Method for cleaning reverse osmosis membrane

Abstract

The invention relates to the technical field of reverse osmosis membrane assembly cleaning, and particularly discloses a cleaning method of a reverse osmosis membrane. The cleaning method of the reverse osmosis membrane comprises the following steps: (1) washing the reverse osmosis membrane with product water of a reverse osmosis membrane system until concentrated water in the membrane is fully replaced with the product water; (2) immersing the cleaned reverse osmosis membrane into an acidic cleaning solution, and controlling the pH value to be 2-2.5; (3) washing the reverse osmosis membrane with product water of a reverse osmosis membrane system until concentrated water in the membrane is fully replaced with the product water; (4) immersing the cleaned reverse osmosis membrane into an alkaline cleaning solution, and controlling the pH value to be 11.5-12; and (5) repeating the steps (1)-(4), and flushing the reverse osmosis membrane with the product water of the reverse osmosis membrane system until the concentrated water in the membrane is fully replaced with the product water. The prepared reverse osmosis membrane has good cleaning efficiency, the permeation flux and the desalination rate of the reverse osmosis membrane are recovered, and the service life of the reverse osmosis membrane is prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of reverse osmosis membrane assembly cleaning, and more specifically, to a reverse osmosis membrane cleaning method. Background Art

[0002] Reverse osmosis membrane is a semi-permeable reverse osmosis membrane used in the reverse osmosis process. It allows water molecules to pass through while blocking most impurities such as dissolved salts, organic matter, bacteria and viruses. It can effectively remove soluble solids, organic matter, microorganisms and viruses in water. It is widely used in water treatment fields such as seawater desalination, industrial wastewater treatment, and pure water preparation.

[0003] In order to ensure the long-term application of the reverse osmosis membrane, it is necessary to clean the reverse osmosis membrane regularly, because the reverse osmosis membrane will gradually accumulate various pollutants during use, such as inorganic salt scale, organic matter, microorganisms and colloids, etc. These pollutants will block the pores of the reverse osmosis membrane, reduce the permeability of the reverse osmosis membrane, and even cause permanent damage to the reverse osmosis membrane.

[0004] Existing cleaning methods usually use physical cleaning, using high-pressure water jet cleaning. The high-speed water flow generated by the high-pressure water gun washes away the dirt and loose contaminants on the surface of the reverse osmosis membrane. The operation is simple, but the cleaning efficiency is low and the chemical contaminants on the reverse osmosis membrane cannot be removed. Summary of the invention

[0005] In order to improve the problem of low efficiency in the physical cleaning process, the present application provides a method for cleaning a reverse osmosis membrane.

[0006] In a first aspect, the present application provides a method for cleaning a reverse osmosis membrane, using the following technical solution: A method for cleaning a reverse osmosis membrane comprises the following steps: (1) Use product water from the reverse osmosis membrane system to flush the reverse osmosis membrane. Use pulse flushing with a flushing temperature of 30-35°C and a flushing pressure difference of less than 0.1 bar / s until the concentrated water in the membrane is fully replaced by product water; (2) immersing the reverse osmosis membrane cleaned in step (1) in an acidic cleaning solution at a cleaning temperature of 33-38° C. for 9-10 h, and controlling the pH value to be 2-2.5; (3) Rinse the reverse osmosis membrane again with the product water of the reverse osmosis membrane system, using pulse flushing, the flushing temperature is 35-39°C, the flushing pressure difference is less than 0.1 bar / s, and flushing is performed until the concentrated water in the membrane is fully replaced by product water; (4) immersing the reverse osmosis membrane cleaned in step (3) in an alkaline cleaning solution at a cleaning temperature of 30-35° C. for 9-10 h, and controlling the pH value to be 11.5-12; (5) After repeating steps (1) to (4), the reverse osmosis membrane is flushed with product water from the reverse osmosis membrane system by pulse flushing at a flushing temperature of 30-35°C and a flushing pressure difference of <0.1 bar / s until the concentrated water in the membrane is fully replaced by product water.

[0007] By adopting the above technical solution, the reverse osmosis membrane is first rinsed with product water to remove pollutants such as suspended matter, colloids, and microorganisms on the membrane surface, reduce membrane pollution, and improve the permeability and stability of the membrane. Then the reverse osmosis membrane is cleaned with an acidic cleaning solution. Acid washing can dissolve inorganic salt scales on the surface of the reverse osmosis membrane, such as calcium carbonate, calcium sulfate, barium sulfate, etc. The accumulation of these inorganic salt scales on the surface of the reverse osmosis membrane will reduce the permeability of the reverse osmosis membrane; the acidic cleaning agent can also react with metal oxides such as manganese on the surface of the reverse osmosis membrane, converting them into soluble substances, thereby removing them from the surface of the reverse osmosis membrane. In addition, the acidic cleaning agent can also decompose silicate, phosphate and other scales on the surface of the reverse osmosis membrane. These scales will significantly reduce the flux and desalination rate of the reverse osmosis membrane. Acid cleaning can effectively restore the permeation flux and desalination rate of the reverse osmosis membrane and extend the service life of the reverse osmosis membrane.

