A method for simultaneous removal of carbon, nitrogen, and phosphorus from wastewater based on membrane-aerated biofilm.

Abstract

This invention provides a method for simultaneously removing carbon, nitrogen, and phosphorus from wastewater based on a membrane-aerated biofilm reactor. The method comprises the following steps: S1: The wastewater is fed into a membrane-aerated biofilm reactor and subjected to a sequencing batch reactor reaction under intermittent membrane aeration conditions; S2: At the end of the reaction, the outermost phosphorus-rich membrane biofilm is sloughed off from below the membrane module by aeration, followed by settling and drainage; wherein the intermittent membrane aeration conditions are: no aeration for 0.5-4 hours followed by aeration for 5-20 hours. This method significantly improves the removal rates of total phosphorus and total nitrogen.

Description

Technical Field

[0001] This invention relates to the field of wastewater biological treatment technology, and in particular to a treatment method for the simultaneous removal of carbon, nitrogen, and phosphorus from wastewater based on a membrane-aerated biofilm. Background Technology

[0002] Although the anaerobic / anoxic / aerobic activated sludge process commonly used in my country's wastewater treatment plants has the function of simultaneous carbon, nitrogen and phosphorus removal, it has problems such as increased operating costs due to the large proportion of nitrification liquor recirculation and insufficient carbon source required for deep denitrification due to carbon removal followed by denitrification. As a result, external carbon sources are required to meet Class A and higher emission standards, which is not in line with the high-quality development direction of "carbon peaking and carbon neutrality".

[0003] Traditional biofilm processes using inert materials such as polypropylene as carriers can achieve a certain degree of simultaneous carbon, nitrogen, and phosphorus removal. In wastewater, pollutants (organic matter, nitrogen, phosphorus, etc.) and dissolved oxygen undergo co-current mass transfer from the main flow to the interior of the traditional biofilm, gradually forming aerobic, anoxic, and anaerobic zones from the outside in. During the mass transfer from the outside to the inside of the biofilm, the carbon source organic matter in the wastewater first passes through the aerobic zone and is largely consumed by aerobic microorganisms, leading to insufficient carbon source reaching the anoxic zone and ultimately limiting the denitrification effect.

[0004] like Figure 1 As shown, membrane-aerated biofilms possess the characteristics of efficient oxygen transfer in bubble-free aeration membranes and heterogeneous mass transfer within the biofilm. They readily form a stratified biofilm structure, with nitrifying bacteria enriched near the aeration membrane side and denitrifying bacteria (including denitrifying polyphosphate-accumulating bacteria) enriched near the mains flow side. This allows the carbon source in the mains to pass first through the denitrifying bacteria biofilm, thus preferentially being used for denitrification (including simultaneous polyphosphate accumulation), giving them a certain advantage in simultaneous carbon and nitrogen removal. However, the phosphorus removal efficiency of traditional membrane-aerated biofilm processes relying solely on cellular synthesis and assimilation is limited.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the simultaneous removal of carbon, nitrogen, and phosphorus from wastewater based on a membrane-aerated biofilm, which can significantly improve the removal rates of total phosphorus and total nitrogen.

[0007] This invention provides a method for the simultaneous removal of carbon, nitrogen, and phosphorus from wastewater based on a membrane-aerated biofilm, comprising the following steps:

[0008] S1: The wastewater is sent to the membrane aeration biofilm reactor and carried out in a sequencing batch reaction under intermittent membrane aeration conditions;

[0009] S2: At the end of the reaction, the outermost phosphorus-rich membrane aerated biofilm is peeled off by aeration and flushing from below the membrane module, and then left to stand and drain.

[0010] In step S1 above, the wastewater can be low carbon-to-nitrogen ratio wastewater, and the ratio of chemical oxygen demand (COD) to total nitrogen content in low carbon-to-nitrogen ratio wastewater can be 5-8; more specifically, for low carbon-to-nitrogen ratio municipal wastewater, its chemical oxygen demand (COD) is 200-400 mg / L, ammonia nitrogen is 20-50 mg / L, total nitrogen is 25-60 mg / L, and total phosphorus content is 5-10 mg / L.

