Method for evaluating anti-pollution-separation performance of nanofiltration membrane for printing and dyeing wastewater
By designing phased pollution experiments and graded cleaning, a standardized nanofiltration membrane evaluation system was constructed, which solved the problem of parameter disconnect between laboratory and industrial applications. This enabled accurate performance evaluation and modification optimization of nanofiltration membranes for dyeing and printing wastewater, and is applicable to the engineering selection of polyamide nanofiltration membranes.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-23
- Publication Date
- 2026-03-13
AI Technical Summary
In the existing technology, the laboratory evaluation methods for nanofiltration membranes for dyeing and printing wastewater have inconsistent parameters, test scenarios that are out of touch with engineering, and evaluation dimensions that are one-sided. This results in a large discrepancy between laboratory evaluation results and engineering applications, making it impossible to accurately assess the long-term operating performance of the membrane.
Experiments were designed for the basic and enhanced contamination stages to determine the initial and real-time performance of the nanofiltration membrane. The membrane was then subjected to graded cleaning, and the overall flux attenuation rate, separation performance stability coefficient, charge stability coefficient, and hydrophilicity enhancement rate were calculated. A standardized evaluation system was constructed by combining dual-wavelength detection and dual-scenario cleaning.
It achieves precise matching between experimental conditions and industrial operating conditions, with evaluation results deviating from actual operating data by less than 5%. It provides a unified testing benchmark, which can guide the modification and optimization of nanofiltration membranes and engineering selection, reduce testing costs, and adapt to engineering needs.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of membrane separation technology performance testing, specifically relating to a method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater, applicable to the performance verification and engineering selection of polyamide nanofiltration membranes. Background Technology
[0002] Dyeing and printing wastewater is characterized by its large volume (1.8-2 billion tons annually), complex composition (containing dyes, surfactants, inorganic salts, and biological pollutants), and recalcitrant nature (BOD / COD ratio often below 0.2). Nanofiltration membranes are the core material for its advanced treatment. In laboratory research and performance evaluation of nanofiltration membranes for dyeing and printing, a simplified and idealized testing and evaluation paradigm is often used. This method involves conducting short-cycle (several hours to several days) filtration tests on membrane sheets or small-area membrane modules under controlled laboratory conditions using simulated wastewater with a single composition (usually just a simple mixture of one or two dyes and inorganic salts) and fixed operating parameters (such as pressure and flow rate). The core evaluation indicators are typically limited to water flux and the rejection rate of target pollutants (such as dyes and COD).
[0003] Traditional evaluation methods suffer from several drawbacks, including inconsistent process parameters, a disconnect between testing scenarios and engineering applications, mismatch between indicators and results, and a one-sided evaluation approach. For example, they fail to consider the membrane surface charge control capability, do not differentiate between laboratory and industrial cleaning reagents, and do not specify the appropriate application scenarios for the MB (methylene blue) detection wavelength. This leads to significant discrepancies between laboratory evaluation results and engineering applications, making it impossible to accurately assess the long-term operational performance of the membrane. Therefore, there is an urgent need to construct a standardized system that ensures highly consistent process conditions and test results, and provides comprehensive evaluation dimensions. Summary of the Invention
[0004] To address the problems existing in the prior art, this invention provides a method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater. This method involves designing basic and enhanced fouling phase experiments to measure the initial pure water flux and initial potential of the nanofiltration membrane before the experiment; the real-time flux, methylene blue rejection, and NaCl rejection rate during the fouling phase; the flux data, methylene blue rejection rate, and NaCl rejection rate during continuous filtration of actual dyeing and printing wastewater; the pure water flux, membrane surface potential, and the methylene blue and NaCl rejection rates after staged regeneration and cleaning; and the performance level of the nanofiltration membrane is determined by calculation and analysis based on the measured experimental data.
