Method for cleaning irreversible membrane fouling

Abstract

This invention discloses a method for cleaning irreversible membrane fouling. After rinsing the fouled membrane with deionized water to remove deposited contaminants, the membrane is cleaned using a mixed solution of permanganate and persulfate as the cleaning system, followed by cleaning with a reducing agent. This completes the membrane cleaning process. Throughout the cleaning process, permanganate and persulfate react with each other under the influence of electron-rich contaminants, decomposing to produce active manganese (Mn(V)). aq Mn(VI) aq ), reactive oxygen species ( · OH, SO4 ·‑ O2 ·‑ , 1 O2 and MnO2, along with ROS and RMnS, oxidize contaminants on the membrane, causing them to detach. A reducing agent is then used to reduce the MnO2 produced during decomposition back to Mn. 2+ During this process, the formed manganese-impurity complex flows out of the membrane pores along with the reducing agent, achieving a cleaning effect. Compared with existing cleaning methods, this invention has better cleaning ability, shorter cleaning time, less energy consumption, good stability, simple operation, wide applicability, and good application prospects.

Description

Technical Field

[0001] This invention relates to the field of membrane cleaning technology, and in particular to a cleaning method for irreversible membrane fouling. Background Technology

[0002] In recent years, membrane technology has gained increasing attention in the water treatment field due to its advantages of high flux and good effluent quality. Commonly used membrane materials include ceramic membranes, polyvinylidene fluoride membranes, cellulose acetate membranes, polyethylene membranes, polysulfone membranes, and polyamide membranes. However, during membrane treatment, due to prolonged operation, contaminants inevitably adsorb or deposit on the membrane surface, causing membrane fouling, which reduces the membrane pore size or even causes blockage. Generally, flux reduction due to concentration polarization, membrane pore fouling, and gel layer formation in a short period is reversible fouling, which can be quickly removed by surface physical cleaning methods such as backwashing, aeration, and cross-flow. Irreversible fouling, caused by contaminant adsorption or deposition on the membrane material surface and resulting pore blockage, cannot be removed by physical cleaning methods but can be removed by chemical cleaning. Membrane fouling reduces membrane flux, shortens membrane life, and increases operating costs, limiting the large-scale application of membrane technology in practice. Furthermore, membrane fouling is unavoidable regardless of whether it is ultrafiltration, microfiltration, nanofiltration, or reverse osmosis. Therefore, developing effective membrane cleaning technologies is crucial for improving the practical performance of membranes.

[0003] Currently, the main pollutants are divided into inorganic pollutants, such as inorganic salts and colloids like CaCO3, SiO2, and MgCO3; and organic pollutants, such as some large molecular proteins and natural high-molecular-weight organic compounds. Membranes that have become contaminated to a certain extent need to have their flux restored to a certain level through physical, chemical, and biological methods before being reintroduced into the process flow. The main cleaning methods include: 1. Physical cleaning: using backwashing, ultrasonic cleaning, and sponge ball wiping to remove pollutants; 2. Acid and alkali cleaning: using acids (hydrochloric acid, sulfuric acid, nitric acid, etc.) and alkalis (hydroxides, carbonates, phosphates, etc.) to increase the solubility of pollutants, thereby removing them; 3. Biological cleaning: using biological enzymes to degrade pollutants; 4. Oxidative cleaning: using oxidation (mainly H2O2, NaClO, etc.) to cause pollutants to detach. Physical cleaning is insufficient to remove irreversible contaminants, resulting in unsatisfactory cleaning effects. Acid and alkali cleaning require long cleaning times, and the addition of chemical agents can easily shorten membrane lifespan and may generate waste liquid causing secondary pollution. Enzyme cleaning has poor environmental adaptability and is difficult to apply on a large scale. For example, invention patent CN1931419A discloses a membrane cleaning device in membrane separation technology, which uses the principle of gas-water backwashing to physically clean the membrane. Although improvements to the device and method have achieved better results and efficiency than traditional backwashing, the device is still somewhat complex, has low reliability, and the cleaning effect is unsatisfactory in long-term operation. Another example is invention patent CN102512967A, which discloses a ceramic membrane cleaning method. This method involves first adding sodium dodecyl sulfate as an auxiliary cleaning agent in the alkaline washing stage, followed by rinsing, then using citric acid as an acid cleaning agent for acid washing, and finally rinsing. This method has a long cleaning cycle, and the cleaning effect of citric acid, as a weak acid, is not very stable. The applicable concentration range varies greatly for different water qualities, and adding auxiliary agents to alkaline washing increases costs and poses a risk of secondary pollution. For example, invention patent CN102492663A discloses a membrane cleaning and regeneration enzyme preparation and cleaning method for pure draft beer. It combines enzyme cleaning with chemical cleaning to clean the membrane by inventing an enzyme preparation. The process is complicated and the environmental requirements are relatively strict. It is difficult to replicate in other fields of membrane treatment and has poor applicability.