[0011] The overall operating time of each cycle of a sequencing batch reactor (SBR) can be determined based on the influent carbon, nitrogen, and phosphorus concentrations. For typical municipal wastewater, the operating time of each cycle of a SBR is generally between 6 and 24 hours.

[0012] The influent time for each cycle of the sequencing batch reactor can be determined based on the preset volume of wastewater pumped into the membrane aerated biofilm reactor; specifically, the influent time can be 5-30 minutes.

[0013] The intermittent membrane aeration conditions for each cycle of the sequencing batch reactor are as follows: no aeration for 0.5-4 hours followed by aeration for 5-20 hours, with an inlet pressure of 8-12 kPa, and the aeration membrane being a dense or microporous breathable membrane.

[0014] The sequencing batch reaction under the above-mentioned intermittent membrane aeration conditions can provide an anaerobic and anoxic / aerobic alternating environment for the biofilm, thereby enriching polyphosphate-accumulating bacteria (including denitrifying polyphosphate-accumulating bacteria) in the outermost layer, thus solving the technical problem of how to provide an anaerobic and anoxic / aerobic alternating environment for the outer biofilm to enrich polyphosphate-accumulating bacteria.

[0015] In step S2 above, the intensity and duration of aeration scouring below the membrane module at the end of each sequential batch reaction cycle can be determined based on the yield stress of the outermost biofilm combined with the aeration scouring shear force derived from computational fluid dynamics. This allows for precise detachment of the proliferating biofilm that needs to be removed. For membrane-aerated biofilms treating typical municipal wastewater, the aeration scouring intensity below the membrane module, calculated based on the aeration rate per unit reactor cross-section, is generally 10-120 m³ / h. 3 / m 2 The aeration and flushing time is generally 10-120 seconds per hour. Additionally, the settling and drainage time can be 5-30 minutes. Perforated aeration pipes are installed below the membrane module for aeration and flushing, and these pipes are connected to the flushing aeration pump.

[0016] At the end of the reaction, a short-term aeration flushing method is used below the membrane module to remove the polyphosphate-accumulating bacteria that have absorbed excessive phosphorus from the outermost layer, which are then discharged through sedimentation, ultimately achieving the biological phosphorus removal function.

[0017] The treatment method of the present invention can be carried out using a reaction system based on a membrane aerated biofilm. The reaction system includes an inlet tank, a membrane aerated biofilm reactor, and an outlet tank. The inlet tank and the outlet tank are connected to the membrane aerated biofilm reactor through an inlet pipe and an outlet pipe, respectively. The inner cavity of the membrane module of the membrane aerated biofilm reactor is connected to a membrane aeration pump. A perforated aeration pipe is installed below the membrane module of the membrane aerated biofilm reactor and is connected to a flushing aeration pump. A circulation pipe is provided on the membrane aerated biofilm reactor. An inlet pump, an outlet pump, and a circulation pump are respectively installed on the inlet pipe, the outlet pipe, and the circulation pipe.

[0018] Furthermore, a time controller can be set to control the start and stop of the influent pump and effluent pump so that wastewater is pumped into and out of the membrane aeration biofilm reactor at preset times; the start and stop of the circulation pump can be controlled to achieve uniform mixing inside the membrane aeration biofilm reactor at preset times; the start and stop of the membrane aeration pump can be controlled to achieve intermittent membrane aeration working mode at preset times; and the start and stop of the flushing aeration pump can be controlled to achieve aeration flushing and stripping of the outermost phosphorus-rich membrane aeration biofilm at preset times.

[0019] In the processing method of the present invention, a complete operating cycle can consist of the following steps:

[0020] 1) The inlet pump pumps the wastewater in the inlet tank to the membrane aerated biofilm reactor and fills it to a predetermined volume. The start and stop of the inlet pump are controlled by a time controller.

