Modified anion exchange membrane and method for treating high-sulfate organic wastewater

Abstract

The application discloses a modified anion exchange membrane which is prepared by cross-linking of polyvinyl alcohol, positively charged amine compounds and beta-cyclodextrin, and is prepared by surface modification through electrodeposition in the presence of polyanion modifier. The modified anion exchange membrane can effectively separate salt and organic matter in high-sulfate organic wastewater in electrodialysis treatment, and solves the problem of long-term difficult treatment of high-sulfate organic wastewater. Further, most of the organic matter is finally converted into methane through subsequent anaerobic reaction, resource recycling is realized, carbon dioxide emission and energy consumption are reduced, and the double-carbon development concept is met. The modified anion exchange membrane has the characteristics of strong anti-pollution ability and high ion exchange rate, and has high application value.

Description

Technical Field

[0001] This invention relates to a modified anion exchange membrane that can be used to treat high-sulfate organic wastewater, belonging to the field of membrane separation technology. Background Technology

[0002] High-sulfate organic wastewater exists in various industries such as chemical, pharmaceutical, papermaking, food processing, and mining. Traditional treatment methods include chemical methods, simple biochemical methods, two-stage anaerobic processes, and biological desulfurization technology. However, the presence of high sulfate makes it difficult to remove organic matter from the wastewater.

[0003] The chemical method involves adding lime to convert sulfate into calcium sulfate precipitate, while simultaneously employing chemical flocculation. This process generates a large amount of unusable chemical sludge, causing secondary pollution, and has limited sulfate removal efficiency. A more traditional, simpler biological method is a primary anaerobic process, but under anaerobic conditions, sulfate is reduced to sulfur by sulfate-reducing bacteria (SRB). 2- The sulfate ion, which has strong biotoxicity and a significant inhibitory effect on microbial communities, generally requires the sulfate concentration in the primary anaerobic reactor to be less than 2000 mg / L, as described in patent CN103771670A. To avoid competition between sulfate-reducing bacteria and methanogenic bacteria during the anaerobic process, a two-stage anaerobic process can be used to treat high-sulfate organic wastewater, as described in patent CN105439374A. The primary anaerobic process is controlled in the hydrolysis and acidification stage, and the secondary anaerobic process is controlled in the methanogenesis stage. However, the process control and actual operation of the two-stage anaerobic process are quite difficult. Biological desulfurization technology, in which sulfate is converted into elemental sulfur under the action of specific bacteria, as described in patents CN102795739A and CN103172218A, has stringent requirements, is difficult to control, and suffers from poor separation effect and low sulfur purity. Currently, it is still some distance from industrial application. Currently, there are also studies on the treatment of high-salt organic wastewater with special salt-tolerant bacteria using direct aerobic processes. However, direct aerobic processes for treating high-salt organic wastewater require a large amount of aeration, have low treatment loads, and high energy consumption. The organic matter is eventually converted into carbon dioxide, failing to effectively utilize the carbon source.

[0004] Membrane separation technology is an emerging technology that uses separation membranes as its core for separation, concentration, and purification. Commonly used membrane separation technologies include ultrafiltration, nanofiltration, and reverse osmosis. The pore sizes of these membranes are mostly at the nanometer level, making them very susceptible to clogging by organic matter and suspended solids. They are primarily used for domestic water purification and, in wastewater treatment, mainly for end-of-pipe desalination. Electrodialysis is a new technology that combines membrane separation with electrochemistry. It uses a semi-permeable membrane, which is an ion exchange membrane, to achieve the separation of anions and cations under the drive of an external DC electric field. Due to its simple operation and long service life, electrodialysis has been widely used in seawater desalination and brackish water desalination. However, for industrial wastewater, especially high-sulfate organic wastewater, which contains not only soluble inorganic salts but also a large amount of organic matter, especially negatively charged organic matter, the separation and concentration process easily leads to anion exchange membrane fouling, thus restricting the further development of this technology.