[0008] Rinse the reverse osmosis membrane with product water again to remove the residual acidic cleaning solution and pollutants, and then use alkaline cleaning solution to clean. Alkaline cleaning can decompose organic pollutants on the surface of the reverse osmosis membrane, such as grease, protein, polysaccharide, etc. The accumulation of these organic substances on the surface of the reverse osmosis membrane will reduce the permeability of the reverse osmosis membrane; alkaline cleaning agents can also destroy the structure of microbial reverse osmosis membranes, kill bacteria, algae and other microorganisms attached to the surface of the reverse osmosis membrane, and prevent the formation of biofilms, because biofilms will significantly reduce the flux and desalination rate of the reverse osmosis membrane. In addition, alkaline cleaning agents can react with metal oxide inorganic substances such as iron and aluminum, converting them into soluble substances, thereby removing them from the surface of the reverse osmosis membrane, restoring the permeation flux and desalination rate of the reverse osmosis membrane, and extending the service life of the reverse osmosis membrane.

[0009] Repeat steps (1)-(4) again to improve the cleaning efficiency, and then rinse the reverse osmosis membrane with product water to effectively remove pollutants on the membrane surface, restore membrane performance, and prevent membrane scaling and membrane biofouling. Using the above cleaning method, a reverse osmosis membrane with good cleaning effect and long service life can be obtained.

[0010] Optionally, the acidic cleaning solution comprises the following raw materials: 8-10 parts of citric acid, 1-2 parts of fatty alcohol polyoxyethylene ether, 0.2-0.5 parts of benzotriazole and 95-98 parts of deionized water.

[0011] By adopting the above technical scheme, citric acid can form soluble complexes with metal ions such as calcium, magnesium, and iron in water, effectively remove hard scales such as calcium carbonate and calcium sulfate, and improve the permeability of reverse osmosis membranes; it can also destroy the structure of biological reverse osmosis membranes, inhibit the growth of microorganisms, reduce the pollution of biological reverse osmosis membranes to reverse osmosis membranes, and improve the cleaning effect of reverse osmosis membranes. Fatty alcohol polyoxyethylene ether has good emulsification and dispersibility, enhances the wettability of the cleaning agent on the surface of the reverse osmosis membrane, improves the penetration and diffusion ability of the cleaning agent, can effectively remove organic pollutants such as grease and protein on the surface of the reverse osmosis membrane, and improves the cleaning effect of the reverse osmosis membrane.

[0012] Citric acid and fatty alcohol polyoxyethylene ether have a synergistic effect. In the formula containing fatty alcohol polyoxyethylene ether, citric acid can ensure the stability of non-ionic surfactants and avoid degradation or performance degradation that may occur under different pH conditions; citric acid and fatty alcohol polyoxyethylene ether can also enhance the decontamination ability of detergents and improve the cleaning effect of cleaning fluids on grease and dirt. Benzotriazole can form a stable protective reverse osmosis membrane with the metal surface to prevent metal oxidation and corrosion, thereby reducing the release of metal ions and avoiding metal ion contamination of the reverse osmosis membrane. In addition, benzotriazole has certain bactericidal and antibacterial effects, can effectively remove biofilms, can react with organic matter, decompose or complex it, and restore the permeability and performance of the membrane.

[0013] The mixture of benzotriazole and fatty alcohol polyoxyethylene ether has a synergistic effect. Fatty alcohol polyoxyethylene ether has good emulsification, dispersing and cleaning properties, which can enhance the cleaning effect, while benzotriazole can provide additional anti-corrosion protection to prevent corrosion of the metal surface during the cleaning process. The mixture of citric acid and benzotriazole also has a synergistic effect, has good cleaning performance, and can effectively remove oxides and dirt on the metal surface. The acidity of citric acid can accelerate the dissolution of oxides on the metal surface, while benzotriazole can enhance the adsorption of the cleaning agent on the metal surface. The combination of the two can improve the cleaning efficiency and make the metal surface cleaner. The above components cooperate with each other to improve the cleaning effect of the acid cleaning solution.

