Enhanced secondary sedimentation tank endogenous denitrification nitrogen removal device and method

Abstract

The invention discloses an endogenous denitrification nitrogen removal device and method for an enhanced secondary sedimentation tank, and relates to the technical field of water treatment.The endogenous denitrification nitrogen removal device for the enhanced secondary sedimentation tank is an endogenous denitrification nitrogen removal secondary sedimentation tank and is connected to the tail end of a biochemical tank of a sewage treatment plant; comprising two rectangular sedimentation tanks arranged in parallel, a water inlet device, a sludge return gallery, a pipeline aeration stirring device and a static water level drainage control system, the sludge backflow galleries are arranged at the bottoms and the positions close to the middles of the rectangular sedimentation tanks, the pipeline aeration stirring devices are arranged in the rectangular sedimentation tanks, and the static water level drainage control systems are arranged at the water outlet pipe ends of the rectangular sedimentation tanks; the enhanced secondary sedimentation tank endogenous denitrification nitrogen removal device controls the two rectangular sedimentation tanks to execute sludge backflow, stirring and sedimentation stages and water inlet and drainage stages respectively in an alternate operation mode. The method has a better total nitrogen removal effect.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to an enhanced denitrification device and method for secondary sedimentation tanks. Background Technology

[0002] my country's local and sensitive areas have gradually tightened their wastewater treatment plant discharge standards. Based on the Class A standard of the "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants" (GB18918-2002) with COD≤50mg / L, BOD5≤10mg / L, SS≤10mg / L, total nitrogen≤15mg / L, ammonia nitrogen≤5mg / L, and total phosphorus≤0.5mg / L, the focus has been on raising the discharge standards for COD, total nitrogen, ammonia nitrogen, and total phosphorus. However, for many remote and economically underdeveloped areas, the overall C / N ratio of collected wastewater is low, making total nitrogen removal difficult and requiring a high removal rate. Adding external carbon sources is costly and uneconomical. At the same time, the traditional activated sludge process requires increasing the internal recirculation flow rate to improve the total nitrogen removal rate, and the effect gradually becomes less significant as the removal rate increases.

[0003] Related technologies can be found in Chinese Patent No. CN202211213132.3, which discloses a method for enhancing endogenous denitrification in the secondary sedimentation tank of a wastewater treatment plant. This method may include: Step 1: Presetting initial parameters; Step 2: Calculating the average influent flow rate over the i-th interval and calculating the initial operating frequency; Step 3: Calculating and adjusting the operating frequency based on the average concentration of externally returned sludge and the average concentration of sludge in the aeration tank over the i-th interval; Step 4: Stepping time, repeating step 24 for the (i+1)-th interval until the time step ends. This invention automatically optimizes the amount of externally returned sludge, controls the start / stop and operating frequency of the externally returned sludge pump, reduces the flow rate of returned activated sludge, increases the concentration of externally returned sludge, increases the residence time of sludge in the secondary sedimentation tank, and enhances the effect of endogenous denitrification in the secondary sedimentation tank, thereby achieving the goal of reducing energy consumption.

[0004] However, the above methods cannot achieve the goal of increasing total nitrogen treatment at low cost without adding major equipment, reducing the total nitrogen concentration in the effluent, and ensuring that the final produced water meets the discharge standards. Summary of the Invention

[0005] This application provides an enhanced denitrification device and method for secondary sedimentation tanks, which has a better total nitrogen removal effect.

