High-efficiency off-line cleaning method for reverse osmosis membrane microbial contamination

Abstract

This invention discloses a highly efficient offline cleaning method for microbial fouling of reverse osmosis membranes, belonging to the field of reverse osmosis membrane cleaning technology. The method includes: firstly, pre-treating the reverse osmosis membrane; then, placing it in a cleaning water tank containing nutrients for carbon source circulation; anaerobic fermentation; and finally, enhancing biofilm loosening through an aerobic-anaerobic environment. The membrane is then cleaned offline under high pressure, followed by alkaline washing, acid washing, and rinsing. The method of this invention achieves a reverse osmosis membrane standardized permeate flow recovery rate >80% and a pressure differential increase rate >1.8 Pa / m² after cleaning. 2 / h; After cleaning using this method, the standardized permeate flow rate of the reverse osmosis membrane recovered to >97%, and the rate of pressure differential increase decreased to 1.4 Pa / m 2 The method of this invention is more membrane-friendly and has wide applicability.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane cleaning technology, and more specifically to a highly efficient offline cleaning method for microbial contamination of reverse osmosis membranes. Background Technology

[0002] Reverse osmosis membranes, as semi-permeable polymeric separation materials, purify water or separate substances by trapping impurities such as salt, organic matter, and microorganisms, and are widely used in water treatment. Prevention and cleaning of reverse osmosis membrane fouling are core tasks in its operation and maintenance. Membrane fouling is categorized into inorganic fouling (scaling), organic fouling, and microbial fouling. While there are mature methods for preventing and cleaning inorganic and organic fouling, prevention is always the primary approach for microbial fouling. Once it occurs, only intensive cleaning using traditional methods can be employed, often with poor results, leading to severe degradation of membrane performance and threatening its lifespan. Among reverse osmosis membrane fouling types, microbial fouling is the most difficult to clean, and cleaning results are often poor, making effective restoration difficult.

[0003] Microbial contamination is complex. First, it is inseparable from both inorganic and organic contamination. Inorganic contamination creates conditions for biofilm adhesion, while organic contamination provides substrates and matrices for biofilms. Second, microorganisms generally develop drug resistance. After long-term operation, the microorganisms in the system have developed resistance to non-oxidizing bactericides, making sterilization more difficult. Third, intensified cleaning reduces membrane lifespan. If a stronger concentration of the agent (the upper limit in the product instructions) is used, it will inevitably affect the membrane lifespan, and the contamination curve will be steeper after cleaning, shortening the cleaning cycle.

[0004] Existing research reports on reverse osmosis membrane cleaning mainly include:

[0005] Application No. 200710063148.X discloses a method for cleaning reverse osmosis membranes, which first cleans the reverse osmosis membranes with an alkaline cleaning agent, then cleans them with an acidic cleaning agent, and finally cleans them with a bactericide.

[0006] Application No. 201811510851.5 discloses a bactericide for cleaning reverse osmosis membranes, comprising by weight percentage: 30%-45% hydroxyethyl hexahydrotriazine, 5%-10% isothiazolinone, 4%-10% glutaraldehyde, 20-30% isopropanol, with the balance being deionized water.

[0007] The former of the aforementioned prior art studies the cleaning process of reverse osmosis membranes, while the latter studies the bactericides used in cleaning reverse osmosis membranes.

[0008] Industry research on reverse osmosis membrane cleaning largely focuses on physicochemical methods such as reagents and reagent concentrations. The core idea is to use reagents to remove contaminants, kill microorganisms, and perform strong alkaline cleaning. Technological advancements often involve developing new reagents or increasing reagent concentrations, but the core remains the same: killing contaminants and physicochemical removal.

[0009] This shows that the existing technology needs further improvement. Summary of the Invention

[0010] The purpose of this invention is to provide an efficient offline cleaning method for microbial contamination of reverse osmosis membranes. The method first involves adding a small amount of carbon source to anaerobically culture the microbial contaminants, thereby loosening the biofilm through anaerobic gas-producing fermentation. Then, a short-term aerobic environment is provided, causing the microorganisms to alternate between aerobic and anaerobic states for a short period of time, further enhancing the loosening of the biofilm. Finally, high-pressure cleaning is combined to improve the cleaning effect.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A highly efficient offline cleaning method for microbial contamination of reverse osmosis membranes, comprising the following steps:

[0013] a. Cleaning pretreatment: Remove the reverse osmosis membrane from the reverse osmosis membrane module as the membrane to be cleaned, and measure its wet weight W1 before cleaning; place the membrane to be cleaned with a wet weight of W1 for a period of time to allow all the residual water to flow out, and weigh it after 3 hours as W2; add water to the newly activated reverse osmosis membrane and run it for 1 hour, place it for a period of time to allow all the residual water to flow out, and weigh it after 3 hours as W0. W0 is used as the initial value for comparison.