[0005] To achieve the purpose of the invention, the following technical solution is provided: This invention provides a method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater, comprising the following steps: Pre-treating the nanofiltration membrane to be tested, removing surface impurities, and then measuring the initial pure water flux of the nanofiltration membrane. and the initial Zeta potential ; Design a staged fouling experiment for the nanofiltration membrane to be tested, including the basic fouling stage and the enhanced fouling stage, and respectively test the real-time flux , methylene blue rejection and NaCl rejection in the basic fouling stage, and the real-time flux , methylene blue rejection [[ID=;14]]and NaCl rejection ; Continuously filter the actual printing and dyeing wastewater with the nanofiltration membrane to be tested, perform hierarchical cleaning, and record the pure water flux after primary physical cleaning , and then continue to record the pure water flux after chemical deep cleaning , and the Zeta potential on the membrane surface ; Filter the basic fouling solution with the nanofiltration membrane to be tested after hierarchical cleaning, and measure the methylene blue rejection , NaCl rejection ; Calculate the comprehensive flux decay rate, hierarchical recovery rate, separation performance stability coefficient, charge stability coefficient and hydrophilic promotion rate by using the data of the above staged fouling experiment, hierarchical cleaning and regeneration; Among them, the calculation formula of the comprehensive flux decay rate is: DR , FRR , NaCl1 , MB1 , J , c2 , , R , J , R , , J , NaCl3 , MB3 , c1 , R , J , R , FRR , K , , FRR , J =[( J 0 - J t2 ) / J 0] × 100% ( is the real-time flux after 10 h in the enhanced fouling stage); Hierarchical recovery rate: primary cleaning recovery rate FRR 1 = J c1 / J 0 × 100%, deep cleaning recovery rate FRR 2 = J c2 / J 0 × 100%, and it is required that FRR 2 ≥ 70%; Separation performance stability coefficient: K = 0.5 × 丨 R MB3 - R MB1 丨 + 丨 R NaCl3 - R NaCl1 丨 × 100%, and it is required that K ≤ 5%; Charge stability coefficient: Z = | g c - g 0| / g 0 × 100%, and it is required that Z ≤ 10%; Hydrophilicity improvement rate: H = ( i max - i c ) / ( i max - i 0) × 100% ( is the water contact angle after deep cleaning, take 36° as the hydrophilicity reference value; if , characterizes the hydrophilicity improvement rate), and it is required that , ; Judge the anti - fouling and separation performance level of the to - be - tested nanofiltration membrane according to the calculation results; Excellent level: , , , , , the flux decay of actual wastewater in 7 days ≤ 30%; Qualified level: , , , , , the flux decay of actual wastewater in 7 days ≤ 40%; if , and the other indicators meet the standards, it is judged as qualified; Unqualified level: Any indicator fails to reach the qualified - level threshold.
[0006] Furthermore, in the basic fouling stage, use the to - be - tested nanofiltration membrane to filter the basic fouling solution under a pressure of 0.1 MPa, and record the real - time flux every 30 min , and sample at different time intervals to measure the methylene blue concentration and NaCl concentration; the basic fouling solution is a mixed aqueous solution containing 100 mg / L methylene blue (MB), 2000 mg / L NaCl, and 100 mg / L bovine serum albumin (BSA), and the pH is adjusted to 7.0.
[0007] Furthermore, in the enhanced fouling stage, use the to - be - tested nanofiltration membrane that has gone through the basic fouling stage to filter the enhanced fouling solution, and record the real - time flux every 1 h The concentrations of methylene blue and NaCl were measured at different time periods. The enhanced pollutant solution was a mixed aqueous solution containing 100 mg / L methylene blue, 2000 mg / L NaCl, 100 mg / L bovine serum albumin, 10 mM CaCl2, and 100 mg / L sodium dodecylbenzenesulfonate (LAS) to simulate the complex pollution of dyeing and printing wastewater by organic-inorganic-surfactant composition.
[0008] Furthermore, the primary physical cleaning involved circulating deionized water at a flow rate of 7 L / min to rinse the surface of the nanofiltration membrane to be tested after continuous filtration of actual dyeing and printing wastewater for 0.5 h. After rinsing, the pure water flux was measured at a pressure of 0.1 MPa. .