[0006] This application provides an enhanced internal denitrification and nitrogen removal device and method for a secondary sedimentation tank, which adopts the following technical solution: An enhanced secondary sedimentation tank internal denitrification denitrification device and method are disclosed. The enhanced secondary sedimentation tank internal denitrification denitrification device is an internal denitrification denitrification secondary sedimentation tank connected to the end of the biological treatment tank in a wastewater treatment plant. It includes two parallel rectangular sedimentation tanks, an influent device, a sludge return corridor, a pipeline aeration and stirring device, and a static water level drainage control system. The sludge return corridor is located at the bottom and near the middle of each rectangular sedimentation tank. The pipeline aeration and stirring device is located inside each rectangular sedimentation tank. The static water level drainage control system is located at the effluent pipe end of each rectangular sedimentation tank. The enhanced secondary sedimentation tank internal denitrification denitrification device controls the two rectangular sedimentation tanks to perform sludge return, stirring, and sedimentation stages and influent and drainage stages respectively through an alternating operation mode.

[0007] Preferably, the sludge return corridor includes at least two return channels arranged vertically at intervals, and the return channels are located near the outer wall of the bottom and middle area of ​​the rectangular sedimentation tank.

[0008] Preferably, the pipeline aeration and mixing device includes an air mixing main pipe and an air mixing branch pipe. Several air mixing branch pipes are provided on the air mixing main pipe. The aeration holes provided on the air mixing main pipe and the air mixing branch pipes have a diameter greater than 3mm to form coarse bubbles.

[0009] Preferably, the static water level drainage control system includes a liftable magnetic sealing assembly and an electromagnetic drive mechanism for driving the magnetic sealing assembly. The magnetic sealing assembly normally closes the drain outlet and releases the seal when energized.

[0010] Preferably, the alternating operation mode includes a single operation cycle divided into a first half-cycle and a second half-cycle. The first half-cycle includes a sludge return duration of no more than 20 minutes, an air stirring duration of no more than 5 minutes, and a static sedimentation duration of no less than 50 minutes.

[0011] Preferably, the sedimentation tank has an aspect ratio between 16:9 and 20:9 and an effective water depth of not less than 4.5m. The specific dimensions of the sedimentation tank are determined based on its single-unit treatment capacity, the maximum single-unit treatment capacity of which does not exceed 8000m³ / d. The dimensions are ultimately calculated based on the treated water volume, half-cycle drainage volume, and tank volume ratio.

[0012] Preferably, the chemical oxygen demand (COD) of the mixed liquor received by the secondary sedimentation tank is not higher than 50 mg / L, the total nitrogen is not higher than 20 mg / L, the ammonia nitrogen is not higher than 5 mg / L, and the dissolved oxygen is not higher than 1.5 mg / L; and the secondary sedimentation tank, calculated by the endogenous denitrification rate test, has a denitrification rate of 0.015 kg NO3-N / kg MLSS·d at 20°C, which is used to achieve a total nitrogen removal concentration of 5 mg / L at 12°C.

[0013] Preferably, the front-end biological treatment process is a complete wastewater biological denitrification process, in which the sludge concentration maintained in the front-end biological tank is not higher than 4500 mg / L. The process forms include, but are not limited to, A2O, inverted A2O, modified A2O, and multi-stage AO.

[0014] Preferably, when the single set of sedimentation tank has a treatment capacity of 8000 m³ / d, the sludge return rate of the sedimentation tank is 80 m³ / min and the return flow rate can be adjusted according to the treatment scale, and its air stirring air volume is 1200 Nm³ / hr.

[0015] Preferably, a method for enhancing endogenous denitrification in a secondary sedimentation tank, based on the aforementioned enhanced endogenous denitrification device for a secondary sedimentation tank, and used to enhance the endogenous denitrification function of the secondary sedimentation tank, adopts a dual-tank alternating operation mode, adjusted according to water quality requirements, with each typical cycle being 2.5 hours; a complete 2.5-hour cycle consists of two 1.25-hour half-cycles, with the two tanks alternating in function, and the steps include: S1: 1.25 hours to process half a cycle; Sludge is rapidly returned via the sludge return corridor using airlift or pipeline suction; total time: 12 minutes. Aeration is achieved by controlling the air mixing pipe with an electric valve, generating a large number of coarse bubbles to fully mix the mud and water in the tank and create a 3-minute oxygen-deficient environment. Let it stand and settle for 1 hour, while denitrifying bacteria use endogenous substances to carry out endogenous denitrification and nitrogen removal; S2: 1.25-hour inlet / outlet half-cycle; Water enters from the bottom of the pool and exits from near the liquid surface at the top of the pool. A static water level drainage control system is adopted, in which a magnetic ball at the end of the pipe is controlled by an inductive coil to open the drain outlet during the inlet / outlet half cycle and close the drain outlet during the processing half cycle. S3: Alternating operation; Within any 1.25-hour half-cycle, while one tank is in S1 processing half-cycle sludge return, mixing, and sedimentation, the other tank is simultaneously in the influent / effluent half-cycle; every 1.25 hours, the functions of the two tanks are switched to ensure continuous and stable operation of the system.