[0014] Optionally, step (3) further includes adding pepsin to the product water of the reverse osmosis membrane system, adjusting the pH to 2-3 with hydrochloric acid, and flushing the reverse osmosis membrane.

[0015] By adopting the above technical solution, when jellyfish breaks out, it will cause great pressure on the cleaning of the reverse osmosis membrane device. Some jellyfish colloids or mucus will enter the reverse osmosis module and then adhere to the membrane surface, making it difficult to clean. Pepsin is added to the product water. On the one hand, the reverse osmosis membrane is prone to form a biofilm during long-term use, that is, the deposition of organic matter such as microorganisms, proteins, and fats on the membrane surface. Pepsin can effectively degrade protein, thereby destroying the structure of the biofilm, reducing the deposition of organic matter on the membrane surface, and improving the cleaning effect of the membrane. On the other hand, jellyfish are mainly composed of water and a small amount of protein, of which the protein part can be decomposed by pepsin. Pepsin can decompose jellyfish colloids or mucus, break the peptide bonds of the protein, and decompose it into smaller peptide segments and amino acids, which will help to flush out the product water and improve the cleaning efficiency.

[0016] Optionally, the dosage of pepsin is 1-2 U / mg based on the reaction system.

[0017] By adopting the above technical solution, the dosage of pepsin is further limited, the cleaning efficiency of pepsin is improved, membrane pollution is reduced, the flux and desalination rate of the membrane are improved, and the cleaning cycle of the membrane is extended.

[0018] Optionally, the mass ratio of the citric acid, fatty alcohol polyoxyethylene ether and benzotriazole is 5-8:1:0.2-0.4.

[0019] By adopting the above technical scheme, the mass ratio of citric acid, fatty alcohol polyoxyethylene ether and benzotriazole is further limited within a certain range. The combination of citric acid, fatty alcohol polyoxyethylene ether and benzotriazole has a synergistic effect and jointly improves the cleaning effect of the acidic cleaning agent. Citric acid has good cleaning performance and can effectively remove oxides and dirt on the metal surface. Fatty alcohol polyoxyethylene ether, as a surfactant, can improve the emulsification, dispersion and cleaning effect of the cleaning agent. Benzotriazole provides anti-corrosion protection for the metal surface to prevent corrosion of the metal during the cleaning process. The combination of the three can significantly improve the cleaning and anti-corrosion effects.

[0020] The acidity of citric acid accelerates the dissolution of oxides on the metal surface, fatty alcohol polyoxyethylene ether enhances the dispersibility of the cleaning agent, and benzotriazole enhances the adsorption of the cleaning agent on the metal surface. The synergistic effect of the three can significantly improve the cleaning efficiency. The combined use of the three can simultaneously remove inorganic and organic pollutants and metal oxides on the surface of the reverse osmosis membrane, improve the cleaning effect, and thus improve the performance and service life of the reverse osmosis membrane.

[0021] Optionally, the alkaline cleaning solution comprises the following raw materials: 10-12 parts of sodium hydroxide, 3-5 parts of tridecyl isobutyl alcohol polyoxyethylene ether, 1-2 parts of disodium ethylenediaminetetraacetate and 90-92 parts of deionized water.

[0022] By adopting the above technical scheme, sodium hydroxide can effectively decompose organic pollutants such as oil, protein, polysaccharide on the surface of the reverse osmosis membrane, improve the permeability of the reverse osmosis membrane, and destroy the membrane structure of microorganisms such as bacteria and algae attached to the surface of the reverse osmosis membrane, prevent the formation of biofilm, and improve the flux and desalination rate of the reverse osmosis membrane; sodium hydroxide can also react with metal oxides such as iron and aluminum, converting them into soluble substances, thereby removing them from the surface of the reverse osmosis membrane, restoring the permeability flux and desalination rate of the reverse osmosis membrane, and extending the service life of the reverse osmosis membrane.

[0023] Tridecyl isoalcohol polyoxyethylene ether can reduce the surface tension of water, enhance the wettability of the cleaning liquid on the reverse osmosis membrane surface, make the cleaning liquid more easily penetrate into the pores of the reverse osmosis membrane, and improve the cleaning effect and cleaning efficiency; it can also effectively disperse and emulsify organic pollutants such as grease, protein, and some inorganic pollutants on the surface of the reverse osmosis membrane, making these pollutants more easily carried away by the cleaning liquid. In addition, the mixture of tridecyl isoalcohol polyoxyethylene ether and sodium hydroxide has a synergistic effect. Tridecyl isoalcohol polyoxyethylene ether enhances the wettability of the cleaning liquid on the reverse osmosis membrane surface, making it easier for sodium hydroxide to penetrate into the pores of the reverse osmosis membrane, improving the decontamination ability and enhancing the cleaning effect.

