Self-assembled modified ultrafiltration membrane for efficient separation of phosphate and sodium chloride and application of self-assembled modified ultrafiltration membrane in water treatment
By using a self-assembled modified ultrafiltration membrane preparation method, and employing PDADMAC and PSS self-assembled solution layer-by-layer coating and stirring-pressure assisted technology, the problem of separating phosphate and sodium chloride in high-salt pickling wastewater was solved, achieving efficient separation and low-cost membrane modification.
Patent Information
- Application Number
- CN202511433678.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-09
- Publication Date
- 2026-01-16
AI Technical Summary
Existing technologies struggle to efficiently separate phosphates and sodium chloride from high-salt pickling wastewater, and existing membrane modification methods suffer from problems such as reduced water flux, high costs, and limited application scenarios.
A self-assembled modified ultrafiltration membrane was prepared by washing the ultrafiltration base membrane with isopropanol solution, coating it layer by layer with PDADMAC and PSS self-assembly solutions, and forming the modified ultrafiltration membrane with stirring and pressure assistance. The surface charge and pore size of the membrane were controlled to achieve high phosphate rejection rate and low sodium chloride rejection rate.
It achieves efficient separation of phosphate and sodium chloride in high-salt pickling wastewater, increases water flux, reduces modification costs, is applicable to different application scenarios, and has economic and environmental benefits.
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Figure CN121338565A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of water treatment, and particularly relates to a self-assembled modified ultrafiltration membrane for efficient separation of phosphate and sodium chloride and application thereof in water treatment. BACKGROUND
[0002] Food processing industry is one of the industries with the largest water resource consumption in the world, accounting for 70% of the total water resource consumption in the world. Pickled food is an important part of China's food processing industry, and its wastewater discharge accounts for 7% of the entire food processing industry. It has the characteristics of high salinity, high COD, and high nitrogen and phosphorus. According to the results of previous studies, high-salt pickling wastewater treated by conventional biochemical process still contains high concentrations of sodium chloride and phosphate, and direct discharge may cause land salinization and water eutrophication. Not only that, sodium chloride and phosphate are the main raw materials in the process of vegetable pickling and fertilizers for vegetable planting, respectively. If sodium chloride and phosphate can be efficiently recovered, the economic value and environmental benefits they contain are considerable. However, the ion properties of NaCl and phosphate are highly overlapped, and the solution system is stable, which makes it difficult to separate the two. A simple method is needed to separate sodium chloride and phosphate in high-salt pickling wastewater in order to achieve efficient recovery.
[0003] Membrane separation technology is widely used in drinking water purification and wastewater treatment due to its energy saving, environmental protection, high efficiency and no introduction of new substances. However, there is still a lack of membrane materials or technologies for efficient separation of phosphate and sodium chloride in wastewater. Although it has been reported that membrane modification strategies can effectively improve the separation effect of the membrane, there are still key challenges in practical application: 1) Under the condition of high salinity of wastewater, the water flux of conventional nanofiltration (NF) membrane decreases sharply; 2) It is difficult to balance the three factors of water flux, phosphate rejection rate and sodium chloride rejection rate; 3) The application scene is limited, and the constraints are more significant in complex or special scenes; 4) The modification cost is high, and the preparation process is complex, which has problems of economy and operability in practical application. Therefore, it is of great significance to develop a membrane modification method that can efficiently separate phosphate and sodium chloride in wastewater. SUMMARY
[0004]
Technical problem
[0005]
Technical scheme
[0006] The technical scheme of the present application is as follows: The first object of the present application is to provide a preparation method of a self-assembled modified ultrafiltration membrane for efficient separation of phosphates and sodium chloride, comprising the following steps: S1, soaking and cleaning the surface of the ultrafiltration base membrane with isopropanol solution, and cleaning the membrane surface with clean water to remove residual isopropanol; S2, dissolving NaCl and polydiallyldimethylammonium chloride (PDADMAC) in water to prepare a PDADMAC self-assembly solution; dissolving NaCl and poly (styrene sulfonate) sodium (PSS) in water to prepare a PSS self-assembly solution; S3, coating the PDADMAC self-assembly solution on the surface of the membrane prepared in step S1, and after reaction, pouring out the PDADMAC self-assembly solution, washing the membrane several times, and blowing the residual liquid on the membrane surface dry with inert gas to obtain a PDADMAC-loaded membrane; coating the PSS self-assembly solution on the surface of the PDADMAC-loaded membrane, and after reaction, pouring out the PSS self-assembly solution, washing the membrane several times, and blowing the residual liquid on the membrane surface dry with inert gas to obtain a self-assembled modified ultrafiltration membrane with two layers of self-assembly.
