Sequencing batch type low-carbon nitrogen and phosphorus removal device and method for selectively retaining heavy sludge

Abstract

The invention discloses a sequencing batch type low-carbon nitrogen and phosphorus removal device and method capable of selectively retaining heavy sludge, which are mainly used for low-carbon sewage treatment, sewage enters a reactor in three times, stirring is started to carry out anoxic reaction after the first time of water feeding and the second time of water feeding, the method comprises the following steps: firstly carrying out anaerobic reaction after water is fed for the first time, then starting low-oxygen aeration to generate nitrification, short-cut denitrification and anaerobic ammonia oxidation denitrification and phosphorus uptake, firstly carrying out anoxic reaction after water is fed for the third time, then starting normal aeration to generate nitrification and enhanced phosphorus uptake, and finally realizing low-carbon nitrogen and phosphorus removal: then carrying out static precipitation, and discharging supernate; and finally, starting slow stirring, and discharging sludge-water mixed liquid on the middle inclined plate precipitation device as residual sludge. According to the method, low-carbon nitrogen and phosphorus removal of sewage can be realized by partially transforming the existing SBR configuration, so that the device transformation cost of a sewage treatment plant is reduced, the low-carbon sewage treatment efficiency is effectively improved, and the use of an external carbon source for sewage treatment is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, and more specifically, relates to a sequencing batch reactor (SBR) for low-carbon nitrogen and phosphorus removal and a method for selectively retaining heavy sludge. Background Technology

[0002] Treatment processes need to meet stricter total nitrogen (TN) and total phosphorus (TP) emission requirements while minimizing external carbon sources and aeration energy consumption. Sequencing batch reactors (SBRs) are widely used in small and medium-sized wastewater treatment plants and integrated systems due to their simple structure, flexible operation, and small footprint. However, SBRs often rely on a time-series cycle of "aerobic nitrification – anoxic denitrification – sedimentation – effluent." When the influent C / N ratio is low or operating energy consumption is limited, problems often arise such as insufficient carbon sources for denitrification, over-nitrification leading to nitrate nitrogen accumulation, unstable simultaneous phosphorus removal, and high operating energy consumption.

[0003] Existing SBR improvement practices mainly include: intermittent / segmented aeration to control dissolved oxygen, segmented influent to improve denitrification efficiency, external carbon sources to compensate for insufficient electron donors, and improving sludge properties through selectors or external sedimentation equipment. However, these methods generally have the following limitations: First, dependence on external carbon sources increases operating costs and carbon footprint; second, relying solely on time-period dissolved oxygen (DO) control makes it difficult to maintain a suitable nitrite nitrogen level stably in the long term; third, SBR operates intermittently in a single tank, lacking supporting structures and sludge discharge strategies that are synchronized with the cycle and can selectively retain high-velocity heavy sludge in the tank while prioritizing the discharge of light sludge, resulting in insufficient retention efficiency of key slow-growing bacteria (such as nitrifying bacteria), thus affecting deep nitrogen removal and simultaneous phosphorus removal.

[0004] Therefore, how to achieve the following key technical problems in the current SBR field to meet the needs of low carbon and upgrading standards, without relying on external carbon sources and with overall aeration volume under the premise of controlled time series control and selective separation / sludge discharge strategies: optimized community structure with priority enrichment of heavy sludge and selective discharge of light sludge; controlled nitrification and nitrite supply during low dissolved oxygen periods; and synergistic stability of denitrification and phosphorus removal processes.

[0005] To address the aforementioned technical problems, this application proposes a sequencing batch reactor (SBR) low-carbon nitrogen and phosphorus removal device and method that facilitates the modification of existing SBRs, effectively saves external carbon sources, reduces aeration energy consumption, and improves the stability of effluent TN / TP levels to meet standards, while selectively retaining heavy sludge. Summary of the Invention

[0006] The purpose of this invention is to provide a sequencing batch process (SBR) low-carbon nitrogen and phosphorus removal device and method that selectively retains heavy sludge. While reducing energy consumption and carbon emissions, it significantly improves the efficiency of nitrogen and phosphorus removal, thereby effectively reducing treatment costs and land area, and providing a more economical, efficient and sustainable solution for urban wastewater treatment.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a sequencing batch reactor (SBR) for selectively retaining heavy sludge, comprising: Biological tank, which is a single tank structure and is equipped with a dissolved oxygen probe inside; An inclined plate sedimentation device is installed in the middle of the biological treatment tank to separate the sludge in the tank. The wastewater tank is located outside the biochemical tank and is used to store wastewater to be treated. The wastewater tank is connected to the lower side of the biochemical tank. The microporous aeration head is installed on the bottom wall of the biological treatment tank, and the lower end of the microporous aeration head passes through the bottom wall of the biological treatment tank and is connected to the air intake device. The agitator is rotatably connected to the top of the biological tank, and the agitator head extends downward into the interior of the biological tank to continuously and slowly stir the contents of the tank.