[0009] Furthermore, the nanofiltration membrane under test, after initial physical cleaning, underwent deep chemical cleaning. In the laboratory setting, the membrane was sequentially rinsed with deionized water for 5 min, soaked in 2wt% NaOH solution for 30 min, rinsed with deionized water until neutral, and ultrasonically cleaned at 50 kHz for 15 min. After cleaning, the pure water flux was measured. and the zeta potential of the membrane surface .
[0010] Furthermore, the nanofiltration membrane under test, after initial physical cleaning, undergoes deep chemical cleaning. In industrial settings, this is replaced with a triethanolamine-based alkaline cleaning agent / citric acid-based acidic cleaning agent. After cleaning, the pure water flux is measured. and the zeta potential of the membrane surface .
[0011] Furthermore, the nanofiltration membrane under test was continuously filtered for dyeing and printing wastewater for 7 days under a pressure of 0.1 MPa. Flux data, methylene blue rejection rate, and NaCl rejection rate were recorded at the same time each day to evaluate the performance degradation pattern under real conditions.
[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The evaluation method proposed in this invention is based on the complex pollution characteristics of organic, inorganic, surfactant and biological components in dyeing and printing wastewater, rather than the traditional use of simulated wastewater with a single component (usually just a simple combination of one or two dyes and inorganic salts). The experimental system is strictly calibrated with the actual parameters of dyeing and printing wastewater, achieving precise matching between experimental conditions and industrial operating conditions. This solves the technical defects of traditional evaluation systems, such as parameter disconnect and one-sided dimensions. The evaluation results can directly guide the modification and optimization of nanofiltration membranes for dyeing and printing wastewater treatment and engineering selection.
[0013] 2. The evaluation method proposed in this invention is scientific, practical, standardized, and comprehensive. Its core parameters are derived from the inventor's previous project measurement data. The physical meaning of the hydrophilicity formula matches the actual performance. The dual-wavelength detection and dual-scenario cleaning design solves the parameter confusion problem in traditional evaluations. Parallel testing ensures data accuracy and repeatability. The pollution system reproduces the real working conditions of dyeing and printing wastewater. The evaluation results deviate from the actual operating data of a nanofiltration system in a dyeing and printing plant by ≤5%, which can directly guide membrane modification (and engineering selection). At the same time, it distinguishes between laboratory and industrial cleaning schemes, improving the practicality of the technology. The unified test pressure, cleaning process, and detection method enable horizontal comparison of the performance of different membrane materials, providing a unified benchmark for membrane performance iteration. It integrates five dimensions: flux decay, cleaning recovery, separation stability, charge maintenance, and long-term operating conditions, filling the dimensional gaps in the traditional evaluation system.
[0014] 3. In the evaluation method proposed in this invention, the equipment used in the experimental design process are all conventional laboratory equipment, without the need for customized instruments, thus reducing testing costs; in industrial scenarios, online monitoring equipment can be used instead, adapting to engineering needs; the reagents used are all conventional laboratory chemical / biochemical reagents (methylene blue and NaCl are analytical grade, BSA is a biochemical reagent), without highly toxic or corrosive components; the industrial cleaning package uses triethanolamine and citric acid, both of which are food-grade additives, non-corrosive, and suitable for the long-term use requirements of membrane modules. Detailed Implementation
[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0016] Unless otherwise specified, all raw materials used in the following examples were purchased commercially.
[0017] Unless otherwise specified, the methods used in the following embodiments are conventional operating methods in the art.
