High-salinity wastewater anaerobic-microalgae coupling treatment membrane, preparation method and application

Abstract

The application provides a high-salinity wastewater anaerobic-microalgae coupling treatment membrane, a preparation method and application, relates to the technical field of water treatment, and the treatment membrane comprises a support layer, a hydrophilic anti-pollution layer, a photocatalytic self-cleaning layer and a polydopamine coating layer covering the surface of the double-layer hetero composite membrane. The application has excellent anti-pollution, salt resistance and visible light self-cleaning performance, and the preparation process is simple and easy to scale up.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to an anaerobic-microalgae coupled treatment membrane for high-salt wastewater, its preparation method, and its application. Background Technology

[0002] High-salinity wastewater (such as mariculture wastewater, food processing wastewater, and shale gas backflow liquid) is difficult to treat, and traditional biological treatment is inhibited by salinity. Anaerobic membrane bioreactors (AnMBRs) can effectively treat high-salinity organic wastewater, but membrane fouling is severe, and the effluent still contains ammonia nitrogen, phosphorus, etc., requiring further treatment. Microalgae cultivation can recover nutrients, but the high-salinity environment is stressful for microalgae, and suspended solids and organic matter in the anaerobic effluent affect microalgae growth. Therefore, coupling anaerobic digestion with microalgae cultivation and achieving solid-liquid separation and mass transfer through membrane separation is a promising process. However, existing membrane materials are prone to fouling under high salinity, high organic matter, and high microbial concentrations, and cannot simultaneously meet the different needs of the anaerobic and microalgae sides.

[0003] In existing technologies, PVDF membranes are used to improve antifouling properties by adding hydrophilic nanoparticles (such as SiO2 and GO), but the effect is limited, especially in high-salt wastewater where inorganic salt crystallization and organic pollution are severe. Meanwhile, photocatalytic self-cleaning membranes mostly use TiO2, but require ultraviolet light excitation and are inefficient in the visible light environment of microalgae cultivation. Furthermore, the membrane structure is too simple to adapt to the complex operating conditions of anaerobic-microalgae coupling systems. Summary of the Invention

[0004] The purpose of this invention is to provide an anaerobic-microalgae coupled treatment membrane for high-salt wastewater, its preparation method, and its application. The membrane has excellent antifouling properties, salt tolerance, and visible light self-cleaning performance, and the preparation process is simple and easy to scale up.

[0005] To achieve the above objectives, the present invention provides an anaerobic-microalgae coupled treatment membrane for high-salinity wastewater, comprising: Support layer; A hydrophilic antifouling layer is formed on one side of the support layer by a phase inversion of a first casting solution. The first casting solution, based on its total mass, contains the following components in the following mass fractions: 12%–18% polyvinylidene fluoride, 0.1%–1.0% graphene oxide, 1.0%–3.0% hydrophilic nano-silica, 1.0%–5.0% zwitterionic copolymer, 4.0%–8.0% polyethylene glycol, 1.0%–3.0% lithium chloride, and N,N-dimethylacetamide to bring the total to 100%. A photocatalytic self-cleaning layer, formed by phase transformation of a second casting solution, is located on the side of the hydrophilic antifouling layer opposite to the support layer and is integrally bonded to the hydrophilic antifouling layer. Based on the total mass of the second casting solution, the second casting solution contains the following components in the following mass fractions: polyvinylidene fluoride 14%~20%, graphene oxide 0.1%~1.0%, visible light responsive g-C3N4 / GO heterojunction photocatalyst 1.0%~4.0%, anatase nano-titanium dioxide 0.5%~2.0%, polyethylene glycol 4.0%~8.0%, lithium chloride 1.0%~3.0%, and N,N-dimethylacetamide to bring the total to 100%. And a polydopamine coating covering the surface of the bilayer heterogeneous composite membrane.

[0006] Preferably, the zwitterionic copolymer is selected from at least one of polysulfobetaine methacrylate-co-methyl methacrylate, polycarboxybetaine methacrylate-co-methyl methacrylate, and poly(2-methacryloyloxyethyl phosphocholine-co-butyl methacrylate), with a number average molecular weight of 30,000 to 100,000. The support layer is selected from polyester nonwoven fabric, polypropylene nonwoven fabric, polyethylene nonwoven fabric or polyamide nonwoven fabric, with a thickness of 50~200 μm and a porosity of 40%~80%; The visible light responsive g-C3N4 / GO heterojunction photocatalyst has a g-C3N4 to GO mass ratio of (0.5~2):1 and a sheet diameter of 50-500 nm.