[0014] b. Nutrient preparation: Sodium acetate carbon source and nitrate are prepared in the cleaning water tank. The conditions in the cleaning water tank that are conducive to gas production and fermentation are set as follows: COD concentration 10-50mg / L, pH 7.5-8.2, and nitrate concentration 3-8mg / L.

[0015] c. Carbon source circulation: Place the membrane to be cleaned with a wet weight of W2 on the offline reverse osmosis membrane cleaning device. This device is connected to the cleaning water tank containing nutrients in step b. After circulating for 20-40 minutes, take it out and let it stand for 3 hours to allow all the residual water to flow out.

[0016] d. Remove the membrane obtained in step c and allow it to stand. This standing time is used for microbial fermentation, gas production, loosening, and membrane peeling. The standing time is related to the degree of membrane fouling and should be determined according to WRL.

[0017] d1. Anaerobic gas-producing fermentation: The membrane obtained in step c is sealed and the internal oxygen is removed, so that the membrane is in a closed state and at this time the membrane is in an anaerobic environment; through anaerobic gas-producing fermentation, the biofilm formed by microbial contamination is loosened.

[0018] d2. Provide an aerobic-anaerobic environment to enhance biofilm loosening: Spray nutrients once every 12 hours to prevent the membrane from completely dehydrating. When spraying, remove the membrane's sealing wrapping to provide an aerobic-anaerobic environment to enhance biofilm loosening. The spraying time is 50-60 seconds.

[0019] The formula for calculating WRL is shown in equation (1):

[0020] (1);

[0021] When WRL ≤ 0.1, the settling time is 24 hours; when WRL ≥ 0.5, the settling time is 72 hours; when 0.1 < WRL < 0.5, the settling time is... ;

[0022] e. Offline high-pressure cleaning: The membrane obtained after step d is placed in another reverse osmosis membrane offline cleaning device for high-pressure rinsing; then it is washed with alkali, acid and rinsed, and the wet weight after cleaning is W3; the membrane with a wet weight of W3 is left for a period of time to allow all the residual water to flow out, and the weight is W4 after 3 hours.

[0023] f. Cleaning Evaluation: If the membrane's standardized permeate flow recovery rate after cleaning is >97%, or If the cleaning is successful, then step BE is repeated.

[0024] In the above-mentioned efficient offline cleaning method for microbial contamination of reverse osmosis membranes, in step e, during high-pressure cleaning, the inlet water pressure is ≥1MPa or greater than or equal to 70% of the membrane's allowable pressure; the recovery rate is ≤15%; the number of high-pressure flushes is ≥3 times, the flushing time for each flush is ≥10min, and the flushing interval is 5min.

[0025] In the above-mentioned efficient offline cleaning method for microbial contamination of reverse osmosis membranes, in step e, the alkaline cleaning agent is sodium hydroxide, and the concentration of the alkaline cleaning agent is 80% of its recommended concentration.

[0026] In the above-mentioned efficient offline cleaning method for microbial contamination of reverse osmosis membranes, in step e, the acid cleaning agent is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 80% of its recommended concentration.

[0027] In the above-mentioned efficient offline cleaning method for microbial contamination of reverse osmosis membranes, step e involves alkaline washing, acid washing, and then rinsing for 10-20 minutes.

[0028] The above-mentioned efficient offline cleaning method for microbial contamination of reverse osmosis membranes results in a pressure differential increase rate of <1.4 Pa / m after cleaning. 2 •h.

[0029] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0030] 1) This invention proposes a highly efficient offline cleaning method for microbial contamination of reverse osmosis membranes. The core technology lies in utilizing biological principles. First, microbial contaminants are cultivated, followed by gas-generating fermentation under anaerobic conditions, enhanced biofilm loosening under aerobic-anaerobic conditions, offline high-pressure cleaning, acid and alkali washing, and rinsing. This reduces the use of chemical cleaning agents, minimizes damage to the membrane itself, minimizes the loss of standardized desalination rate, and doubles the cleaning cycle from 30 days to 60 days. The average service life of the membrane exceeds 7 years.