[0018] Example 1 This embodiment provides a method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater, including the following steps: (1) Nanofiltration membrane pretreatment stage: The nanofiltration membrane sample was cut to have an effective area of 10 cm². 2The membranes must be free of edge damage and have an effective area error of ≤ ±0.5 cm². Each membrane sample must be tested in parallel 3 times, and the average value is taken as the final data. The deviation of a single test data from the average value is: flux ≤ ±3%, contact angle ≤ ±1°, and rejection rate ≤ ±2%. Test data exceeding the deviation must be discarded and retested. The initial pure water flux of the unmodified polyamide nanofiltration membrane (PA-0) and four types of PVA-grafted modified polyamide nanofiltration membranes (PA-50, PA-100, PA-150, and PA-200) was determined. water contact angle Initial Zeta potential The specific steps are as follows: A 50kHz, 100W ultrasonic cleaner was used to ultrasonically clean the surface with deionized water for 30 minutes to remove impurities. Install the membrane sheet into the membrane tank and pre-pressurize it at a constant pressure of 0.1 MPa for 30 minutes. If the flux fluctuation is greater than 5%, extend the pre-pressurization time to 40 minutes until the flux stabilizes. Record the initial pure water flux. ; The initial water contact angle of the membrane surface was determined using the seated drop method at 25°C and 50% relative humidity. Five points were selected from the center and surrounding area of each membrane, with a droplet volume of 5 μL. The average value was taken as the final value. Simultaneously, the initial Zeta potential on the membrane surface was measured. ; The nanofiltration membrane pretreatment stage was carried out at a temperature of 25°C and a relative humidity of 50%. The preparation methods of the four PVA-grafted modified polyamide nanofiltration membranes (PA-50, PA-100, PA-150, PA-200) in this embodiment are as follows: Commercial polyamide nanofiltration membranes were selected, cut to 15cm×15cm size, ultrasonically cleaned at 50kHz and 100W for 30min, rinsed with deionized water until the conductivity of the filtrate was ≤5μS / cm, and vacuum dried for 2h. Prepare aqueous solutions of polyvinyl alcohol (PVA, degree of polymerization 1750±50) with mass concentrations of 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, respectively, add 0.5 wt% glutaraldehyde as a crosslinking agent, and adjust the pH to 4.5; immerse the treated base film in PVA solutions of different concentrations, react in a constant temperature water bath at 60℃ for 2 h, and then heat treat in an oven at 80℃ for 1 h; The modified membrane was rinsed with deionized water to remove ungrafted PVA from the surface and then vacuum dried for 4 hours to prepare the modified nanofiltration membrane material.
[0019] The initial performance data of each membrane (average of three parallel tests) are shown in Table 1 below. The test method complies with the relevant requirements of GB / T32360-2015 "Nanofiltration Membranes Test Methods". Table 1 Initial performance data of the diaphragm
[0020] (2) Design a phased fouling experiment for the nanofiltration membrane to be tested, including a basic fouling stage and an enhanced fouling stage; Basic pollution stage: Prepare the basic contaminant solution: a mixed aqueous solution containing 100 mg / L methylene blue (MB, analytical grade), 2000 mg / L NaCl (analytical grade), and 100 mg / L bovine serum albumin (BSA, biochemical reagent, purity ≥98%), and adjust the pH to 7.0 with 0.1 mol / L HCl or NaOH; after preparation, the contaminant solution should be filtered through a 0.45 μm filter membrane to remove impurities, and should be prepared and used immediately. The basic contaminated liquid was filtered under a pressure of 0.1 MPa, and the real-time flux was recorded every 30 minutes. Samples were taken at 0h, 3.5h, and 7h. The first 10mL of permeate was drained before sampling. The MB concentration was measured using a UV-Vis spectrophotometer, and the NaCl concentration was measured using a conductivity meter. The results were then analyzed according to the formula. R =(1- C p / C f ) × 100% to calculate the retention rate , ; The flux and rejection rate of each nanofiltration membrane are shown in Table 2 below (MB concentration was precisely quantified using a 590nm wavelength; a standard curve was plotted before testing, and the equation is...). Correlation coefficient (Complies with the requirements of QB / T 4814-2015 "Test Methods for Material Properties for Membrane Separation") Table 2. Membrane performance data during the basic fouling stage.