[0024] Disodium ethylenediaminetetraacetate forms stable complexes with various metal ions (such as calcium, magnesium, iron, copper, etc.), thereby removing these metal ions, preventing them from forming deposits on the surface of the reverse osmosis membrane, reducing the permeability and desalination rate of the reverse osmosis membrane, and reducing their corrosion to the reverse osmosis membrane material, protecting the reverse osmosis membrane from damage. Sodium hydroxide has strong alkalinity and can decompose organic pollutants and grease, while disodium ethylenediaminetetraacetate can chelate metal ions. The combination of the two can enhance the decontamination ability of the cleaning solution and improve the cleaning efficiency. In addition, tridecyl isomeric alcohol polyoxyethylene ether can reduce the potential corrosiveness of sodium hydroxide to the reverse osmosis membrane material, while disodium ethylenediaminetetraacetate can prevent the corrosion of metal ions to the reverse osmosis membrane, and jointly protect the reverse osmosis membrane from damage.

[0025] Optionally, the mass ratio of the sodium hydroxide, tridecyl isobutyl alcohol polyoxyethylene ether and disodium ethylenediaminetetraacetate is 7-10:2-3:1.

[0026] By adopting the above technical scheme, the mass ratio of sodium hydroxide, tridecyl isomeric alcohol polyoxyethylene ether and disodium ethylenediaminetetraacetic acid is further limited within a certain range, thereby improving the cleaning efficiency of the alkaline cleaning solution. Tridecyl isomeric alcohol polyoxyethylene ether can reduce the surface tension of water, enhance the wettability of the cleaning solution on the surface of the reverse osmosis membrane, make it easier for sodium hydroxide and disodium ethylenediaminetetraacetic acid to penetrate into the pores of the reverse osmosis membrane, improve the decontamination ability, chelate metal ions, and enhance the cleaning effect. In addition, tridecyl isomeric alcohol polyoxyethylene ether can reduce the potential corrosion of sodium hydroxide to the reverse osmosis membrane material, while disodium ethylenediaminetetraacetic acid can prevent the corrosion of metal ions to the reverse osmosis membrane, thereby jointly protecting the reverse osmosis membrane from damage.

[0027] Sodium hydroxide is a strong alkaline substance that can effectively remove grease and organic dirt. Tridecyl isobutyl alcohol polyoxyethylene ether, as a nonionic surfactant, can improve the emulsification, dispersion and cleaning effects of the cleaning agent. Disodium ethylenediaminetetraacetic acid is a chelating agent that can combine with hardness ions (such as calcium and magnesium ions) in water to prevent the formation of scale and improve the stability of the cleaning agent.

[0028] Optionally, in step (1), step (3) and step (5), the flushing circulation flow rate is 1344-1728m 3 , the flushing pressure is 2.3-2.5bar.

[0029] By adopting the above technical solution, the circulation flow rate and flushing pressure are further limited to ensure that the cleaning liquid circulates in the membrane module at a sufficient speed, which helps to remove pollutants on the membrane surface and pores. Appropriate flow can enhance the shear force of the cleaning liquid and promote the loosening and removal of pollutants.

[0030] Limiting the flushing pressure can prevent excessive pressure from causing physical damage to the membrane components. During reverse osmosis membrane cleaning, excessive pressure may cause deformation or rupture of the membrane pores, affecting the performance and life of the membrane. Limiting the flushing pressure can ensure that the cleaning process is carried out within a safe range.

[0031] Optionally, in step (2), pulse flushing is used, the flushing pressure difference is less than 0.1 bar / s, and the flushing pressure is 2-2.5 bar.

[0032] By adopting the above technical solution, pulse flushing generates pulse flow by introducing periodic pressure fluctuations during the flushing process. This flow change can enhance the physical cleaning effect, help loosen and remove pollutants on the membrane surface and pores, and set the flushing pressure, which helps to quickly flush the reverse osmosis membrane and improve the membrane flushing efficiency.

[0033] Optionally, in step (4), pulse flushing is used, the flushing pressure difference is less than 0.1 bar / s, and the flushing pressure is 2.5-3 bar.

[0034] By adopting the above technical solutions, pulse flushing can shorten the cleaning cycle because the physical action of the pulse flow can accelerate the removal of pollutants, thereby reducing the time required for cleaning; by improving cleaning efficiency and reducing cleaning time, pulse flushing can reduce chemical consumption and energy costs during the cleaning process, thereby reducing the overall cleaning cost.

