An automatic cleaning system for membrane modules of a marine MBR domestic sewage treatment device

Abstract

The present invention relates to an automatic cleaning system for membrane components of a marine MBR domestic sewage treatment device, wherein a membrane component is placed in a membrane cabinet, and the membrane cabinet is connected to a coagulation-aeration flushing membrane device, a sludge cabinet, and an offline chemical cleaning device through pipelines, and the membrane component is connected to a reverse air washing device and an online reverse chemical cleaning device through pipelines; an air pump is connected to a coagulation-aeration flushing membrane device, a reverse air washing device, an online reverse chemical cleaning device, and an offline chemical cleaning device through a gas distributor; a membrane cabinet discharge valve is provided at the bottom of the membrane cabinet, and a membrane cabinet low liquid level is provided on the membrane cabinet. The present invention can form large-size flocs of organic matter that is easy to block the membrane by coagulation-aeration flushing the membrane surface, and precipitate and remove them in a sedimentation cabinet by air lift, so that they are not easy to cause clogging of membrane pores, and at the same time, aeration flushing can use bubbles to shake and flush the surface of the membrane element, so that pollutants are not easy to stay on the surface of the membrane element, reducing the possibility of clogging the membrane.

Description

Technical Field

[0001] The invention relates to an automatic cleaning system for a membrane component of a sewage treatment device, in particular to an automatic cleaning system for a membrane component of a marine MBR domestic sewage treatment device. Background Art

[0002] The development of membrane separation water treatment technology began in the 1950s. Since the 1960s, membrane separation technology has been applied in large-scale industry. By the 1980s, microfiltration, ultrafiltration and reverse osmosis membrane separation water treatment technologies have been applied in large-scale industry worldwide. More than 90% of ships in developed countries in Europe and the United States use biochemical sewage treatment devices. In 2000, Hamworthy Company in the United Kingdom produced the first membrane bioreactor treatment device for ships, and completed the actual ship test in 2001. Since then, companies in the United States, Germany, China and other countries have developed marine domestic sewage treatment devices based on membrane biochemical method that meet the requirements of MEPC.227 (64) resolution.

[0003] The decrease in permeate flux caused by the accumulation of retained solutes in membrane separation and membrane fouling is the main obstacle to the promotion of marine membrane separation water treatment technology. The decrease in permeate flux leads to reduced production capacity and production stability. The factors that cause membrane fouling in membrane biochemical treatment devices are mainly divided into: particulate matter in sewage, soluble organic matter (mainly soluble microbial products, extracellular polymers, microorganisms), and inorganic substances (Fangang Meng, So-Ryong Chae. et al. Recent advances in membrane bioreactors (MBRs): Membrane fouling and membrane material [J]. Water research, 2009, 43: 1489-1512). In order to ensure the smooth operation of membrane separation water treatment, the membrane assembly must be backwashed, chemically cleaned, and even replaced, which requires the crew to operate. The crew's inaccurate judgment of the status of the membrane assembly leads to delayed membrane washing, which shortens the service life of the membrane, and premature membrane cleaning increases the crew's operating workload.

[0004] In land-based projects, aeration fans are often used to flush the membrane surface, so that pollutants are not easily adhered to the membrane surface and the pollution to the membrane is reduced. This method is effective in reducing membrane pollution within a certain organic matter concentration and particulate matter concentration. However, in the actual use of marine domestic sewage treatment equipment, in order to ensure that the effluent meets the standards, the membrane assembly may be turned on and used when the front-end biochemical operation is not good. If the organic matter and particulate matter that cause membrane clogging are not removed, the membrane assembly will be blocked faster. In the membrane cleaning technology, the membrane assembly permeate is usually used to hydraulically backwash the membrane element. Although this method can achieve a better cleaning effect, it also saves resources. However, this method reduces the final system water production. When the water production demand remains unchanged, the number of membrane elements needs to be increased and the device volume needs to be increased. It is also necessary to add a pump to reverse the produced water to the membrane element, which increases energy consumption and system complexity. Under ship conditions, the device needs to be as small as possible and the operation is simplified, which is very unfavorable. Summary of the invention

