A cleaning and repairing method for retired nanofiltration membranes and application of the repaired retired nanofiltration membranes

Abstract

The application discloses a kind of cleaning and repair methods of retired nanofiltration membrane and the application of nanofiltration membrane after repair, belong to nanofiltration membrane cleaning regeneration repair technical field.By retired nanofiltration membrane is sorted, calibration, cleaning, repair and other processes, obtain the nanofiltration membrane of Ca 2+ , Mg 2+ Retention rate is lower, but SO4 2‑ Retention rate is high, that is, the nanofiltration membrane of repaired Ca 2+ Retention rate is 42-50%, Mg 2+ Retention rate is 50-55%, SO4 2‑ Retention rate is more than 99%, wherein SO4 2‑ Retention rate reaches new membrane above standard, can be applied to chlor-alkali to be denitrified light brine or seawater desalination pretreatment removal SO4 2‑ Field, not only make retired nanofiltration membrane get reused, prolong the service life of nanofiltration membrane, reduce the purchase of new membrane, increase economic benefits, more effectively alleviate environmental pressure, achieve a hit multi-effect.The method is simple and effective, easy for industrial application.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membrane cleaning, repair and regeneration technology, specifically to a cleaning and repair method for a decommissioned nanofiltration membrane and the application of the repaired decommissioned nanofiltration membrane. Background Technology

[0002] Nanofiltration membranes are widely used in the water treatment industry for the directional separation of monovalent and divalent ions, especially in seawater or brine to achieve the separation of Ca2+ ions. 2+ Mg 2+ SO4 2- Localized separation. The lifespan of nanofiltration membranes is generally 3-5 years. After multiple cleanings, the lifespan and performance of the membrane decline sharply (unlike the performance degradation of a new membrane). Although cleaning the nanofiltration membrane again can improve its performance, it is difficult to restore its full performance. Recycling and reusing decommissioned nanofiltration membranes that have reached the end of their life cycle is a manifestation of cost reduction and efficiency improvement for enterprises and has important guiding significance for actual production operations.

[0003] The reuse of decommissioned nanofiltration membranes includes three methods: direct reuse, conversion regeneration, and remediation regeneration. Direct reuse has certain requirements on membrane performance and the quality of the permeate water in the reuse scenario. Conversion regeneration involves converting the membrane into a nanofiltration or ultrafiltration membrane for reuse or even other materials through oxidation treatment, although the fouling resistance of the converted membrane is reduced. Remediation treatment through physical or chemical modification can restore the separation performance of nanofiltration membranes and improve their chlorine resistance and fouling resistance to a certain extent, making it the best way to regenerate and repair decommissioned nanofiltration membranes.

[0004] With the increasing emphasis on environmental protection in China, the comprehensive utilization of industrial water, wastewater recycling, and zero discharge are becoming increasingly important. Nanofiltration membranes are being used more and more widely in various fields, leading to a surge in membrane usage. The large number of decommissioned membranes not only significantly increases production costs but also poses a major challenge for solid waste disposal. While there is considerable research on restoring the performance of nanofiltration membranes through chemical cleaning and on hydrophilic modification of new membranes, research on further repairing decommissioned membranes after cleaning is scarce. Therefore, there is an urgent need to develop a method for cleaning and repairing decommissioned nanofiltration membranes to achieve their tiered utilization.

[0005] Chinese invention patent document CN109289539A discloses a cleaning agent for nanofiltration membranes used in brine refining and its preparation method. The method utilizes a cleaning agent containing components such as acids, alkalis, bactericides, and surfactants to clean used nanofiltration membranes (that have suffered membrane fouling), and the pH of this cleaning agent is 2-8. Therefore, this method essentially uses acidic or alkaline components to clean the membrane. After cleaning, the performance of the nanofiltration membrane recovers by a maximum of about 10% compared to before cleaning. However, it is difficult to restore the membrane's performance using only acidic and alkaline cleaning agents. Furthermore, long-term chemical cleaning gradually damages the hydrophilic functional groups on the membrane surface, further reducing the nanofiltration membrane's lifespan.

[0006] Chinese invention patent document CN111729515A discloses a nanofiltration membrane repair agent and its preparation method for brine refining. The method utilizes nanofiltration membrane activating and repairing agent A and nanofiltration membrane curing and maintaining agent B to "repair" the nanofiltration membrane. Nanofiltration membrane activating and repairing agent A is mixed with an acidic regulator (citric acid) to adjust the pH to 2-4 for further "repair," while nanofiltration membrane curing and maintaining agent B is mixed with an alkaline regulator (sodium carbonate or sodium bicarbonate) to adjust the pH to 7-9 for further "repair." Therefore, the essence of this patent is to utilize acidic and alkaline cleaning solutions to remove contaminants from the nanofiltration membrane, representing an optimization and improvement of the acidic and alkaline cleaning solution formulation. Although this method improves the Ca... 2+ Mg 2+ While the method improves the rejection rate, it also reduces membrane flux. Furthermore, with prolonged cleaning, membrane flux decreases further, and the membrane's operating cycle is not improved; in fact, it may decrease. Additionally, this method introduces repair components, but these are added to acidic and alkaline cleaning agents, resulting in simultaneous cleaning and repair. Since repair is performed without removing contaminants, the repair effect of the components is reduced.

[0007] Chinese invention patent document CN109351198A discloses a desalination rate repair agent and repair method for forward osmosis, nanofiltration, and reverse osmosis membranes. The preparation of this repair agent requires high-temperature reactions, resulting in high energy consumption. Since the method involves adding the repair agent after acidic and alkaline cleaning, the desalination rate of the membrane increases after both acidic and alkaline cleaning. Simply measuring the conductivity (desalination rate) of the permeate after adding the repair agent does not demonstrate that the repair agent has a cleaning and repairing effect or that it is highly effective. Using the desalination rate to evaluate the repair of nanofiltration membranes is inappropriate, as nanofiltration membranes achieve directional separation of monovalent and divalent ions, while reverse osmosis membranes retain all ions. The main components of this repair agent are acid and surfactant, both primarily removing organic pollutants from the membrane. Therefore, this repair agent is essentially a "bactericidal cleaning agent," cleaning organic contaminants from the membrane without repairing its structure.

[0008] Chinese invention patent document with publication number CN114130204A discloses an anti-attenuation agent for forward osmosis, reverse osmosis and nanofiltration membranes and its preparation method. This anti-fading agent is composed of a reducing agent, a bactericide, a surfactant, a surface-modifying protective agent, and water. The surface-modifying protective agent is one or a mixture of several of the following: trimesoyl chloride, polyphenylene diamine, and polyvinyl alcohol. This method utilizes the principle of interfacial polymerization to generate a protective layer on the membrane surface. However, acyl chlorides such as trimesoyl chloride are organic phase monomers that require an organic phase and a certain reaction temperature (generally 50°C) to undergo interfacial polymerization and form a protective layer. Under the conditions of this method, it is difficult to achieve interfacial polymerization and form a protective layer. The principle of the surface-modifying protective agent in this method is essentially surface coating rather than interfacial polymerization, and it repairs the pores on the membrane surface. In this method, we found that the agent components mainly target microbial sterilization (organic pollution), achieving the purpose by reducing organic pollution, but it does not alleviate the problem of inorganic scaling. At the same time, although the anti-fading agent improves the antifouling resistance of the nanofiltration membrane with long-term addition, it also affects the cost of long-term addition of the agent and the quality of subsequent products. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a cleaning and repair method for decommissioned nanofiltration membranes and the application of the repaired nanofiltration membranes, specifically targeting the Ca content in decommissioned nanofiltration membranes that have reached the end of their lifespan after 3-5 years of operation. 2+ Mg 2+ SO4 2- To address the issue of ion reduction, this method can remove the target divalent ion Ca from decommissioned nanofiltration membranes. 2+ Mg 2+ The retention rate of SO4 recovered slightly and increased significantly. 2- Retention rate, thereby achieving Ca 2+ Mg 2+ and SO4 2- The segmented separation technology can be applied to denitrified brine in chlor-alkali plants and pre-treated seawater for desalination, reducing the need to purchase new nanofiltration membranes, improving the utilization efficiency of decommissioned nanofiltration membranes, and increasing economic benefits.