[0004] Advanced oxidation process (AOP) S As a novel membrane cleaning method, advanced oxidation technology (AOP) can be considered a suitable membrane cleaning technology because it can generate active substances and reduce the size of contaminants, thereby achieving good removal of irreversible contaminants. Currently, there are few domestic inventions that apply various advanced oxidation technologies to membrane cleaning, and certain shortcomings exist. Invention patents CN103521081A and CN105289311A utilize advanced oxidation technology to generate singlet oxygen (…). 1O2 is used to clean the membrane, which is simple to operate, but since there is only one type of active oxygen, the efficiency needs to be further improved. Invention patent 101597096A discloses an electrocatalytic membrane reaction treatment device, which combines a filter membrane and a catalytic coating into an electrocatalytic composite membrane as the anode, which solves the membrane fouling problem to a certain extent, but has the problems of high energy consumption and low reaction efficiency.

[0005] In summary, existing membrane cleaning technologies suffer from problems such as poor performance, low efficiency, poor system stability, and high cost. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a cleaning method for irreversible membrane fouling, which solves the problems of poor effect, low efficiency, poor system stability and high cost of existing membrane cleaning technology.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for cleaning irreversible membrane fouling involves rinsing the fouled membrane with deionized water to remove contaminants deposited on the membrane surface, then cleaning it with a mixed solution of permanganate and persulfate as the cleaning system, followed by cleaning with a reducing agent, thus completing the membrane cleaning process.

[0009] During the cleaning process, permanganate and persulfate react with each other under the catalysis of electron-rich pollutants. Permanganate decomposes to produce active manganese RMnS(Mn(V)). aq Mn(VI) aq MnO2 and active manganese play a decisive role in the removal of irreversible pollution; at the same time, persulfate is activated by MnO2 produced by the decomposition of permanganate, generating reactive oxygen species (ROS). · OH, SO4 ·- O2 ·- , 1 O2 plays a major role in removing residual pollutants. The main mechanism of both RMnS and ROS in cleaning pollutants is oxidation, causing their chemical bonds to break and detach under the shear force of the water flow. Experiments show that MnO2 is generated inside the membrane fouling layer, occupying the active sites between the pollutants and the membrane, reducing the contact between the pollutants and the membrane, and transitioning the contact from pollutants to MnO2, and then from MnO2 to the membrane. When MnO2 is reduced to Mn... 2+ At that time, pollutants and MnO2 detach from the membrane simultaneously, achieving irreversible pollution removal.

[0010] Furthermore, in the cleaning system, the concentration of permanganate is 0.05 mM to 0.5 mM, and the concentration of persulfate is 1 mM to 20 mM. Preferably, the concentration of permanganate is 0.05 mM to 0.2 mM, and the concentration of persulfate is 1 mM to 5 mM.

[0011] Furthermore, the concentration of the reducing agent is 0.5-5 g / L. -1 Preferably 1g L -1 .