[0007] In an embodiment of the present application, step S3 is repeated 0-4 times after step S3 is completed, to obtain a self-assembled modified ultrafiltration membrane with 1-5 layers of self-assembly.
[0008] In an embodiment of the present application, in step S1, the ultrafiltration base membrane material is selected from one of PES (polyether sulfone), PS (polysulfone), and PAN (polyacrylonitrile); the molecular weight cut-off of the ultrafiltration base membrane is 10-200 kDa, preferably 20-150 kDa; the volume fraction of isopropanol in the isopropanol solution is 40-60%, preferably 45-55%.
[0009] In an embodiment of the present application, in step S1, the method of soaking cleaning is: soaking the base film in the isopropanol solution of the constant temperature water bath, the water bath temperature is 20-30℃, and the soaking cleaning time is 18-30 h; after the soaking cleaning is completed, the base film is taken out and repeatedly washed with deionized water until the residual isopropanol on the film surface is removed.
[0010] In an embodiment of the present application, in step S1, the shaking rate of the soaking cleaning is 50-150 rpm / min.
[0011] In an embodiment of the present application, in step S2, the concentration of PDADMAC in the PDADMAC self-assembly solution is 0.01-0.3 M, the concentration of NaCl is 0.25-1 M, and the solution pH is 6-8; the concentration of PDADMAC in the PSS self-assembly solution is 0.01-0.3 M, the concentration of NaCl is 0.25-1 M, and the solution pH is 6-8; the pH value of the solution is adjusted by using HCl and NaOH.
[0012] In an embodiment of the present application, in step S3, the coating amount of the PDADMAC and PSS self-assembly solutions is all 10-30 mL / 800 cm 2 ; the reaction time after each coating of the self-assembly solution is 5-15 min; and the cleaning times are 1-5 times.
[0013] In an embodiment of the present application, in step S3, the container used for the self-assembly reaction can realize stirring and pressurization operation; and is provided with a magnetic stirring system and a nitrogen pressurization system.
[0014] In an embodiment of the present application, in step S3, stirring and pressure are applied to the PDADMAC self-assembly solution or the PSS self-assembly solution during the reaction; and the stirring rate applied during the reaction process is all 100-1000 rpm / min, and the pressure is all 0.5-3 bar.
[0015] The second object of the present application is to provide the self-assembly modified ultrafiltration membrane prepared by the above preparation method and used for high-efficiency separation of phosphate and sodium chloride.
[0016] The third object of the present application is to provide the application of the above self-assembly modified ultrafiltration membrane in the field of water treatment.
[0017] In an embodiment of the present application, the above self-assembly modified ultrafiltration membrane is used for high-efficiency separation of phosphate and sodium chloride in high-salinity wastewater containing phosphate and sodium chloride; the salinity of the wastewater is 0-5%, the concentration of phosphate is 10-100 mg / L, and the pH is 5-9.
[0018] The salinity is the mass percentage of sodium chloride in the solution.
[0019] In one embodiment of the present application, the wastewater salinity is controlled by varying the amount of sodium chloride.
[0020] The layer-by-layer self-assembly technology is a low-cost, simple operation and significant functional membrane modification method, which can regulate the membrane surface charge, pore size and hydrophilicity / hydrophobicity by changing the number of layers, deposition conditions, the properties of the outermost electrolyte, etc. As a typical sulfonic acid group polyelectrolyte, PSS can endow the membrane surface with strong electronegativity as the outermost layer of the modified ultrafiltration membrane, which can effectively improve the rejection of phosphate by Donnan effect and achieve high-efficiency rejection of phosphate. Secondly, compared with traditional polyamide NF membranes, the thickness and compactness of the polyelectrolyte multilayer structure constructed by layer-by-layer self-assembly are much lower than those of the polyamide layer, so the rejection rate of sodium chloride can be effectively reduced and the water flux can be improved. In addition, since PSS and PDADMAC are both hydrophilic polyelectrolytes, the hydrophilicity of the membrane surface can be effectively improved, making the water transport process smoother and more conducive to improving the water flux of the modified ultrafiltration membrane. Moreover, the stirring-pressure-assisted PSS-PDADMAC layer-by-layer self-assembly membrane can effectively form a more uniform, stable and defect-free separation layer in the internal pores of the base membrane and on the membrane surface by the action of stirring and pressure, further improving the performance of the modified ultrafiltration membrane.