[0010] To address the above problems, the present invention provides a cleaning and repair method for decommissioned nanofiltration membranes, which specifically includes the following steps:

[0011] (1) Select decommissioned nanofiltration membranes with a dry membrane weight increase of ≤6% and no obvious damage to the appearance for calibration using seawater as the medium. Those that meet the following calibration standards shall proceed to the next step. The calibration standards are: Ca 2+ Retention rate 28-38%, Mg 2+ The retention rate was 43-48%, SO4 2- Retention rate is 82-92%, flux is 8-10 L / (m³) 2 ·h);

[0012] (2) Load the decommissioned nanofiltration membrane that meets the calibration standard into the nanofiltration membrane cleaning device. First, use alkaline cleaning solution and acidic cleaning solution to circulate and soak for more than 1 hour each at the rated operating flow rate. Then, use alkaline cleaning solution and acidic cleaning solution to circulate and soak for 30-60 minutes each at a rinsing flow rate of 1.5 times the rated operating flow rate. Then, use repair solution A, repair solution B and repair solution C to circulate and soak for more than 1 hour each to obtain the decommissioned nanofiltration membrane after cleaning and repair.

[0013] (3) The decommissioned nanofiltration membrane obtained in step (2) after cleaning and repair is calibrated using seawater as the medium. The decommissioned nanofiltration membrane that meets the following qualification standards is considered to be qualified after repair. The qualification standards are: Ca 2+ Retention rate 42-50%, Mg 2+ Retention rate of 50-55%, SO4 2- With a rejection rate of over 99% and a flux of 11-13 L / (m³), the system achieved a high rejection rate of over 99%. 2 ·h);

[0014] The alkaline cleaning solution comprises an alkaline cleaning agent, an alkaline auxiliary agent, a non-oxidizing bactericide, a surfactant, and water. The alkaline cleaning agent is sodium hydroxide or sodium carbonate. The alkaline cleaning auxiliary agent is one of sodium tripolyphosphate and tetrasodium ethylenediaminetetraacetate, or a combination of both in any mass ratio. The non-oxidizing bactericide is a combination of an organic bromine compound and an amphoteric bactericide. The organic bromine compound is one of 2,2-dibromo-3-azolidinamide and 2-bromo-2-nitro-1,3-propanediol, or a combination of both in any mass ratio. The amphoteric bactericide is one of dodecyl betaine and hexadecyl dimethyl(2-sulfite)ethylammonium, or a combination of both in any mass ratio. The surfactant is hexadecyl dimethyl allyl ammonium chloride and trichloroethyl dodecyl ether sulfide. The acidic cleaning solution comprises one of sodium bis(succinate) and sodium butylene glycol disuccinate chlorohydroxypropyl quaternary ammonium salt type diester sulfonate; the acidic cleaning solution is composed of an acidic cleaning agent, an acidic auxiliary agent, and water, wherein the acidic cleaning agent is one or a combination of two or more of citric acid, oxalic acid, aminosulfonic acid, acetic acid, and hydrochloric acid in any mass ratio, and the acidic cleaning auxiliary agent is one or a combination of sodium metabisulfite and sodium dithionite in any mass ratio; the repair solution A is an aqueous solution of piperazine; the repair solution B is a hexane solution or cyclohexane solution of trimesoyl chloride; the repair solution C is an aqueous solution of dopamine and a surfactant, wherein the surfactant is one of hexadecyl dimethyl allyl ammonium chloride, sodium trichloroethyl dodecyl ether sulfate, and sodium butylene glycol disuccinate chlorohydroxypropyl quaternary ammonium salt type diester sulfonate.

[0015] The alkaline cleaning solution contains the following components by mass fraction: alkaline cleaning agent 0.1-0.3%, alkaline additive 0.01-0.05%, non-oxidizing bactericide 0.05-0.1%, surfactant 0.05-0.15%, and the remainder is water; the acidic cleaning solution contains the following components by mass fraction: acidic cleaning agent 1-3%, acidic additive 0.5-1%, and the remainder is water; in repair solution A, the concentration of piperazine is 500-1000 mg / L; in repair solution B, the concentration of trimesoyl chloride is 500-1000 mg / L; in repair solution C, the concentrations of dopamine and surfactant are 500-1000 mg / L and 100-500 mg / L, respectively; the mass ratio of organic bromine compounds to amphoteric bactericides in the non-oxidizing bactericide is 1-4:1.

[0016] In step (1), the increase in dry membrane weight refers to the increase in dry weight of the waste nanofiltration membrane compared to the new membrane. In step (1), the increase in dry membrane weight is preferably ≤3.0%.

[0017] The calibration conditions for the seawater medium in steps (1) and (3) are: pressure: 1.5-3.0 MPa;

[0018] In step (2), the alkaline cleaning solution and acidic cleaning solution are circulated and soaked under a pressure of 1.2-3.0 MPa; the rated operating flow rate is 20-60 m³ / h; the circulated soaking and rinsing conditions for repair solution A, repair solution B and repair solution C are: temperature 50-60℃, pressure 1.2-3.0 MPa, and operating flow rate 20-30 m³ / h. 3 / h ；

[0019] The seawater medium calibration in steps (1) and (3) and the cleaning and repair in step (2) are all carried out by a nanofiltration membrane cleaning device.

[0020] In step (2), the meaning of cyclic soaking and rinsing is: the cleaning solution or repair solution is sent from its respective storage tank into the nanofiltration membrane cleaning device, flows out and then returns to its respective storage tank, thereby realizing the cyclic soaking and rinsing of the decommissioned nanofiltration membrane by the cleaning solution or repair solution.

[0021] The nanofiltration membrane repaired using the method described in this invention can be used to filter and remove SO4 from chlor-alkali-treated brine or pre-treated seawater for denitrification. 2- .

[0022] The Ca in the chlor-alkali denitrification brine 2+ Mg 2+ SO4 2-The concentrations were 0-0.002 mg / L, 0-0.002 mg / L, and 5000-8000 mg / L, respectively; the Ca content in the pretreated seawater for desalination was... 2+ Mg 2+ SO4 2- The contents were 600-900 mg / L, 4000-5000 mg / L, and 6000-8000 mg / L, respectively.

[0023] The increased dry membrane weight of the decommissioned nanofiltration membrane in this invention is mainly caused by the accumulation of salt scale and organic matter on the membrane surface. When the accumulation reaches a certain level, the membrane cleaning cycle and cost increase significantly.

[0024] The organic bromine compound non-oxidizing bactericide in this invention has excellent bactericidal effects against halophilic bacteria and sulfate-reducing bacteria. 2,2-Dibromo-3-azapropanamide is characterized by low dosage, rapid bactericidal speed, good compatibility with other bactericides, low toxicity, and easy degradation. 2-Bromo-2-nitro-1,3-propanediol has good water solubility and compatibility; when combined with 2,2-dibromo-3-azapropanamide, it exhibits a broad-spectrum and highly effective bactericidal effect, and the two have an excellent synergistic effect.

[0025] The amphoteric bactericide of this invention is a non-oxidizing bactericide with high resistance to organic matter and slow-release capability, low toxicity, sensitivity to halophilic bacteria and sulfate-reducing bacteria, good compatibility, and good degradability. The combination of organic bromine compounds and the amphoteric bactericide exhibits excellent synergistic effects.

[0026] In this invention, the surfactant not only has the function of emulsifying pollutants in water, but also has the function of killing pollutants in water and improving the hydrophilicity of nanofiltration membrane surface; the compounding of surfactants not only enhances water solubility, but also enhances bactericidal properties.

[0027] The repair solution in this invention consists of a main aqueous phase (piperazine) and an oil phase (trimethylammonium chloride) monomer used in nanofiltration membrane manufacturing and repair. These monomers repair the damaged membrane surface through interfacial polymerization, thereby improving the rejection rate. Another component, dopamine, repairs the membrane surface through a surface coating deposition reaction, depositing a layer of dopamine to improve hydrophilicity and rejection rate. The surfactant imparts hydrophilicity modification to the nanofiltration membrane through hydroxyl and amino functional groups, and has a synergistic effect with dopamine.

[0028] By adopting the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0029] The cleaning and repair method of this invention involves sorting, calibrating, cleaning, and repairing decommissioned nanofiltration membranes. First, decommissioned nanofiltration membranes are screened. Then, contaminants are removed using alkaline and acidic cleaning solutions. The alkaline cleaning solution is a composite formulation of alkaline cleaning agents, alkaline additives, non-oxidizing bactericides, and surfactants. The acidic cleaning solution is a composite formulation of acidic cleaning agents and acidic additives. These solutions react, soften, penetrate, and repair various inorganic and organic scales and biofilms, yielding Ca... 2+ Mg 2+ SO4 2- Partially restored decommissioned nanofiltration membranes were then repaired using repair solutions A, B, and C, respectively. Repair solutions A and B achieved surface repair through interfacial polymerization, improving the rejection rate but reducing the flux. Repair solution C then underwent a surface coating reaction to achieve hydrophilic modification, further increasing the flux and improving SO42- retention. 2- The high rejection rate extends the membrane's lifespan.