[0012] Furthermore, the cleaning time of the cleaning system is 10-30 minutes, preferably 15 minutes.

[0013] Furthermore, the reducing agent is hydroxylamine hydrochloride, hydroxylamine sulfate, sodium sulfite, sodium bisulfite, disodium sulfite, sodium thiosulfate, or potassium thiosulfate.

[0014] Furthermore, the cleaning is performed using a dynamic filtration method at an operating pressure of 0.05 MPa. Dynamic filtration cleaning avoids altering the water flow direction and prevents the disassembly of the ceramic membrane.

[0015] Furthermore, the cleaning system also includes citric acid or tartaric acid. Citric acid and tartaric acid are charged small-molecule acidic substances. The addition of electron-carrying groups can promote the cleaning effect of permanganate and persulfate. The acidic substances can play a role in acid washing, which can enhance the removal effect of pollutants.

[0016] Furthermore, the persulfate is a permonosulfate.

[0017] Furthermore, the cleaning method can be applied to the cleaning of membranes used in microfiltration, nanofiltration, ultrafiltration, and reverse osmosis. Even after replacing the ceramic membrane with a polyvinylidene fluoride (PVDF) membrane, the flux can still be restored from 75% after physical cleaning to 93%, making it suitable for cleaning membranes used in microfiltration, nanofiltration, ultrafiltration, and reverse osmosis.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention provides a method for cleaning irreversible membrane fouling by using a combination of permanganate and persulfate to clean the fouled membrane. Through the interaction of permanganate and persulfate, active manganese RMnS(Mn(V)) is generated. aq Mn(VI) aq ), reactive oxygen species (ROS) · OH, SO4 ·- O2 ·- , 1The method utilizes various active substances such as O2 and MnO2. Under the influence of these substances, pollutants are removed through a reaction mechanism involving oxidation, shedding, and the MnO2 effect, effectively mitigating irreversible membrane fouling. Membrane flux recovers from 71% to 99% after physical cleaning within 15 minutes, achieving excellent cleaning effect and efficiency. Furthermore, after 20 cycles of cleaning experiments, the flux recovery rate remains above 96%, indicating that the method also possesses good stability.

[0020] 2. In this invention, when cleaning the membrane using the PM / PMS system, there is no need to modify the membrane to prepare a catalytic membrane. The strong oxidation resistance of the ceramic membrane ensures the membrane life of the membrane cleaned by PM / PMS, and avoids the problems of catalyst introduction and shedding, which greatly reduces the complexity and cost of operation and is beneficial to practical application.

[0021] 3. This invention has low energy consumption, low cost, and a wide cleaning range. It has good cleaning performance for both organic and inorganic pollutants and has good application prospects.

[0022] 4. This invention has a high flux recovery rate on both ceramic and polymer membranes, and is suitable for membrane cleaning of microfiltration, nanofiltration, ultrafiltration and reverse osmosis, demonstrating its wide applicability. Attached Figure Description

[0023] Figure 1 The cleaning process flow and membrane flux comparison diagram of the cleaning method for irreversible membrane fouling of the present invention are shown.

[0024] Figure 2 The bar chart shows the membrane flux recovery rates of different pollutants in Examples 1-3 under physical cleaning and PM / PMS mixed cleaning.

[0025] Figure 3 The bar chart shows the membrane flux recovery rate under illumination conditions in Example 4 and under light-shielded conditions in Example 5.

[0026] Figure 4 Bar charts showing the membrane flux recovery rates of Comparative Examples 1, 2, and 4 after physical cleaning, cleaning with only PM or PMS, and cleaning with PM / PMS, respectively.

[0027] Figure 5 Bar charts showing the membrane flux recovery rates of Comparative Examples 3-5 after cleaning with NaOH, NaClO, and NaOH / NaClO respectively, and Example 4 after cleaning with a PM / PMS mixed solution.

[0028] Figure 6The energy consumption bar charts for comparative examples 3-5 cleaned with NaOH, NaClO and NaOH / NaClO respectively, and for example 4 cleaned with PM / PMS mixed solution.