[0035] In summary, this application has the following beneficial effects: 1. In this application, the reverse osmosis membrane is rinsed with product water to remove pollutants such as suspended matter, colloids, and microorganisms on the membrane surface, reduce membrane pollution, and improve the permeability and stability of the membrane. The reverse osmosis membrane is then cleaned with an acidic cleaning solution. Acid cleaning can dissolve inorganic salt scale on the surface of the reverse osmosis membrane, such as calcium carbonate, calcium sulfate, barium sulfate, etc. The accumulation of these inorganic salt scales on the surface of the reverse osmosis membrane will reduce the permeability of the reverse osmosis membrane; the acidic cleaning agent can also react with metal oxides such as manganese on the surface of the reverse osmosis membrane, converting them into soluble substances, thereby removing them from the surface of the reverse osmosis membrane.

[0036] 2. In this application, alkaline cleaning solution is used for cleaning. Alkaline cleaning can decompose organic pollutants on the surface of the reverse osmosis membrane, such as grease, protein, polysaccharides, etc. The accumulation of these organic substances on the surface of the reverse osmosis membrane will reduce the permeability of the reverse osmosis membrane; alkaline cleaning agents can also destroy the structure of the microbial reverse osmosis membrane, kill bacteria, algae and other microorganisms attached to the surface of the reverse osmosis membrane, and prevent the formation of biofilms, because biofilms will significantly reduce the flux and desalination rate of the reverse osmosis membrane.

[0037] 3. In this application, when jellyfish break out, it causes great pressure on the cleaning of the reverse osmosis membrane device. Some jellyfish colloids or mucus enter the reverse osmosis module and then adhere to the membrane surface, making it difficult to clean. Pepsin is added to the product water. During long-term use, the reverse osmosis membrane is prone to form a biofilm, that is, the deposition of organic matter such as microorganisms, proteins, and fats on the membrane surface. Pepsin can effectively degrade protein, thereby destroying the structure of the biofilm, reducing the deposition of organic matter on the membrane surface, and improving the cleaning effect of the membrane. In addition, jellyfish are mainly composed of water and a small amount of protein, of which the protein part can be decomposed by pepsin. Pepsin can decompose jellyfish colloids or mucus, break the peptide bonds of the protein, and decompose it into smaller peptide segments and amino acids, which helps to flush out the product water and improve the cleaning efficiency. DETAILED DESCRIPTION Example

[0038] Example 1 A method for cleaning a reverse osmosis membrane comprises the following steps: (1) Use product water from the reverse osmosis membrane system to flush the reverse osmosis membrane using pulse flushing at a flushing temperature of 35°C and a flushing pressure difference of 0.05 bar / s until the concentrated water in the membrane is fully replaced by product water; (2) immersing the reverse osmosis membrane cleaned in step (1) in an acidic cleaning solution at a cleaning temperature of 38° C. for 9 h and controlling the pH value to be 2; (3) Rinse the reverse osmosis membrane again with the product water of the reverse osmosis membrane system by pulse flushing, with a flushing temperature of 35°C and a flushing pressure difference of 0.05 bar / s, until the concentrated water in the membrane is fully replaced by product water; (4) immersing the reverse osmosis membrane cleaned in step (3) in an alkaline cleaning solution at a cleaning temperature of 30° C. for 9 h and controlling the pH value to be 11.5; (5) After repeating steps (1) to (4), the reverse osmosis membrane is rinsed with product water from the reverse osmosis membrane system by pulse flushing at a flushing temperature of 30°C and a flushing pressure difference of 0.05 bar / s until the concentrated water in the membrane is fully replaced by product water.

[0039] The acid cleaning solution includes the following raw materials: 8 kg citric acid, 1 kg fatty alcohol polyoxyethylene ether, 0.2 kg benzotriazole and 95 kg deionized water.

[0040] The alkaline cleaning solution includes the following raw materials: 10 kg of sodium hydroxide, 3 kg of tridecyl isobutyl alcohol polyoxyethylene ether, 1 kg of disodium ethylenediaminetetraacetate and 90 kg of deionized water.

[0041] In step (1), step (3) and step (5), the flushing circulation flow rate is 1344m 3 , the flushing pressure is 2.3 bar.

[0042] In step (2), pulse flushing is used, the flushing pressure difference is 0.05 bar / s, and the flushing pressure is 2 bar.

[0043] In step (4), pulse flushing is adopted, the flushing pressure difference is 0.05 bar / s, and the flushing pressure is 2.5 bar.