[0005] The purpose of the present invention is to provide an automatic cleaning system for membrane components of a marine MBR domestic sewage treatment device. The use of this cleaning technology can extend the offline cleaning cycle, reduce the frequency of high-concentration offline chemical membrane washing, and reduce the workload of operators in daily work.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present invention is: an automatic cleaning system for membrane components of a marine MBR domestic sewage treatment device, comprising a sludge tank, an air pump, a gas distributor, a membrane cabinet, a membrane component, a coagulation-aeration membrane flushing device, a reverse air washing device, an online reverse chemical cleaning device, an offline chemical cleaning device, and an electronic control system, wherein the membrane component is placed in the membrane cabinet, and the membrane cabinet is connected to the coagulation-aeration membrane flushing device, the sludge tank, and the offline chemical cleaning device through pipelines, respectively, and the membrane component is connected to the reverse air washing device and the online reverse chemical cleaning device through pipelines; the air pump is connected to the coagulation-aeration membrane flushing device, the reverse air washing device, the online reverse chemical cleaning device, and the offline chemical cleaning device through a gas distributor; a membrane cabinet discharge valve is provided at the bottom of the membrane cabinet, and a membrane cabinet low liquid level, a membrane cabinet middle liquid level and a UV254 sensor are provided on the membrane cabinet.

[0007] Furthermore, the coagulation-aeration flushing membrane device includes a flocculant medicine box, a dosing pump, an air lift valve, a gas flow meter, an air lift device, a membrane aeration valve, a gas flow meter, and a membrane aeration pipe. The flocculant medicine box is connected to the membrane assembly through the dosing pump, and the air inlet end of the air lift device is connected to the gas distributor and the air pump through the gas flow meter and the air lift valve; the membrane aeration pipe is arranged at the bottom of the membrane assembly and is connected to the gas distributor and the air pump through the gas flow meter and the membrane aeration valve; the reverse air washing device includes a gas backwashing electric valve, a backwashing pipeline, and a pressure sensor. The backwashing pipeline is connected to the gas distributor and the air pump through the gas backwashing electric valve, wherein the backwashing pipeline is a water production pipeline of the membrane assembly; The online reverse chemical cleaning device includes a chemical backwashing solenoid valve, a backwashing pipeline, a membrane cleaning medicine box, a pressure sensor, a membrane component water production electric valve, a suction pump, and a liquid flow meter. The backwashing pipeline is connected to the membrane cleaning medicine box through the chemical backwashing solenoid valve, and is connected to the gas distributor and the air pump through the gas backwashing electric valve. The backwashing pipeline is connected to the membrane component water production pipeline, and the membrane component water production pipeline is connected to the suction pump through the membrane component water production electric valve. The water outlet of the suction pump is provided with a liquid flow meter, and the membrane component water production pipeline is provided with a pressure sensor; the offline chemical cleaning device includes an offline chemical cleaning solenoid valve and a membrane cleaning medicine box. The membrane cleaning medicine box is connected to the membrane cabinet through the offline chemical cleaning solenoid valve.

[0008] A method for automatically cleaning a membrane assembly of a marine MBR domestic sewage treatment device, using the automatic cleaning system for the membrane assembly, includes four methods: coagulation-aeration flushing of the membrane surface, reverse air washing, reverse online chemical cleaning, and offline chemical cleaning. The specific steps are as follows:

[0009] 1) In normal operation, the dosing pump adds coagulant to the membrane tank to coagulate the organic matter in the sewage, and the flocs and sewage mixed liquid are lifted to the sludge tank by the air stripper at a certain reflux ratio for sedimentation;

[0010] 2) During normal operation, the coagulation-aeration flushing membrane device is used to flush and clean the membrane assembly surface with gas;

[0011] 3) During normal operation, after the suction pump is started and stopped a certain number of times, the membrane assembly is reversely air-washed using a reverse air-washing device;

[0012] 4) When the pressure of the pressure sensor reaches the set value, during the low-peak period of system use, the membrane assembly is cleaned online by using an online reverse chemical cleaning device;

[0013] 5) Within a set time period, when the number of times that the pressure sensor pressure reaches the set value exceeds the set value, an offline chemical cleaning device is used to perform offline chemical cleaning on the membrane assembly.

[0014] Furthermore, the coagulant in step 1) is a drug having a coagulant effect such as PAC, and the reflux ratio of the mixed liquid is 0 to 300%, which is specifically controlled by a gas flow meter.

[0015] Furthermore, in step 2), the coagulation-aeration flushing membrane device performs gas flushing and cleaning on the membrane surface by placing an aeration pipeline under the membrane assembly to flush and clean the membrane surface with gas at a certain gas flow rate, wherein the gas flow rate per unit membrane area is 8L / m 2 , which is specifically controlled by the gas flow meter.