[0005] To broaden the application scope of electrodialysis technology, current research focuses primarily on the modification of ion exchange membranes. For example, patents CN104815568A and CN106925357A modify the surface of commercial anion exchange membranes, achieving excellent selective separation of monovalent and polyvalent anions. Patents CN108479405A and CN109225357A prepare anion exchange membranes that not only possess monovalent ion selectivity but also exhibit antifouling and antibacterial properties. However, when dealing with high-salt organic wastewater primarily composed of sulfate, these modified anion exchange membranes, while maintaining high chloride ion permeability, retain a large amount of sulfate ions in the original solution, failing to solve the problem of separating salts and organic matter. Summary of the Invention

[0006] To address the above shortcomings, this invention provides a modified anion exchange membrane that is particularly suitable for treating high-sulfate organic wastewater. During the treatment process, it can efficiently separate salts and organic matter, which is conducive to the further utilization of organic matter, realizing the resource utilization of organic matter in wastewater, and has the advantages of energy saving and environmental protection.

[0007] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows: The technical objective of the first aspect of this invention is to provide a method for preparing a modified anion exchange membrane, comprising the following steps: Step a: Add polyvinyl alcohol to water to prepare a polyvinyl alcohol aqueous solution, then add positively charged amine compounds and β-cyclodextrin to the above solution respectively, mix and react to obtain a casting solution; Step b: Cast the casting solution obtained in step a onto a horizontal panel, dry it, and obtain the base film; Step c: Immerse the base film obtained in step b in a crosslinking solution composed of crosslinking agent, sodium sulfate, sulfuric acid, and water; Step d: Wash the cross-linked membrane, alkalize it in an alkaline solution, and then soak it in water to obtain a polyvinyl alcohol anion exchange membrane; Step e: Dissolve the polyanionic modifier and sodium chloride in Tris-HCl buffer solution, and adjust the pH to 8-9 with hydrochloric acid to obtain the modified solution; Step f: Place the anion exchange membrane obtained in step d in the middle of the DC electrodeposition apparatus to form two compartments. Put the modified solution prepared in step e into the compartment on the cathode side and put water into the compartment on the anode side to carry out the electrodeposition reaction and obtain the modified anion exchange membrane.

[0008] Furthermore, the positively charged amine compound is one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxychloropropaneamine, and quaternized chitosan, preferably 2,3-epoxypropyltrimethylammonium chloride; the mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1 to 0.6:1.

[0009] Furthermore, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.05:1 to 0.4:1.

[0010] Furthermore, in step a, the mass fraction of the polyvinyl alcohol aqueous solution is 5% to 15%, and the reaction time with the positively charged amine compound and β-cyclodextrin is 2 to 10 hours.

[0011] Furthermore, the polyvinyl alcohol aqueous solution is prepared by stirring at 60–90°C to dissolve the polyvinyl alcohol in water.

[0012] Furthermore, the drying in step b involves first drying at room temperature for 2–6 hours, and then continuing to dry under vacuum at 40–80°C for 4–10 hours.

[0013] Furthermore, the crosslinking agent is selected from aldehyde or acid crosslinking agents, preferably glutaraldehyde.

[0014] Furthermore, the crosslinking solution contains, by weight, 2%–8% crosslinking agent, 4%–15% sodium sulfate, and 1%–4% sulfuric acid, with the remainder being water.

[0015] Furthermore, in step c, the base membrane is immersed in the crosslinking solution for 1 to 6 hours; crosslinking is formed in the membrane through an acetal reaction.

[0016] Furthermore, the washing described in step d is washing with water until neutral.

[0017] Furthermore, the alkalization is performed using a 0.5–3 mol / L sodium hydroxide aqueous solution for 12–24 hours.

[0018] Furthermore, the soaking time in step d is 12 to 24 hours.

[0019] Furthermore, the polyanionic modifier is one or more of sodium poly4-styrene sulfonate, sodium p-styrene sulfonate, sodium polyethylene sulfonate, and sodium polypropylene sulfonate, preferably sodium poly4-styrene sulfonate.