[0031] 2) The method of this invention is particularly suitable for cleaning reverse osmosis membranes contaminated with microorganisms. It can significantly improve the cleaning effect for biocontaminated reverse osmosis membranes. After cleaning with traditional chemical cleaning methods, the standardized permeate flow recovery rate of the reverse osmosis membrane is >80%, and the pressure difference increase rate after cleaning is >1.8 Pa / m. 2 / h; After cleaning using this method, the standardized permeate flow rate of the reverse osmosis membrane recovered to >97%, and the rate of pressure differential increase decreased to 1.4 Pa / m 2 / h and below.

[0032] 3) Compared with existing physical and chemical cleaning methods, the present invention can reduce the amount of reagents added, and the method is more suitable for membrane cleaning and has a wide range of applications. Detailed Implementation

[0033] This invention proposes an efficient offline cleaning method for microbial contamination of reverse osmosis membranes. To make the advantages and technical solutions of this invention clearer and more explicit, the invention will be further described below with reference to specific embodiments.

[0034] The technical terms used in this invention are specifically explained as follows:

[0035] Standardized permeate flow recovery rate: The ratio of the standardized permeate flow of the reverse osmosis membrane after cleaning to the standardized permeate flow of the reverse osmosis membrane during initial operation, %; The higher the value, the better the cleaning effect.

[0036] Pressure differential increase rate after cleaning: The rate of increase in membrane pressure differential during reverse osmosis permeate operation after cleaning, in Pa / m 2 / h; the lower this value, the better the cleaning effect; (membrane pressure difference from the start of the cleaning cycle to the end of the cleaning cycle - membrane pressure difference at the start of the cleaning cycle) / cleaning cycle interval / membrane area, which reflects the membrane fouling rate after cleaning and is also an important indicator for measuring the cleaning effect.

[0037] Wet weight: Considering that reverse osmosis cannot completely dehydrate and dry, the wet weight method is adopted. Let the water in the reverse osmosis membrane flow out naturally. When it is ensured that no water flows out from all directions, the weight of the reverse osmosis membrane is measured, which is the wet weight. Generally, let it stand for 3 hours, and change the placement direction of the reverse osmosis membrane every hour to ensure that no water flows out from all directions before weighing.

[0038] The rate of pressure differential increase after cleaning is an important indicator for evaluating the cleaning effect of reverse osmosis membranes, measured in Pa / m³. 2 •h. The technical concept of this invention: In actual operation, due to continuous offline cleaning of reverse osmosis membranes, it was found that membranes of the same batch and with the same level of contamination showed significant differences in cleaning effects, which attracted the attention of the R&D team. Through further analysis of the differences and repeated experimental verification, the technical solution of this invention was finally formed. According to common knowledge in the art, traditional cleaning mainly involves chemical cleaning, the core idea of ​​which is to forcibly peel off the contaminated membrane after sterilization, which has limited effectiveness. This invention breaks away from the conventional thinking of "adding more chemicals if the effect is poor" in traditional microbial contamination cleaning. Instead, it takes the opposite approach, first conducting targeted cultivation of microorganisms, using microbial fermentation to loosen the attached contaminants, and then performing cleaning, achieving significantly better results.

[0039] The present invention will be further described below with reference to specific embodiments.

[0040] Example 1:

[0041] The reverse osmosis membrane, BW30XFR-400 / 34, has a new wet weight of 14 kg (W0 = 14 kg) and has been operating for 7 years in the first stage of a wastewater desalination plant. The designed permeate flux is 16.57 L / m³. 2 The operating rate is [per hour], with an inlet water pressure between 1.0 and 1.45 MPa. The raw water is effluent from a wastewater treatment plant, and the pollution is mainly organic matter and microbial contamination. Before cleaning, the wet weight W2 = 23.5 kg, indicating relatively severe pollution.