[0021] Enhanced pollution phase: Prepare the enhanced contamination solution: a mixed aqueous solution containing 100 mg / L methylene blue (MB, analytical grade), 2000 mg / L NaCl (analytical grade), 100 mg / L bovine serum albumin (BSA, biochemical reagent, purity ≥98%), 10 mM CaCl2 (analytical grade), and 100 mg / L sodium dodecylbenzenesulfonate (LAS, analytical grade), and adjust the pH to 7.0 with 0.1 mol / L HCl or NaOH; the prepared contamination solution should be filtered through a 0.45 μm filter membrane to remove impurities and should be prepared and used immediately. After the initial contamination stage, the process switches to enhanced contamination filtration, with real-time flux recorded every hour. Samples were taken at 10h, 15h, and 17h. The first 10mL of permeate was drained before sampling. MB concentration was measured using a UV-Vis spectrophotometer, and NaCl concentration was measured using a conductivity meter, according to the formula... R =(1- C p / C f )×100% calculation , The test temperature was maintained at 25℃ throughout the entire process. Overall flux attenuation rate of each membrane The final values of the rejection rate are shown in Table 3 below. The flux decay pattern conforms to the typical decay characteristics of nanofiltration membranes in a complex pollution system (initial rapid decay stage of 6-8 hours, and later slow decay stage of 8-17 hours): Table 3. Membrane performance data during the enhanced fouling stage.
[0022] (3) The nanofiltration membrane to be tested was used to filter dyeing and printing wastewater for 7 consecutive days. Flux data and MB and NaCl rejection rates were recorded at the same time every day to evaluate the performance degradation law under real working conditions. Wastewater from the advanced treatment stage of a cotton textile dyeing and printing factory was collected (water quality indicators: COD=850mg / L, TDS=3500mg / L, pH=7.2, methylene blue dye concentration 85mg / L, LAS concentration 92mg / L, Ca...). 2+ The water sample (concentration 120 mg / L) was pretreated in a sedimentation tank and used as the actual wastewater test sample. It was continuously filtered for 7 days under a pressure of 0.1 MPa. The flux data and MB and NaCl rejection rates were recorded at the same time every day (9:00 am) to evaluate the performance degradation law under real working conditions. The water temperature was maintained at 24-26℃ during the test.
[0023] Table 4 Actual wastewater 7-day operating flux decline data
[0024] (4) After continuously filtering actual dyeing and printing wastewater through the nanofiltration membrane to be tested, perform graded cleaning and calculate the graded cleaning flux recovery rate. Primary physical cleaning: The surface of the nanofiltration membrane continuously filtering actual dyeing and printing wastewater was rinsed with deionized water at a flow rate of 7 L / min for 0.5 h. After rinsing, the pure water flux was measured at a pressure of 0.1 MPa. ; Deep chemical cleaning: Laboratory cleaning involved sequential rinsing with deionized water for 5 min, soaking in 2wt% NaOH solution (analytical grade, prepared at room temperature) for 30 min, rinsing with deionized water until neutral, and ultrasonic cleaning at 50 kHz for 15 min; the industrial cleaning scheme used alternating cleaning with a triethanolamine-based alkaline cleaning agent (3wt% effective ingredient concentration, pH=10.5) and a citric acid-based acidic cleaning agent (2wt% effective ingredient concentration, pH=3.0); after cleaning, the pure water flux was measured. and the zeta potential of the membrane surface ; The flux and recovery rate of each membrane after cleaning are shown in Table 5 below: The measured recovery rate in industrial scenarios is 5%-10% higher than that in laboratory settings, which is consistent with the actual effect of cleaning industrial membrane modules. Table 5. Membrane flux recovery data after staged cleaning
[0025] (5) Separation performance and charge stability after regeneration: After primary physical cleaning and deep chemical cleaning, the nanofiltration membrane was used to filter the basic contaminated liquid at a pressure of 0.1 MPa, and the MB rejection rate after regeneration was measured. NaCl retention rate The retention rate, charge stability, and hydrophilicity data of each membrane after regeneration are shown in Table 6 below. (Hydrophilicity...) The contact angle was measured using the corrected formula, with the droplet method (droplet volume 5 μL, ambient temperature 25℃, relative humidity 50%), and the zeta potential was measured using electrophoresis (test voltage 100V, electrolyte pH=7.0). Table 6. Overall performance data of the regenerated membrane
[0026] (6) Performance level determination The final grades of each nanofiltration membrane are shown in Table 7 below: Although the hydrophilicity improvement rate of PA-100 and PA-150 is slightly lower than the 40% threshold, considering that their flux decay rate meets the standard and their separation stability is good in actual wastewater operation, they are judged to be qualified based on the actual needs of engineering applications; PA-200, due to the formation of a dense hydrophilic layer by high-concentration PVA grafting, achieves excellent standards in all indicators. Table 7 Membrane performance level determination results
[0027] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.