[0020] Furthermore, in step e, the mass concentration of the polyanionic modifier in the modified solution is 1–10 g / L, and the mass concentration of sodium chloride is 3–30 g / L.

[0021] Furthermore, the concentration of the Tris-HCl buffer in step e is 10–50 mmol / L.

[0022] Furthermore, the electrodeposition reaction time in step f is 0.2–2 h, and the current density is 1–50 mA / cm². 2 A polyanion modifier was deposited on the surface of the anion exchange membrane using an electrodeposition method to modify the membrane surface.

[0023] Furthermore, after obtaining the modified anion exchange membrane, it is stored in a sodium chloride solution with a mass concentration of 5–20 g / L.

[0024] The technical objective of the second aspect of this invention is to provide a modified anion exchange membrane prepared by the above-described preparation method.

[0025] The technical objective of the third aspect of this invention is to provide a method for treating high-sulfate organic wastewater using the above-mentioned modified anion exchange membrane, wherein the modified anion exchange membrane is used as the anion exchange membrane in the electrodialysis unit to perform electrodialysis concentration treatment on the high-sulfate organic wastewater.

[0026] Furthermore, the high-sulfate organic wastewater has a COD ≥ 2000 mg / L and a sulfate content ≥ 3000 mg / L.

[0027] Furthermore, the cation exchange membrane of the electrodialysis unit is a general-purpose cation exchange membrane. The electrodialysis is mainly used for the separation of organic matter and salts. After separation, the organic matter is mainly present in the desalination solution, and the salts are mainly present in the concentrate. The electrodialysis treatment time is 0.5–5 hours, and the current density is 1–80 mA / cm². 2 .

[0028] Those skilled in the art should understand that most organic pollutants present in natural water bodies or wastewater, such as surfactants, humic acids, and proteins, are negatively charged. The anion exchange membrane of this invention, after modification with a polyanion modifier, carries a negatively charged surface, exhibiting electrostatic repulsion against negatively charged organic matter in the water, thus inhibiting organic pollution of the anion exchange membrane. While the negative surface charge prevents organic pollution through electrostatic interaction, it also affects the migration rate of inorganic anions; the higher the ion charge, the greater the impact. Therefore, sulfate ions are more affected than chloride ions. The addition of β-cyclodextrin to the anion exchange membrane imparts strong hydrophilicity and alters the migration rates between anions. Anions with lower hydration levels, such as bromide and nitrate ions, show a reduced migration rate relative to chloride ions, while anions with higher hydration levels, such as sulfate ions, show an increased migration rate relative to chloride ions. Furthermore, increased membrane hydrophilicity reduces van der Waals forces between the membrane and organic solutes, decreasing attraction. Simultaneously, hydrogen bonding between the hydrophilic membrane and water molecules forms a hydration layer, which further hinders the adsorption of pollutants on the membrane surface. Therefore, after the anion exchange membrane of the present invention is modified by a polyanion modifier and β-cyclodextrin, the membrane’s antifouling ability is greatly increased, and the selective permeability of sulfate ions is significantly increased.

[0029] The technical objective of the fourth aspect of this invention is to provide a treatment process for high-sulfate organic wastewater, including a softening and conditioning unit, an electrodialysis unit, an anaerobic biochemical unit, a methane purification unit, and a post-treatment unit; wherein the anion exchange membrane in the electrodialysis unit is the modified anion exchange membrane described above.

[0030] As a more specific implementation, the treatment process for the high-sulfate organic wastewater is as follows: the high-sulfate organic wastewater first enters a softening and conditioning unit to remove calcium and magnesium hardness, and then enters an electrodialysis unit; the anion exchange membrane of the electrodialysis unit is a modified anion exchange membrane, and the cation exchange membrane is a general-purpose cation exchange membrane. The electrodialysis desalination solution enters an anaerobic biological treatment unit, and the electrodialysis concentrate enters a post-treatment unit; the methane produced by the anaerobic biological treatment unit is treated by a methane purification unit and then recycled, and the effluent from the anaerobic biological treatment unit enters the post-treatment unit in the same way as the electrodialysis concentrate.