[0030] The cleaning and repair method of the present invention obtains Ca 2+ Mg 2+ The retention rate is low, but SO4 2- Nanofiltration membranes with high rejection rates, i.e., repaired nanofiltration membranes (Ca) 2+ Retention rate is 42-50%, Mg 2+ Retention rate is 50-55%, SO4 2- The retention rate is over 99%, of which SO4 2- With a rejection rate exceeding that of new membranes, it can be applied to SO4 removal in chlor-alkali denitrification brine or as part of the pretreatment process for seawater desalination. 2- This method not only enables the reuse of decommissioned nanofiltration membranes, extending their lifespan and reducing the need for new membrane purchases, thus increasing economic benefits, but also effectively alleviates environmental pressure, achieving multiple benefits in one fell swoop. The method is simple, effective, and easy to apply industrially. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the nanofiltration membrane cleaning device in this invention. Detailed Implementation

[0032] The present invention will be further described below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] This invention provides a method for cleaning and repairing decommissioned nanofiltration membranes, which employs a nanofiltration membrane cleaning device. The structure of the nanofiltration membrane cleaning device is shown in the attached specification. Figure 1 .

[0034] Reference Figure 1The nanofiltration membrane cleaning device mainly consists of a shut-off valve, flow meter, pH meter, pressure gauge, booster pump 10, temperature control system, membrane element 16, nanofiltration membrane 15, plate and frame filter 8, product water sampling port 60, turbidity meter, security filter 9, and cleaning and repair water tank. The shut-off valve comprises a test liquid tank outlet valve 7, a product water main valve 21, a test liquid tank product water inlet valve 22, a concentrate main valve 23, a test liquid tank concentrate inlet valve 24, a test liquid tank drain valve 25, an alkali tank outlet valve 26, an alkali tank product water inlet valve 28, an alkali tank concentrate inlet valve 29, an alkali tank drain valve 30, an acid tank outlet valve 31, and an acid tank outlet valve. 33. Inlet valve for product water in tank; 34. Inlet valve for concentrated water in acid tank; 35. Outlet valve for acid tank; 36. Outlet valve for repair solution A tank; 37. Inlet valve for product water in repair solution A tank; 38. Inlet valve for concentrated water in repair solution A tank; 39. Outlet valve for repair solution A tank; 40. Outlet valve for product water in repair solution B tank; 41. Inlet valve for concentrated water in repair solution B tank; 42. Outlet valve for repair solution B tank; 43. Outlet valve for repair solution C tank; 44. Inlet valve for product water in repair solution C tank; 45. Inlet valve for concentrated water in repair solution C tank; 46. Outlet valve for concentrated water in repair solution C tank; 47. Outlet valve for drain water in repair solution C tank; 55. Inlet valve for product water in cleaning water tank; 56. Inlet valve for concentrated water in clean water tank; 58. Inlet valve for clean water tank. The system comprises a drain valve 59; a flow meter consisting of an inlet flow meter 13 and a product water flow meter 19; a pH meter consisting of an alkaline solution pH meter 27 and an acid solution pH meter 32; a pressure gauge consisting of an inlet pressure gauge 12 and a product water pressure gauge 20; a temperature control system consisting of a test liquid tank temperature control system 48, an alkaline solution tank temperature control system 49, an acid solution tank temperature control system 50, a repair solution A tank temperature control system 51, a repair solution B tank temperature control system 52, and a repair solution C tank temperature control system 53, wherein the temperature control system is controlled by a jacketed heater; a turbidity meter consisting of an inlet water turbidity meter 9 and a product water turbidity meter 54; and a cleaning and repair water tank consisting of a test liquid tank. 1. Alkali tank; 2. Acid tank; 3. Repair solution A tank; 4. Repair solution B tank; 5. Repair solution C tank; 6. Clean water tank; 7. All cleaning and repair water tanks are equipped with drain lines, sample inlets, and supporting pipelines. The sample inlets of the cleaning and repair water tanks are: 61 (test solution tank), 62 (alkali tank), 63 (acid tank), 64 (repair solution A tank), 65 (repair solution C tank), 66 (repair solution C tank), and 67 (clean water tank). The sampling position of the product water sampling port can be set at any position in the product water pipeline. The filtration accuracy of the plate and frame filter is 1 μm. The filtration accuracy of the security filter is 1 micrometer.

[0035] The test liquid tank 1 is connected in series with the plate and frame filter 8, the inlet turbidity meter 9, the booster pump 10, the security filter 11, the inlet pressure gauge 12, and the inlet flow meter 13 via the outlet valve 7 of the test liquid tank. Then, it is connected to the inlet pipeline 14 and enters the membrane element 16. The concentrate from the membrane element 16 returns to the test liquid tank 1 via the concentrate pipeline 18, the main concentrate valve 23, and the concentrate inlet valve 24 of the test liquid tank. The permeate from the membrane element 16 returns to the test liquid tank 1 via the permeate pipeline 17, the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, and the permeate inlet valve 22 of the test liquid tank.

[0036] The alkaline solution tank 2 is connected in series with the alkaline solution tank outlet valve 26, alkaline solution pH meter 27, plate and frame filter 8, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to the inlet pipeline 14 to enter the membrane element 16. The concentrate from the membrane element 16 returns to the alkaline solution tank 2 via the concentrate pipeline 18, the concentrate main valve 23, and the alkaline solution tank concentrate inlet valve 29. The permeate from the membrane element 16 returns to the alkaline solution tank 2 via the permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and the alkaline solution tank permeate inlet valve 28.

[0037] The acid tank 3 is connected in series with the acid tank outlet valve 31, acid pH meter 32, plate and frame filter 8, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to the inlet pipeline 14 to enter the membrane element 16. The concentrate from the membrane element 16 returns to the acid tank 2 via the concentrate pipeline 18, the concentrate main valve 23, and the acid tank concentrate inlet valve 34. The permeate from the membrane element 16 returns to the acid tank 3 via the permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and the acid tank permeate inlet valve 33.

[0038] Repair fluid tank 4 is connected in series with repair fluid tank A outlet valve 36, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to inlet pipeline 14 to enter membrane element 16. The concentrate from membrane element 16 returns to repair fluid tank A 4 via concentrate pipeline 18, concentrate main valve 23, and repair fluid tank A concentrate inlet valve 38. The permeate from membrane element 16 returns to repair fluid tank A 4 via permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and repair fluid tank A permeate inlet valve 37.

[0039] Repair fluid tank 5 is connected in series with repair fluid tank B outlet valve 40, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to inlet pipeline 14 to enter membrane element 16. The concentrate from membrane element 16 returns to repair fluid tank B 5 via concentrate pipeline 18, concentrate main valve 23, and repair fluid tank B concentrate inlet valve 42. The permeate from membrane element 16 returns to repair fluid tank B 5 via permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and repair fluid tank B permeate inlet valve 41.

[0040] The repair fluid tank 6 is connected in series with the repair fluid tank outlet valve 44, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to the inlet pipeline 14 to enter the membrane element 16. The concentrate from the membrane element 16 returns to the repair fluid tank 6 via the concentrate pipeline 18, the main concentrate valve 23, and the repair fluid tank C concentrate inlet valve 46. The permeate from the membrane element 16 returns to the repair fluid tank 6 via the permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and the repair fluid tank C permeate inlet valve 45.

[0041] The clear water tank 57 is connected in series with the clear water tank inlet valve 58, the booster pump 10, the security filter 11, the inlet pressure gauge 12, and the inlet flow meter 13. Then, the water enters the membrane element 16 through the inlet pipeline 14. The concentrate from the membrane element 16 returns to the clear water tank 57 through the concentrate pipeline 18, the concentrate main valve 23, and the clear water tank concentrate inlet valve 56. The permeate from the membrane element 16 returns to the clear water tank 57 through the permeate pipeline 17, the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, and the clear water tank permeate inlet valve 55.

[0042] In step (2), the calibration procedure is explained as follows: Seawater enters the test liquid tank 1 through the test liquid tank inlet 61. The test tank outlet valve 7 is opened, and the water enters the plate and frame filter 8 through the pipeline. Then, it passes through the turbidity meter 9, the booster pump 10, the inlet pressure gauge 12, and the inlet flow meter 13 before entering the membrane element 16. The permeate from the membrane element can be sampled at any time through the permeate sampling port. The water sample is analyzed by an inductively coupled plasma optical emission spectrometer (ICP) to obtain Ca2+. 2+ Mg 2+ SO4 2- The content of the membrane element is further used to obtain the rejection rate data. The permeate passes through the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, the permeate main valve 20, and the permeate inlet valve 22 of the test liquid tank, and returns to the test liquid tank 1. The flow rate obtained by the permeate flow meter 20 is further used to obtain the flux based on the membrane area and the running time, thereby obtaining the membrane calibration performance. The concentrate from the membrane element passes through the concentrate pipeline 18, the concentrate main valve 23, and the concentrate inlet valve 24 of the test liquid tank, and returns to the test liquid tank 1. During operation, all other valves are closed.