[0021] 2) The membrane aeration pump pumps air into the inner cavity of the membrane module of the membrane aeration biofilm reactor. The air flows along the length of the membrane module, and the oxygen in the air passes through the membrane wall and enters the biofilm on the outside of the membrane to start the reaction process. The remaining exhaust gas is discharged into the atmosphere through the pipe. The air pressure is adjusted by the valve, and the start and stop of the membrane aeration pump is controlled by the time controller to realize the intermittent membrane aeration working mode. At the same time, the circulation pump is turned on to promote mixing and mass transfer inside the membrane aeration biofilm reactor.

[0022] 3) When the reaction is about to end, turn on the flushing aeration pump to perform short-term air flushing through the perforated aeration pipe to peel off the outermost phosphorus-rich aerated biofilm. Adjust the flow rate through the valve and control the start and stop of the flushing aeration pump through the time controller.

[0023] 4) After the reaction is complete, stop the aeration pump and circulation pump, and let the membrane aerated biofilm reactor stand still.

[0024] 5) Turn on the effluent pump to empty the membrane aerated biofilm reactor. Control the start and stop of the effluent pump using a timer.

[0025] The implementation of this invention has at least the following advantages:

[0026] The treatment method of this invention, using a sequencing batch membrane aeration biofilm under intermittent membrane aeration conditions, achieves removal rates of 85-95% for chemical oxygen demand (COD), 80-90% for total nitrogen (TNO), and 70-90% for total phosphorus (TP) in typical municipal wastewater. Compared to traditional membrane aeration biofilms, the treatment method of this invention significantly improves the TNO removal rate. Compared to traditional inert carrier biofilms, the treatment method of this invention significantly improves the TNO removal rate. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of a membrane-aerated biofilm; where: (a) is a cross-sectional view, and (b) is a schematic diagram of anisotropic mass transfer;

[0029] Figure 2 This is a schematic diagram of a reaction system based on a membrane-aerated biofilm.

[0030] Figure 3 The graph shows the change in phosphorus concentration with anaerobic (i.e., non-membrane aeration) time in Example 1.

[0031] Figure 4 This is a graph showing the changes in COD concentration and COD removal rate in the effluent of Example 1 over operating time.

[0032] Figure 5 The graph shows the changes in the concentrations of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the effluent of Example 1 over the operating time.

[0033] Figure 6 This is a graph showing the changes in ammonia nitrogen and total inorganic nitrogen removal rates over operating time in Example 1.

[0034] Figure 7 The graph shows the changes in phosphorus concentration and phosphorus removal rate in the effluent of Example 1 over time.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1: Inlet tank; 2: Inlet pump; 3: Circulation pump; 4: Outlet tank; 5: Valve; 6: Membrane module; 7: Pressure gauge; 8: Membrane aeration pump; 9: Outlet pump; 10: Perforated aeration pipe; 11: Flushing aeration pump. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] Combination Figure 2 As shown, the method for simultaneous removal of carbon, nitrogen, and phosphorus from wastewater in this embodiment employs a membrane aeration biofilm reaction system. The entire reaction system includes an inlet tank 1, a membrane aeration biofilm reactor, and an outlet tank 4. The inlet tank 1 and the outlet tank 4 are connected to the membrane aeration biofilm reactor via inlet and outlet pipes, respectively. The inner cavity of the membrane module 6 of the membrane aeration biofilm reactor is connected to the membrane aeration pump 8. A perforated aeration pipe 10 is installed below the membrane module 6 of the membrane aeration biofilm reactor, and the perforated aeration pipe 10 is connected to the flushing aeration pump 11. A circulation pipe is provided on the membrane aeration biofilm reactor, and an inlet pump 2, an outlet pump 9, and a circulation pump 3 are respectively installed on the inlet pipe, outlet pipe, and circulation pipe. As needed, valves 5 and pressure gauges 7 are installed on the corresponding pipes, and the start and stop of the inlet pump 2, outlet pump 9, circulation pump 3, membrane aeration pump 8, and flushing aeration pump 11 are controlled by a time controller.