[0042] Nutrient preparation: Sodium acetate carbon source and nitrate are prepared in the cleaning water tank. The conditions in the cleaning water tank that are conducive to gas-producing fermentation are set as follows: COD concentration 10-50 mg / L, pH>7.5, nitrate concentration 3-8 mg / L; Carbon source circulation: The membrane to be treated is placed in the cleaning water tank containing nutrients and circulated for 20-40 minutes, then removed and left to stand for 3 hours to allow all residual water to flow out;

[0043] Standing: Anaerobic gas-producing fermentation: The membrane is sealed and the internal oxygen is removed; the membrane is in a closed state, and at this time the membrane is in an anaerobic environment; the biofilm formed by microbial contamination is loosened through anaerobic gas-producing fermentation; an aerobic-anaerobic environment is provided to enhance the loosening of the biofilm: nutrients are sprayed once every 12 hours to prevent the membrane from being completely dehydrated, and an aerobic-anaerobic environment is provided to enhance the loosening of the biofilm. The spraying time is 5-10 seconds; the WRL calculation formula is shown in formula (1):

[0044] (1);

[0045] Calculations show that when WRL ≥ 0.5 in this example, the settling time is 72 hours. Offline high-pressure cleaning is employed: the membrane obtained after settling is placed in an offline cleaning device for high-pressure rinsing; subsequently, it is obtained through alkaline washing, acid washing, and rinsing.

[0046] Comparative Example 1-1:

[0047] The membrane was from the same group as the one in Example 1, and the contamination was the same. Before cleaning, the wet weight W2 was 23.5 kg, indicating severe contamination.

[0048] Cleaning method: The membrane to be treated was left to stand for 24 hours, and then placed in an offline cleaning device for high-pressure rinsing, followed by alkaline washing, acid washing, and rinsing. Compared with Example 1, this method only involved standing, without adding nutrients, without airtight packaging, without providing an alternating anaerobic-aerobic environment, and with insufficient standing time.

[0049] Comparative Examples 1-2:

[0050] The membrane was from the same group as the one in Example 1, and the contamination was the same. Before cleaning, the wet weight W2 was 23.5 kg, indicating severe contamination.

[0051] Cleaning method: The membrane to be treated was left to stand for 72 hours, and then placed in an offline cleaning device for high-pressure rinsing, followed by alkaline washing, acid washing, and rinsing. Compared with Example 1, only standing was performed, without the addition of nutrients, airtight packaging, or provision of an alternating anaerobic-aerobic environment.

[0052] Comparative Examples 1-3:

[0053] The membrane was from the same group as the one in Example 1, and the contamination was the same. Before cleaning, the wet weight W2 was 23.5 kg, indicating severe contamination.

[0054] Cleaning method: Compared with Example 1, no nutrients were sprayed during the standing process, and a closed anaerobic environment was maintained at all times. No aerobic-anaerobic environment was provided, and all other conditions were the same.

[0055] Comparative Examples 1-4:

[0056] The membrane was from the same group as the one in Example 1, and the contamination was the same. Before cleaning, the wet weight W2 was 23.5 kg, indicating severe contamination.

[0057] Cleaning method: Compared with Example 1, the steps of settling, adding nutrients, sealing and wrapping, and providing alternating anaerobic-aerobic environment are omitted. Alkali washing, acid washing and rinsing are performed directly.

[0058] Table 1

[0059]

[0060] The above data represents the first membrane data for 5 groups of reverse osmosis systems, with 26 pressure vessels per group, totaling 130 membranes. Within each group, Comparative Examples 1-1, 1-2, and 1-3 each have 4 membranes, Comparative Example 1-4 has 6 membranes, and Example 1 has 8 membranes. In total, Comparative Examples 1-1, 1-2, and 1-3 each have 20 membranes, Comparative Example 1-4 has 30 membranes, and Example 1 has 40 membranes.

[0061] A comparison of Example 1 with Comparative Examples 1-1, 1-2, 1-3, and 1-4 in Table 1 reveals that the present invention significantly outperforms other methods in terms of standardized desalination rate, standardized membrane flux recovery rate, wet weight after cleaning, and pressure differential growth rate after cleaning. Comparative Examples 1-1 and 1-2 show that simple settling yields no significant difference in effect compared to Comparative Examples 1-4, indicating that simple settling alone cannot improve membrane cleaning performance. Comparative Example 1-3 is far superior to Comparative Example 1-2, highlighting the crucial role of nutrient-rich fermentation. However, Comparative Example 1-3 still lags behind Example 1, demonstrating that anaerobic alternation is also critical for improving the final membrane cleaning effect. Through extensive experimental research, this crucial method of microbial fermentation and anaerobic alternation—a method easily derived from simple thinking by those outside the field—was discovered, yielding superior results despite its unconventional approach.