[0007] Preferably, the hydrophilic nano-silica has a particle size of 10-100 nm and is modified with a silane coupling agent; The anatase nano-titanium dioxide has a particle size of 2-20 nm.

[0008] Preferably, an interpenetrating transition zone is formed between the hydrophilic antifouling layer and the photocatalytic self-cleaning layer.

[0009] A method for preparing an anaerobic-microalgae coupled membrane for treating high-salt wastewater includes the following steps: Preparation of g-C3N4 / GO heterojunction photocatalysts; Preparation of the first casting solution: Dissolve lithium chloride in N,N-dimethylacetamide, add graphene oxide and hydrophilic nano silica, disperse evenly, then add zwitterionic copolymer and polyethylene glycol, mix evenly, and finally add polyvinylidene fluoride, stir to dissolve and degas; Preparation of the second casting solution: Lithium chloride is dissolved in N,N-dimethylacetamide, g-C3N4 / GO heterojunction photocatalyst and anatase nano titanium dioxide are added and dispersed evenly, then polyethylene glycol is added and mixed evenly, and finally polyvinylidene fluoride is added, stirred to dissolve and degass. Double-layer co-coating film formation: On the support layer, a double-groove scraper is used to simultaneously coat the first casting liquid and the second casting liquid to form a double-layer liquid film; Phase transformation: The bilayer liquid membrane is immersed in deionized water to undergo phase transformation, resulting in a bilayer heterogeneous composite membrane; Polydopamine surface modification: The bilayer heterogeneous composite membrane is immersed in a buffer solution of dopamine hydrochloride to form a coating on the membrane surface, followed by cleaning and drying.

[0010] Preferably, the preparation of the g-C3N4 / GO heterojunction photocatalyst specifically involves: Melamine was calcined at 500-600℃ for 3-5 hours to obtain bulk g-C3N4, which was then ground and ultrasonically exfoliated into nanosheets. The g-C3N4 nanosheets and graphene oxide were dispersed in deionized water at a mass ratio of 0.5:1-2:1 and ultrasonicated for 1-3 hours. The mixture was then transferred to a hydrothermal reactor and reacted at 160-200℃ for 4-8 hours. After centrifugation, washing, and drying, the g-C3N4 / GO heterojunction photocatalyst was obtained.

[0011] Preferably, when preparing the first casting solution, lithium chloride is dissolved in N,N-dimethylacetamide and stirred at 50~70°C for 1~3 hours; graphene oxide and hydrophilic nano silica are added and ultrasonically dispersed for 0.5~2 hours; zwitterionic copolymer and polyethylene glycol are added and stirred for 20~60 minutes; polyvinylidene fluoride is added in three portions and stirred at 50~80°C for 8~16 hours, followed by degassing for 6~12 hours.

[0012] Preferably, when preparing the second casting solution, lithium chloride is dissolved in N,N-dimethylacetamide and stirred at 50~70℃ for 1~3 hours; g-C3N4 / GO heterojunction photocatalyst and anatase nano titanium dioxide are added and ultrasonically dispersed for 0.5~2 hours; polyethylene glycol is added and stirred for 20~60 minutes; polyvinylidene fluoride is added in three portions and stirred at 50~80℃ for 8~16 hours, followed by degassing for 6~12 hours.

[0013] Preferably, when the two layers are co-coated to form a film, the wet film thickness of the first casting solution is 100~200 μm, the wet film thickness of the second casting solution is 100~200 μm, and the total thickness is 200~400 μm; During phase transformation, the temperature of deionized water is 15~35℃, and the soaking time is 15~60 minutes.

[0014] When modifying polydopamine surfaces, the buffer solution is an alkaline buffer solution with pH 8.0~9.0, selected from one of Tris-HCl buffer, phosphate buffer, carbonate buffer, borate buffer or organic zwitterionic buffer. The concentration of dopamine hydrochloride is 1~5 mg / mL. The solution is shaken at room temperature in the dark for 8~24 hours. After washing, it is soaked in 2~10 wt% glycerol aqueous solution for 12~48 hours and then air-dried.

[0015] Application of an anaerobic-microalgae coupled membrane for high-salt wastewater treatment in water treatment.