[0043] In step (2), the alkaline cleaning procedure is explained as follows: The prepared alkaline cleaning solution is introduced into the alkaline tank 2 through the alkaline tank sample inlet 62. The alkaline tank outlet valve 26 is opened, and the solution enters the plate and frame filter 8 through the pH meter 27. Then, it passes through the turbidity meter 9, the booster pump 10, the inlet pressure gauge 12, and the inlet flow meter 13, and enters the membrane element 16. The permeate passes through the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, the permeate main valve 20, and the alkaline tank permeate inlet valve 28, and returns to the alkaline tank 2. The concentrate from the membrane element returns to the alkaline tank 2 through the concentrate pipeline 18, the concentrate main valve 23, and the alkaline tank concentrate inlet valve 29. During operation, all other valves are closed. The pH meter and the inlet turbidity meter 9 are observed at all times. If the pH meter change exceeds 1, alkaline cleaning solution is added through the alkaline tank sample inlet 61. If the inlet turbidity meter change exceeds 5 NTU, the cleaning solution is replaced.

[0044] In step (2), the operation procedure for rinsing the clear water tank with pure water is as follows: Pure water enters the clear water tank 57 through the sample inlet 67. The clear water tank outlet valve 58 is opened, and the water enters the membrane element 16 through the booster pump 10, the inlet pressure gauge 12, and the inlet flow meter 13. The permeate from the membrane element returns to the clear water tank 57 through the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, the permeate main valve 20, and the clear water tank permeate inlet valve 55. The concentrate from the membrane element returns to the clear water tank 57 through the concentrate pipeline 18, the concentrate main valve 23, and the clear water tank concentrate inlet valve 56. During operation, all other valves are closed.

[0045] In step (2), the acid cleaning procedure is as follows: Before performing the acid cleaning procedure, the water can be rinsed with pure water from the clean water tank. This step is often omitted to improve cleaning efficiency. The prepared acid cleaning solution is introduced into the acid tank 3 through the sample inlet 63. The acid tank outlet valve 31 is opened, and the solution enters the plate and frame filter 8 through the pH meter 32. Then, it passes through the turbidity meter 9, the booster pump 10, the inlet pressure gauge 12, and the inlet flow meter 13 before entering the membrane element 16. The permeate from the membrane element is then tested by the permeate turbidity meter. 54. The permeate flow meter 19, permeate pressure gauge 20, permeate main valve 20, and permeate inlet valve 33 of the acid tank return to the acid tank 3; the concentrate from the membrane element returns to the acid tank 3 via the concentrate pipeline 18, the concentrate main valve 23, and the concentrate inlet valve 34 of the acid tank; during operation, all other valves are closed, and the pH meter and the inlet turbidity meter 9 are observed at any time. If the pH meter change exceeds 1, acidic cleaning solution is added through the acid tank sample inlet 63. If the inlet turbidity meter exceeds 5 NTU, the cleaning solution is replaced.

[0046] In step (2), the operation procedure for repairing with repair solution is as follows: Before performing the repair solution repair procedure, the acidic cleaning solution can be rinsed clean with pure water from the clean water tank. This step is often omitted to improve cleaning efficiency; (1) The prepared repair solution A is introduced into the repair solution A tank 4 through the sample addition port 64 of the repair solution A tank. When the temperature of the repair solution A is raised to the target temperature by the temperature control system of the repair solution A, the outlet valve 36 of the repair solution A tank is opened. The water enters the membrane element 16 through the inlet turbidity meter 9, the booster pump 10, the inlet pressure gauge 12, and the inlet flow meter 13. The permeate of the membrane element is introduced through the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, and the permeate flow meter 54. The main valve 20 and the inlet valve 37 of the repair solution A tank return to the repair solution A tank 4; the concentrate of the membrane element returns to the repair solution A tank 4 via the concentrate pipeline 18, the main concentrate valve 23, and the concentrate inlet valve 38 of the repair solution A tank; during operation, all other valves are closed, and the repair solution A is replaced after 10 days of operation; (2) The prepared repair solution B enters the repair solution B tank 5 through the sample addition port 65 of the repair solution B tank. When the temperature of the repair solution B is raised to the target temperature by the temperature control system of the repair solution B, the outlet valve 40 of the repair solution B tank is opened, and the solution enters the membrane element 16 through the inlet turbidity meter 9, the booster pump 10, the inlet pressure gauge 12, and the inlet flow meter 13. The permeate from the membrane element passes through the permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, permeate main valve 20, and permeate inlet valve 41 of the repair solution B tank, and returns to the repair solution B tank 5; the concentrate from the membrane element passes through the concentrate pipeline 18, concentrate main valve 23, and concentrate inlet valve 42 of the repair solution B tank, and returns to the repair solution B tank 5; during operation, all other valves are closed, and the repair solution B is replaced after 10 days of operation; (3) The prepared repair solution C is introduced into the repair solution C tank 6 through the sample addition port 66 of the repair solution C tank. When the temperature of the repair solution C is raised to the target temperature by the temperature control system of the repair solution C, the outlet valve 44 of the repair solution C tank is opened, and the water is introduced through the inlet valve. Turbidity meter 9, booster pump 10, inlet pressure gauge 12, inlet flow meter 13 enter the membrane element 16. The permeate from the membrane element passes through permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, permeate main valve 20, and permeate inlet valve 45 of the repair solution C tank, and returns to the repair solution C tank 6. The concentrate from the membrane element passes through concentrate pipeline 18, concentrate main valve 23, and concentrate inlet valve 46 of the repair solution C tank, and returns to the repair solution C tank 6. During operation, all other valves are closed, and the repair solution C is replaced after 10 days of operation. (4) After the repair solution C is repaired, the repair solution C is rinsed clean using the pure water program of the clean water tank. Example 1

[0047] This invention provides a method for cleaning and repairing a decommissioned nanofiltration membrane and the application of the repaired decommissioned nanofiltration membrane, wherein the cleaning and repair agent is prepared as follows:

[0048] Preparation of alkaline cleaning solution: Add 3.0 kg sodium hydroxide (0.2%), 0.15 kg sodium tripolyphosphate (0.01%), 0.15 kg tetrasodium ethylenediaminetetraacetate (0.01%), 0.6 kg 2,2-dibromo-3-azolidinyl propionamide (0.04%), 0.3 kg 2-bromo-2-nitro-1,3-propanediol (0.02%), 0.15 kg dodecyl betaine (0.01%), 0.15 kg hexadecyl dimethyl (2-sulfite) ethylammonium (0.01%), and 1.5 kg hexadecyl dimethyl allyl ammonium chloride (0.1%) to a 1.49 m³ solution. 3 Mix thoroughly with water (99.6%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0049] Preparation of acidic cleaning solution: Add 30 kg of acetic acid (2%), 7.5 kg of citric acid (0.5%), 4.5 kg of sodium metabisulfite (0.3%), and 4.5 kg of sodium disulfite (0.3%) to a 1.45 m³ / h solution. 3 Mix thoroughly with water (96.9%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0050] Preparation of Repair Solution A: Dissolve 1.2 kg of piperazine in 1.5 ml of water. 3 Prepare repair solution A by stirring in water until well mixed (Repair solution A: 800 mg / L).

[0051] Preparation of Repair Solution B: Dissolve 1.2 kg of trimesoyl chloride in 1.5 ml of water. 3 Prepare repair solution B (800 mg / L) by stirring thoroughly in n-hexane organic solvent.

[0052] Preparation of Repair Solution C: Dissolve 1.2 kg of dopamine and 0.45 kg of hexadecyl dimethyl allyl ammonium chloride in 1.5 mL of water. 3 Prepare repair solution B by stirring thoroughly in water (dopamine: 800 mg / L; surfactant: 300 mg / L).