[0016] Furthermore, in step 3), the reverse gas washing is implemented by starting and stopping the suction pump for 4 minutes and stopping for 1.5 minutes, and gas backwashing is performed every 30 times. The backwashing pipeline is the membrane component water production pipeline. The backwashing time is 1min10s, and the backwashing pressure is less than 0.025MPa. The chemical backwashing solenoid valve and the water production electric valve need to be closed during gas backwashing.

[0017] Further, in step 4), when the pressure of the pressure sensor 16 reaches the set value -0.045MPa, the system is used in the off-peak period from 12:00 at night to 4:00 in the morning, and the sodium hypochlorite solution with an effective chlorine content of 0.3 parts per million is used for online reverse chemical cleaning, and the duration is 2 hours; the online reverse chemical cleaning in step 4) is implemented by closing the membrane module water production electric valve, closing the membrane module aeration valve, closing the air lift valve, opening the chemical backwashing solenoid valve, and a certain concentration of alkaline chemical cleaning agent flows back into the membrane element along the membrane module water production pipeline. When the pressure of the pressure sensor is 0.020MPa, the chemical backwashing solenoid valve is closed. After soaking for 2 hours, the membrane module water production electric valve is opened, the suction pump is turned on, and the chemical agent inside the membrane module is extracted and discharged. The suction pump is stopped after the membrane cabinet liquid level reaches a low level; after the online reverse chemical cleaning is completed, the membrane module is restored to the normal working mode.

[0018] Furthermore, the setting condition in step 5) is that within 7 days after the pressure sensor pressure reaches the set value -0.045 MPa for the first time, when the pressure sensor pressure reaches -0.045 MPa three times, the membrane assembly needs to be chemically cleaned offline.

[0019] Furthermore, the offline chemical cleaning in step 5) is implemented by stopping the operation of the domestic sewage treatment device. The membrane assembly is first subjected to chemical backwashing in step 4). After the backwashing is completed, the offline chemical cleaning solenoid valve is opened, and the prepared chemical agent is placed in the membrane cabinet to soak the membrane assembly. First, the membrane cabinet is soaked in acid for 2 hours and the liquid in the membrane cabinet is drained, and then the membrane cabinet is soaked in alkaline solution for 2 hours and the liquid in the membrane cabinet is drained; after the offline reverse chemical cleaning is completed, the recovery device and the membrane assembly are in normal working mode.

[0020] Furthermore, the acid solution is a mixture of citric acid, oxalic acid or one or more other liquids, and the pH value is controlled at 2 to 3. The alkali solution is a sodium hypochlorite solution with an effective concentration of 1%.

[0021] The beneficial effects of the present invention are:

[0022] The present invention provides a membrane component automatic cleaning system suitable for a marine MBR domestic sewage treatment device, which adopts a combined membrane automatic cleaning technology of coagulation-aeration flushing membrane surface, reverse gas washing, reverse online chemical cleaning and offline chemical cleaning. Organic matter that is easy to block the membrane can be formed into large-particle flocs by coagulation-aeration flushing of the membrane surface, and precipitated and removed in a sedimentation tank by air lift, so that it is not easy to cause blockage of the membrane pores. At the same time, aeration flushing can use bubbles to shake and flush the surface of the membrane element, so that pollutants are not easy to stay on the surface of the membrane element, reducing the possibility of membrane blockage. During the suction interval, gas backwashing is used to backwash the pollutants in the membrane pores, and the pollutants can be blown out of the membrane pores. Using a low-concentration alkaline liquid to perform chemical backwashing of membrane pollution during the low-peak period of device use can react with organic pollution in the membrane pores to make the pollutants leave the membrane material. The above method can reduce the amount of membrane cleaning agent and the number of offline chemical cleaning times, improve the utilization rate of the membrane component, and reduce the workload of operators. The offline chemical cleaning of the technology of the present invention does not require the membrane assembly to be disassembled from the domestic sewage treatment device, and the offline chemical cleaning can be performed in situ, reducing the difficulty of cleaning. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the automatic cleaning device of the membrane module of the present invention;

[0024] Figure 2 It is a schematic diagram of the implementation process of the present invention;