[0044] Example 2 A method for cleaning a reverse osmosis membrane comprises the following steps: (1) Use product water from the reverse osmosis membrane system to flush the reverse osmosis membrane using pulse flushing at a flushing temperature of 30°C and a flushing pressure difference of 0.05 bar / s until the concentrated water in the membrane is fully replaced by product water; (2) immersing the reverse osmosis membrane cleaned in step (1) in an acidic cleaning solution at a cleaning temperature of 33° C. for 10 h and controlling the pH value to be 2.5; (3) Rinse the reverse osmosis membrane again with the product water of the reverse osmosis membrane system by pulse flushing, with a flushing temperature of 39°C and a flushing pressure difference of 0.05 bar / s, until the concentrated water in the membrane is fully replaced by product water; (4) immersing the reverse osmosis membrane cleaned in step (3) in an alkaline cleaning solution at a cleaning temperature of 35° C. for 10 h and controlling the pH value to be 12; (5) After repeating steps (1) to (4), the reverse osmosis membrane is flushed with product water from the reverse osmosis membrane system by pulse flushing at a flushing temperature of 35°C and a flushing pressure difference of 0.05 bar / s until the concentrated water in the membrane is fully replaced by product water.

[0045] The acid cleaning solution includes the following raw materials: 10 kg citric acid, 2 kg fatty alcohol polyoxyethylene ether, 0.5 kg benzotriazole and 98 kg deionized water.

[0046] The alkaline cleaning solution includes the following raw materials: 12 kg of sodium hydroxide, 3 kg of tridecyl isobutyl alcohol polyoxyethylene ether, 2 kg of disodium ethylenediaminetetraacetate and 92 kg of deionized water.

[0047] In step (1), step (3) and step (5), the flushing circulation flow rate is 1728m 3 , the flushing pressure is 2.5 bar.

[0048] In step (2), pulse flushing is used with a flushing pressure difference of 0.05 bar / s and a flushing pressure of 2.5 bar.

[0049] In step (4), pulse flushing is used with a flushing pressure difference of 0.05 bar / s and a flushing pressure of 3 bar.

[0050] Example 3 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that the mass ratio of citric acid, fatty alcohol polyoxyethylene ether and benzotriazole is 5:1:0.4.

[0051] Example 4 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that the mass ratio of citric acid, fatty alcohol polyoxyethylene ether and benzotriazole is 8:1:0.2.

[0052] Example 5 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that fatty alcohol polyoxyethylene ether is not added.

[0053] Example 6 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that benzotriazole is not added.

[0054] Example 7 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that the mass ratio of sodium hydroxide, tridecyl isoalcohol polyoxyethylene ether and disodium ethylenediaminetetraacetate is 7:2:1.

[0055] Example 8 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that the mass ratio of sodium hydroxide, tridecyl isoalcohol polyoxyethylene ether and disodium ethylenediaminetetraacetate is 10:3:1.

[0056] Example 9 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that tridecyl isomeric alcohol polyoxyethylene ether is not added.

[0057] Example 10 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that disodium ethylenediaminetetraacetate is not added.

[0058] Embodiment 11 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that step (3) also includes adding pepsin to the product water of the reverse osmosis membrane system, adjusting the pH to 3 with hydrochloric acid, and flushing the reverse osmosis membrane; the amount of pepsin used is 1 U / mg based on the reaction system, and is purchased from Nanning Dongheng Huadao Biotechnology Co., Ltd.

[0059] Example 12 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that step (3) also includes adding pepsin to the product water of the reverse osmosis membrane system, adjusting the pH to 2 with hydrochloric acid, and flushing the reverse osmosis membrane; the amount of pepsin used is 2 U / mg based on the reaction system, and is purchased from Nanning Dongheng Huadao Biotechnology Co., Ltd.

[0060] Comparative Example Comparative Example 1 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that no alkaline cleaning is performed.

[0061] Comparative Example 2 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that acid washing is not performed.

[0062] Comparative Example 3 A method for cleaning a reverse osmosis membrane, which differs from Example 1 in that step (5) is not performed.

[0063] Performance testing The cleaning performance test was carried out according to the method of Examples 1-12 and Comparative Examples 1-3; The cleaning experiment was carried out in an indoor laboratory at a temperature of 25°C. The reverse osmosis membrane that had been in operation for 3 years was dissected and cut into 1×1m 2 The square was cleaned according to the cleaning methods of the embodiments and comparative examples, and a 2000 mg / L sodium chloride solution was prepared. Under the condition of 0.65 MPa, the water production and desalination rate of the reverse osmosis membrane were measured; the recovery of the reverse osmosis membrane performance before and after cleaning was recorded. The performance of the reverse osmosis membrane was mainly determined by the recovery of the water production and desalination rate; Standard water production (25℃) = actual water production (L / (m 2 h))×temperature correction factor; Desalination rate (%) = [1-product water conductivity (us / cm) / concentrated water conductivity (us / cm)] × 100%; The test results are shown in Table 1.