[0031] Furthermore, the softening regulating unit preferably uses a combination of sodium hydroxide and sodium carbonate as the de-hardening agent, with sodium hydroxide added at 1 to 4 times the mass concentration of magnesium ions and sodium carbonate added at 1 to 3 times the mass concentration of calcium ions.

[0032] Furthermore, the electrodialysis treatment time is 0.5–5 hours, and the current density is 1–80 mA / cm². 2 .

[0033] Furthermore, the methane purification unit employs one of the following technologies to purify the gas generated by the anaerobic biochemical unit: solid desulfurizing agent adsorption, biological desulfurization, alkaline desulfurization, or amine desulfurization, to obtain methane with a purity greater than 96%.

[0034] Furthermore, the post-treatment unit is one or a combination of technologies such as advanced oxidation, halophilic aerobic biochemical treatment, membrane concentration, and evaporation concentration, which can achieve COD emission standards or zero emissions through treatment.

[0035] By employing the above-described technology, the beneficial effects of the present invention compared to the prior art are as follows: The modified anion exchange membrane of this invention, when applied in electrodialysis, can effectively separate salts and organic matter in high-sulfate organic wastewater, solving the long-standing problem of its difficult treatment. Furthermore, subsequent anaerobic reactions convert most of the organic matter into methane, achieving resource recovery and reducing carbon dioxide emissions and energy consumption, aligning with current dual-carbon development principles. The modified anion exchange membrane exhibits strong anti-fouling capabilities, high ion exchange rate, and a simple preparation method, making it highly valuable for application.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0037] Figure 1 Schematic diagram of anion exchange membrane electrodeposition modification in Example 1; Figure 2 Flowchart of high sulfate organic wastewater treatment in Example 1. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0039] Example 1 Modified anion exchange membranes were prepared using the following method: Step a: Add polyvinyl alcohol to deionized water to prepare a 10% aqueous solution. Stir at 80°C to dissolve it. Then add 2,3-epoxypropyltrimethylammonium chloride and β-cyclodextrin to the water. The mass ratio of 2,3-epoxypropyltrimethylammonium chloride to polyvinyl alcohol is 0.4:1, and the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.2:1. React for 5 hours to obtain a viscous liquid, which is the casting solution. Step b: Cast the casting solution onto a horizontal glass plate and dry it at room temperature for 3 hours. Then, continue to dry the formed film under vacuum at 60°C for 6 hours to obtain the base film. Step c: The vacuum-dried membrane is further immersed in a mixed solution composed of glutaraldehyde, sodium sulfate, sulfuric acid and deionized water, with the mass percentages of glutaraldehyde, sodium sulfate and sulfuric acid being 5%, 8% and 2% respectively, and the remainder being deionized water. The membrane is soaked for 3 hours to form crosslinks in the membrane through acetal reaction. Step d: Wash the cross-linked membrane with deionized water until neutral, then alkalize it in a 1 mol / L sodium hydroxide aqueous solution for 16 h, and then soak it in deionized water for 16 h to obtain a polyvinyl alcohol anion exchange membrane. Step e: Dissolve the polyanionic modifier and sodium chloride in 20 mmol / L Tris–HCl buffer, adjust the pH to 8.5 with hydrochloric acid, the mass concentration of the polyanionic modifier is 3 g / L, the mass concentration of sodium chloride is 10 g / L, and the polyanionic modifier is sodium poly4-styrene sulfonate, to obtain the modified solution. Step f: Surface modification is performed using an electrodeposition method, such as... Figure 1 As shown, the anion exchange membrane to be modified was placed in the middle of a DC electrodeposition apparatus, forming two compartments. The cathode-side compartment contained the modification solution, and the anode-side compartment contained deionized water. The electrodeposition time was 0.8 hours, and the current density was 20 mA / cm². 2 A modified anion exchange membrane was obtained; Step g: Remove the modified anion exchange membrane and place it in a sodium chloride solution with a mass concentration of 10 g / L for later use.