[0042] The steps of the method for simultaneously removing carbon, nitrogen, and phosphorus from wastewater in this embodiment are as follows:

[0043] S1: The wastewater is sent to the membrane aeration biofilm reactor and carried out in a sequencing batch reaction under intermittent membrane aeration conditions;

[0044] S2: At the end of the reaction, the outermost phosphorus-rich membrane aerated biofilm is peeled off by aeration and flushing from below the membrane module, and then left to stand and drain.

[0045] Specifically, a complete operating cycle consists of the following steps:

[0046] 1) The inlet pump 2 pumps the wastewater in the inlet tank 1 to the membrane aerated biofilm reactor and fills it to a predetermined volume (90-95% of the full volume). The start and stop of the inlet pump 2 are controlled by the time controller.

[0047] 2) Start the circulation pump 3 to promote mixing and mass transfer inside the membrane aeration biofilm reactor, and start the anaerobic phosphorus release reaction stage (i.e., the non-membrane aeration stage); after the anaerobic phosphorus release is completed, start the membrane aeration pump 8 to pump air into the inner cavity of the membrane module 6 of the membrane aeration biofilm reactor. The air flows along the length of the membrane module 6, and the oxygen in the air passes through the membrane wall and enters the biofilm on the outside of the membrane, starting the synchronous denitrification, carbon removal and phosphorus absorption reaction process. The remaining tail gas is discharged into the atmosphere through the pipe. The inlet pressure is adjusted by the valve 5, and the start and stop of the membrane aeration pump 8 are controlled by the time controller to realize the intermittent aeration working mode.

[0048] 3) When the synchronous denitrification, carbon removal and phosphorus absorption reaction is about to end, turn on the flushing aeration pump 11 to perform short-term air flushing through the perforated aeration pipe 10 to peel off the outer layer of proliferating biofilm. Adjust the flow rate through valve 5 and control the start and stop of flushing aeration pump 11 through time controller.

[0049] 4) After the entire reaction is completed, stop the membrane aeration pump 8, the flushing aeration pump 11 and the circulation pump 3, and let the membrane aeration biofilm reactor stand still.

[0050] 5) Turn on the effluent pump 9 to empty the membrane aerated biofilm reactor. Control the start and stop of the effluent pump 9 through the time controller.

[0051] After a complete running cycle is completed, the next complete running cycle will begin using the same method described above.

[0052] The above reaction system and method were used to treat wastewater with a low carbon-to-nitrogen ratio (COD 1100 mg / L, ammonia nitrogen 220 mg / L, total phosphorus 9 mg / L and 18 mg / L), with an operating cycle of 24 hours. First, the anaerobic (i.e., non-membrane aeration) phosphorus release time was determined; for example... Figure 3 As shown, in the first 80 minutes, the phosphorus concentration in the wastewater decreased instead of increasing. This may be because the influent and biofilm still contain a certain concentration of dissolved oxygen, and the biofilm absorbs phosphorus in the early stage of influent, thus reducing the phosphorus concentration in the water. From 120 minutes onwards, the phosphorus content in the wastewater began to rise, indicating that the anaerobic phosphorus release stage had begun. After 200 minutes, the rate of increase in phosphorus concentration slowed down, and the phosphorus concentration rose very slowly after reaching 11 mg / L. Considering the subsequent aerobic stage, the anaerobic time in this embodiment was determined to be 4 hours. Therefore, the operating parameters for one cycle of 24 hours in this embodiment were determined as follows: Influent (5 minutes) → Reaction (4 hours of non-membrane aeration followed by 20 hours of membrane aeration, influent pressure 10 kPa) → Aeration flushing and stripping of biofilm (intensity 40 m 3 / m2 / h, duration 30s) → let it stand and drain (5min).