[0016] In summary, this application has the following beneficial effects: 1. To achieve better total nitrogen removal and meet effluent discharge standards, this continuous operation enhanced endogenous denitrification secondary sedimentation tank process, based on the traditional activated sludge process, enhances the endogenous denitrification reaction in the secondary sedimentation tank. Without adding an external carbon source, a certain amount of nitrate nitrogen is removed by denitrification, reducing the total nitrogen concentration in the effluent at low cost, improving the total nitrogen removal rate, and ensuring that the final effluent meets discharge standards.

[0017] 2. Without adding major equipment, improve total nitrogen treatment at low cost, reduce the total nitrogen concentration in the effluent, and ensure that the final produced water meets the discharge standards.

[0018] 3. The entire set of equipment has continuous water inlet and outlet, which has the advantages of homogeneous reaction in a fully mixed reaction tank, and can overcome the problems of intermittent operation in a sequencing batch reactor. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the front-end biochemical system structure in this embodiment; Figure 2 This is a schematic diagram of the typical single-cycle 2.5H structure of pools A and B in this embodiment; Explanation of reference numerals in the attached diagram: 1. Water inlet device; 2. Main air mixing pipe; 3. Branch air mixing pipe; 4. Sludge return corridor; 5. Sludge return shaft; 6. Static water level drainage control system; 7. Pool A; 8. Pool B. Detailed Implementation

[0020] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content. Example

[0021] This invention discloses an enhanced internal denitrification denitrification device and method for secondary sedimentation tanks, such as... Figure 1 As shown, the enhanced secondary sedimentation tank is an internal denitrification denitrification secondary sedimentation tank connected to the end of the biological treatment tank of the sewage treatment plant. It includes two rectangular sedimentation tanks arranged in parallel, a blower, a pipeline aeration and stirring device, a sludge return corridor 4, a sludge return shaft 5 set in the sludge return corridor 4, and a static water level drainage control system 6.

[0022] The rectangular sedimentation tank is equipped with an inlet device 1 at the bottom, and a sludge return channel 4 is located at the bottom and near the middle of the rectangular sedimentation tank. The sludge return channel 4 is used to return settled sludge and discharge excess sludge to the sludge tank. The rectangular sedimentation tank is equipped with a pipeline aeration and stirring device, which has a short action time and good stirring effect. The rectangular sedimentation tank and the biological treatment tank share a blower. The two sedimentation tanks are arranged side by side as a series, and the stirring, sedimentation, and effluent discharge are carried out alternately, which can ensure continuous influent and effluent of a series. It has the advantages of homogeneous reaction in a completely mixed reaction tank, and can overcome the problems of batch reactor operation.

[0023] Before entering the secondary sedimentation tank, the wastewater has already undergone nitrification in the aerobic zone of the biological treatment tank, which will reduce ammonia nitrogen (NH4+). +-N is converted into nitrate nitrogen "NO3" - -N". The mixture containing nitrate nitrogen then enters the secondary sedimentation tank.