[0008] Furthermore, a peristaltic pump and an inlet valve are sequentially installed on the inlet pipe between the sewage tank and the biological treatment tank. An outlet valve is also installed on the upper part of the side wall of the biological treatment tank. An online sensor is installed on the upper end of the dissolved oxygen probe. The online sensor is positioned at the upper end of the biological treatment tank and is plugged into the biological treatment tank. An electromagnetic air volume regulating valve is installed at the connection between the air intake equipment and the microporous aeration head.

[0009] Furthermore, it also includes a control cabinet, which is electrically connected to each component to perform logic control on each electric component.

[0010] A sequencing batch process for low-carbon nitrogen and phosphorus removal using the above-mentioned device for selective retention of heavy sludge; comprising the following steps: S1: The sewage is divided into three batches through the inlet valve. Calcium chloride solution is added into the inlet pipe to control the calcium ion concentration in the sewage to 80-150 mg / L. The first batch flows into the biological treatment tank through a peristaltic pump. S2: Activated sludge from the wastewater treatment plant is added to the biological treatment tank; S3: Start stirring to initiate the anoxic reaction, followed by the first low-oxygen aeration, in which the dissolved oxygen concentration is controlled at 0.2-0.6 mg / L; S4: The second batch of sewage flows into the biological treatment tank, is continuously stirred and the aeration is turned off to carry out the anoxic reaction, and then a second low oxygen aeration is carried out. The dissolved oxygen concentration in the second low oxygen aeration is controlled at 0.2-0.6 mg / L. S5: The third batch of wastewater flows into the biological treatment tank, is continuously stirred and the aeration is turned off to carry out the anoxic reaction, and then the third aerobic aeration is carried out. The dissolved oxygen concentration in the aerobic aeration is controlled at 2.0-3.0 mg / L. S6: Stop aeration and allow sedimentation, then discharge the supernatant from the biological treatment tank through the outlet valve; S7: After the system is drained, start the slow stirring to discharge the light sludge on the inclined plate sedimentation device as residual sludge.

[0011] By setting up batch influent, each anoxic stage fully utilizes the organic matter in urban sewage to store internal carbon sources for endogenous denitrification. By alternating between anoxic and aerobic stages in different batches of water, polyphosphate-accumulating bacteria can decompose the polyphosphates stored in their cells, releasing inorganic phosphorus. At the same time, they use the energy generated from the decomposition of polyphosphates to absorb volatile fatty acids (VFAs) in sewage and synthesize them into organic matter that is stored in their cells.

[0012] Furthermore, in step S1, calcium chloride solution needs to be continuously added to the wastewater to be treated through the inlet pipe every day. In steps S1, S4 and S5, the first batch of wastewater is 40%-70% of the total wastewater volume, the second batch is 20%-40%, and the third batch is 10%-20%. After three inlets, the sludge concentration is controlled at 3500-4200 mg / L.

[0013] Furthermore, in step S3, the sludge retention time is controlled to be 12 to 14 days by adjusting the amount of residual sludge discharged, and the total HRT (total hydraulic retention time) of the biological treatment tank system is 12-15 hours. Specifically, the HRT is 3-4 hours after the first water intake, 4-5 hours after the second water intake, and 5-6 hours after the third water intake. The ratio of the HRT of the anoxic section to the HRT of the aerobic section after each batch of water intake is 1:2.