[0053] The steps for cleaning and repairing decommissioned nanofiltration membranes are as follows:

[0054] (1) The decommissioned nanofiltration membranes were sorted according to the increase in dry membrane weight and the degree of membrane damage. Decommissioned nanofiltration membranes with an increase in dry membrane weight of 1.6% and no obvious damage to the membrane elements were calibrated using seawater as the medium. Under the condition of an operating pressure of 2.0 MPa, the permeate was analyzed and tested. According to the calibration standard, the Ca was obtained. 2+ Mg 2+ SO4 2- The rejection rates were 36%, 45%, and 86%, respectively, and the flux was 9 L / (m³). 2•h) decommissioned nanofiltration membranes;

[0055] (2) Load the decommissioned nanofiltration membrane obtained in step (1) into the nanofiltration membrane cleaning device, and clean it at 40m. 3 Under the conditions of rated operating flow rate (liquid flow rate into the nanofiltration membrane cleaning device) and pressure (liquid pressure inside the nanofiltration membrane cleaning device) of 2.0 MPa, the membrane is first soaked and rinsed with alkaline cleaning solution for 2 hours, and then soaked and rinsed with acidic cleaning solution for 2 hours. After completion, the membrane is then rinsed at a depth of 60 m³. 3 Under the conditions of a flushing flow rate (liquid flow rate into the nanofiltration membrane cleaning device) of 2.0 MPa and a pressure (liquid pressure inside the nanofiltration membrane cleaning device), the membrane is first soaked and rinsed with alkaline cleaning solution for 50 minutes, and then soaked and rinsed with acidic cleaning solution for 50 minutes. Then, under the conditions of a temperature of 55℃, a pressure (liquid pressure inside the nanofiltration membrane cleaning device) of 2.0 MPa and an operating flow rate (liquid flow rate into the nanofiltration membrane cleaning device) of 25 m3 / h, the membrane is soaked and rinsed with repair solution A for 2 hours, repair solution B for 2 hours, and repair solution C for 2 hours in sequence. After completion, the repair solution is rinsed off with clean water to obtain the cleaned and repaired decommissioned nanofiltration membrane.

[0056] (3) The cleaned and repaired decommissioned nanofiltration membrane obtained in step (2) was calibrated using seawater as the medium. Under an operating pressure of 2.0 MPa, the permeate was analyzed by ICP. The Ca of the repaired nanofiltration membrane was measured. 2+ Mg 2+ SO4 2- The rejection rates were 50%, 55%, and 99.5%, respectively, and the flux was 12 L / (m³). 2 •h), a repaired and qualified decommissioned nanofiltration membrane is obtained, which meets the aforementioned qualification standards.

[0057] Repaired and qualified decommissioned nanofiltration membrane elements were installed on a nanofiltration unit to treat chlor-alkali denitrification brine and seawater desalination pretreatment water. The unit operated at 2.0 MPa, and the product water was treated with Ca2+. 2+ Mg 2+ SO4 2- Flux detection and membrane cleaning cycle testing.

[0058] The water quality conditions for denitrification saline water in chlor-alkali environments are: Ca 2+ Mg 2+ SO4 2- The concentrations were 0.001 mg / L, 0.001 mg / L, and 6000 mg / L, respectively; the water quality conditions for the pretreated seawater were: Ca 2+ Mg 2+ SO4 2-The concentrations were 800 mg / L, 4500 mg / L, and 7000 mg / L, respectively. The Ca content of a properly repaired decommissioned nanofiltration membrane in a chlor-alkali denitrification brine solution... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.5%, respectively, and the flux was 12 L / (m³). 2 •h), the cleaning cycle is 50 days, and the concentrate is used for salt production in salt fields; the repaired and qualified decommissioned nanofiltration membranes are used in the pretreatment water for seawater desalination to remove Ca. 2+ Mg 2+ SO4 2- The rejection rates were 48%, 54%, and 99.5%, respectively, and the flux was 12 L / (m³). 2 •h), the washing cycle is 50 days, and the concentrated water is used for salt production in the salt fields. Example 2

[0059] This invention discloses a method for cleaning and repairing a decommissioned nanofiltration membrane and the application of the repaired decommissioned nanofiltration membrane, wherein the cleaning and repair agent is prepared as follows:

[0060] Preparation of alkaline cleaning solution:

[0061] Add 1.5 kg sodium carbonate (0.1%), 0.15 kg sodium tripolyphosphate (0.01%), 0.6 kg 2,2-dibromo-3-azapropanamide (0.04%), 0.15 kg dodecyl betaine (0.01%), and 0.75 kg sodium trichloroethyl dodecyl ether sulfate (0.05%) to 1.49 m³. 3 Mix thoroughly with water (99.79%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0062] Preparation of acidic cleaning solution:

[0063] Add 15 kg of hydrochloric acid (1%) and 7.5 kg of sodium metabisulfite (0.5%) to 1.48 m³. 3 Mix thoroughly with water (98.5%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0064] Preparation of Repair Solution A:

[0065] Dissolve 0.75 kg of piperazine in 1.5 ml of water. 3 Prepare repair solution A by stirring in water until well mixed (Repair solution A: 500 mg / L).

[0066] Preparation of Repair Solution B:

[0067] Dissolve 0.75 kg of pyromellitic acid chloride in 1.5 ml of water. 3Prepare repair solution B (500 mg / L) by stirring thoroughly in cyclohexane organic solvent.

[0068] Preparation of Repair Solution C:

[0069] Dissolve 0.75 kg of dopamine and 0.15 kg of butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate in 1.5 ml of water. 3 Prepare repair solution B by stirring thoroughly in water (dopamine: 500 mg / L; surfactant: 100 mg / L).

[0070] The steps for cleaning and repairing decommissioned nanofiltration membranes are as follows:

[0071] (1) The decommissioned nanofiltration membranes were sorted according to the weight increase of the dry membrane and the degree of damage to the membrane appearance. Decommissioned nanofiltration membranes with a dry membrane weight increase of 3.0% and no obvious damage to the membrane element were calibrated using seawater as the medium. Under an operating pressure of 1.5 MPa, the product water was analyzed and tested to obtain Ca 2+ Mg 2+ SO4 2- The rejection rates were 38%, 48%, and 92%, respectively, and the flux was 8 L / (m³). 2 •h) decommissioned nanofiltration membranes;

[0072] (2) The decommissioned nanofiltration membrane obtained in step (1) is loaded into the nanofiltration membrane cleaning device, and the pressure is 1.5 MPa and the rated operating flow rate is 20 m³ / h. 3 Under the condition of / h, first soak and rinse with alkaline cleaning solution for 1 hour, then soak and rinse with acidic cleaning solution for 1 hour; after completion, under a pressure of 1.5MPa and a rinsing flow rate of 30m³ / h, 3 Under the condition of / h, first soak and rinse with alkaline cleaning solution for 30min, then soak and rinse with acidic cleaning solution for 30min. Then, at a temperature of 50℃, a pressure of 1.5MPa and an operating flow rate of 20m3 / h, soak and rinse with repair solution A for 1h, repair solution B for 1h, and repair solution C for 1h in sequence. Then rinse off the repair solution with clean water to obtain the cleaned and repaired decommissioned nanofiltration membrane.

[0073] (3) The decommissioned nanofiltration membrane obtained in step (2) after cleaning and repair was calibrated using seawater as the medium. Under an operating pressure of 1.5 MPa, the permeate was analyzed by ICP. The Ca of the decommissioned nanofiltration membrane after cleaning and repair was determined. 2+ Mg 2+ SO4 2- The rejection rates were 49%, 53%, and 99.3%, respectively, and the flux was 11 L / (m³). 2 •h), to obtain a qualified decommissioned nanofiltration membrane after repair.

[0074] Repaired and qualified decommissioned nanofiltration membrane elements were installed on a nanofiltration unit to treat chlor-alkali denitrification brine and seawater desalination pretreatment water. The unit operated at 1.0 MPa and 90% concentration, and the product water was treated with Ca2+. 2+ Mg 2+ SO4 2- Detection of throughput and cleaning cycle.

[0075] The water quality conditions for denitrification saline water in chlor-alkali environments are: Ca 2+ Mg 2+ SO4 2- The concentrations were 0 mg / L, 0 mg / L, and 5000 mg / L, respectively; the water quality conditions for the pretreated seawater were: Ca 2+ Mg 2+ SO4 2- The concentrations were 600 mg / L, 4000 mg / L, and 6000 mg / L, respectively; the rehabilitated nanofiltration membranes, after successful repair, were placed in a chlor-alkali denitrification brine solution containing Ca... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.2%, respectively, and the flux was 11 L / (m³). 2 •h), the cleaning cycle is 40 days, and the concentrated water is used for salt production in salt fields; the repaired and qualified decommissioned nanofiltration membranes are used in the pretreatment water of seawater desalination. 2+ Mg 2+ SO4 2- The rejection rates were 48.5%, 53%, and 99.2%, respectively, and the flux was 11 L / (m³). 2 •h), the washing cycle is 40 days, and the concentrated water is used for salt production in the salt fields. Example 3

[0076] This invention discloses a method for cleaning and repairing a decommissioned nanofiltration membrane and the application of the repaired nanofiltration membrane, wherein the cleaning and repair agent is prepared as follows:

[0077] Preparation of alkaline cleaning solution:

[0078] 4.5 kg sodium hydroxide (0.3%), 0.75 kg tetrasodium ethylenediaminetetraacetate (0.05%), 0.6 kg 2,2-dibromo-3-azapropanamide (0.04%), 0.3 kg 2-bromo-2-nitro-1,3-propanediol (0.02%), 0.3 kg dodecyl betaine (0.02%), and 2.25 kg sodium butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate (0.15%) were added to a 1.49 m³ solution. 3 Mix thoroughly with water (99.4%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0079] Preparation of acidic cleaning solution:

[0080] Add 15 kg of acetic acid (1.0%), 7.5 kg of citric acid (0.5%), 7.5 kg of oxalic acid (0.5%), 7.5 kg of sulfamic acid (0.5%), 7.5 kg of hydrochloric acid (0.5%), and 15 kg of sodium disulfite (1%) to a 1.44 m³ solution. 3 Mix thoroughly with water (96%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0081] Preparation of Repair Solution A:

[0082] Dissolve 1.5 kg of piperazine in 1.5 ml of water. 3 Prepare repair solution A by stirring in water until homogeneous (Repair solution A: 1000 mg / L).