Claims
1. A method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater, characterized in that, Includes the following steps: Pre-treating the nanofiltration membrane to be tested, removing surface impurities, and then measuring the initial pure water flux of the nanofiltration membrane. and initial Zeta potential ; A phased fouling experiment was designed for the nanofiltration membrane under test, including a basic fouling stage and an enhanced fouling stage. The real-time flux of the nanofiltration membrane under test was measured in the basic fouling stage. Methylene blue rejection rate and NaCl retention rate Enhance real-time flux during the pollution phase Methylene blue rejection rate and NaCl retention rate ; The nanofiltration membrane under test was used to continuously filter dyeing and printing wastewater, and then subjected to staged cleaning. The pure water flux after the initial physical cleaning was recorded. Continue with deep chemical cleaning and pure water flux Zeta potential on the membrane surface ; After graded cleaning, the base contaminant solution filtered by the nanofiltration membrane was used to determine the methylene blue rejection rate after regeneration. NaCl retention rate ; Using the data from the above-mentioned phased pollution experiments and after graded cleaning and regeneration, the overall flux decline rate, graded recovery rate, separation performance stability coefficient, charge stability coefficient, and hydrophilicity enhancement rate were calculated. The antifouling and separation performance level of the nanofiltration membrane under test is determined based on the calculation results.
2. The method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater according to claim 1, characterized in that: During the initial fouling stage, the initial fouling solution was filtered using the nanofiltration membrane under test at a pressure of 0.1 MPa, and the real-time flux was recorded every 30 minutes. The concentrations of methylene blue and NaCl were measured at different time points; the basic contaminant solution was a mixed aqueous solution containing 100 mg / L methylene blue, 2000 mg / L NaCl, and 100 mg / L bovine serum albumin.
3. The method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater according to claim 2, characterized in that: During the enhanced contamination phase, the nanofiltration membrane used in the basic contamination phase continues to filter the enhanced contamination solution, and the real-time flux is recorded every 1 hour. The concentrations of methylene blue and NaCl were measured at different time points; the enhanced contaminant solution was a mixed aqueous solution containing 100 mg / L methylene blue, 2000 mg / L NaCl, 100 mg / L bovine serum albumin, 10 mM CaCl2, and 100 mg / L sodium dodecylbenzenesulfonate.
4. The method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater according to claim 1, characterized in that: The primary physical cleaning involved rinsing the surface of the nanofiltration membrane to be tested with deionized water at a flow rate of 7 L / min for 0.5 h after continuous filtration of dyeing and printing wastewater. Following rinsing, the pure water flux was measured at a pressure of 0.1 MPa. .
5. The method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater according to claim 4, characterized in that: After initial physical cleaning, the nanofiltration membrane under test underwent deep chemical cleaning, which involved sequentially rinsing with deionized water for 5 min, soaking in 2wt% NaOH solution for 30 min, rinsing with deionized water until neutral, and ultrasonic cleaning at 50 kHz for 15 min. The pure water flux was then measured. and the zeta potential of the membrane surface .
6. The method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater according to claim 4, characterized in that: After initial physical cleaning, the nanofiltration membrane under test underwent deep chemical cleaning using a triethanolamine-based alkaline cleaning agent / citric acid-based acidic cleaning agent. The pure water flux was then measured. and the zeta potential of the membrane surface .
7. The method for evaluating the antifouling and separation performance of nanofiltration membranes for dyeing and printing wastewater according to claim 1, characterized in that: The nanofiltration membrane under test was continuously filtered for dyeing and printing wastewater for 7 days under a pressure of 0.1 MPa. Flux data, methylene blue rejection rate, and NaCl rejection rate were recorded at the same time each day to evaluate the performance degradation law under real conditions.