[0029] Figure 7 This is a comparison chart of membrane flux recovery rates after 20 cycles of cleaning experiments. Detailed Implementation

[0030] The invention will be further described in detail below with reference to the accompanying drawings and specific examples.

[0031] The numerical ranges in this invention should be understood to also specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail. The terms “comprising,” “including,” “having,” “containing,” etc., as used herein are open-ended, meaning that they include but are not limited to.

[0033] Unless otherwise specified, the experimental methods used in this invention are all conventional methods.

[0034] Unless otherwise specified, all materials and reagents used in this invention can be purchased or synthesized by known methods.

[0035] In the quantitative experiments of this invention, each experiment was repeated three times, and the average value of the results was taken.

[0036] The original ceramic membrane (Al2O3, 50nm) used in this invention is soaked in 0.1mM NaOH solution for 12 hours and repeatedly rinsed with deionized water to remove impurities before use in experiments.

[0037] The contaminants used in this invention are mainly a mixed solution of humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA), abbreviated as HBS. In this invention, the contaminant mixture is stored at 4°C for later use and filtered through a 0.45 μm membrane before the experiment.

[0038] The oxidants used in the embodiments of this invention are permanganate (PM) and persulfate (PMS), referred to as the PM / PMS cleaning system.

[0039] Figure 1 This is a cleaning process flow diagram of an irreversible membrane fouling cleaning method according to the present invention, and a comparison diagram of membrane flux after cleaning by existing cleaning methods and the cleaning method of the present invention.

[0040] Depend on Figure 1 As can be seen, the present invention mainly utilizes the active manganese (Mn(V)) produced by the decomposition of permanganate. aq Mn(VI) aq ) and reactive oxygen species produced by the decomposition of persulfate ( · OH, SO4 ·- O2 ·- , 1 O2) is used to oxidize and remove pollutants; then, hydroxylamine hydrochloride, a reducing agent, is used to reduce the manganese dioxide produced by the decomposition of permanganate to Mn. 2+ The PM / PMS system of this invention removes irreversible membrane fouling along with hydroxylamine hydrochloride, thus achieving the goal of removing the fouling. Compared with traditional membrane cleaning methods, the membrane flux recovery rate is significantly improved within the same time frame using the PM / PMS system of this invention, exhibiting a higher membrane flux recovery rate. Furthermore, the cleaning method of this invention does not involve the introduction of a catalyst, making it non-toxic, environmentally friendly, and economical.

[0041] 1. The calculation formulas for the membrane flux recovery rate of the present invention are shown in equations (1) and (2):

[0042]

[0043] Where J is the pure water flux (L m) -2 h -1 V is the permeation volume (L), and S is the effective filtration area (M). 2 ), where t is the filtering time (h). Data in the experiment were recorded by monitoring software.

[0044]

[0045] Among them, J c J represents the pure water flux after cleaning. w F is the pure water flux of the original membrane. R This represents the flux recovery rate.

[0046] 2. The energy consumption calculation formulas of this invention are shown in equations (3) and (4):

[0047]

[0048] Among them, Eq 氧化剂It is the equivalent electrical energy (kWh / mol) required to produce 1 mole of oxidant. -1 M 氧化剂 It is the molar amount (mol) of the oxidizing agent, F R It is the flux recovery rate (%).

[0049]

[0050] Where price represents the average price of oxidant ($kg) -1 The molar mass is the molar mass of the oxidant (g mol). -1 Purity refers to the purity (%) of the oxidant, and average power consumption ($kWh). -1 Data from Alibaba.com (September 2022) shows that the average prices of PMS (99.5%) and PM (99%) are $2.2 and $3.4 per kilogram, respectively, while the average prices of NaOH (96%) and NaClO (1%) are $0.75 and $0.64 per kilogram, respectively. Assuming an exchange rate of 6.47 USD to CNY, the average electricity cost in Chongqing, China is approximately $0.102 kWh. -1 Therefore, 1 mol of PMS, PM, NaOH, and NaClO can be converted into 6.86 kWh, 5.27 kWh, 0.29 kWh, and 0.44 kWh, respectively.