[0064] Table 1 Test data of embodiments and comparative examples Combining the data in the examples and Table 1, it can be seen that the reverse osmosis membranes in Examples 1-2 have a better cleaning effect than before cleaning, and the performance of the reverse osmosis membranes after cleaning is still very good. Among them, the conductivity of the produced water in Example 1 is 12.4 us / cm, the conductivity of the concentrated water is 3954 us / cm, and the standard water production is 8.8 L / m 2 h, the desalination rate is 99.90%, indicating that the cleaning method of the present application has a high cleaning efficiency, a good cleaning effect, and a long service life. Repeated washing with product water, combined with acid washing and alkali washing, effectively restores the permeation flux and desalination rate of the reverse osmosis membrane and prolongs the service life of the reverse osmosis membrane.

[0065] Example 3-4 further defines the mass ratio of citric acid, fatty alcohol polyoxyethylene ether and benzotriazole. As can be seen from Table 1, the performance of each data of Example 3-4 is better than that of Example 1-2, while Examples 5-6 do not add fatty alcohol polyoxyethylene ether and benzotriazole respectively, and the data of Examples 5-6 are all worse than those of Examples 1-4. It shows that citric acid, fatty alcohol polyoxyethylene ether and benzotriazole have a synergistic effect, which jointly improves the cleaning effect of the acidic cleaning agent. The acidity of citric acid accelerates the dissolution of metal surface oxides, fatty alcohol polyoxyethylene ether enhances the dispersibility of the cleaning agent, and benzotriazole enhances the adsorption of the cleaning agent on the metal surface. The synergistic effect of the three can significantly improve the cleaning efficiency. The combination of the three can simultaneously remove inorganic and organic pollutants and metal oxides on the surface of the reverse osmosis membrane, improve the cleaning effect, and thus improve the performance and service life of the reverse osmosis membrane.

[0066] Examples 7-8 change the mass ratio of sodium hydroxide, tridecyl isoalcohol polyoxyethylene ether and disodium ethylenediaminetetraacetate, and Examples 9-10 do not add tridecyl isoalcohol polyoxyethylene ether and disodium ethylenediaminetetraacetate, respectively. The various properties of Examples 7-8 are better than those of Examples 1-2, and the various properties of Examples 9-10 are worse than those of Examples 1-2 and Examples 7-8, indicating that sodium hydroxide has strong alkalinity and can effectively remove grease and organic dirt. Tridecyl isoalcohol polyoxyethylene ether, as a nonionic surfactant, can improve the emulsification, dispersion and cleaning effects of the cleaning agent. Disodium ethylenediaminetetraacetate is a chelating agent that can combine with hardness ions in water to prevent the formation of scale and improve the stability of the cleaning agent.

[0067] In step (3), Example 11-12 further includes adding pepsin to the product water of the reverse osmosis membrane system. As shown in Table 1, the conductivity of the produced water of Example 11 is 8.2 us / cm, the conductivity of the concentrated water is 3998 us / cm, and the standard water production is 9.9 L / m 2 h, the desalination rate is 99.99%, indicating that pepsin can effectively degrade protein, thereby destroying the structure of the biofilm, reducing the deposition of organic matter on the membrane surface, and improving the cleaning effect of the membrane. In addition, there are a large number of jellyfish in the seawater, and some jellyfish colloids or mucus enter the reverse osmosis module and then adhere to the membrane surface. Pepsin can decompose jellyfish colloids or mucus, break the peptide bonds of proteins, and decompose them into smaller peptides and amino acids, which helps to flush out the product water and improve the cleaning efficiency.

[0068] In comparative example 1, no alkali washing was performed, the conductivity of the produced water was 17.6us / cm, the conductivity of the concentrated water was 3812us / cm, and the standard water production was 7.0L / m 2 h, the desalination rate is 99.35%, indicating that alkaline cleaning can decompose the organic pollutants on the surface of the reverse osmosis membrane. The alkaline cleaning agent can also destroy the structure of the microbial reverse osmosis membrane, kill bacteria, algae and other microorganisms attached to the surface of the reverse osmosis membrane, restore the permeation flux and desalination rate of the reverse osmosis membrane, and extend the service life of the reverse osmosis membrane.