[0040] The modified anion exchange membrane prepared above was used for electrodialysis treatment of high-sulfate organic wastewater.

[0041] The process flow diagram for treating high-sulfate organic wastewater is as follows: Figure 2 As shown, high-sulfate organic wastewater first enters the softening and conditioning unit to remove calcium and magnesium hardness, and then enters the electrodialysis unit; the electrodialysis desalination solution enters the anaerobic biological treatment unit, and the electrodialysis concentrate enters the post-treatment unit; the methane produced in the anaerobic biological treatment unit is treated by the methane purification unit and then recycled; the effluent from the anaerobic biological treatment unit, like the electrodialysis concentrate, enters the post-treatment unit; the wastewater is further treated by the post-treatment unit to achieve COD compliance or zero discharge.

[0042] The high-sulfate organic wastewater used in this embodiment is wastewater generated from a dicarboxylic acid fermentation process. It is a typical high-sulfate organic wastewater with the following water quality: COD 5100 mg / L, sulfate 5000 mg / L, chloride concentration 1800 mg / L, calcium ion concentration 150 mg / L, magnesium ion concentration 50 mg / L, total salt content 10800 mg / L, and wastewater flow rate 10 t / h.

[0043] The organic matter in the high-content dicarboxylic acid fermentation wastewater mainly consists of lactones, furans, and benzenes, which are stable compounds with five-membered rings, six-membered rings, and benzene rings. These are mostly neutral organic compounds without a charge. However, the wastewater also contains a certain amount of negatively charged acidic organic matter. If electrodialysis desalination is directly used, this negatively charged organic matter can easily foul the anion exchange membrane, affecting its ion permeability. Therefore, in this embodiment, the anion exchange membrane used for electrodialysis is the modified anion exchange membrane prepared above, which has strong anti-fouling ability and high ion permeability. The cation exchange membrane is a general-purpose cation exchange membrane (product of Hefei Kaijie Polymer Co., Ltd., China, model CJ-MC-3).

[0044] The specific operating parameters and results for treating dicarboxylic acid fermentation wastewater are as follows: The wastewater is first softened and conditioned by adding a dehardening agent at a concentration of 120 mg / L sodium hydroxide and 300 mg / L sodium carbonate. After clarification, the calcium ion concentration in the supernatant is reduced to below 10 mg / L and the magnesium ion concentration to below 5 mg / L. The effluent then enters electrodialysis; the electrodialysis treatment time is 1 hour, and the current density is 25 mA / cm³. 2 Data from one week of stable operation of the electrodialysis unit showed that the COD concentration of the desalinated solution was 6360 mg / L, the salt content was 2910 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 2160 mg / L, the salt content was 29210 mg / L, and the flow rate was 3 t / h. The selective permeability of sulfate ions was 78.2%, the selective permeability of chloride ions was 86.1%, and the retention rate of organic matter was 87.3%.

[0045] Subsequently, the electrodialysis desalination solution enters the anaerobic biological treatment unit. The methane produced is purified to a purity of 98.6% after being purified by alkaline solution. The COD concentration of the effluent from the anaerobic biological treatment unit is 650 mg / L, and the salt content is 2940 mg / L. It then enters the post-treatment unit. The COD concentration of the mixed influent to the post-treatment unit is 1103 mg / L, and the salt content is 10821 mg / L. The combined process of halophilic bacteria aerobic biological treatment and ozone catalytic oxidation can be further treated to achieve COD compliance for discharge.

[0046] As can be seen from this embodiment, the present invention can effectively treat high-sulfate organic wastewater similar to dicarboxylic acid fermentation wastewater. Electrodialysis with modified anion exchange membrane as the core achieves excellent separation of organic matter and salts, with high organic matter retention rate and high resource utilization rate. Among them, 78.4% of the organic matter is utilized as methane, and only a small amount of organic matter is treated by high-energy-consuming aerobic aeration and ozone catalytic oxidation. The overall process is more energy-saving and environmentally friendly.