[0083] Preparation of Repair Solution B:

[0084] Dissolve 1.5 kg of pyromellitic acid chloride in 1.5 ml of water. 3 Prepare repair solution B (1000 mg / L) by stirring thoroughly in n-hexane organic solvent.

[0085] Preparation of Repair Solution C:

[0086] Dissolve 1.5 kg of dopamine and 0.75 kg of sodium trichloroethyl dodecyl ether sulfate in 1.5 ml of water. 3 Prepare repair solution B by stirring thoroughly in water (dopamine: 1000 mg / L; surfactant: 500 mg / L).

[0087] The steps for cleaning and repairing decommissioned nanofiltration membranes are as follows:

[0088] (1) The decommissioned nanofiltration membranes were sorted according to the weight increase of the dry membrane and the degree of damage to the membrane appearance. Decommissioned nanofiltration membranes with a dry membrane weight increase of 6.0% and no obvious damage to the membrane element were calibrated using seawater as the medium. Under the condition of an operating pressure of 3.0 MPa, the permeate was analyzed by ICP detection to obtain Ca 2+ Mg 2+ SO4 2- The rejection rates were 28%, 43%, and 82%, respectively, and the flux was 10 L / (m³). 2 •h) decommissioned nanofiltration membranes;

[0089] (2) The decommissioned nanofiltration membrane obtained in step (1) is loaded into the nanofiltration membrane cleaning device, and the pressure is 3.0 MPa and the rated operating flow rate is 60 m³ / h. 3Under the condition of / h, first soak and rinse with alkaline cleaning solution for 2 hours, then soak and rinse with acidic cleaning solution for 2 hours; after completion, under a pressure of 3.0MPa and a rated rinsing flow rate of 60m³ / h, 3 Under the condition of / h, first soak and rinse with alkaline cleaning solution for 60min, then soak and rinse with acidic cleaning solution for 60min; then, at a temperature of 60℃ and a pressure of 3.0MPa and 30m 3 / h running traffic Under the conditions, The membrane was sequentially soaked and rinsed with repair solution A for 5 hours, repair solution B for 5 hours, and repair solution C for 5 hours. Then, the repair solution was rinsed off with clean water to obtain the cleaned and repaired decommissioned nanofiltration membrane.

[0090] (3) The decommissioned nanofiltration membrane obtained in step (2) after cleaning and repair was calibrated using seawater as the medium. Under the condition of an operating pressure of 3.0 MPa, the product water was analyzed and tested. The Ca of the repaired nanofiltration membrane was measured. 2+ Mg 2+ SO4 2- The rejection rates were 42%, 50%, and 99%, respectively, and the flux was 13 L / (m³). 2 •h), to obtain a qualified decommissioned nanofiltration membrane after repair.

[0091] Repaired and qualified decommissioned nanofiltration membrane elements were installed on a nanofiltration unit to treat chlor-alkali denitrification brine and seawater desalination pretreatment water. The unit operated at 3.0 MPa, and the product water was treated with Ca2+. 2+ Mg 2+ SO4 2- Detection of throughput and cleaning cycle.

[0092] Water quality conditions for denitrified saline water in chlor-alkali environments: Ca 2+ Mg 2+ SO4 2- The concentrations were 0 mg / L, 0 mg / L, and 8000 mg / L, respectively; the water quality conditions for the pretreated seawater were: Ca 2+ Mg 2+ SO4 2- The concentrations were 900 mg / L, 5000 mg / L, and 8000 mg / L, respectively; the rehabilitated nanofiltration membranes, after successful repair, were placed in a chlor-alkali denitrification brine solution containing Ca... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99%, respectively, and the flux was 13 L / (m³). 2 •h), the cleaning cycle is 40 days, and the concentrated water is used for salt production in salt fields; the repaired and qualified decommissioned nanofiltration membranes are used in the pretreatment water of seawater desalination. 2+ Mg 2+ SO4 2-The rejection rates were 42%, 50%, and 99%, respectively, and the flux was 13 L / (m³). 2 •h), the washing cycle is 40 days, and the concentrated water is used for salt production in the salt fields. Example 4

[0093] The steps of the cleaning and repair method for the decommissioned nanofiltration membrane in this embodiment are the same as those in Embodiment 1, except that the alkaline cleaning solution and the acidic cleaning solution are different. The alkaline cleaning solution and the acidic cleaning solution in this embodiment are prepared as follows.

[0094] Preparation of alkaline cleaning solution: Add 3.0 kg sodium carbonate (0.2%), 0.3 kg tetrasodium ethylenediaminetetraacetate (0.02%), 0.9 kg 2-bromo-2-nitro-1,3-propanediol (0.06%), 0.3 kg hexadecyl dimethyl (2-sulfite) ethylammonium (0.03%), and 1.5 kg hexadecyl dimethyl allyl ammonium chloride (0.1%) to a 1.49 m³ solution. 3 Mix thoroughly with water (99.6%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0095] Preparation of acidic cleaning solution: Add 37.5 kg of acetic acid (2.5%) and 9.0 kg of sodium disulfite (0.6%) to a 1.45 m³ solution. 3 Mix thoroughly with water (96.9%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0096] In this embodiment, the successfully repaired decommissioned nanofiltration membrane is used to treat chlor-alkali denitrification brine and seawater desalination pretreatment water in the same way as in Example 1. The Ca content of the successfully repaired decommissioned nanofiltration membrane in the chlor-alkali denitrification brine in this embodiment is... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.1%, respectively, and the flux was 11.5 L / (m³). 2 •h), the cleaning cycle is 45 days, and the concentrate is used for salt production in salt fields; in this embodiment, the Ca in the pretreated water of seawater desalination is restored to a qualified decommissioned nanofiltration membrane. 2+ Mg 2+ SO4 2- The rejection rates were 47%, 53%, and 99.1%, respectively, and the flux was 11.5 L / (m³). 2 •h), the washing cycle is 45 days, and the concentrated water is used for salt production in the salt fields. Example 5

[0097] The steps of the cleaning and repair method for the decommissioned nanofiltration membrane in this embodiment are the same as those in Embodiment 4, except that the alkaline cleaning solution and the acidic cleaning solution are different. The alkaline cleaning solution and the acidic cleaning solution in this embodiment are prepared as follows.

[0098] Preparation of alkaline cleaning solution: Add 3.0 kg sodium carbonate (0.2%), 0.3 kg tetrasodium ethylenediaminetetraacetate (0.02%), 0.9 kg 2-bromo-2-nitro-1,3-propanediol (0.06%), 0.3 kg hexadecyl dimethyl (2-sulfite) ethylammonium (0.03%), and 1.5 kg butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate (0.1%) to a 1.49 m³ / h solution. 3 Mix thoroughly with water (99.6%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0099] Preparation of acidic cleaning solution: Add 37.5 kg of sulfamic acid (2.5%) and 9.0 kg of sodium disulfite (0.6%) to a 1.45 m³ solution. 3 Mix thoroughly with water (96.9%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0100] In this embodiment, the successfully repaired decommissioned nanofiltration membrane is used to treat chlor-alkali denitrification brine and seawater desalination pretreatment water in the same way as in Example 4. The Ca content of the successfully repaired decommissioned nanofiltration membrane in the chlor-alkali denitrification brine in this embodiment is... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.1%, respectively, and the flux was 11.5 L / (m³). 2 •h), the cleaning cycle is 46 days, and the concentrate is used for salt production in salt fields; in this embodiment, the Ca in the pretreated water of seawater desalination is restored to a qualified decommissioned nanofiltration membrane. 2+ Mg 2+ SO4 2- The rejection rates were 47%, 53%, and 99.1%, respectively, and the flux was 11.5 L / (m³). 2 •h), the washing cycle is 46 days, and the concentrated water is used for salt production in the salt fields. Example 6