[0069] In comparative example 2, no alkali washing was performed, the conductivity of the produced water was 17.9 us / cm, the conductivity of the concentrated water was 3807 us / cm, and the standard water production was 6.7 L / m 2 h, the desalination rate is 99.21%, indicating that acid cleaning can dissolve inorganic salt scale on the surface of the reverse osmosis membrane, such as calcium carbonate, calcium sulfate, barium sulfate, etc. The acidic cleaning agent can also react with metal oxides such as manganese on the surface of the reverse osmosis membrane, converting them into soluble substances, thereby removing them from the surface of the reverse osmosis membrane, restoring the permeation flux and desalination rate of the reverse osmosis membrane, and extending the service life of the reverse osmosis membrane.

[0070] In comparative example 3, step (5) was not performed, the conductivity of the produced water was 16.3 us / cm, the conductivity of the concentrated water was 3834 us / cm, and the standard water production was 7.3 L / m 2 h, the desalination rate was 99.45%, indicating that steps (1)-(4) were repeated again to improve the cleaning efficiency, and then the reverse osmosis membrane was rinsed with product water to effectively remove pollutants on the membrane surface, restore membrane performance, and prevent membrane scaling and membrane biofouling. The above cleaning method was used to obtain a reverse osmosis membrane with good cleaning effect and long service life.

[0071] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed. However, as long as it is within the scope of the claims of the present application, it shall be protected by the patent law.

Claims

1. A method for cleaning a reverse osmosis membrane, characterized in that: The steps include: (1) Use the product water of the reverse osmosis membrane system to flush the reverse osmosis membrane. Use pulse flushing with a flushing temperature of 30-35°C and a flushing pressure difference of less than 0.1 bar / s. Flush until the concentrated water in the membrane is fully replaced by product water. (2) immersing the reverse osmosis membrane cleaned in step (1) in an acidic cleaning solution at a cleaning temperature of 33-38°C for 9-10 hours and controlling the pH value to be 2-2.5; (3) Rinse the reverse osmosis membrane again with the product water of the reverse osmosis membrane system, using pulse flushing, the flushing temperature is 35-39°C, the flushing pressure difference is less than 0.1 bar / s, and flush until the concentrated water in the membrane is fully replaced by product water; (4) immersing the reverse osmosis membrane cleaned in step (3) in an alkaline cleaning solution at a cleaning temperature of 30-35°C for 9-10 hours and controlling the pH value to be 11.5-12; (5) After repeating steps (1) to (4), flush the reverse osmosis membrane with the product water of the reverse osmosis membrane system. Use pulse flushing with a flushing temperature of 30-35°C and a flushing pressure difference of less than 0.1 bar / s. Flush until the concentrated water in the membrane is fully replaced by product water.

2. A method for cleaning a reverse osmosis membrane according to claim 1, characterized in that: The acid cleaning solution comprises the following raw materials: 8-10 parts of citric acid, 1-2 parts of fatty alcohol polyoxyethylene ether, 0.2-0.5 parts of benzotriazole and 95-98 parts of deionized water.

3. A method for cleaning a reverse osmosis membrane according to claim 1, characterized in that: Step (3) also includes adding pepsin to the product water of the reverse osmosis membrane system, adjusting the pH to 2-3 with hydrochloric acid, and flushing the reverse osmosis membrane.

4. A method for cleaning a reverse osmosis membrane according to claim 3, characterized in that: The dosage of pepsin is 1-2 U / mg based on the reaction system.

5. A method for cleaning a reverse osmosis membrane according to claim 2, characterized in that: The mass ratio of the citric acid, fatty alcohol polyoxyethylene ether and benzotriazole is 5-8:1:0.2-0.

4.

6. A method for cleaning a reverse osmosis membrane according to claim 1, characterized in that: The alkaline cleaning solution comprises the following raw materials: 10-12 parts of sodium hydroxide, 3-5 parts of tridecyl isocyanate polyoxyethylene ether, 1-2 parts of disodium ethylenediaminetetraacetate and 90-92 parts of deionized water.

7. A method for cleaning a reverse osmosis membrane according to claim 6, characterized in that: The mass ratio of the sodium hydroxide, tridecyl isomeric alcohol polyoxyethylene ether and disodium ethylenediaminetetraacetate is 7-10:2-3:

1.

8. A method for cleaning a reverse osmosis membrane according to claim 1, characterized in that: In step (1), step (3) and step (5), the flushing circulation flow rate is 1344-1728m 3 , the flushing pressure is 2.3-2.5bar.

9. A method for cleaning a reverse osmosis membrane according to claim 1, characterized in that: In step (2), pulse flushing is used, the flushing pressure difference is less than 0.1 bar / s, and the flushing pressure is 2-2.5 bar.

10. A method for cleaning a reverse osmosis membrane according to claim 1, characterized in that: In step (4), pulse flushing is used, the flushing pressure difference is less than 0.1 bar / s, and the flushing pressure is 2.5-3 bar.

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