[0047] Example 2 Modified anion exchange membranes were prepared using the following method: Except that the mass concentration of the polyanionic modifier in the modified solution in step e is 4 g / L and the electrodeposition time in step f is 1 h, the rest is the same as in Example 1.

[0048] The modified anion exchange membrane prepared above was used for electrodialysis treatment of high-sulfate organic wastewater. The wastewater quality was as follows: COD 3000 mg / L, sulfate 4000 mg / L, chloride concentration 1000 mg / L, calcium ion concentration 100 mg / L, magnesium ion concentration 100 mg / L, total salt content 7850 mg / L, wastewater flow rate 10 t / h. The organic matter in the wastewater was mainly neutral organic matter (uncharged), which is typical high-sulfate organic wastewater.

[0049] In this embodiment, the anion exchange membrane used in electrodialysis is the modified anion exchange membrane prepared above, and the cation exchange membrane is a general-purpose cation exchange membrane (product of Hefei Capgemini Polymer Co., Ltd., China, model CJ-MC-3).

[0050] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows: The wastewater is first softened and conditioned by adding a dehardening agent at a concentration of 200 mg / L sodium hydroxide and 200 mg / L sodium carbonate. After clarification, the calcium ion concentration in the supernatant is reduced to below 8 mg / L and the magnesium ion concentration to below 6 mg / L. The effluent then enters electrodialysis; the electrodialysis treatment time is 1 hour, and the current density is 25 mA / cm³. 2 Data from one week of stable operation of the electrodialysis unit showed that the COD concentration of the desalinated solution was 4007 mg / L, the salt content was 2691 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 650 mg / L, the salt content was 19886 mg / L, and the flow rate was 3 t / h. The selective permeability of sulfate ions was 73.3%, the selective permeability of chloride ions was 81.4%, and the retention rate of organic matter was 93.5%.

[0051] The electrodialysis desalination solution then enters the anaerobic biological treatment unit. The methane produced is purified to a purity of 98.1% by alkaline solution. The COD concentration of the effluent from the anaerobic biological treatment unit is 510 mg / L, and the salt content is 2752 mg / L. It then enters the post-treatment unit. The COD concentration of the mixed influent to the post-treatment unit is 552 mg / L, and the salt content is 7892 mg / L. The combined process of halophilic bacteria aerobic biological treatment and ozone catalytic oxidation can further treat the COD to meet the discharge standards.

[0052] As can be seen from this embodiment, the present invention can effectively treat high-sulfate organic wastewater. Electrodialysis with modified anion exchange membrane as the core can achieve an organic matter rejection rate of up to 93.5%, of which 81.6% of the organic matter is utilized as methane, which has a higher organic matter rejection rate and a higher resource utilization rate.

[0053] Example 3 Modified anion exchange membranes were prepared using the following method: Except that the positively charged amine compound in step a is polyethyleneimine, the mass ratio of polyethyleneimine to polyvinyl alcohol is 0.5:1, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.25:1, and the reaction time in step a is 6 hours, everything else is the same as in Example 1.

[0054] The modified anion exchange membrane prepared above was used for electrodialysis treatment of high-sulfate organic wastewater: The wastewater quality is as follows: COD 6500 mg / L, sulfate 7000 mg / L, chloride concentration 2000 mg / L, calcium ion concentration 150 mg / L, magnesium ion concentration 100 mg / L, total salt content 13900 mg / L, wastewater flow rate 10 t / h, the organic matter in the wastewater is mainly neutral organic matter (uncharged), which is a typical high sulfate and high organic wastewater.

[0055] In this embodiment, the anion exchange membrane used in electrodialysis is the modified anion exchange membrane prepared above, and the cation exchange membrane is a general-purpose cation exchange membrane (product of Hefei Capgemini Polymer Co., Ltd., China, model CJ-MC-3).