[0053] Figure 4 The results show that the COD removal rate during operation was above 90% in the effluent, fluctuating between 50-100 mg / L, indicating a good carbon removal effect.

[0054] Figure 5 and Figure 6 The results show that the effluent ammonia nitrogen concentration was 13-45 mg / L, the effluent nitrite nitrogen concentration was stable at 0-1 mg / L, the effluent nitrate nitrogen concentration was stable at less than 2 mg / L, and the total inorganic nitrogen removal rate was higher than 80%, indicating a good denitrification effect.

[0055] Figure 7 The phosphorus removal performance was as follows: During cycles 1-14, the influent phosphorus concentration was 9 mg / L. The effluent phosphorus concentration fluctuated and decreased over time, reaching 2 mg / L in cycle 14, achieving a phosphorus removal rate of 80% and a phosphorus removal capacity of 7 mg / L. To further investigate the phosphorus removal effect of the reaction system, the load was doubled (i.e., the influent phosphorus concentration increased to 18 mg / L). The phosphorus removal effect temporarily worsened after the concentration increase, with the actual phosphorus removal capacity decreasing from 7 mg / L to 5 mg / L. The total phosphorus content in the biofilm before and after the increase in influent phosphorus concentration was measured to be 38.8 mg / gVSS and 95 mg / gVSS, respectively. The ratio of these two values ​​was close to 1:2.25, not significantly different from the ratio of the influent phosphorus concentration. The phosphorus removal rate gradually increased after 15-20 cycles, and then slowed down when it reached about 40%. After reaching 45%, it only fluctuated slightly and stopped rising. At this time, the phosphorus removal capacity reached 8.5 mg / L, which was about 20% higher than the low influent phosphorus concentration, indicating that the phosphorus removal capacity of polyphosphate-accumulating bacteria has been further improved.

[0056] Example 2

[0057] In this embodiment, the aeration and scouring intensity below the membrane removal module is increased to 60m. 3 / m 2 Except for / h, the rest is the same as in Example 1.

[0058] The results of 30 cycles showed that the average removal rates of chemical oxygen demand (COD), total inorganic nitrogen (TNI), and total phosphorus (TP) in this embodiment for treating wastewater with a low carbon-to-nitrogen ratio (COD 1100 mg / L, ammonia nitrogen 220 mg / L, and total phosphorus 9 mg / L) were 94%, 90%, and 88%, respectively. These figures were all further improved compared to Example 1, indicating that enhanced aeration and flushing to remove the outermost biofilm helps to improve the removal efficiency of carbon, nitrogen, and phosphorus.

[0059] Example 3

[0060] This implementation is used to treat typical low carbon-to-nitrogen ratio municipal wastewater (chemical oxygen demand 260 mg / L, ammonia nitrogen 31 mg / L, total nitrogen 37 mg / L, total phosphorus 5 mg / L). Except for the different operating parameters within one cycle, it is the same as Example 1.

[0061] The operating parameters for one cycle in this embodiment are determined as follows: Influent (5 min) → Reaction (first 1 h without membrane aeration, then 3 h with membrane aeration, influent pressure 12 kPa) → Aeration flushing and stripping of biofilm (intensity 50 m 3 / m 2 / h, duration 60s) → let it stand and drain (5min).

[0062] The results of 100 cycles show that the average removal rates of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus in this embodiment for treating typical low C / N ratio municipal wastewater are 91%, 95%, 92%, and 90%, respectively.

[0063] Compare with Example 1

[0064] Example 3 uses a continuous aeration sequencing batch membrane aeration biofilm treatment to treat typical low C / N ratio municipal wastewater (COD 260 mg / L, ammonia nitrogen 31 mg / L, total nitrogen 37 mg / L, total phosphorus 5 mg / L). The operating parameters for one cycle (4 hours) of this control example are determined as follows: influent (5 min) → reaction (continuous membrane aeration for 4 hours, influent pressure 12 kPa) → aeration flushing and biofilm stripping (intensity 50 m). 3 / m 2 / h, duration 60s) → let it stand and drain (5min).