[0101] The steps for cleaning and repairing the decommissioned nanofiltration membrane in this embodiment are the same as in Embodiment 4, except for the different acidic cleaning solution. The acidic cleaning solution in this embodiment is prepared as follows: Preparation of acidic cleaning solution: Add 37.5 kg of oxalic acid (2.5%) and 9.0 kg of sodium disulfite (0.6%) to a 1.45 m³ / h solution. 3 Mix thoroughly with water (96.9%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0102] In this embodiment, the successfully repaired decommissioned nanofiltration membrane is used to treat chlor-alkali denitrification brine and seawater desalination pretreatment water in the same way as in Example 4. The Ca content of the successfully repaired decommissioned nanofiltration membrane in the chlor-alkali denitrification brine in this embodiment is...2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.2%, respectively, and the flux was 11.5 L / (m³). 2 •h), the cleaning cycle is 47 days, and the concentrate is used for salt production in salt fields; the repaired nanofiltration membrane is used in the pretreatment water of seawater desalination for Ca 2+ Mg 2+ SO4 2- The rejection rates were 47%, 53%, and 99.1%, respectively, and the flux was 11.5 L / (m³). 2 •h), the washing cycle is 47 days, and the concentrated water is used for salt production in the salt fields. Example 7

[0103] The steps for cleaning and repairing the decommissioned nanofiltration membrane in this embodiment are the same as in Embodiment 4, except for the different acidic cleaning solution. The acidic cleaning solution in this embodiment is prepared as follows: Preparation of acidic cleaning solution: Add 37.5 kg of citric acid (2.5%) and 9.0 kg of sodium disulfite (0.6%) to a 1.45 m³ / h solution. 3 Mix thoroughly with water (96.9%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0104] In this embodiment, the successfully repaired decommissioned nanofiltration membrane is used to treat chlor-alkali denitrification brine and seawater desalination pretreatment water in the same way as in Example 4. The Ca content of the successfully repaired decommissioned nanofiltration membrane in the chlor-alkali denitrification brine in this embodiment is... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.2%, respectively, and the flux was 11.5 L / (m³). 2 •h), the cleaning cycle is 47 days, and the concentrate is used for salt production in salt fields; in this embodiment, the Ca in the pretreated water of seawater desalination is restored to a qualified decommissioned nanofiltration membrane. 2+ Mg 2+ SO4 2- The rejection rates were 47%, 53%, and 99.1%, respectively, and the flux was 11.5 L / (m³). 2 •h), the washing cycle is 46 days, and the concentrated water is used for salt production in the salt fields. Example 8

[0105] The steps of the cleaning and repair method for the decommissioned nanofiltration membrane in this embodiment are the same as those in Embodiment 2. The difference lies in the different alkaline cleaning solution, acidic cleaning solution, repair solution A, repair solution B, and repair solution C. The preparation of the alkaline cleaning solution, acidic cleaning solution, repair solution A, repair solution B, and repair solution C in this embodiment is as follows.

[0106] Preparation of alkaline cleaning solution:

[0107] Add 4.5 kg of sodium carbonate (0.3%), 0.75 kg of sodium tripolyphosphate (0.05%), 0.75 kg of 2,2-dibromo-3-azapropanamide (0.05%), 0.75 kg of dodecyl betaine (0.05%), and 2.25 kg of sodium trichloroethyl dodecyl ether sulfate (0.15%) to a 1.49 m³ solution. 3 Mix thoroughly with water (99.4%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0108] Preparation of acidic cleaning solution:

[0109] Add 45 kg of hydrochloric acid (3%) and 15 kg of sodium metabisulfite (1.0%) to 1.44 m³. 3 Mix thoroughly with water (96.0%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0110] Preparation of Repair Solution A:

[0111] Dissolve 1.5 kg of piperazine in 1.5 ml of water. 3 Prepare repair solution A by stirring in water until homogeneous (Repair solution A: 1000 mg / L).

[0112] Preparation of Repair Solution B:

[0113] Dissolve 1.5 kg of pyromellitic acid chloride in 1.5 ml of water. 3 Prepare repair solution B (1000 mg / L) by stirring thoroughly in cyclohexane organic solvent.

[0114] Preparation of Repair Solution C:

[0115] Dissolve 1.5 kg of dopamine and 0.75 kg of butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate in 1.5 ml of water. 3 Prepare repair solution B by stirring thoroughly in water (dopamine: 1000 mg / L; surfactant: 500 mg / L).

[0116] In this embodiment, the successfully repaired decommissioned nanofiltration membrane is used to treat chlor-alkali denitrification brine and seawater desalination pretreatment water in the same way as in Example 2. The successfully repaired decommissioned nanofiltration membrane in this embodiment is used in the chlor-alkali denitrification brine with Ca... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.3%, respectively, and the flux was 11 L / (m³). 2 •h), the cleaning cycle is 41 days, and the concentrate is used for salt production in salt fields; in this embodiment, the repaired and qualified decommissioned nanofiltration membrane is used in the pretreatment water of seawater desalination. 2+ Mg 2+ SO42- The rejection rates were 48.5%, 53%, and 99.3%, respectively, and the flux was 11 L / (m³). 2 •h), the washing cycle is 41 days, and the concentrated water is used for salt production in the salt fields. Example 9

[0117] The difference between this embodiment and Embodiment 1 is that after cleaning with alkaline cleaning solution and acidic cleaning solution, the parts are rinsed with pure water in a clean water tank before repair with repair solution AC.

[0118] After cleaning and repair, the decommissioned nanofiltration membrane was calibrated using seawater as the medium. Under an operating pressure of 2.0 MPa, ICP analysis was performed on the permeate. The Ca content of the repaired nanofiltration membrane was... 2+ Mg 2+ SO4 2- The rejection rates were 49.9%, 55%, and 99.4%, respectively, and the flux was 12 L / (m³). 2 •h).

[0119] In this embodiment, the successfully repaired decommissioned nanofiltration membrane is used to treat chlor-alkali denitrification brine and seawater desalination pretreatment water in the same way as in Example 1. The Ca content of the successfully repaired decommissioned nanofiltration membrane in the chlor-alkali denitrification brine in this embodiment is... 2+ Mg 2+ SO4 2- The rejection rates were 0%, 0%, and 99.5%, respectively, and the flux was 12 L / (m³). 2 •h), the cleaning cycle is 50 days, and the concentrate is used for salt production in salt fields; the repaired and qualified decommissioned nanofiltration membranes are used in the pretreatment water for seawater desalination to remove Ca. 2+ Mg 2+ SO4 2- The rejection rates were 48%, 54%, and 99.5%, respectively, and the flux was 12 L / (m³). 2 •h), the washing cycle is 50 days, and the concentrated water is used for salt production in the salt fields.

[0120] Comparative Example 1

[0121] Step (1) of Comparative Example 1 is the same as step (1) of Example 1. Step (2) of Comparative Example 1 is to use the alkaline cleaning solution of Example 1 to clean the decommissioned nanofiltration membrane under the alkaline cleaning solution operating conditions of Step (2) of Example 1. After cleaning, the repaired decommissioned nanofiltration membrane is obtained.

[0122] Comparative Example 2

[0123] Step (1) of Comparative Example 2 is the same as step (1) of Example 1. Step (2) of Comparative Example 2 is performed under the same operating conditions as the acidic cleaning solution in step (2) of Example 1. Only the acidic cleaning solution of Example 1 is used to clean the decommissioned nanofiltration membrane. After cleaning, the repaired decommissioned nanofiltration membrane is obtained.

[0124] Comparative Example 3

[0125] Step (1) of Comparative Example 3 is the same as step (1) of Example 1. Step (2) of Comparative Example 3 is performed under the same operating conditions as the alkaline and acidic cleaning solutions in step (2) of Example 1. Only the alkaline and acidic cleaning solutions of Example 1 are used to clean the decommissioned nanofiltration membrane. After cleaning, the repaired decommissioned nanofiltration membrane is obtained.

[0126] Comparative Example 4

[0127] Step (1) of Comparative Example 4 is the same as step (1) of Example 1; Step (2) of Comparative Example 4 is basically the same as step (2) of Example 1, except that the decommissioned nanofiltration membrane is cleaned with alkaline cleaning solution and acidic cleaning solution, and then cleaned with repair solution A to obtain the repaired decommissioned nanofiltration membrane.

[0128] Comparative Example 5

[0129] Step (1) of Comparative Example 5 is the same as step (1) of Example 1; Step (2) of Comparative Example 5 is basically the same as step (2) of Example 1, except that the decommissioned nanofiltration membrane is cleaned with alkaline cleaning solution and acidic cleaning solution, and then cleaned with repair solution B to obtain the repaired decommissioned nanofiltration membrane.