[0024] Unlike traditional continuously aerated secondary sedimentation tanks, the pipeline aeration and mixing device includes a main air mixing pipe 2 and several branch air mixing pipes 3. The branch air mixing pipes 3 are installed on the main air mixing pipe 2, and the aeration holes on both the main air mixing pipe 2 and the branch air mixing pipes 3 have a diameter greater than 3mm to form coarse bubbles. This device achieves precise control of the tank environment through the pipeline aeration and mixing device and control system. During a specific operating cycle, the blower may stop or reduce the air supply, or the mixing device may only provide mixing without introducing a large amount of oxygen, thus creating an anoxic or even anaerobic environment inside the secondary sedimentation tank.

[0025] Endogenous denitrification is key. A large amount of activated sludge accumulates in the secondary sedimentation tank. Under anaerobic conditions, the microorganisms in this activated sludge utilize their stored organic matter or trace amounts of readily biodegradable organic matter remaining in the wastewater as a carbon source.

[0026] In an anaerobic environment, denitrifying bacteria in activated sludge use nitrate nitrogen as an electron acceptor to reduce nitrate nitrogen to nitrite nitrogen, and finally reduce it to nitrogen gas, which escapes to the water surface in the form of bubbles.

[0027] The sludge return corridor 4 includes at least two return channels arranged vertically at intervals. The return channels are located near the outer wall of the bottom and middle area of ​​the rectangular sedimentation tank. The return channels in the sludge return corridor 4 return the settled activated sludge rich in denitrifying bacteria, ensuring that there are enough microorganisms in the reaction zone to carry out denitrification reactions and promoting the internal circulation and contact of sludge.

[0028] The two parallel sedimentation tanks work alternately for stirring, sedimentation, and effluent discharge, meaning that at any given time, at least one tank can handle both sedimentation and effluent discharge, thus ensuring the continuity of wastewater treatment and the quality of the effluent.

[0029] This enhanced internal denitrification and nitrogen removal device in the secondary sedimentation tank eliminates the need for a separate denitrification tank. By integrating the denitrification function into the secondary sedimentation tank, it significantly saves land area and reduces civil engineering investment costs, making it particularly advantageous for wastewater treatment plant renovation or new construction projects with limited land resources.

[0030] This secondary sedimentation tank method employs an alternating intermittent operation mode, with each standard operating cycle lasting 2.5 hours. The specific cycle length can be dynamically adjusted according to the influent and effluent water quality requirements. Within a complete operating cycle, tanks A (7) and B (8) will each perform different functions and alternately perform the following operations: S1: First half-cycle: "Pool A 7: Sludge return, mixing, sedimentation; Pool B 8: Water inlet, water outlet" T1: Sludge Return to Tank A (12 Minutes): Sludge in Tank A (7) is first returned via sludge return corridor 4 using air lift or pipe suction to ensure the sludge concentration remains at the optimal level. Sludge return stops after this step.

[0031] T2: Air Agitation in Tank A 7 for 3 Minutes: Immediately following, compressed air is introduced into Tank A 7 via an electrically controlled pipeline aeration system, resulting in vigorous agitation for 3 minutes. This process aims to utilize the disturbance of a large number of coarse air bubbles to thoroughly mix the sludge and water in the sedimentation tank, and simultaneously create an oxygen-deficient environment conducive to subsequent biological reactions.

[0032] T3: Static sedimentation of Tank A 7 for 1 hour: After stirring, Tank A 7 enters a 1-hour static sedimentation stage. During this period, the flocculated suspended solids settle, and at the same time, denitrifying bacteria utilize the endogenous organic matter in the tank to carry out a highly efficient endogenous denitrification reaction, thereby achieving nitrogen removal.

[0033] The three steps of sludge return, stirring and sedimentation in the above-mentioned pool A7 together constitute its first half-cycle, which lasts for a total of 1 hour and 15 minutes.

[0034] Synchronous operation of tank B8: During the first half-cycle of the above-mentioned sludge return, stirring and sedimentation operations in tank A7, tank B8 continuously performs water inflow and drainage operations.