[0016] Therefore, the present invention employs the above-mentioned anaerobic-microalgae coupled treatment membrane for high-salt wastewater, its preparation method, and its application, with the following technical effects: The double-sided heterogeneous structure design simultaneously meets the requirements of anti-fouling on the anaerobic side and photocatalytic self-cleaning on the microalgae side.

[0017] The zwitterionic copolymer, in synergy with polydopamine, significantly enhances the ability to resist crystallization contamination by proteins, polysaccharides, and inorganic salts.

[0018] The visible light-responsive g-C3N4 / GO / TiO2 heterojunction photocatalyst can degrade organic pollutants in situ under microalgae cultivation and illumination conditions, achieving self-cleaning.

[0019] The polydopamine biomimetic adhesion layer firmly anchors the photocatalyst, extending its service life.

[0020] The preparation process is simple, and the double-layer co-coating method is easy to scale up. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the double-layer heterogeneous composite membrane of the present invention; Figure 2 This is a comparison chart of the antifouling performance of the membranes in Example 1 and Comparative Example 1. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] Example 1 (1) Preparation of g-C3N4 / GO heterojunction: Melamine was calcined at 550℃ for 4h, and g-C3N4 nanosheets were obtained by grinding and ultrasonic exfoliation. The g-C3N4 nanosheets and GO were dispersed in deionized water at a mass ratio of 1:1, ultrasonicated for 2h, transferred to a hydrothermal reactor and reacted at 180℃ for 6h. After centrifugation, washing and drying, g-C3N4 / GO heterojunction with a diameter of about 200nm was obtained.

[0025] (2) Preparation of the first casting solution: Dissolve 2.0% LiCl in 73.0% DMAc by mass fraction and stir at 60℃ for 2h; add 0.5% GO and 1.5% modified SiO2 (20-50nm) and ultrasonically disperse for 1h; add 3.0% PSBMA-co-MMA (number average molecular weight 50,000) and 6.0% PEG-600 and stir for 30min; add 14.0% PVDF in three portions, stir at 60℃ for 12h, and vacuum degas for 8h.

[0026] (3) Preparation of the second casting solution: Dissolve 2.0% LiCl in 72.5% DMAc and stir at 60℃ for 2h; add 2.0% g-C3N4 / GO and 1.0% anatase TiO2 (5-10nm) and disperse by ultrasonication for 1h; add 6.0% PEG-600 and stir for 30min; add 16.0% PVDF in three portions, stir at 60℃ for 12h, and degas for 8h.

[0027] (4) Double-layer co-scraping: Using polyester nonwoven fabric (100μm thick) as the support layer, the first casting liquid and the second casting liquid are scraped simultaneously using a double-groove scraper, controlling the thickness of the first wet film to be 150μm, the thickness of the second wet film to be 150μm, and the total thickness to be 300μm.

[0028] (5) Phase transformation: Immediately immerse in 25℃ deionized water and keep for 30 minutes.

[0029] (6) Polydopamine modification: The membrane was immersed in Tris-HCl buffer (pH 8.5, 10mM) with 2 mg / mL dopamine hydrochloride, shaken at room temperature in the dark for 12 h, washed with deionized water, soaked in 5 wt% glycerol aqueous solution for 24 h, and dried to obtain a bilayer heterogeneous composite membrane M1. The structure of the composite membrane is as follows. Figure 1 As shown.

[0030] Example 2 The process was essentially the same as in Example 1, except that the amount of zwitterionic copolymer PSBMA-co-MMA added to the first casting solution was adjusted from 3.0% to 1.5%, and the corresponding DMAc content was adjusted to 74.5%. All other conditions remained unchanged. Membrane M2 was thus prepared.

[0031] Example 3 The process was essentially the same as in Example 1, except that the amount of zwitterionic copolymer PSBMA-co-MMA added to the first casting solution was adjusted from 3.0% to 5.0%, and the corresponding DMAc content was adjusted to 71.0%. All other conditions remained unchanged. Membrane M3 was thus prepared.

[0032] Example 4 The process was essentially the same as in Example 1, except that the amount of g-C3N4 / GO heterojunction photocatalyst added to the second casting solution was adjusted from 2.0% to 3.0%, the amount of anatase TiO2 added was adjusted from 1.0% to 1.5%, and the corresponding DMAc content was adjusted from 72.5% to 70.0%. Other conditions remained unchanged. Film M4 was thus prepared.