[0014] Furthermore, in step S6, the sedimentation time is 20-30 minutes, and the supernatant-to-water ratio is 25%-60%. Compared with existing technologies, it has the following beneficial effects: By implementing batch influent, each anoxic stage fully utilizes the organic matter in urban wastewater, storing internal carbon sources for endogenous denitrification. The anoxic stage also allows polyphosphate-accumulating bacteria to decompose stored polyphosphates, releasing inorganic phosphorus. Simultaneously, they utilize the energy generated from polyphosphate decomposition to absorb volatile fatty acids (VFAs) in the wastewater and synthesize organic matter, storing it within their cells. During the low-oxygen aeration stage, low-oxygen nitrification controls the rate of nitrate formation, limiting the subsequent supply of nitrate nitrogen to denitrification substrates, thus controlling the rate of nitrite production and generating low-concentration nitrite nitrogen. This provides a long-term, stable substrate supply for anaerobic ammonia oxidation. Furthermore, low-oxygen aeration reduces the oxidation of internal carbon sources, allowing more carbon to be used for nitrite production during endogenous denitrification. During the normal aeration stage, the nitrogen and phosphorus removal efficiency of the biological treatment tank is maintained. Adding calcium ions to the biological treatment tank promotes the connection between extracellular polymers and microbial cells, which helps to form granular sludge. Adding an inclined plate sedimentation device to the top of the biological treatment tank allows heavy sludge with more particles to remain at the bottom of the tank, which is beneficial for the retention of anaerobic ammonia oxidizing bacteria. Only light sludge is discharged as excess sludge, which improves the sludge settling properties of the system and avoids sludge bulking.

[0015] The above-described apparatus and method offer the following advantages over conventional processing methods: 1) Make full use of the organic matter in the influent to enhance the storage of internal carbon sources and achieve low-carbon denitrification and phosphorus removal; 2) Adding calcium ions promotes the formation of granular sludge from activated sludge, resulting in good sludge settling properties and preventing sludge bulking in the system; 3) The carbon source in the sludge is used for denitrification, resulting in less sludge production in the system. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only preferred embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the overall structure of a sequencing batch low-carbon nitrogen and phosphorus removal device for selectively retaining heavy sludge according to the present invention.

[0018] In the diagram: 1-Biological tank; 11-Dissolved oxygen probe; 12-Outlet valve; 13-Online sensor; 14-Inlet pipe; 2-Inclined plate sedimentation device; 3-Sewage tank; 31-Peristaltic pump; 32-Inlet valve; 4-Microporous aeration head; 5-Air intake equipment; 51-Electromagnetic air volume regulating valve; 6-Agitator; 7-Control cabinet. Detailed Implementation

[0019] To better understand the structure, functional features, and advantages of the present invention, preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings: Using the method of this invention, low-carbon urban sewage flows into the inlet pipe 14 and then flows into the biological treatment tank 1 in three batches through the inlet valve 32. In the anoxic stage, denitrifying bacteria reduce nitrates and nitrites to gaseous nitrogen compounds such as nitrogen, thus achieving denitrification. Polyphosphate-accumulating bacteria can decompose the polyphosphates stored in their cells, releasing inorganic phosphorus. Simultaneously, they utilize the energy generated from the decomposition of polyphosphates to absorb volatile fatty acids (VFAs) in the sewage and synthesize them into organic matter stored within their cells. In the first and second aerobic stages of low-oxygen aeration, controlling the nitrate nitrogen generation rate through low-oxygen aeration further controls the nitrate nitrogen supply rate during denitrification. Since nitrate nitrogen is converted to nitrite during denitrification, controlling the nitrite production rate allows for a long-term, stable supply of low-concentration nitrites for the anaerobic ammonium oxidation reaction. This effectively prevents the inhibition of anaerobic ammonium oxidation bacteria growth due to excessively high nitrite concentrations, achieving endogenous denitrification-anaerobic ammonium oxidation. An inclined plate sedimentation device 2 is installed at the top of biological treatment tank 1 to allow heavy sludge to settle. The heavy sludge encapsulates anaerobic ammonia oxidizing bacteria. Within the heavy sludge, there is a gradient distribution of dissolved oxygen and substrate concentration in different areas, which can create a suitable anaerobic or anoxic environment for anaerobic ammonia oxidizing bacteria, meeting their strict requirements for low-oxygen or even anaerobic conditions. Therefore, the sedimentation of heavy sludge is beneficial to the retention of anaerobic ammonia oxidizing bacteria. Normal aeration is carried out in the third aerobic stage to ensure the treatment effect of nitrogen and phosphorus. The sludge-water mixture after the three stages of treatment is settled to achieve sludge-water separation. The supernatant is discharged, and the settled sludge is stirred by the agitator to form mixed sludge. The overflow light sludge is discharged through the effluent valve 12. The bottom sludge with more particles is retained at the bottom of biological treatment tank 1. Adding calcium ions to biological treatment tank 1 can promote the formation of heavy sludge.