[0035] S2: Water Inlet and Drainage System Mechanism T1: Water inlet method: The water inlet to the sedimentation tank is located at the bottom of the inlet end to ensure uniform water flow and reduce disturbance to the settled sludge.

[0036] T2: Water outlet method: The water outlet pipe is set up with multiple small-diameter pipes located near the liquid surface at the high end of the water production end to collect the supernatant.

[0037] T3: Drainage Control System: The drainage process is precisely managed by a unique static water level drainage control system. The core mechanism of this system involves a small magnetic ball vertically positioned at the end of the drainage pipe, which can move up and down inside the pipe. The levitation position of the magnetic ball is controlled by whether an external inductor coil is energized.

[0038] When drainage is needed, i.e., during the "inlet-drainage half-cycle", the inductor coil releases the ball, causing it to fall and opening the drainage inlet.

[0039] When it is necessary to close the drainage channel, i.e., during the sludge return, stirring, and sedimentation half-cycle, the inductor coil is energized, controlling the small ball at the bottom bayonet, effectively isolating the drainage inlet.

[0040] S3: In the second half of the cycle, "Pool A 7: Water inlet and outlet; Pool B 8: Sludge return, stirring, and sedimentation"; In the second half of the cycle, "also 1.25 hours", the functions of Pools A and B are interchanged.

[0041] T1: Operation of Tank A 7: At this time, after completing its sedimentation stage, Tank A 7 immediately starts the drainage system and enters a continuous 1.25-hour water inflow and drainage operation to handle the new wastewater flow.

[0042] T2: Operation of Tank B8: Simultaneously, Tank B8 shuts off its drainage system and initiates its own operating procedure: First, sludge is returned for 12 minutes via air lift or pipe suction; then, the electric valve is opened for 3 minutes of air agitation. Finally, it enters a 1-hour static sedimentation phase.

[0043] This series of operations in Pool B8 constitutes a complete half-cycle of "1.25 hours in total," which corresponds perfectly to the first half-cycle operation mode of Pool A7. Through this periodic alternation, the system is ensured to continuously and efficiently perform solid-liquid separation and biological denitrification.

[0044] Furthermore, the length-to-width ratio of a single rectangular sedimentation tank is 16:9 to 20:9, with the specific dimensions depending on the single-unit treatment capacity, and the maximum single-unit treatment capacity not exceeding 8000 m³. 3 / d, with an effective water depth of 4.5m or more, calculated based on the treatment volume, half-cycle drainage volume, and pool volume ratio.

[0045] Furthermore, the sludge concentration in the front-end biological treatment tank is ≤4500mg / L, and the front-end biological treatment process belongs to a complete wastewater biological denitrification process, including "A2O, inverted A2O, modified A2O, multi-stage AO, etc."

[0046] Furthermore, the mixed liquor entering the secondary sedimentation tank has a chemical oxygen demand (COD) of ≤50 mg / L, total nitrogen (TN) of ≤20 mg / L, ammonia nitrogen (NH3) of ≤5 mg / L, and dissolved oxygen (DO) of ≤1.5 mg / L. The calculated value of the internal denitrification rate in the secondary sedimentation tank is 0.015 kg NO3-N / (kg MLSS.d) (20℃), and the designed total nitrogen removal concentration is 5 mg / L at 12℃.

[0047] Furthermore, a single unit of 8000m 3 / d The sludge return rate in the sedimentation tank reaches 80m 3 / min, return flow rate adjusted according to scale; 8000m³ per unit. 3 The air agitation volume for the sedimentation tank is 1200 Nm / d. 3 / hr.

[0048] Working principle: The typical single operating cycle is 2.5 hours, which can be adjusted according to the water quality requirements of the influent and effluent. After entering an operating cycle, the A tank 7 uses the sludge return corridor 4 to return the sludge by air lifting or pipeline suction. This process takes 12 minutes, after which the sludge return stops.