[0051] Example 1

[0052] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 Sodium alginate and 100mg L -1 A mixed solution of calcium carbonate (CaCO3) was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Subsequently, the membrane was dynamically cleaned for 15 min using a mixed solution (300 mL) of 0.2 mM PM and 5 mM PMS instead of pure water. The membrane was then rinsed with hydroxylamine hydrochloride (NH2OH·HCl, 1 g L / L). -1 Dynamic filtration and cleaning are used to remove MnO2 generated on the membrane. The pure water flux is then measured and recorded. The membrane flux recovery rate is calculated, and the data is plotted. Figure 2 .

[0053] Example 2

[0054] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 Sodium alginate and 100mg L -1 A mixed solution of magnesium carbonate (MgCO3) was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Subsequently, the membrane was dynamically cleaned for 15 min using a mixed solution (300 mL) of 0.2 mM PM and 5 mM PMS instead of pure water. The membrane was then rinsed with hydroxylamine hydrochloride (NH2OH·HCl, 1 g L / L). -1 Dynamic filtration and cleaning are used to remove MnO2 generated on the membrane. The pure water flux is then measured and recorded. The membrane flux recovery rate is calculated, and the data is plotted. Figure 2 .

[0055] Example 3

[0056] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 Sodium alginate and 100mg L -1 A mixed solution of silica (SiO2) was used as a simulated contaminant. Contamination filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Subsequently, the membrane was dynamically cleaned for 15 min using a mixed solution (300 mL) of 0.2 mM PM and 5 mM PMS instead of pure water. The membrane was then rinsed with hydroxylamine hydrochloride (NH2OH·HCl, 1 g L / L). -1 Dynamic filtration and cleaning are used to remove MnO2 generated on the membrane. The pure water flux is then measured and recorded. The membrane flux recovery rate is calculated, and the data is plotted. Figure 2 .

[0057] Example 4

[0058] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1Bovine serum albumin, 30 mg / L -1 A mixed solution of sodium alginate was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Subsequently, the membrane was dynamically cleaned for 15 min using a mixed solution (300 mL) of 0.2 mM PM and 5 mM PMS instead of pure water. The membrane was then rinsed with hydroxylamine hydrochloride (NH₂OH·HCl, 1 g L⁻¹). -1 Dynamic filtration and cleaning are used to remove MnO2 generated on the membrane. The pure water flux is then measured and recorded. The membrane flux recovery rate is calculated, and the data is plotted. Figure 3 .

[0059] Example 5

[0060] In a light-protected environment at T=293K, the pure water flux of the original ceramic membrane was tested and recorded at 0.05 MPa for 15 minutes. Then, a 40 mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 A mixed solution of sodium alginate was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Subsequently, the membrane was dynamically cleaned for 15 min using a mixed solution (300 mL) of 0.2 mM PM and 5 mM PMS instead of pure water. The membrane was then rinsed with hydroxylamine hydrochloride (NH₂OH·HCl, 1 g L⁻¹). -1 Dynamic filtration and cleaning are used to remove MnO2 generated on the membrane. The pure water flux is then measured and recorded. The membrane flux recovery rate is calculated, and the data is plotted. Figure 3 .

[0061] Comparative Example 1

[0062] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1A mixed solution of sodium alginate was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Subsequently, the membrane was dynamically cleaned with 300 mL of 0.2 mM PM solution instead of pure water for 15 min, and the pure water flux was measured and recorded again. The membrane flux recovery rate was calculated, and the data were plotted. Figure 4 .

[0063] Comparative Example 2

[0064] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 A mixed solution of sodium alginate was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Subsequently, the membrane was dynamically cleaned with 300 mL of 5 mM PMS solution instead of pure water for 15 min, and the pure water flux was measured and recorded again. The membrane flux recovery rate was calculated, and the data were plotted. Figure 4 .