[0033] Example 5 The process was essentially the same as in Example 1, except that the photocatalyst composition in the second casting solution was adjusted to 1.5% g-C3N4 / GO heterojunction and 2.5% anatase TiO2 (the total amount of both remained at 4.0%), and the corresponding DMAc content was adjusted to 70.5%. All other conditions remained unchanged. Membrane M5 was thus prepared.

[0034] Example 6 The process is basically the same as in Example 1, except that: the zwitterionic copolymer in the first casting solution is changed to polycarboxybenzene methacrylate-co-methyl methacrylate, the support layer is changed to polypropylene nonwoven fabric, and the buffer solution is changed to phosphate buffer solution.

[0035] Example 7 The process is basically the same as in Example 1, except that: the zwitterionic copolymer in the first casting solution is changed to poly(2-methacryloyloxyethyl phosphocholine-co-butyl methacrylate), the support layer is changed to polypropylene nonwoven fabric, and the buffer solution is changed to carbonate buffer solution.

[0036] Example 8 The support layer was changed to polyamide nonwoven fabric, and the buffer solution was changed to borate buffer solution.

[0037] Example 9 The buffer solution was adjusted to an organic zwitterionic buffer solution.

[0038] Comparative Example 1 The traditional homogeneous PVDF membrane is used without adding zwitterionic copolymers and photocatalysts, and without polydopamine modification. The specific formula is: PVDF 16%, PEG-600 6%, LiCl 2%, DMAc 76%, which is single-layered and coated on polyester nonwoven fabric. After phase inversion, membrane C1 is obtained.

[0039] Comparative Example 2 The process is basically the same as in Example 1, except that the polydopamine surface modification step is not performed, and other conditions remain unchanged, resulting in film C2.

[0040] Performance testing The membranes prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to performance tests, including: pure water flux (0.1 MPa), bovine serum albumin (BSA) rejection rate, water contact angle, antifouling performance (expressed as flux recovery rate after BSA solution filtration), salt tolerance (flux decay rate after soaking in 3.5% NaCl for 30 days), and visible light self-cleaning performance (expressed as methylene blue degradation rate after irradiation with visible light λ>420 nm for 2 hours).

[0041] The test results are shown in Table 1.

[0042] Table 1. Comparison of membrane performance between each embodiment and the comparative example.

[0043] Note: C2 was not modified with polydopamine, and its photocatalyst was directly exposed. The initial MB degradation rate could reach 85%, but after three backwashes, it dropped to below 40% (data not listed), indicating that the photocatalyst was easily lost.

[0044] Comparing Examples 1, 2, and 3, it can be seen that as the PSBMA-co-MMA content increases from 1.5% to 5.0%, the water contact angle on the membrane surface significantly decreases (48°→36°), the antifouling performance (FRR) increases from 90% to 98%, and the salt tolerance flux decay rate decreases from 15% to 5%. This indicates that increasing the zwitterionic copolymer content can significantly enhance the surface hydration layer and inhibit protein and salt crystallization adsorption. However, the pure water flux decreases from 135 L / (m²) 2 The concentration of ·h) decreased to 116 L / (m 2 This is because the increased polymer content densifies the membrane surface, increasing mass transfer resistance. Therefore, an addition of 3.0% achieves a good balance between flux and antifouling properties.

[0045] Comparing Examples 1 and 4, it can be seen that when the g-C3N4 / GO ratio increases from 2.0% to 3.0% and the TiO2 ratio increases from 1.0% to 1.5%, the visible light MB degradation rate increases from 92% to 96%, and the self-cleaning performance is enhanced. However, the pure water flux decreases from 128 L / (m³) to 121 L / (m³). 2 The high content of photocatalyst may partially clog the membrane pores. In Example 5, increasing the TiO2 ratio to 2.5% and decreasing the g-C3N4 / GO ratio to 1.5% resulted in a MB degradation rate of 95%, slightly lower than in Example 4, but with a greater decrease in flux (112 L / (m²)). 2 The presence of excessive TiO2 agglomeration (·h) indicates that the excessive agglomeration of TiO2 affects the membrane pore structure. Therefore, the ratio in Example 1 (g-C3N4 / GO 2.0%, TiO2 1.0%) maintains good flux while ensuring photocatalytic activity.

[0046] The FRR, salt tolerance, and photocatalytic degradation rate of all examples were significantly better than those of Comparative Example 1, demonstrating the synergistic effect of the zwitterionic copolymer, the visible light catalyst, and the polydopamine coating. Although Comparative Example 2 showed high initial photocatalytic activity, the lack of polydopamine anchoring led to easy photocatalyst loss and poor long-term stability. In Examples 1-5, due to the presence of polydopamine, the degradation rate of the photocatalyst decreased by only <5% after three backwashes, exhibiting excellent stability.