[0021] Beneficial effects: The beneficial technical effects of the present application are: The present application establishes a stirring-pressure-assisted PSS-PDADMAC layer-by-layer self-assembly membrane modification method, which can effectively retain the advantages of low sodium chloride rejection rate and high water flux of the ultrafiltration membrane, and fully utilize the characteristics of the self-assembly active layer formed under the action of stirring and pressure, i.e. high phosphate rejection rate, to achieve efficient separation of phosphate and sodium chloride in wastewater.
[0022] The self-assembly modified ultrafiltration membrane proposed in the present application can regulate the water flux, phosphate and sodium chloride rejection rate and other performance parameters of the modified ultrafiltration membrane by optimizing the number of layers of layer-by-layer self-assembly, the properties of the outermost self-assembly solution and the operation method of the assembly process, to meet the requirements of different types of sewage and treatment processes.
[0023] The self-assembly composite coating membrane of the present application uses non-toxic, harmless and inexpensive common chemicals as the required materials, has low application cost and simple process without toxic and harmful risks.
[0024] The self-assembly modified ultrafiltration membrane proposed in the present application is simple and fast to apply, does not require special environmental conditions, has a clean process without secondary pollution, and has relatively low reagent cost, which has high practicality and economic benefits.
[0025] The self-assembled modified ultrafiltration membrane can be applied not only to wastewater treatment, but also to a recovery process of phosphates and sodium chloride in wastewater, and can achieve the purpose of efficient separation of phosphates and sodium chloride in wastewater, thereby providing a basis for high-quality recovery of phosphates and sodium chloride in the future, and having important economic value and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS
[0026] Figure 1 Performance evaluation results of modified ultrafiltration membranes of Examples 1-4; Figure 2 Performance evaluation results of modified ultrafiltration membranes of Examples 5, 6 and Comparative Example 1; Figure 3 Performance evaluation results of a commercially available nanofiltration membrane of Comparative Example 2. DETAILED DESCRIPTION
[0027] The application will be described in detail below with reference to the drawings and examples.
[0028] Phosphate and sodium chloride separation effect test method: A dead-end filtration system was used to experimentally evaluate the phosphate and sodium chloride separation effect of the self-assembled modified ultrafiltration membrane. The phosphate concentration of the simulated wastewater (feed liquid) was 50 mg / L, the salinity was 5%, and the pH value of the solution was adjusted by HCl and NaOH. The phosphate concentration in the feed liquid and the permeate liquid (i.e. the membrane filtration effluent) was determined by the ammonium molybdate spectrophotometric method in GB 11893-89; the sodium chloride concentration in the permeate liquid was determined by an ion chromatograph, and the retention rate (R) of phosphates and sodium chloride was calculated by the following formula.
[0029]
[0030] In the formula, C f represents the concentration of phosphates or sodium chloride in the feed liquid, mg / L; C p represents the concentration of phosphates or sodium chloride in the permeate liquid, mg / L.
[0031] PSS, PDADMAC, Na2HPO4, NaCl, NaOH, HCl and NaCl involved in the following examples are all analytical pure and purchased from the National Pharmaceutical Group.
[0032] Example 1 A preparation method of a self-assembled modified ultrafiltration membrane for efficient separation of phosphates and sodium chloride, comprising the following steps: S1, soaking and cleaning the surface of the PES ultrafiltration base membrane with an isopropanol solution, and rinsing with deionized water to remove residual isopropanol on the membrane surface; The molecular weight cut-off of the PES ultrafiltration base membrane is 20 kDa, and is purchased from China Kureha Membrane Technology (Beijing) Co., Ltd. The base membrane was immersed in a beaker containing the isopropanol solution with a volume fraction of 50%, and the beaker was placed in a constant temperature water bath shaker, the water bath temperature was 25°C, the shaking rate was 100 rpm / min, and the immersion time was 24 h; after washing, the base membrane was taken out and repeatedly rinsed with deionized water until the residual isopropanol on the membrane surface was removed.