[0056] The specific operating parameters for treating wastewater with high sulfate and high organic content are as follows: The wastewater is first softened and conditioned by adding a dehardening agent at a concentration of 220 mg / L sodium hydroxide and 280 mg / L sodium carbonate. After clarification, the calcium ion concentration in the supernatant is reduced to below 9 mg / L and the magnesium ion concentration to below 5 mg / L. The effluent then enters electrodialysis; the electrodialysis treatment time is 1.2 hours, and the current density is 30 mA / cm³. 2Data from one week of stable operation of the electrodialysis unit showed that the COD concentration of the desalinated solution was 8560 mg / L, the salt content was 3207 mg / L, and the flow rate was 6.5 t / h. The COD concentration of the concentrate was 2674 mg / L, the salt content was 33757 mg / L, and the flow rate was 3.5 t / h. The sulfate ion selective permeability was 81.5%, the chloride ion selective permeability was 91.3%, and the organic matter rejection rate was 85.6%.

[0057] The electrodialysis desalination solution then enters the anaerobic biological treatment unit. The methane produced is purified to a purity of 99.2% by alkaline solution. The COD concentration of the effluent from the anaerobic biological treatment unit is 712 mg / L, and the salt content is 3256 mg / L. It then enters the post-treatment unit. The COD concentration of the mixed influent to the post-treatment unit is 1398 mg / L, and the salt content is 13931 mg / L. By adopting a combination of halophilic bacteria aerobic biological treatment, ozone catalytic oxidation, reverse osmosis concentration, and multi-effect evaporation, zero wastewater discharge can be further achieved, and the treatment cost is controllable.

[0058] As can be seen from this embodiment, the present invention can effectively treat higher concentrations of sulfate-containing organic wastewater. Electrodialysis with modified anion exchange membrane as the core can achieve an organic matter retention rate of up to 85.6%, of which 78.5% of the organic matter is utilized as methane. A small amount of organic matter is treated through high-energy-consuming aerobic aeration, ozone catalytic oxidation and other processes, which greatly reduces the treatment cost and has outstanding energy-saving and environmental protection effects.

[0059] Comparative Example 1 The source and quality of the high-sulfate organic wastewater are the same as in Example 1. The process route and implementation steps for treating the high-sulfate organic wastewater are also the same as in Example 1. The difference is that the anion and cation exchange membranes used in the electrodialysis are both general-purpose membranes. The anion exchange membrane is a product of Asahi Glass Co., Ltd. (SELEMION AMV) from Japan, and the cation exchange membrane is a product of Hefei Kaijie Polymer Co., Ltd. (model CJ-MC-3) from China.

[0060] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows: The wastewater was first softened and conditioned in the same manner as in Example 1, and the effluent then entered electrodialysis; the electrodialysis treatment time was 1 hour, and the current density was 25 mA / cm³. 2Data from one week of stable operation of the electrodialysis unit showed that the COD concentration of the desalinated solution was 5537 mg / L, the salt content was 5522 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 4080 mg / L, the salt content was 23115 mg / L, and the flow rate was 3 t / h. The sulfate ion selective permeation rate was 62.3%, and the chloride ion selective permeation rate was 68.5%, which were significantly lower than in Example 1. The decrease in membrane flux may be related to membrane fouling. The organic matter rejection rate dropped to 76%, indicating that a large amount of negatively charged organic matter passed through the anion exchange membrane, increasing the possibility of membrane fouling. The desalinated solution after electrodialysis entered the anaerobic biological treatment unit. The COD concentration of the effluent from the anaerobic biological treatment unit was 3550 mg / L. This is because the salt content of the anaerobic unit water (electrodialysis desalinated solution) was as high as 5522 mg / L, and it was mainly sulfate, which easily generates sulfur dioxide (S₂O₃) in anaerobically. 2- These ions severely affect the methanogenesis reaction.

[0061] This comparative example shows that conventional electrodialysis cannot effectively separate organic matter and salts, which leads to excessively high salt content and hindered anaerobic reaction. Only 27.3% of the organic matter is utilized as methane. Moreover, the anion exchange membrane of electrodialysis is easily contaminated, resulting in a significant decrease in ion exchange flux and a substantial shortening of membrane lifespan.