[0025] Description of the marks in the accompanying drawings: 1. Sludge tank, 2. Flocculant medicine box, 3. Dosing pump, 4. Air pump, 5. Gas distributor, 6. Gas lift valve, 7. Gas flow meter, 8. Gas lift, 9. Membrane aeration valve, 10. Gas flow meter, 11. Membrane aeration tube, 12. Gas backwash electric valve, 13. Membrane cleaning medicine box, 14. Chemical backwash solenoid valve, 15. Off-line chemical cleaning solenoid valve, 16. Pressure sensor, 17. Water production electric valve, 18. Suction pump, 19. Liquid flow meter, 20. Membrane assembly, 21. UV254 sensor, 22. Electronic control system, 23. Membrane cabinet discharge valve, 24. Membrane cabinet low liquid level, 25. Membrane cabinet middle liquid level. DETAILED DESCRIPTION

[0026] In order to make the advantages and technical solutions of the present invention more clear and explicit, the present invention is described in detail below in conjunction with specific embodiments.

[0027] like Figure 1As shown, the present invention proposes an automatic cleaning system for membrane components of a marine MBR domestic sewage treatment device, comprising a sludge tank 1, an air pump 4, a gas distributor 5, a membrane cabinet, a membrane component 20, a coagulation-aeration flushing membrane device, a reverse air washing device, an online reverse chemical cleaning device, an offline chemical cleaning device, and an electronic control system.

[0028] The membrane assembly 20 is placed in the membrane cabinet, and the membrane cabinet is connected to the coagulation-aeration membrane flushing device, the sludge cabinet 1, and the offline chemical cleaning device through pipelines. The membrane assembly 20 is connected to the reverse air washing device and the online reverse chemical cleaning device through pipelines. The air pump 4 is connected to the coagulation-aeration membrane flushing device, the reverse air washing device, the online reverse chemical cleaning device, and the offline chemical cleaning device through the gas distributor 5. A membrane cabinet discharge valve 23 is provided at the bottom of the membrane cabinet. The membrane cabinet is provided with a membrane cabinet low liquid level 24, a membrane cabinet middle liquid level 25, and a UV254 sensor 21.

[0029] The coagulation-aeration flushing membrane device includes a flocculant medicine box 2, a dosing pump 3, an air lift valve 6, a gas flow meter 7, an air lifter 8, a membrane aeration valve 9, a gas flow meter 10, and a membrane aeration tube 11. The flocculant medicine box 2 is connected to the membrane assembly 20 through the dosing pump 3, and the coagulant is added to the membrane cabinet through the dosing pump 3 to coagulate the particulate matter and dissolved organic matter in the sewage to convert them into macromolecular substances. The air inlet end of the air lifter 8 is connected to the gas distributor 5 and the air pump 4 through the gas flow meter 7 and the air lift valve 6. The flocs and sewage mixed liquid in the membrane cabinet are lifted to the sludge cabinet 1 by the air lifter 8 at a certain reflux ratio for precipitation, thereby reducing the concentration of the flocs and the sewage mixed liquid. The membrane aeration pipe 11 is arranged at the bottom of the membrane assembly 20, and is connected to the gas distributor 5 and the air pump 4 through the gas flow meter 10 and the membrane aeration valve 9. During the normal use of the membrane assembly, the membrane surface is aerated and flushed to prevent pollutants from adhering to the membrane surface. During the interval of suction, gas backwashing is performed to backwash the pollutants in the membrane pores out of the membrane pores, so that the membrane pores return to normal, reduce membrane blockage, and extend the membrane service time.

[0030] The reverse gas washing device comprises a gas backwashing electric valve 12 and a backwashing pipeline. The backwashing pipeline is connected to the gas distributor 5 and the air pump 4 through the gas backwashing electric valve 12. The backwashing pipeline is a water production pipeline of the membrane assembly.

[0031] The online reverse chemical cleaning device includes a chemical backwashing solenoid valve 14, a backwashing pipeline, a membrane cleaning medicine box 13, a pressure sensor 16, a membrane module water production electric valve 17, a suction pump 18, and a liquid flow meter 19. The backwashing pipeline is connected to the membrane cleaning medicine box 13 through the chemical backwashing solenoid valve 14, and is connected to the gas distributor 5 and the air pump 4 through the gas backwashing electric valve 12, and the backwashing pipeline is connected to the membrane module water production pipeline, and the membrane module water production pipeline is connected to the suction pump 18 through the membrane module water production electric valve 17, and the water outlet of the suction pump 18 is provided with a liquid flow meter 19, and the membrane module water production pipeline is provided with a pressure sensor 16.