[0033] S2, NaCl and PDADMAC were dissolved in water to prepare a PDADMAC self-assembly solution; NaCl and PSS were dissolved in water to prepare a PSS self-assembly solution; The concentration of PDADMAC in the PDADMAC self-assembly solution was 0.02 M, the concentration of NaCl was 0.5 M, and the pH was 7; the concentration of PDADMAC in the PSS self-assembly solution was 0.02 M, the concentration of NaCl was 0.5 M, and the pH was 7.
[0034] S3, the PDADMAC self-assembly solution was coated on the surface of the membrane prepared in step S1, the coating amount was 20 mL / 800 cm 2 , and the PDADMAC self-assembly solution was subjected to stirring at 700 rpm / min and pressure of 2 bar, after 10 min of reaction, the PDADMAC solution was poured out and rinsed with deionized water for 3 times, the residual liquid on the membrane surface was blown dry with nitrogen, to obtain a PDADMAC-loaded membrane; the PSS solution was coated on the surface of the PDADMAC-loaded membrane, the coating amount was 20 mL / 800 cm 2 , the PSS self-assembly solution was subjected to stirring at 700 rpm / min and pressure of 2 bar, after 10 min of reaction, the PSS solution was poured out and rinsed with deionized water for 3 times, the residual liquid on the membrane surface was blown dry with nitrogen, to obtain a self-assembly modified ultrafiltration membrane with a self-assembly double layer number of +1; The self-assembly solution reaction process was completed in a specific container which was equipped with a magnetic stirring system and a nitrogen pressurizing system, so that stirring and pressurizing operations during the modification process could be realized.
[0035] S4, step S3 was repeated 3 times to obtain a self-assembly modified ultrafiltration membrane with a self-assembly double layer number of 4.
[0036] Example 2 The difference from Example 1 was that step S3 was repeated only 2 times in step S4, to obtain a self-assembly modified ultrafiltration membrane with a self-assembly double layer number of 3.
[0037] Example 3 The difference from Example 1 was that step S3 was repeated only 1 time in step S4, to obtain a self-assembly modified ultrafiltration membrane with a self-assembly double layer number of 2.
[0038] Example 4 The difference from Example 1 is only that step S4 is not performed, to obtain a self-assembled modified ultrafiltration membrane with a self-assembled bilayer number of 1.
[0039] Example 5 The difference from Example 1 is only that in step S3, no stirring and pressure are applied to the PDADMAC self-assembled solution and the PSS self-assembled solution, i.e., the PDADMAC and PSS layers are sequentially coated on the surface of the base membrane by means of static deposition.
[0040] Example 6 The difference from Example 1 is only that in step S1, the PES ultrafiltration base membrane with a molecular weight cut-off of 150 kDa is selected.
[0041] Comparative Example 1 The difference from Example 1 is only that in step S2, the pH of the PDADMAC self-assembled solution is adjusted to 6, and the pH of the PSS self-assembled solution is adjusted to 8.
[0042] Comparative Example 2 Commercially available polyamide NF membranes, model numbers: NF3, NF4, NF8, corresponding molecular weight cut-offs: 300-400 Da, 400-500 Da, 800-1000 Da, respectively.
[0043] The membranes prepared in Examples 1-6 and Comparative Examples 1 and 2 above are used for the separation of phosphates and sodium chloride in wastewater, and the treatment method is as follows: A simulated wastewater containing phosphates and sodium chloride is prepared, with a salinity of 5%, a phosphate concentration of 50 mg / L, and a pH of 7.
[0044] The above membrane pieces are fixed in an ultrafiltration cup, and the modified ultrafiltration membrane is operated under a pressure of 2 bar. The contents of phosphates and sodium chloride in the filtrate and the feed liquid are tested to evaluate the separation effect of the modified ultrafiltration membrane on phosphates and sodium chloride, and the results are shown in Tables Figure 1 , 2 , 3.