[0047] Depend on Figure 2 It can be seen that the relative flux decrease of the bilayer heterogeneous composite membrane prepared in Example 1 during the filtration of simulated high-salt wastewater (containing BSA) was significantly slower than that of Comparative Example 1. Within a 120-minute filtration cycle, the flux of the membrane in Example 1 decreased only from 1.0 to approximately 0.86, while the flux of the membrane in Comparative Example 1 rapidly decreased to approximately 0.58. After hydraulic cleaning, the flux recovery rate (FRR) of the membrane in Example 1 reached 96%, while that of the membrane in Comparative Example 1 was only 65%.

[0048] The above results demonstrate that the membrane in Example 1, through the introduction of zwitterionic copolymers, hydrophilic nano-SiO2 / GO, and a polydopamine surface coating, significantly enhances the membrane surface's resistance to organic fouling and inorganic salt crystallization, effectively slowing down the formation of irreversible fouling. This results in maintaining higher operating flux and superior cleaning and recovery performance in high-salt wastewater environments. In contrast, Comparative Example 1, lacking the aforementioned functional components, exhibits poor hydrophilicity on its membrane surface, making it prone to pollutant deposition and embedding within the membrane pores, leading to rapid flux decay and limited cleaning and recovery.

[0049] Therefore, the present invention employs the above-mentioned anaerobic-microalgae coupled treatment membrane for high-salt wastewater, its preparation method, and its application, which has excellent anti-fouling properties, salt tolerance, and visible light self-cleaning performance, and the preparation process is simple and easy to scale up.

[0050] 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 them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A membrane for anaerobic-microalgae coupling treatment of high-salinity wastewater, characterized in that, include: Support layer; A hydrophilic antifouling layer is formed on one side of the support layer by a phase inversion of a first casting solution. The first casting solution, based on its total mass, comprises the following components in the following mass fractions: 12%–18% polyvinylidene fluoride, 0.1%–1.0% graphene oxide, 1.0%–3.0% hydrophilic nano-silica, 1.0%–5.0% zwitterionic copolymer, 4.0%–8.0% polyethylene glycol, 1.0%–3.0% lithium chloride, and N,N-dimethylacetamide to bring the total to 100%. The zwitterionic copolymer is selected from at least one of polysulfobetaine methacrylate-co-methyl methacrylate, polycarboxybetaine methacrylate-co-methyl methacrylate, and poly(2-methacryloyloxyethyl phosphocholine-co-butyl methacrylate), with a number average molecular weight of 30,000–100,000. A photocatalytic self-cleaning layer, formed by phase transformation of a second casting solution, is located on the side of the hydrophilic antifouling layer opposite to the support layer and is integrally bonded to the hydrophilic antifouling layer. Based on the total mass of the second casting solution, the second casting solution contains the following components in the following mass fractions: polyvinylidene fluoride 14%~20%, graphene oxide 0.1%~1.0%, visible light responsive g-C3N4 / GO heterojunction photocatalyst 1.0%~4.0%, anatase nano-titanium dioxide 0.5%~2.0%, polyethylene glycol 4.0%~8.0%, lithium chloride 1.0%~3.0%, and N,N-dimethylacetamide to bring the total to 100%. And a polydopamine coating covering the surface of the bilayer heterogeneous composite membrane.

2. The anaerobic-microalgae coupled treatment membrane for high-salinity wastewater according to claim 1, characterized in that, The support layer is selected from polyester nonwoven fabric, polypropylene nonwoven fabric, polyethylene nonwoven fabric or polyamide nonwoven fabric, with a thickness of 50~200μm and a porosity of 40%~80%; The visible light responsive g-C3N4 / GO heterojunction photocatalyst has a g-C3N4 to GO mass ratio of (0.5~2):1 and a sheet diameter of 50-500 nm.

3. The anaerobic-microalgae coupled treatment membrane for high-salinity wastewater according to claim 1, characterized in that, The hydrophilic nano-silica has a particle size of 10-100 nm and is modified with a silane coupling agent; The anatase nano-titanium dioxide has a particle size of 2-20 nm.

