludge from the -N phase is returned to the pre-anoxic tank via an external return pipe.

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