[0045] From Figure 1It can be seen that with the increase of the number of self-assembled bilayers, the rejection rates of phosphate and sodium chloride show a significant upward trend. The rejection rates of phosphate and sodium chloride increase from 55.89% and 0.98% when the number of bilayers is 1 to 82.12% and 2.12% when the number of bilayers is 4, respectively. Correspondingly, the water flux shows a downward trend, and the water flux increases from 17.7 LMH / bar when the number of bilayers is 1 to 8.4 LMH / bar when the number of bilayers is 4. This is because with the increase of the number of bilayers, the membrane pore size decreases, the surface charge density increases, the size sieving and Donnan effect also increase, and thus the rejection rates of phosphate and sodium chloride increase and the water flux decreases. It can be seen that the modified ultrafiltration membranes prepared by stirring-pressure assisted method with different number of bilayers have great differences in phosphate rejection rate, sodium chloride rejection rate and water flux. The self-assembled modified ultrafiltration membrane with more number of bilayers can realize high selective separation of phosphate and sodium chloride due to high phosphate rejection rate and slightly improved sodium chloride rejection rate, and is suitable for precise separation of phosphate and sodium chloride. The self-assembled modified ultrafiltration membrane with less number of bilayers has advantages of maintaining phosphate rejection rate above 50%, low sodium chloride rejection rate and high water flux, and shows better applicability in pretreatment and other application links.
[0046] From Figure 2 It can be seen from Example 5 that the preparation method of the self-assembled modified ultrafiltration membrane is adjusted to the self-assembled modified ultrafiltration membrane with 4 number of bilayers prepared by static deposition, and the phenomenon of significant decrease of phosphate rejection rate, slight increase of sodium chloride rejection rate and significant increase of water flux occurs. Specifically, the phosphate rejection rate, sodium chloride rejection rate and water flux change from 82.12%, 2.12%, 8.40 LMH / bar under stirring-pressure assisted conditions to 74.53%, 2.74%, 12.9 LMH / bar under static deposition conditions, respectively. This is because, compared with the preparation method of static deposition, the preparation method of stirring-pressure assistance can improve the performance of the self-assembled modified ultrafiltration membrane in mass transfer effect, structure compactness, defect rate and pore modification degree. It can be seen that the preparation method of stirring-pressure assistance can effectively improve the separation effect of phosphate and sodium chloride in wastewater under the condition of the same number of bilayers. Combined with Figure 1 It can be seen that the modified ultrafiltration membrane with 3 number of bilayers prepared by stirring-pressure assistance (Example 2) and the modified ultrafiltration membrane with 4 number of bilayers prepared by static deposition (Example 5) have similar separation effects of phosphate and sodium chloride, and the preparation method of stirring-pressure assistance can effectively improve the preparation efficiency, shorten the preparation period and save the cost of reagents, which has significant economic and practicality.
[0047] From Figure 2As can be seen from Comparative Example 1 and Example 6, changing the pH of the self-assembly modification solution and the pore size of the base membrane can both result in a decrease in the phosphate rejection rate. Although the water flux of Example 6 is significantly improved, the lower phosphate and sodium chloride separation effect also significantly restricts the applicability of this preparation method.
[0048] From Figure 3 As can be seen, the NF3 nanofiltration membrane has a higher phosphate and sodium chloride rejection rate and a lower water flux than the self-assembly modified ultrafiltration membrane in Comparative Example 1. Specifically, the phosphate rejection rate of the NF3 nanofiltration membrane is 86.58%, the sodium chloride rejection rate is 6.29%, and the water flux is 4.31 LMH. Compared with Example 1, the phosphate rejection rate of the NF3 nanofiltration membrane is only increased by 4.46%, but the sodium chloride rejection rate is increased by 300%, and the water flux is reduced by about 50%. Obviously, the NF3 nanofiltration membrane has obvious deficiencies in the selective separation effect of phosphate and sodium chloride and water flux. The phosphate rejection rate of the NF4 nanofiltration membrane is 83.89%, the sodium chloride rejection rate is 3.76%, and the water flux is 5.02. Compared with Example 1, the phosphate rejection rates of the two are basically the same, but the sodium chloride rejection rates and water fluxes are significantly different. The higher sodium chloride rejection rate and lower water flux still restrict the application effect of the NF4 nanofiltration membrane. In addition, the phosphate rejection rate of the NF8 nanofiltration membrane is 56.31%, the sodium chloride rejection rate is 2.88%, and the water flux is 13.72 LMH. The phosphate rejection rate of the NF8 nanofiltration membrane is basically the same as that of Example 4, but the NF8 nanofiltration membrane also has obvious deficiencies in the sodium chloride rejection rate and water flux. In addition, the self-assembly double-layer number of the modified ultrafiltration membrane in Example 4 is only 1, and the preparation cost is significantly lower than that of the traditional polyamide nanofiltration membrane. The dual factors of performance and cost limit the application of the NF8 nanofiltration membrane.