[0065] Comparative Example 3

[0066] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 A mixed solution of sodium alginate was used as a simulated contaminant. Contamination filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Next, the membrane was dynamically cleaned with 300 mL of 0.1 M NaOH solution instead of pure water for 15 min, and the pure water flux was measured and recorded again. The membrane flux recovery rate was calculated, and the data were plotted. Figure 5 Then, calculate the energy consumption based on the amount of oxidant used, and plot the energy consumption on... Figure 6 .

[0067] Comparative Example 4

[0068] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 A mixed solution of sodium alginate was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Afterwards, 5 g / L of... -1 A NaClO solution (300 mL) was used instead of pure water to dynamically clean the membrane for 15 min. The pure water flux was then measured and recorded. The membrane flux recovery rate was calculated, and the data were plotted. Figure 5 Then, calculate the energy consumption based on the amount of oxidant used, and plot the energy consumption on... Figure 6 .

[0069] Comparative Example 5

[0070] In an environment with T=293K and light exposure, the pure water flux of the original ceramic membrane was tested and recorded at 0.05MPa for 15 minutes. Then, a 40mg L... -1 Humic acid, 30mg / L -1 Bovine serum albumin, 30 mg / L -1 A mixed solution of alginate A was used as a simulated contaminant. Contaminated filtration was performed for 60 min at 0.05 MPa, and the pure water flux was recorded. Then, the contaminated membrane was rinsed with deionized water to remove the deposited contaminants, and the pure water flux was measured again. Afterwards, 0.1 M NaOH and 5 g L... -1 A NaClO mixed solution (300 mL) was used instead of pure water to dynamically filter and clean the membrane for 15 min. The pure water flux was then measured and recorded. The membrane flux recovery rate was calculated, and the data were plotted. Figure 5 Then, calculate the energy consumption based on the amount of oxidant used, and plot the energy consumption on... Figure 6 .

[0071] The processing technology is the same for all embodiments and comparative examples, but the reaction conditions, types of pollutants, and types of oxidants differ. A comparison of the differences between the embodiments and comparative examples is shown in Table 1.

[0072] Table 1. Comparison of differences between the embodiments and comparative examples.

[0073]

[0074]

[0075] Figure 2The bar charts for membrane flux recovery rates under physical cleaning and PM / PMS mixed cleaning for different pollutants in Examples 1-3 and Example 4 are provided by [the relevant authority / organization]. Figure 2 It can be seen that the flux recovery rates for HBS+CaCO3, HBS+MgCO3 and HBS+SiO2 pollution reached 80%, 85% and 90% respectively, which shows that the PM / PMS system has good cleaning performance for both organic and inorganic pollutants.

[0076] Figure 3 The bar chart shows the membrane flux recovery rate under illumination conditions in Example 4 and under light-shielded conditions in Example 5. Figure 3 It can be seen that the cleaning performance does not change significantly under both light and dark conditions, and the membrane flux recovery rate can reach 99%. This shows that the present invention has good applicability and feasibility in practical application.

[0077] Figure 4 Bar charts showing the membrane flux recovery rates of Comparative Examples 1, 2, and 4 after physical cleaning, cleaning with only PM or PMS, and cleaning with PM / PMS, respectively. Figure 4 It can be seen that, within the same cleaning time, simple physical cleaning or cleaning with PM or PMS alone results in a lower membrane flux recovery rate compared to cleaning with a PM / PMS mixed solution. Therefore, membrane cleaning with a PM / PMS mixed solution is more efficient.

[0078] Figure 5 Bar charts showing the membrane flux recovery rates after cleaning with NaOH, NaClO, and NaOH / NaClO in Comparative Examples 3-5, respectively, and after cleaning with a PM / PMS mixed solution in Example 4. Figure 5 It can be seen that the flux recovery performance of NaOH, NaClO, and NaOH / NaClO within a shorter cleaning time (15 min) is significantly lower than that of the membrane after cleaning with PM / PMS for the same cleaning time. Therefore, membrane cleaning with a PM / PMS mixed solution is more efficient.