4. The anaerobic-microalgae coupled treatment membrane for high-salinity wastewater according to claim 1, characterized in that, An interpenetrating transition zone is formed between the hydrophilic antifouling layer and the photocatalytic self-cleaning layer.

5. The method for preparing an anaerobic-microalgae coupled membrane for treating high-salinity wastewater according to claim 1, characterized in that, Includes the following steps: Preparation of g-C3N4 / GO heterojunction photocatalysts; Preparation of the first casting solution: Dissolve lithium chloride in N,N-dimethylacetamide, add graphene oxide and hydrophilic nano silica, disperse evenly, then add zwitterionic copolymer and polyethylene glycol, mix evenly, and finally add polyvinylidene fluoride, stir to dissolve and degas; Preparation of the second casting solution: Lithium chloride is dissolved in N,N-dimethylacetamide, g-C3N4 / GO heterojunction photocatalyst and anatase nano titanium dioxide are added and dispersed evenly, then polyethylene glycol is added and mixed evenly, and finally polyvinylidene fluoride is added, stirred to dissolve and degass. Double-layer co-coating film formation: On the support layer, a double-groove scraper is used to simultaneously coat the first casting liquid and the second casting liquid to form a double-layer liquid film; Phase transformation: The bilayer liquid membrane is immersed in deionized water to undergo phase transformation, resulting in a bilayer heterogeneous composite membrane; Polydopamine surface modification: The bilayer heterogeneous composite membrane is immersed in a buffer solution of dopamine hydrochloride to form a coating on the membrane surface, followed by cleaning and drying.

6. The method for preparing an anaerobic-microalgae coupled membrane for treating high-salinity wastewater according to claim 5, characterized in that, The specific steps for preparing the g-C3N4 / GO heterojunction photocatalyst are as follows: Melamine was calcined at 500-600℃ for 3-5 hours to obtain bulk g-C3N4, which was then ground and ultrasonically exfoliated into nanosheets. The g-C3N4 nanosheets and graphene oxide were dispersed in deionized water at a mass ratio of 0.5:1-2:1 and ultrasonicated for 1-3 hours. The mixture was then transferred to a hydrothermal reactor and reacted at 160-200℃ for 4-8 hours. After centrifugation, washing, and drying, the g-C3N4 / GO heterojunction photocatalyst was obtained.

7. The method for preparing an anaerobic-microalgae coupled membrane for treating high-salinity wastewater according to claim 5, characterized in that, When preparing the first casting solution, lithium chloride is dissolved in N,N-dimethylacetamide and stirred at 50~70℃ for 1~3 hours; graphene oxide and hydrophilic nano silica are added and ultrasonically dispersed for 0.5~2 hours; zwitterionic copolymer and polyethylene glycol are added and stirred for 20~60 minutes; polyvinylidene fluoride is added in three portions and stirred at 50~80℃ for 8~16 hours, followed by degassing for 6~12 hours.

8. The method for preparing an anaerobic-microalgae coupled membrane for treating high-salinity wastewater according to claim 5, characterized in that, When preparing the second casting solution, lithium chloride is dissolved in N,N-dimethylacetamide and stirred at 50~70℃ for 1~3 hours; g-C3N4 / GO heterojunction photocatalyst and anatase nano titanium dioxide are added and ultrasonically dispersed for 0.5~2 hours; polyethylene glycol is added and stirred for 20~60 minutes; polyvinylidene fluoride is added in three portions and stirred at 50~80℃ for 8~16 hours, followed by degassing for 6~12 hours.

9. The method for preparing an anaerobic-microalgae coupled membrane for treating high-salinity wastewater according to claim 5, characterized in that, When the two layers are co-coated to form a film, the wet film thickness of the first casting solution is 100~200 μm, the wet film thickness of the second casting solution is 100~200 μm, and the total thickness is 200~400 μm. During phase transformation, the temperature of deionized water is 15~35℃, and the soaking time is 15~60 minutes; When modifying polydopamine surfaces, the buffer solution is an alkaline buffer solution with pH 8.0~9.0, selected from one of Tris-HCl buffer, phosphate buffer, carbonate buffer, borate buffer or organic zwitterionic buffer. The concentration of dopamine hydrochloride is 1~5 mg / mL. The solution is shaken at room temperature in the dark for 8~24 hours. After washing, it is soaked in 2~10 wt% glycerol aqueous solution for 12~48 hours and then air-dried.

10. The application of the anaerobic-microalgae coupled treatment membrane for high-salt wastewater according to claim 1 in water treatment.

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