[0049] Pool A7 is aerated using an air mixing pipe controlled by an electric valve. The pool is stirred for 3 minutes. The large number of coarse bubbles disturb the sedimentation tank, making the mud and water in the sedimentation tank fully mixed and creating an oxygen-deficient environment.

[0050] Tank A (7) undergoes 1 hour of sedimentation, during which denitrifying bacteria utilize endogenous substances for internal denitrification. Steps 1-3 constitute a single half-cycle. Tank B (8) continuously receives and discharges water during the sludge return, stirring, and sedimentation half-cycles of Tank A (7). The sedimentation tank inlet is located at the bottom of the inlet end, and the outlet pipe has multiple small pipes located near the liquid level at the higher end of the product water end. A static water level drainage control system (6) is used, which includes a liftable magnetic sealing component and an electromagnetic drive mechanism to drive the magnetic sealing component. The magnetic sealing component normally closes the drain outlet and releases the seal when energized. This system can control the drainage switch when the liquid level is constant. The mechanism involves a small magnetic ball at the end of the pipe, which is stuck vertically inside the drain pipe. The energization of an inductor coil controls whether the ball is positioned at the bottom of the locking slot to isolate the drain inlet. During the water inlet / drainage half-cycle, the ball is released to drain water; during the sludge return, stirring, and sedimentation half-cycles, the ball is controlled to close the drain pipe.

[0051] In the second half-cycle, the functions of tanks A and B are switched. Tank A 7 completes sedimentation and opens the drainage system to begin 1.25 hours of water intake and drainage. Tank B 8 closes the drainage system and uses sludge return corridor 4 to return sludge through air lift or pipe suction. This step takes 12 minutes. The tank is aerated using an air mixing pipe controlled by an electric valve for 3 minutes. After agitation, sedimentation takes 1 hour. The half-cycle lasts a total of 1.25 hours.

[0052] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An enhanced secondary sedimentation tank for endogenous denitrification, wherein the enhanced secondary sedimentation tank for endogenous denitrification is an endogenous denitrification secondary sedimentation tank and is connected to the end of the biological treatment tank in a wastewater treatment plant, characterized in that, It includes two rectangular sedimentation tanks arranged side by side, an inlet device (1), a sludge return corridor (4), a pipeline aeration and stirring device, and a static water level drainage control system (6); the sludge return corridor (4) is located at the bottom and near the middle of each rectangular sedimentation tank, the pipeline aeration and stirring device is located inside each rectangular sedimentation tank, and the static water level drainage control system (6) is located at the outlet pipe end of the rectangular sedimentation tank. The enhanced secondary sedimentation tank internal denitrification denitrification device controls the two rectangular sedimentation tanks to perform sludge return, stirring, sedimentation and inlet and drainage stages respectively through alternating operation mode.

2. The enhanced secondary sedimentation tank endogenous denitrification denitrification device according to claim 1, characterized in that, The sludge return corridor (4) includes at least two return channels arranged vertically at intervals, and the return channels are located near the outer wall of the bottom and middle area of ​​the rectangular sedimentation tank.

3. The enhanced secondary sedimentation tank endogenous denitrification nitrogen removal device according to claim 1, characterized in that, The pipeline aeration and mixing device includes an air mixing main pipe (2) and an air mixing branch pipe (3). The air mixing branch pipe (3) has several aeration holes on the air mixing main pipe (2). The diameter of the aeration holes on the air mixing main pipe (2) and the air mixing branch pipe (3) is greater than 3 mm to form coarse bubbles.

4. The enhanced secondary sedimentation tank endogenous denitrification and nitrogen removal device according to claim 1, characterized in that, The static water level drainage control system (6) includes a liftable magnetic sealing component and an electromagnetic drive mechanism for driving the magnetic sealing component. The magnetic sealing component normally closes the drain outlet and releases the seal when energized.