[0062] Example 2:

[0063] The reverse osmosis membrane (domestic membrane) has been operating in the wastewater desalination plant for 3 years, currently in the first stage, first branch. The designed permeate flux is 16.11 L / m³. 2 The operating inlet water pressure is between 1.0 and 1.35 MPa per hour. The main contamination is microbial. The wet weight before cleaning, W2, was 19.8 kg, which is considered general contamination.

[0064] Nutrient preparation: Sodium acetate carbon source and nitrate are prepared in the cleaning water tank. The conditions in the cleaning water tank that are conducive to gas-producing fermentation are set as follows: COD concentration 10-50 mg / L, pH>7.5, nitrate concentration 3-8 mg / L; Carbon source circulation: The membrane to be treated is placed in the cleaning water tank containing nutrients and circulated for 20-40 minutes, then removed and left to stand for 3 hours to allow all residual water to flow out;

[0065] Settling: Anaerobic gas-producing fermentation: The membrane is sealed and oxygen is removed, creating an anaerobic environment. Anaerobic gas-producing fermentation loosens the biofilm formed by microbial contamination. An aerobic-anaerobic environment is provided to enhance biofilm loosening: Nutrients are sprayed every 12 hours to prevent complete dehydration and to provide an aerobic-anaerobic environment to enhance biofilm loosening; spraying time is 5-10 seconds. Settling time is 62 hours. Offline high-pressure cleaning: The settled membrane is placed in an offline cleaning device for high-pressure rinsing; then it is washed with alkali, acid, and rinsed to obtain the final product.

[0066] Comparative Example 2-1:

[0067] The membrane in this example is from the same group as the membrane in Example 2, and the contamination is the same. The wet weight W2 before cleaning is 19.8 kg, which is considered to be of general contamination.

[0068] Cleaning method: The membrane to be treated was left to stand for 24 hours, and then placed in an offline cleaning device for high-pressure rinsing, followed by alkaline washing, acid washing, and rinsing. Compared with Example 2, this method only involved standing, without adding nutrients, without airtight packaging, without providing an alternating anaerobic-aerobic environment, and with insufficient standing time.

[0069] Comparative Example 2-2:

[0070] The membrane in this example is from the same group as the membrane in Example 2, and the contamination is the same. The wet weight W2 before cleaning is 19.8 kg, which is considered to be of general contamination.

[0071] Cleaning method: The membrane to be treated was left to stand for 62 hours, and then placed in an offline cleaning device for high-pressure rinsing, followed by alkaline washing, acid washing, and rinsing. Compared with Example 2, only standing was performed, without the addition of nutrients, airtight packaging, or provision of an alternating anaerobic-aerobic environment.

[0072] Comparative Examples 2-3:

[0073] The membrane in this example is from the same group as the membrane in Example 2, and the contamination is the same. The wet weight W2 before cleaning is 19.8 kg, which is considered to be of general contamination.

[0074] Cleaning method: Compared with Example 2, no nutrients were sprayed during the standing process, and a closed anaerobic environment was maintained at all times. No aerobic-anaerobic environment was provided, and all other conditions were the same.

[0075] Comparative Examples 2-4:

[0076] The membrane in this example is from the same group as the membrane in Example 2, and the contamination is the same. The wet weight W2 before cleaning is 19.8 kg, which is considered to be of general contamination.

[0077] Cleaning method: Compared with Example 2, the steps of settling, adding nutrients, sealing and wrapping, and providing alternating anaerobic-aerobic environment are omitted. Alkali washing, acid washing and rinsing are performed directly.

[0078] Table 2

[0079]

[0080] A comparison of Example 2 with Comparative Examples 2-1, 2-2, 2-3, and 2-4 in Table 2 reveals that the present invention significantly outperforms other methods in terms of standardized desalination rate, standardized membrane flux recovery rate, wet weight after cleaning, and pressure differential growth rate after cleaning. Comparative Examples 2-1 and 2-2 show that simple settling yields no significant difference in effect compared to Comparative Example 2-4, indicating that simple settling alone cannot improve membrane cleaning performance. Comparative Example 2-3 is far superior to Comparative Example 2-2, highlighting the crucial role of nutrient-rich fermentation. However, Comparative Example 2-3 still lags behind Example 2, demonstrating that anaerobic alternation is also critical for improving the final membrane cleaning effect. Through extensive experimental research, this crucial method of microbial fermentation and anaerobic alternation—a method easily derived from simple thinking by those outside the field—was discovered, yielding superior results despite its unconventional approach.