[0020] Example 1 like Figure 1 As shown, this application proposes a sequencing batch reactor (SBR) for selectively retaining heavy sludge, comprising: Biological tank 1 is a single-tank structure, and a dissolved oxygen probe 11 is installed inside it; it serves as the main container for the reaction to occur. Inclined plate sedimentation device 2 is installed in the middle of biological treatment tank 1 to sort the sludge in biological treatment tank 1.

[0021] During sedimentation, heavy sludge falls to the bottom of biological treatment tank 1, while light sludge remains on the surface of inclined plate sedimentation device 2. The light sludge is discharged simultaneously with the supernatant. Wastewater tank 3 is located outside the biochemical tank and is used to store wastewater to be treated. Wastewater tank 3 is connected to the lower side of biochemical tank 1. Wastewater tank 3 adopts a corrosion-resistant design to prevent wastewater from corroding it during long-term storage. At the same time, it adopts a low-sensitivity coating to avoid chemical reaction between it and the internal wastewater.

[0022] The microporous aeration head 4 is installed on the bottom wall of the biological treatment tank 1. The lower end of the microporous aeration head 4 passes through the bottom wall of the biological treatment tank 1 and is connected to the air intake device 5. The aeration head can be a conventional microporous aeration disc or a cylindrical aeration pipe. A waterproof seal is provided at the position where it passes through the bottom wall of the biological treatment tank 1 to prevent water leakage.

[0023] Agitator 6 is rotatably connected to the top of the biological tank 1. The stirring head of agitator 6 extends downward into the interior of the biological tank 1 to continuously and slowly stir the contents of the biological tank 1. Agitator 6 is an electric stirring device, with its electric end located at the top of the biological tank 1. The stirring blades penetrate deep into the interior of the biological tank 1 and pass through the inclined plate sedimentation device 2. The motor of agitator 6 is an adjustable-speed servo motor to adapt to different stirring rate requirements at different stages.

[0024] See Figure 1 A peristaltic pump 31 and an inlet valve 32 are sequentially installed on the inlet pipe 14 between the sewage tank 3 and the biological treatment tank 1. An outlet valve 12 is also installed on the upper side wall of the biological treatment tank 1. The inlet water of the biological treatment tank 1 is supplied by the peristaltic pump 31. At the same time, both the inlet valve 32 and the outlet valve 12 are electromagnetic flow valves to remotely control the inlet and outlet water and control the water volume and flow rate, ensuring that the total hydraulic retention time is controllable. In addition, a solution addition port is provided in the inlet pipe 14 to facilitate the direct addition of calcium chloride solution to the wastewater to be treated in the inlet pipe 14.

[0025] See Figure 1 An online sensor 13 is installed at the upper end of the dissolved oxygen probe 11. The online sensor 13 is positioned at the upper end of the biological tank 1 and is plugged into the biological tank 1. An electromagnetic air volume regulating valve 51 is installed at the connection between the air intake device 5 and the microporous aeration head 4.

[0026] See Figure 1 It also includes a control cabinet 7, which is connected to the online sensor 13, water inlet valve 32, water outlet valve 12, air intake device 5, peristaltic pump 31 and agitator 6 motor by electrical signal. The control cabinet 7 uses semiconductor chips to perform logic control on the above electrical components and can modify the parameters.

[0027] Working principle: The wastewater to be treated is sent into the wastewater tank 3 through the pipeline. The device is started, so that the inlet valve 32 is opened. The peristaltic pump 31 pumps the water in the wastewater tank 3 into the biological treatment tank 1 through the inlet pipe 14. The inlet pipe 14 continuously adds calcium chloride solution to the wastewater to be treated through the solution addition port. Then, the air intake device 5 is started to pump gas into the microporous aeration head 4 to perform low-oxygen aeration and aerobic aeration in the aerobic section. The stirrer 6 is started to stir the water and sludge in the biological treatment tank 1. After the reaction is completed, sedimentation takes place. The outlet valve 12 is opened to discharge the supernatant in the biological treatment tank 1 and the light sludge on the surface of the inclined plate sedimentation device 2.