[0032] The off-line chemical cleaning device comprises an off-line chemical cleaning solenoid valve 15 and a membrane cleaning medicine box 13. The membrane cleaning medicine box 13 is connected to the membrane cabinet via the off-line chemical cleaning solenoid valve 15.

[0033] Preferably, the membrane assembly 20 is a soft film membrane, a flat membrane or a hollow fiber membrane.

[0034] Preferably, the gas source is an air pump provided with the device or compressed air provided on board.

[0035] Preferably, under normal working conditions, the pressure of the membrane assembly 20 is less than -0.045 MPa under the set constant flow state, and the start and stop of the membrane assembly 20 is controlled by the membrane cabinet liquid level meter and the suction pump start and stop ratio.

[0036] Preferably, the low liquid level of the membrane cabinet needs to be 200 mm higher than the height of the membrane assembly, and the liquid level in the membrane cabinet needs to be 500 mm higher than the low liquid level of the membrane cabinet.

[0037] Preferably, the start and stop of the membrane assembly is preferentially controlled by the membrane cabinet liquid level.

[0038] Preferably, the membrane aeration pipe below the membrane assembly is a PVC, PVDF or ABS pipe with cross-openings at an angle of 45° downward and an interval of 50 mm.

[0039] like Figure 2 As shown, a method for automatically cleaning a membrane assembly of a marine MBR domestic sewage treatment device adopts the automatic cleaning system of the membrane assembly of the present invention, including four methods of coagulation-aeration flushing of the membrane surface, reverse air washing, reverse online chemical cleaning and offline chemical cleaning. The specific steps are as follows:

[0040] 1) In normal operation, the dosing pump 3 adds coagulant to the membrane tank to coagulate the organic matter in the sewage, and the flocs and sewage mixed liquid are lifted to the sludge tank 1 by the air stripper 8 at a certain reflux ratio for precipitation;

[0041] 2) During normal operation, the coagulation-aeration membrane flushing device is used to perform gas flushing and cleaning on the surface of the membrane assembly 20;

[0042] 3) During normal operation, after the suction pump 18 is started and stopped a certain number of times, the membrane assembly 20 is reversely air-washed using a reverse air-washing device;

[0043] 4) When the pressure of the pressure sensor 16 reaches the set value, during the low-peak period of system use, the membrane assembly 20 is subjected to online reverse chemical cleaning using an online reverse chemical cleaning device;

[0044] 5) Within a set time period, when the number of times that the pressure of the pressure sensor 16 reaches the set value exceeds the set value, an offline chemical cleaning device is used to perform offline chemical cleaning on the membrane assembly 20.

[0045] Preferably, the coagulant in step 1) is a drug with coagulation effect such as PAC. The mixed liquid reflux ratio is 0-300%, which is specifically controlled by a gas flow meter.

[0046] Preferably, the gas flushing and cleaning of the membrane surface in step 2) is achieved by placing an aeration pipeline under the membrane assembly to flush and clean the membrane surface with a certain gas flow rate. The gas flow rate per unit membrane area is 8L / m 2 , which is specifically controlled by the gas flow meter.

[0047] Preferably, the reverse gas washing in step 3) is implemented by starting and stopping the suction pump for 4 minutes and stopping for 1.5 minutes, performing gas backwashing every 30 times, the backwashing pipeline is the membrane module water production pipeline, the backwashing time is 1 minute 10 seconds, and the backwashing pressure is less than 0.025 MPa. The chemical backwashing solenoid valve and the water production electric valve need to be closed during gas backwashing.

[0048] Preferably, in step 4), when the pressure of the pressure sensor 16 reaches the set value -0.045 MPa, an online reverse chemical cleaning is performed using a sodium hypochlorite solution with an effective chlorine content of 0.3 parts per million during the off-peak period of system use from 12:00 a.m. to 4:00 a.m. for 2 hours;

[0049] Preferably, the online reverse chemical cleaning in step 4) is implemented by closing the membrane module water production electric valve, closing the membrane module aeration valve, closing the air lift valve, opening the chemical backwashing electromagnetic valve, and a certain concentration of alkaline chemical cleaning agent flows reversely into the membrane element along the membrane module water production pipeline. When the pressure of the pressure sensor is 0.020MPa, the chemical backwashing electromagnetic valve is closed. After soaking for 2 hours, the membrane module water production electric valve is opened, and the suction pump is turned on to extract and discharge the chemical agent inside the membrane module. The suction pump is stopped after the membrane cabinet liquid level reaches a low level. After the online reverse chemical cleaning is completed, the membrane module is restored to the normal working mode.