[0049] In summary, the self-assembly modified ultrafiltration membrane prepared by stirring-pressure assistance can control the performance of the membrane by controlling the self-assembly double-layer number to meet the requirements of different application scenarios. As can be seen from the comprehensive comparison, the self-assembly modified ultrafiltration membrane prepared by stirring-pressure assistance can significantly reduce the sodium chloride rejection rate and improve the water flux while effectively retaining the phosphate rejection rate. The self-assembly modified ultrafiltration membrane prepared by stirring-pressure assistance proposed in the present application can effectively improve the separation effect of phosphate and sodium chloride and obtain a higher water flux, thereby improving the operation efficiency of the membrane system, reducing the use area of the membrane, and reducing the operating pressure of the membrane system, effectively realizing the efficient separation of phosphate and sodium chloride in wastewater.
[0050] The above examples are not intended to limit the scope of the present application, nor are the described steps intended to limit the order in which they are performed. Modifications apparent to one skilled in the art in light of the above teachings are intended to fall within the scope of the claims.
Claims
1. A method for preparing a self-assembled modified ultrafiltration membrane for efficient separation of phosphate and sodium chloride, characterized by, The method comprises the steps of: S1, soaking and cleaning the surface of the ultrafiltration base film with an isopropanol solution, and cleaning the surface of the film with clean water to remove residual isopropanol on the surface of the film; S2, dissolving NaCl and PDADMAC in water to prepare a PDADMAC self-assembly solution; dissolving NaCl and PSS in water to prepare a PSS self-assembly solution; S3, coating the surface of the film prepared in step S1 with the PDADMAC self-assembly solution, pouring out the PDADMAC self-assembly solution after reaction, cleaning the film several times, and blowing the residual liquid on the surface of the film dry with inert gas to obtain a PDADMAC-loaded film; coating the surface of the PDADMAC-loaded film with the PSS self-assembly solution, pouring out the PSS self-assembly solution after reaction, cleaning the film several times, and blowing the residual liquid on the surface of the film dry with inert gas to obtain a self-assembly modified ultrafiltration film with two self-assembly layers.
2. The production method according to claim 1, characterized by, After step S3 is completed, step S3 is repeated 0-4 times to obtain a self-assembly modified ultrafiltration film with 1-5 self-assembly layers.
3. The production method according to claim 1, characterized by, In step S1, the ultrafiltration base film is selected from one of PES, PS and PAN; the molecular weight cut-off of the ultrafiltration base film is 10-200 kDa; and the volume fraction of isopropanol in the isopropanol solution is 40-60%.
4. The production method according to claim 1, characterized by, In step S1, the method for soaking and cleaning is as follows: the base film is soaked in an isopropanol solution in a constant-temperature water bath, the water bath temperature is 20-30℃, and the soaking and cleaning time is 18-30 h; after the soaking and cleaning is completed, the base film is taken out and repeatedly washed with deionized water until the residual isopropanol on the surface of the film is removed.
5. The production method according to claim 1, characterized by, In step S2, the concentration of PDADMAC in the PDADMAC self-assembly solution is 0.01-0.3 M, the concentration of NaCl is 0.25-1 M, and the solution pH is 6-8; the concentration of PDADMAC in the PSS self-assembly solution is 0.01-0.3 M, the concentration of NaCl is 0.25-1 M, and the solution pH is 6-8.
6. The production method according to claim 1, characterized by, In step S3, the coating amount of the PDADMAC and PSS self-assembly solutions is 10-30 mL / 800 cm2; the reaction time after each coating of the self-assembly solution is 5-15 min; and the cleaning times are 1-5.
7. The production method according to claim 1, characterized by, In step S3, stirring and pressure are applied to the PDADMAC self-assembly solution or the PSS self-assembly solution during the reaction; the stirring rate applied during the reaction process is 100-1000 rpm / min, and the pressure is 0.5-3 bar.
8. The self-assembly modified ultrafiltration film prepared by the preparation method in any one of claims 1-7 for efficient separation of phosphate and sodium chloride.
9. The application of the self-assembly modified ultrafiltration film in claim 8 in the field of water treatment.
10. Use according to claim 9, characterized in that, The self-assembly modified ultrafiltration film is used for efficient separation of phosphate and sodium chloride in high-salinity wastewater containing phosphate and sodium chloride; the salinity of the wastewater is 0-5%, the phosphate concentration is 10-100 mg / L, and the pH is 5-9.