[0065] The results of 100 cycles showed that the removal rates of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus in the typical low C / N ratio municipal wastewater treated in Example 3 were only 87%, 78%, 75%, and 32%, respectively.

[0066] Compare with Example 2

[0067] Using an inert carrier (K-1 packing material) biofilm to treat typical low C / N ratio municipal wastewater (COD 260 mg / L, ammonia nitrogen 31 mg / L, total nitrogen 37 mg / L, total phosphorus 5 mg / L) under intermittent aeration sequential batch operation conditions, the operating parameters for one cycle (4 hours) of this control example were determined as follows: Influent (5 min) → Reaction (no aeration for 1 hour, followed by 3 hours of aeration, with dissolved oxygen controlled to be no less than 2 mg / L) → Aeration flushing to remove biofilm (intensity 50 m) 3 / m 2 / h, duration 60s) → let it stand and drain (5min).

[0068] The results of 100 cycles showed that the removal rates of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus in the typical low C / N ratio municipal wastewater treated in Example 3 were only 82%, 74%, 55%, and 80%, respectively.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simultaneous removal of carbon, nitrogen and phosphorus in polluted wastewater based on membrane aeration biofilm, characterized in that, The reaction system is based on a membrane aeration biofilm and comprises a water inlet tank, a membrane aeration biofilm reactor and a water outlet tank, the water inlet tank and the water outlet tank are communicated with the membrane aeration biofilm reactor through a water inlet pipe and a water outlet pipe respectively, the inner cavity of the membrane assembly of the membrane aeration biofilm reactor is communicated with a membrane aeration pump, a perforated aeration pipe is arranged below the membrane assembly of the membrane aeration biofilm reactor and is communicated with a scouring aeration pump, a circulation pipe is arranged on the membrane aeration biofilm reactor, a water inlet pump, a water outlet pump and a circulation pump are arranged on the water inlet pipe, the water outlet pipe and the circulation pipe respectively; The treatment method comprises the following steps: S1: sending the sewage to the membrane aeration biofilm reactor and performing a sequencing batch reaction under intermittent membrane aeration conditions; S2: at the end of the reaction, stripping the phosphorus-rich membrane aeration biofilm of the outermost layer of the over-phosphorus-accumulating bacteria under aeration scouring, and then standing and draining water; The aeration membrane is a dense or microporous gas-permeable membrane, the intermittent membrane aeration conditions are: first not aeration for 1 h and then aeration for 3 h, and the inlet air pressure is 12 kPa; The aeration scouring is performed by a perforated aeration pipe with a gas outlet diameter of 4-6 mm, an aeration amount of 50 m 3 / m 2 / h during the aeration scouring, and an aeration scouring time of 60 s.

2. The treatment method according to claim 1, characterized in that, The sewage is low-carbon-nitrogen-ratio sewage, and the ratio of the chemical oxygen demand to the total nitrogen content of the low-carbon-nitrogen-ratio sewage is 5-8.

3. The treatment method according to claim 1, characterized in that, The running time of each cycle of the sequencing batch reaction is 6-24 h.

4. The treatment method according to claim 1, characterized in that, The water inlet time is 5-30 min.

5. The treatment method according to claim 1, characterized in that, The standing and draining water time is 5-30 min.

6. The treatment method of claim 1, wherein The starting and stopping of the water inlet pump and the water outlet pump are controlled by a time controller to pump the sewage into and out of the membrane aeration biofilm reactor at a preset time, the starting and stopping of the circulation pump are controlled to realize the mixing uniformity of the membrane aeration biofilm reactor at a preset time, the starting and stopping of the membrane aeration pump are controlled to realize the intermittent membrane aeration working mode at a preset time, and the starting and stopping of the scouring aeration pump are controlled to realize the stripping of the phosphorus-rich membrane aeration biofilm of the outermost layer of the over-phosphorus-accumulating bacteria at a preset time.

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