[0081] Any parts not mentioned in this invention can be achieved by referring to existing technologies.

[0082] It should be noted that those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application should fall within the scope of protection claimed in this application.

Claims

1. A highly efficient offline cleaning method for microbial contamination of reverse osmosis membranes, characterized in that, The steps are as follows: a. Cleaning pretreatment: Remove the reverse osmosis membrane from the reverse osmosis membrane module as the membrane to be cleaned, and measure its wet weight W1 before cleaning; place the membrane to be cleaned with a wet weight of W1 for a period of time to allow all the residual water to flow out, and weigh it after 3 hours as W2; add water to the newly activated reverse osmosis membrane and run it for 1 hour, place it for a period of time to allow all the residual water to flow out, and weigh it after 3 hours as W0. W0 is used as the initial value for comparison. b. Nutrient preparation: Sodium acetate carbon source and nitrate are prepared in the cleaning water tank. The conditions in the cleaning water tank that are conducive to gas production and fermentation are set as follows: COD concentration 10-50mg / L, pH 7.5-8.2, and nitrate concentration 3-8mg / L. c. Carbon source circulation: Place the membrane to be cleaned with a wet weight of W2 on the offline reverse osmosis membrane cleaning device. This device is connected to the cleaning water tank containing nutrients in step b. After circulating for 20-40 minutes, take it out and let it stand for 3 hours to allow all the residual water to flow out. d. Remove the membrane obtained in step c and allow it to stand. This standing time is used for microbial fermentation, gas production, loosening, and membrane peeling. The standing time is related to the degree of membrane fouling and should be determined according to WRL. d1. Anaerobic gas-producing fermentation: The membrane obtained in step c is sealed and the internal oxygen is removed, so that the membrane is in a closed state and at this time the membrane is in an anaerobic environment; through anaerobic gas-producing fermentation, the biofilm formed by microbial contamination is loosened. d2. Provide an aerobic-anaerobic environment to enhance biofilm loosening: After step d1, spray nutrients once every 12 hours to prevent the membrane from completely dehydrating. When spraying, remove the membrane's sealing wrapping to provide an aerobic-anaerobic environment to enhance biofilm loosening. The spraying time is 50-60 seconds. The formula for calculating WRL is shown in equation (1): （1）； When WRL ≤ 0.1, the settling time is 24 hours; when WRL ≥ 0.5, the settling time is 72 hours; when 0.1 < WRL < 0.5, the settling time is... ; e. Offline high-pressure cleaning: The membrane obtained after step d is placed in another reverse osmosis membrane offline cleaning device for high-pressure rinsing; then it is washed with alkali, acid and rinsed, and the wet weight after cleaning is W3; the membrane with a wet weight of W3 is left for a period of time to allow all the residual water to flow out, and the weight is W4 after 3 hours. f. Cleaning Evaluation: If the membrane's standardized permeate flow recovery rate after cleaning is >97%, or If the cleaning is successful, then step BE is repeated.

2. The efficient offline cleaning method for microbial contamination of reverse osmosis membranes according to claim 1, characterized in that: In step e, during high-pressure cleaning, the inlet water pressure is ≥1MPa or greater than or equal to 70% of the membrane's allowable pressure; the recovery rate is ≤15%; the number of high-pressure rinsing cycles is ≥3, the rinsing time for each cycle is ≥10min, and the rinsing interval is 5min.

3. The efficient offline cleaning method for microbial contamination of reverse osmosis membranes according to claim 1, characterized in that: In step e, the alkaline cleaning agent is sodium hydroxide.

4. The efficient offline cleaning method for microbial contamination of reverse osmosis membranes according to claim 1, characterized in that: In step e, the pickling cleaning agent is a hydrochloric acid solution.

5. The efficient offline cleaning method for microbial contamination of reverse osmosis membranes according to claim 1, characterized in that: In step e, after alkaline washing and acid washing, rinse for 10-20 minutes.

6. The efficient offline cleaning method for microbial contamination of reverse osmosis membranes according to claim 1, characterized in that: The rate of pressure differential increase after cleaning is <1.4 Pa / m 2 •h.

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