[0028] Example 2 A sequencing batch reactor (SBR) method for selectively retaining heavy sludge to remove nitrogen and phosphorus is disclosed, using the selectively retaining heavy sludge SBR device described in Example 1. This embodiment uses the effluent from the grit chamber of a wastewater treatment plant as the influent. The specific water quality is as follows: influent ammonia nitrogen 17.47-34.83 mg / L, influent total nitrogen (TN) 17.63-35.17 mg / L, influent total phosphorus 2.37-4.69 mg / L, influent COD 50.47-127.85 mg / L, and an average C / N ratio of 3.8. The experimental system is as follows: Figure 1 As shown, the total reaction volume of the reactor is 5L.

[0029] (1) Start the system: Inoculate activated sludge from the sewage treatment plant into biological tank 1 to make the sludge concentration in biological tank 1 4000 mg / L; (2) The adjustment operation during operation is as follows: 1) Low-carbon urban sewage flows into biochemical tank 1 in three batches through inlet valve 32; calcium chloride solution is continuously added to inlet pipe 14 to control the calcium ion concentration in the inlet water to 80 mg / L, and the addition is carried out continuously every day.

[0030] 2) The total HRT (hydraulic retention time) of the biological tank 1 system is 12h, of which the HRT is 3h after the first water intake, 4h after the second water intake, and 5h after the third water intake. The ratio of HRT in the anoxic section to HRT in the aerobic section after each batch of water intake is 1:2.

[0031] 3) During aeration, the dissolved oxygen in the first and second aerobic stages should be controlled at 0.2-0.4 mg / L, and the dissolved oxygen in the third aerobic stage should be controlled at 2.0-2.5 mg / L; during the reaction stage, stirrer 6 should be turned on for continuous stirring at a constant speed. 4) Turn off aeration and allow sedimentation to proceed for 30 minutes; 5) After the system drains water each day, turn on the agitator 6 to slowly stir the water. Discharge the sludge on the inclined plate sedimentation device 2 as residual sludge. The drainage ratio is 25%, and the sludge retention time is controlled to be 13 days.

[0032] The test results show that after the system is in stable operation, the effluent ammonia nitrogen is less than 0.7 mg / L, with an average of 0.35 mg / L; the effluent TN is less than 4.8 mg / L, with an average of 3.8 mg / L; the effluent total phosphorus is less than 0.5 mg / L, with an average of 0.2 mg / L; and the effluent COD is less than 30 mg / L, with an average of 26.4 mg / L.

[0033] Comparative Study Example 1 The process of this comparative study example differs from that of Example 2 of this application in that: this comparative example is replaced with a conventional influent A2O process, without the inclined plate sedimentation device 2, and without the addition of calcium chloride solution, while the wastewater quality and temperature are the same as in Example 2. This comparative example uses the conventional A2O process, which mainly includes an anaerobic tank, an anoxic tank, an aerobic tank, and a secondary sedimentation tank. Wastewater first enters the anaerobic tank for anaerobic phosphorus release, then enters the anoxic tank for denitrification, and finally enters the aerobic tank for ammonia oxidation and aerobic phosphorus uptake. The sludge-water mixture is separated in the secondary sedimentation tank, and the supernatant is discharged. The settled sludge is returned to the anaerobic tank. At the same time, a nitrification liquor return system is also set up, in which the sludge-water mixture in the aerobic tank is returned to the anoxic tank.

[0034] Under the same influent and environmental conditions, the average TN of the effluent from this comparative study example was 6.93 mg / L, which is much higher than the TN concentration of 3.8 mg / L in the effluent from Example 2.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technology of the present invention without departing from the scope of the present invention are within the protection scope of the present invention.

Claims

1. A sequencing batch reactor (SBR) for selectively retaining heavy sludge, characterized in that, include: Biological tank (1), wherein the biological tank (1) is a single tank structure and a dissolved oxygen probe (11) is installed inside it; An inclined plate sedimentation device (2) is installed in the middle of the biological tank (1) to sort the sludge in the biological tank (1); A sewage tank (3) is located outside the biochemical tank and is used to store sewage to be treated. The sewage tank (3) is connected to the lower side of the biochemical tank (1). A microporous aeration head (4) is installed on the bottom wall of the biochemical tank (1), and the lower end of the microporous aeration head (4) passes through the bottom wall of the biochemical tank (1) and is connected to an air intake device (5). A stirrer (6) is rotatably connected to the top of the biochemical tank (1). The stirring head of the stirrer (6) extends downward into the interior of the biochemical tank (1) to continuously and slowly stir the interior of the biochemical tank (1).