5. The enhanced secondary sedimentation tank endogenous denitrification nitrogen removal device according to claim 1, characterized in that, The alternating operation mode includes a single operation cycle divided into a first half cycle and a second half cycle. The first half cycle includes a sludge return duration of no more than 20 minutes, an air stirring duration of no more than 5 minutes, and a static sedimentation duration of no less than 50 minutes.

6. The enhanced secondary sedimentation tank endogenous denitrification denitrification device according to claim 1, characterized in that, The sedimentation tank has an aspect ratio between 16:9 and 20:9 and an effective water depth of not less than 4.5m. The specific dimensions of the sedimentation tank are determined based on its single-unit treatment capacity, with the maximum single-unit treatment capacity not exceeding 8000m³ / d. The dimensions are ultimately calculated based on the treated water volume, half-cycle drainage volume, and tank volume ratio.

7. The enhanced secondary sedimentation tank endogenous denitrification and nitrogen removal device according to claim 1, characterized in that, The mixed liquor received by the secondary sedimentation tank has a chemical oxygen demand (COD) of no more than 50 mg / L, a total nitrogen (TNO) of no more than 20 mg / L, an ammonia nitrogen (AM) of no more than 5 mg / L, and a dissolved oxygen (DO) of no more than 1.5 mg / L. Furthermore, the secondary sedimentation tank, based on an endogenous denitrification rate test, has a denitrification rate of 0.015 kg NO3-N / kg MLSS·d at 20°C, which is used to achieve a total nitrogen removal concentration of 5 mg / L at 12°C.

8. The enhanced secondary sedimentation tank endogenous denitrification and nitrogen removal device according to claim 1, characterized in that, The front-end biological treatment process is a complete wastewater biological denitrification process, in which the sludge concentration maintained in the front-end biological tank is not higher than 4500 mg / L. The process forms include, but are not limited to, A2O, inverted A2O, modified A2O and multi-stage AO.

9. The enhanced secondary sedimentation tank endogenous denitrification and nitrogen removal device according to claim 1, characterized in that, When the single set of sedimentation tank has a treatment capacity of 8000 m³ / d, the sludge return rate of the sedimentation tank is 80 m³ / min and the return flow rate can be adjusted according to the treatment scale, and its air stirring air volume is 1200 Nm³ / hr.

10. A method for enhancing endogenous denitrification in a secondary sedimentation tank, based on the enhanced endogenous denitrification device for a secondary sedimentation tank as described in any one of claims 1-9, and used to enhance the endogenous denitrification function of the secondary sedimentation tank, adopting a dual-tank alternating operation mode, adjusted according to water quality requirements, with each typical cycle being 2.5 hours; A complete 2.5-hour cycle consists of two 1.25-hour half-cycles, with the two pools functioning alternately. Its characteristic is that... The steps include: S1: 1.25 hours to process half a cycle; Sludge is rapidly returned via the sludge return corridor (4) using air lifting or pipeline suction; total 12 minutes. The air mixing pipe is aerated by controlling the electric valve to generate a large number of coarse bubbles, which fully mix the mud and water in the tank and create an oxygen-deficient environment for 3 minutes. Let it stand and settle for 1 hour, while denitrifying bacteria use endogenous substances to carry out endogenous denitrification and nitrogen removal; S2: 1.25-hour inlet / outlet half-cycle; Water enters from the bottom of the pool and water exits from near the liquid surface at the top of the pool. A static water level drainage control system (6) is adopted, which is controlled by an inductor coil through a magnetic ball at the end of the pipe. The drain outlet is opened during the water inlet and outlet half-cycle and closed during the processing half-cycle. S3: Alternating operation; During any 1.25-hour half-cycle, when tank A (7) is in the sludge return, mixing and sedimentation half-cycle of treatment in S1, tank B (8) is simultaneously in the influent and effluent half-cycle; every 1.25 hours, the functions of the two tanks are switched to ensure the continuous and stable operation of the system.

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