[0050] Preferably, the alkaline chemical cleaning agent is sodium hypochlorite, and the effective chlorine content is 0.03%.

[0051] Preferably, the setting condition in step 5) is that within 7 days after the pressure sensor pressure reaches the set value -0.045 MPa for the first time, when the pressure sensor pressure reaches -0.045 MPa three times, the membrane assembly needs to be chemically cleaned offline.

[0052] Preferably, the offline chemical cleaning in step 5) is implemented by stopping the operation of the domestic sewage treatment device. The membrane assembly is first subjected to chemical backwashing in step 4). After the backwashing is completed, the offline chemical cleaning solenoid valve is opened, and the prepared chemical agent is placed in the membrane cabinet to soak the membrane assembly. First, the membrane cabinet is soaked in acid solution for 2 hours and the liquid in the membrane cabinet is drained, and then the membrane cabinet is soaked in alkaline solution for 2 hours and the liquid in the membrane cabinet is drained. After the offline reverse chemical cleaning is completed, the recovery device and the membrane assembly are in normal working mode.

[0053] Preferably, considering the storage conditions on board, the acid solution is a mixture of citric acid, oxalic acid or one or more of them, and the pH is controlled at 2 to 3. The alkali solution is a sodium hypochlorite solution with an effective concentration of 1%.

Claims

1. An automatic cleaning system for membrane modules of a marine MBR domestic sewage treatment device, characterized in that: The invention comprises a sludge tank, an air pump, a gas distributor, a membrane tank, a membrane assembly, a coagulation-aeration membrane flushing device, a reverse air washing device, an online reverse chemical cleaning device, an offline chemical cleaning device, and an electronic control system. The membrane assembly is placed in the membrane tank, and the membrane tank is connected to the coagulation-aeration membrane flushing device, the sludge tank, and the offline chemical cleaning device through pipelines. The membrane assembly is connected to the reverse air washing device and the online reverse chemical cleaning device through pipelines. The air pump is connected to the coagulation-aeration membrane flushing device and the reverse air washing device through a gas distributor. , online reverse chemical cleaning device, offline chemical cleaning device; a membrane cabinet discharge valve is provided at the bottom of the membrane cabinet, and a membrane cabinet low liquid level, a membrane cabinet middle liquid level and a UV254 sensor are provided on the membrane cabinet; the coagulation-aeration membrane flushing device includes a flocculant medicine box, a dosing pump, an air lift valve, a gas flow meter, an air lift device, a membrane aeration valve, a gas flow meter, and a membrane aeration pipe. The flocculant medicine box is connected to the membrane assembly through the dosing pump, and the air inlet end of the air lift device is connected to the gas distributor and the air pump through the gas flow meter and the air lift valve; the membrane aeration The tube is arranged at the bottom of the membrane assembly, and is connected to the gas distributor and the air pump through a gas flowmeter and a membrane aeration valve; the reverse gas washing device comprises a gas backwashing electric valve, a backwashing pipeline, and a pressure sensor, and the backwashing pipeline is connected to the gas distributor and the air pump through a gas backwashing electric valve, wherein the backwashing pipeline is a water production pipeline of the membrane assembly; the online reverse chemical cleaning device comprises a chemical backwashing solenoid valve, a backwashing pipeline, a membrane cleaning medicine box, a pressure sensor, a membrane assembly water production electric valve, a suction pump, and a liquid flowmeter, the backwashing pipeline is connected to the membrane cleaning medicine box through a chemical backwashing solenoid valve, and is connected to the gas distributor and the air pump through a gas backwashing electric valve, and the backwashing pipeline is connected to the membrane assembly water production pipeline, the membrane assembly water production pipeline is connected to the suction pump through the membrane assembly water production electric valve, the water outlet of the suction pump is provided with a liquid flowmeter, and the membrane assembly water production pipeline is provided with a pressure sensor; the offline chemical cleaning device comprises an offline chemical cleaning solenoid valve and a membrane cleaning medicine box, and the membrane cleaning medicine box is connected to the membrane cabinet through an offline chemical cleaning solenoid valve.