2. The sequencing batch reactor (SBR) for selectively retaining heavy sludge as described in claim 1, characterized in that, The sewage tank (3) and the biochemical tank (1) are connected by an inlet pipe (14) and a peristaltic pump (31) and an inlet valve (32) are installed in sequence. An outlet valve (12) is also installed on the upper side wall of the biochemical tank (1).

3. The sequencing batch reactor (SBR) for selectively retaining heavy sludge as described in claim 2, characterized in that, An online sensor (13) is provided at the upper end of the dissolved oxygen probe (11). The online sensor (13) is positioned at the upper end of the biochemical tank (1) and is plugged into the biochemical tank (1). An electromagnetic air volume regulating valve (51) is provided at the connection between the air intake device (5) and the microporous aeration head (4).

4. The sequencing batch reactor (SBR) for selectively retaining heavy sludge as described in claim 3, characterized in that, It also includes a control cabinet (7), which is electrically connected to each component to perform logic control on each electric component.

5. A sequencing batch reactor (SBR) method for selectively retaining heavy sludge to remove nitrogen and phosphorus, using the SBR device for selectively retaining heavy sludge as described in claim 4, characterized in that it includes the following steps: S1: The sewage is divided into three batches through the inlet valve (32), and calcium chloride solution is added into the inlet pipe (14) to control the calcium ion concentration in the sewage to be 80-150 mg / L. The first batch flows into the biochemical tank (1) through the peristaltic pump (31). S2: Activated sludge from the wastewater treatment plant is added to the biological treatment tank (1); S3: Start stirring to initiate an anoxic reaction, followed by the first low-oxygen aeration, in which the dissolved oxygen concentration is controlled at 0.2-0.6 mg / L; S4: The second batch of sewage flows into the biological treatment tank (1), is continuously stirred and the aeration is turned off to carry out the anoxic reaction, and then a second low oxygen aeration is carried out. The dissolved oxygen concentration in the second low oxygen aeration is controlled at 0.2-0.6 mg / L. S5: The third batch of sewage flows into the biological treatment tank (1), is continuously stirred and the aeration is turned off to carry out the anoxic reaction, and then the third aerobic aeration is carried out. The dissolved oxygen concentration in the aerobic aeration is controlled at 2.0-3.0 mg / L. S6: Stop aeration and allow sedimentation, then discharge the supernatant from the biological tank (1) through the outlet valve (12); S7: After the system is drained, start the slow stirring and discharge the light sludge on the inclined plate sedimentation device (2) as the remaining sludge.

6. The sequencing batch reactor (SBR) method for selectively retaining heavy sludge with low carbon nitrogen and phosphorus removal according to claim 5, characterized in that, In step S1, calcium chloride solution needs to be continuously added to the wastewater to be treated through the inlet pipe (14) every day; in steps S1, S4 and S5, the first batch of wastewater is 40%-70% of the total wastewater, the second batch of wastewater is 20%-40%, and the third batch of wastewater is 10%-20%.

7. The sequencing batch reactor (SBR) method for selectively retaining heavy sludge with low carbon nitrogen and phosphorus removal according to claim 5, characterized in that, After three water influent treatments, the sludge concentration was controlled at 3500-4200 mg / L.

8. The sequencing batch reactor (SBR) method for selectively retaining heavy sludge with low carbon nitrogen and phosphorus removal according to claim 5, characterized in that, In step S3, the sludge retention time is controlled to be 12 to 14 days by adjusting the amount of residual sludge discharged.

9. The sequencing batch reactor (SBR) method for selectively retaining heavy sludge with low carbon nitrogen and phosphorus removal according to claim 5, characterized in that, The total HRT (hydraulic retention time) of the biological tank (1) system is 12-15h. The HRT is 3-4h after the first water intake, 4-5h after the second water intake, and 5-6h after the third water intake. The ratio of HRT in the anoxic section to HRT in the aerobic section after each batch of water intake is 1:

2.

10. The sequencing batch reactor (SBR) method for selectively retaining heavy sludge with low carbon nitrogen and phosphorus removal according to claim 5, characterized in that, In step S6, the sedimentation time is 20-30 minutes, and the supernatant-to-water ratio is 25%-60%.

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