[0079] Figure 6 The bar chart shows the energy consumption for cleaning with NaOH, NaClO, and NaOH / NaClO in Comparative Examples 3-5, respectively, and for cleaning with a PM / PMS mixed solution in Example 4. Figure 6 It can be seen that the energy consumption of the PM / PMS system (35×10) -3 kWh) and washing with NaOH (38×10) -3 kWh) or NaClO cleaning (38×10) -3 Similar to the kWh level, but significantly lower than that using the NaOH / NaClO system (74 × 10⁻⁶ kWh). - 3The energy consumption during cleaning (kWh) is shown in the figure. Therefore, cleaning with the PM / PMS mixed solution of this invention has relatively low energy consumption, making it suitable for large-scale application and possessing great potential.

[0080] Figure 7 This is a comparison chart of membrane flux recovery rates after 20 cycles of cleaning experiments on the same membrane using the method described in Example 4. Figure 7 It can be seen that after 20 cycles of cleaning experiments, the flux recovery rate is still above 96%, which shows that the cleaning method of the present invention also has good stability.

[0081] In summary, the cleaning method of this invention for irreversible membrane fouling cleaning achieves excellent cleaning results and efficiency, with membrane flux recovering from 71% to 99% within 15 minutes after physical cleaning. Furthermore, after 20 cycles of cleaning experiments, the flux recovery rate remains above 96%, demonstrating the method's good stability. This invention also boasts advantages such as low energy consumption, low cost, and a wide cleaning range, exhibiting good cleaning performance for both organic and inorganic pollutants, and thus showing promising application prospects.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for cleaning irreversible membrane fouling, characterized in that, After rinsing the contaminated membrane with deionized water to remove the contaminants deposited on the membrane surface, the membrane is cleaned with a mixed solution of permanganate and persulfate as the cleaning system, and then cleaned with a reducing agent to complete the membrane cleaning. During the cleaning process, permanganate and persulfate react with each other under the catalysis of electron-rich pollutants. Permanganate decomposes to produce RMnS and MnO2. Simultaneously, persulfate is activated by the MnO2 produced from the decomposition of permanganate, generating ROS. RMnS and ROS oxidize the pollutants, breaking their chemical bonds, and they are then detached under the shear force of the water flow. MnO2 is generated inside the membrane fouling layer, occupying the active sites between the pollutants and the membrane. When MnO2 is reduced to Mn... 2+ At this time, pollutants and MnO2 detach from the membrane simultaneously, thereby achieving the removal of irreversible membrane fouling; The reducing agent is hydroxylamine hydrochloride, hydroxylamine sulfate, sodium sulfite, sodium bisulfite, sodium thiosulfate, or potassium thiosulfate; The cleaning system also includes citric acid or tartaric acid; The persulfate is a permonosulfate.

2. The cleaning method for irreversible membrane fouling according to claim 1, characterized in that, In the cleaning system, the concentration of permanganate is 0.05mM to 0.5mM, and the concentration of persulfate is 1mM to 20mM.

3. The cleaning method for irreversible membrane fouling according to claim 2, characterized in that, The concentration of the reducing agent is 0.5-5 g / L.

4. The cleaning method for irreversible membrane fouling according to claim 3, characterized in that, The cleaning system takes 10-30 minutes to clean.

5. The cleaning method for irreversible membrane fouling according to claim 1, characterized in that, The cleaning system uses dynamic filtration to clean both the cleaning agent and the reducing agent, with an operating pressure of 0.05 MPa.

6. The cleaning method for irreversible membrane fouling according to claim 1, characterized in that, The cleaning method is applied to the cleaning of membranes used in microfiltration, nanofiltration, ultrafiltration, or reverse osmosis.

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