2. A method for automatically cleaning membrane modules of a marine MBR domestic sewage treatment device, using the automatic cleaning system for membrane modules according to claim 1, characterized in that: There are four methods: coagulation-aeration flushing membrane surface, reverse air washing, reverse online chemical cleaning and offline chemical cleaning. The specific steps are as follows: 1) In normal operation, the dosing pump adds coagulant to the membrane tank to coagulate the organic matter in the sewage, and the flocs and sewage mixed liquid are lifted to the sludge tank by the air stripper at a certain reflux ratio for sedimentation; 2) During normal operation, the coagulation-aeration flushing membrane device is used to flush and clean the membrane assembly surface with gas; 3) During normal operation, after the suction pump is started and stopped a certain number of times, the membrane assembly is reversely air-washed using a reverse air-washing device; 4) When the pressure of the pressure sensor reaches the set value, during the low-peak period of system use, the membrane assembly is cleaned online by using an online reverse chemical cleaning device; 5) Within a set time period, when the number of times that the pressure sensor pressure reaches the set value exceeds the set value, an offline chemical cleaning device is used to perform offline chemical cleaning on the membrane assembly.

3. The automatic cleaning method of the membrane assembly according to claim 2, characterized in that: The coagulant in step 1) is PAC, and the mixed liquid reflux ratio is 0 to 300%.

4. The automatic cleaning method of the membrane assembly according to claim 2, characterized in that: In step 2), the coagulation-aeration flushing membrane device performs gas flushing and cleaning on the membrane surface by placing an aeration pipeline under the membrane assembly to flush and clean the membrane surface with gas at a certain gas flow rate, wherein the gas flow rate per unit membrane area is 8L / m 2 , controlled by a gas flow meter.

5. The automatic cleaning method of membrane assembly according to claim 2, characterized in that: In step 3), the reverse gas washing is implemented by starting and stopping the suction pump for 4 minutes and stopping for 1.5 minutes, and gas backwashing is performed every 30 times. The backwashing pipeline is the membrane component water production pipeline. The backwashing time is 1min10s, and the backwashing pressure is less than 0.025MPa. The chemical backwashing solenoid valve and the water production electric valve need to be closed during gas backwashing.

6. The automatic cleaning method of membrane assembly according to claim 2, characterized in that: In step 4), when the pressure of the pressure sensor (16) reaches the set value -0.045MPa, an online reverse chemical cleaning is performed using a sodium hypochlorite solution with an effective chlorine content of 0.03 parts per million during the low-peak period of system use from 12:00 midnight to 4:00 a.m., for a duration of 2 hours; the online reverse chemical cleaning in step 4) is implemented by closing the membrane module water production electric valve, closing the membrane module aeration valve, closing the air lift valve, opening the chemical backwashing solenoid valve, and a certain concentration of alkaline chemical cleaning agent flows reversely into the membrane element along the membrane module water production pipeline. When the pressure of the pressure sensor is 0.020MPa, the chemical backwashing solenoid valve is closed; after soaking for 2 hours, the membrane module water production electric valve is opened, the suction pump is turned on, the chemical agent inside the membrane module is extracted and discharged, and the suction pump is stopped after the membrane cabinet liquid level reaches a low level; after the online reverse chemical cleaning is completed, the membrane module is restored to a normal working mode.

7. The automatic cleaning method of membrane assembly according to claim 2, characterized in that: The setting condition in step 5) is that within 7 days after the pressure sensor pressure reaches the set value -0.045 MPa for the first time, when the pressure sensor pressure reaches -0.045 MPa three times, the membrane assembly needs to be chemically cleaned offline.

8. The automatic cleaning method of membrane assembly according to claim 2, characterized in that: The offline chemical cleaning in step 5) is implemented by stopping the operation of the domestic sewage treatment device; firstly, the membrane assembly is chemically backwashed in step 4), and after the backwashing is completed, the offline chemical cleaning solenoid valve is opened, and the prepared chemical agent is placed in the membrane cabinet to soak the membrane assembly; first, the membrane cabinet is soaked with acid for 2 hours and the liquid in the membrane cabinet is drained, and then the membrane cabinet is soaked with alkaline solution for 2 hours and the liquid in the membrane cabinet is drained; after the offline reverse chemical cleaning is completed, the device and the membrane assembly are restored to the normal working mode.

9. The automatic cleaning method of the membrane module according to claim 8, characterized in that: The acid solution is a mixture of one or more of citric acid and oxalic acid, and the pH value is controlled at 2-3. The alkali solution is a sodium hypochlorite solution, and the effective concentration is 1%.

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