[0130] Comparative Example 6

[0131] Step (1) of Comparative Example 6 is the same as step (1) of Example 1; Step (2) of Comparative Example 6 is basically the same as step (2) of Example 1, except that the decommissioned nanofiltration membrane is cleaned with alkaline and acidic cleaning solutions and then cleaned with repair solution A and repair solution B to obtain the repaired decommissioned nanofiltration membrane. The difference between Comparative Example 5 and Example 1 is that after cleaning with alkaline and acidic cleaning solutions and then repairing with repair solution A and repair solution B, it is applied to chlor-alkali denitrification brine and seawater desalination pretreatment water. The product water is tested and analyzed to obtain Ca 2+ Mg 2+ SO4 2- Data on retention rate, flux, and cleaning cycle.

[0132] Unwashed decommissioned nanofiltration membranes, new membranes, decommissioned nanofiltration membranes that have been repaired successfully according to Example 1, and decommissioned nanofiltration membranes that have been repaired according to Comparative Examples 1-6 were applied to the treatment of chlor-alkali denitrification brine and seawater desalination pretreatment water according to the usage methods of the examples. The produced water was analyzed to obtain Ca...2+ Mg 2+ SO4 2- The retention rate, flux, and cleaning cycle data are shown in Table 1.

[0133]

[0134] As can be seen from the comparison of Examples 1-9, the concentration affects the cleaning and repair effect; the change of components in single-component alkaline and acidic cleaning solutions has little impact on the cleaning and repair effect; the final cleaning and repair effect achieved by single-component alkaline and acidic cleaning solutions is not as good as that achieved by multi-component alkaline and acidic cleaning solutions. Considering cost issues, single-component alkaline and acidic cleaning solutions can also achieve the purpose of the invention; whether or not pure water is used for rinsing after cleaning with alkaline or acidic cleaning solutions has little impact on the cleaning effect.

[0135] Comparing Comparative Examples 1-6 with Example 1, it can be seen that alkaline cleaning significantly improves the rejection rate, which is related to the membrane's own fouling, mainly organic fouling. Acidic cleaning has a smaller improvement in rejection rate. Alkaline and acid washing are more effective than alkaline and acid washing alone, mainly because they basically remove all contaminants, significantly improving the rejection rate, but without changing the membrane cleaning cycle. After alkaline and acid washing, repair solution A further improves the rejection rate and cleaning cycle, but the membrane flux decreases. After alkaline and acid washing, repair solution B improves both the rejection rate and cleaning cycle, but the flux decreases. After alkaline and acid washing, as well as repair solutions A and B, although the membrane cleaning cycle and rejection rate both improve, SO42-... 2- The retention rate was approximately 93.2%; after alkaline washing, acid washing, and repair solutions A, B, and C, the SO4 content was reduced. 2- The retention capacity of SO42- has been restored to its limit. 2- The rejection rate reached 99%, meeting the standard for new membranes. This indicates that treatment with repair solution A and B, followed by repair solution C, increases SO4 levels. 2- The key to retention rate.

[0136] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. All equivalent variations and modifications described in the scope of the present invention and the description should fall within the scope of the present invention.

Claims

1. A method for cleaning and repairing a decommissioned nanofiltration membrane, characterized in that, Specifically, the steps include: (1) Select decommissioned nanofiltration membranes with a dry membrane weight increase of ≤6% and no obvious damage to the appearance for calibration using seawater as the medium. Those that meet the following calibration standards shall proceed to the next step. The calibration standards are: Ca 2+ Retention rate 28-38%, Mg 2+ The retention rate was 43-48%, SO4 2- Retention rate is 82-92%, flux is 8-10 L / (m³) 2 ·h); (2) Load the decommissioned nanofiltration membrane that meets the calibration standard into the nanofiltration membrane cleaning device. First, use alkaline cleaning solution and acidic cleaning solution to circulate and soak for more than 1 hour each at the rated operating flow rate. Then, use alkaline cleaning solution and acidic cleaning solution to circulate and soak for 30-60 minutes each at a rinsing flow rate of 1.5 times the rated operating flow rate. Then, use repair solution A, repair solution B and repair solution C to circulate and soak for more than 1 hour each to obtain the decommissioned nanofiltration membrane after cleaning and repair. (3) The decommissioned nanofiltration membrane obtained in step (2) after cleaning and repair is calibrated using seawater as the medium. The decommissioned nanofiltration membrane that meets the following qualification standards is considered to be qualified after repair. The qualification standards are: Ca 2+ Retention rate 42-50%, Mg 2+ Retention rate of 50-55%, SO4 2- The rejection rate is over 99%, and the flux is 11-13 L / (m³). 2 ·h); The alkaline cleaning solution comprises an alkaline cleaning agent, an alkaline auxiliary agent, a non-oxidizing bactericide, a surfactant, and water. The alkaline cleaning agent is sodium hydroxide or sodium carbonate. The alkaline cleaning auxiliary agent is one or a combination of sodium tripolyphosphate and tetrasodium ethylenediaminetetraacetate in any mass ratio. The non-oxidizing bactericide is a combination of an organic bromine compound and an amphoteric bactericide. The organic bromine compound is one or a combination of 2,2-dibromo-3-azolidinamide and 2-bromo-2-nitro-1,3-propanediol in any mass ratio. The amphoteric bactericide is one or a combination of dodecyl betaine and hexadecyl dimethyl(2-sulfite)ethylammonium in any mass ratio. The surfactant is hexadecyl dimethyl allyl ammonium chloride and trichloroethyl dodecyl ether sulfate. The solution comprises sodium and sodium butylene glycol disuccinate monochlorohydroxypropyl quaternary ammonium salt type diester sulfonate; the acidic cleaning solution is composed of an acidic cleaning agent, an acidic auxiliary agent, and water, wherein the acidic cleaning agent is one or a combination of two or more of citric acid, oxalic acid, aminosulfonic acid, acetic acid, and hydrochloric acid in any mass ratio, and the acid cleaning auxiliary agent is one or a combination of sodium metabisulfite and sodium dithionite in any mass ratio; the repair solution A is an aqueous solution of piperazine; the repair solution B is a hexane solution or cyclohexane solution of trimesoyl chloride; the repair solution C is an aqueous solution of dopamine and a surfactant, wherein the surfactant is one of hexadecyl dimethyl allyl ammonium chloride, sodium trichloroethyl dodecyl ether sulfate, and sodium butylene glycol disuccinate monochlorohydroxypropyl quaternary ammonium salt type diester sulfonate.

2. The method for cleaning and repairing a decommissioned nanofiltration membrane according to claim 1, characterized in that, The alkaline cleaning solution contains the following components by mass fraction: alkaline cleaning agent 0.1-0.3%, alkaline additive 0.01-0.05%, non-oxidizing bactericide 0.05-0.1%, surfactant 0.05-0.15%, and the remainder is water; the acidic cleaning solution contains the following components by mass fraction: acidic cleaning agent 1-3%, acidic additive 0.5-1%, and the remainder is water; in repair solution A, the concentration of piperazine is 500-1000 mg / L; in repair solution B, the concentration of trimesoyl chloride is 500-1000 mg / L; in repair solution C, the concentrations of dopamine and surfactant are 500-1000 mg / L and 100-500 mg / L, respectively; in the non-oxidizing bactericide, the mass ratio of organic bromine compound to amphoteric bactericide is 1-4:

1.

3. The cleaning and repair method for a decommissioned nanofiltration membrane according to claim 1, characterized in that, In step (1), the increase in dry film weight is ≤3%.

4. The cleaning and repair method for a decommissioned nanofiltration membrane according to claim 1, characterized in that, In steps (1) and (3), the calibration conditions for seawater medium are: pressure 1.2-3.0 MPa.

5. The cleaning and repair method for a decommissioned nanofiltration membrane according to claim 1, characterized in that, In step (2), the alkaline cleaning solution and acidic cleaning solution are circulated and soaked under a pressure of 1.2-3.0 MPa; the rated operating flow rate is 20-60 m³ / h; the circulated soaking and rinsing conditions for repair solution A, repair solution B and repair solution C are: temperature 50-60℃, pressure 1.2-3.0 MPa, and operating flow rate 20-30 m³ / h. 3 / h.

6. An application of a repaired decommissioned nanofiltration membrane, characterized in that, The decommissioned nanofiltration membrane repaired by the cleaning and repair method according to any one of claims 1-5 is used to filter and remove SO4 from chlor-alkali denitrification brine or pre-treated seawater desalination water. 2- .

7. The application of the repaired decommissioned nanofiltration membrane according to claim 6, characterized in that, The Ca in the chlor-alkali denitrification brine 2+ Mg 2+ SO4 2- The concentrations were 0-0.002 mg / L, 0-0.002 mg / L, and 5000-8000 mg / L, respectively; the Ca content in the pretreated seawater for desalination was... 2+ Mg 2+ SO4 2- The contents were 600-900 mg / L, 4000-5000 mg / L, and 6000-8000 mg / L, respectively.

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