[0062] Comparative Example 2 The process for preparing the modified anion exchange membrane is the same as in Example 1, except that β-cyclodextrin is not added in step a.

[0063] The source and quality of the high-sulfate organic wastewater are the same as in Example 1. The process route and implementation steps for treating the high-sulfate organic wastewater are also the same as in Example 1. The difference is that the anion exchange membrane used in electrodialysis is the modified anion exchange membrane mentioned above, and the cation exchange membrane is a product of Hefei Kaijie Polymer Co., Ltd. (model CJ-MC-3).

[0064] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows: The wastewater was first softened and conditioned in the same manner as in Example 1, and the effluent then entered electrodialysis; the electrodialysis treatment time was 1 hour, and the current density was 25 mA / cm³. 2Data from one week of stable operation of the electrodialysis unit were collected. The COD concentration of the desalinated solution after treatment was 6855 mg / L, the salt content was 6612 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 1005 mg / L, the salt content was 20572 mg / L, and the flow rate was 3 t / h. The sulfate ion selective permeability was 47.6%, the chloride ion selective permeability was 77.3%, and the organic matter rejection rate was 94.1%. Compared with Example 1, the sulfate ion selective permeability was significantly lower. The desalinated solution after electrodialysis entered the anaerobic biological treatment unit. The COD concentration of the effluent from the anaerobic biological treatment unit was 5337 mg / L. This is because the salt content of the anaerobic unit's incoming water (electrodialysis desalinated solution) was as high as 6612 mg / L, and it was mainly sulfate, which easily generates sulfur dioxide (S₂O₃) in an anaerobic environment. 2- These ions severely affect the methanogenesis reaction.

[0065] As can be seen from this comparative example, the anion exchange membrane of electrodialysis, through surface polyanion modification, achieves an organic matter rejection rate as high as 94.1%, but at the same time, the rejection rate of sulfate ions also increases significantly, ultimately resulting in poor salt separation effect, excessively high salt content in anaerobic reaction and hindered anaerobic reaction, with only 20.8% of organic matter being utilized as methane.

[0066] Comparative Example 3 Preparation of anion exchange membranes: Polyvinyl alcohol anion exchange membranes were prepared using the same procedures as steps a-d in Example 1, without any subsequent surface modification.

[0067] The source and water quality of the high-sulfate organic wastewater are the same as in Example 1. The process route and implementation steps for treating the high-sulfate organic wastewater are also the same as in Example 1. The difference is that the anion exchange membrane for electrodialysis is the polyvinyl alcohol anion exchange membrane prepared above, and the cation exchange membrane is a product of Hefei Kaijie Polymer Co., Ltd. (model CJ-MC-3).

[0068] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows: The wastewater was first softened and conditioned in the same manner as in Example 1, and the effluent then entered electrodialysis; the electrodialysis treatment time was 1 hour, and the current density was 25 mA / cm³. 2Data from one week of stable operation of the electrodialysis unit were collected. The COD concentration of the desalinated solution after treatment was 5180 mg / L, the salt content was 4551 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 4913 mg / L, the salt content was 25380 mg / L, and the flow rate was 3 t / h. The selective permeation rate of sulfate ions was 67.8%, and the selective permeation rate of chloride ions was 75.8%, which was somewhat lower than that in Example 1. The decrease in membrane flux may be related to membrane fouling. The organic matter rejection rate was 71.1%, indicating that a large amount of negatively charged organic matter passed through the anion exchange membrane, increasing the possibility of membrane fouling. The desalinated solution after electrodialysis entered the anaerobic biological treatment unit. The COD concentration of the effluent from the anaerobic biological treatment unit was 2010 mg / L. The low COD removal rate was related to the high salt content of the anaerobic unit water (electrodialysis desalinated solution), which was mainly sulfate.

[0069] As shown in this comparative example, compared with Example 1, the prepared anion exchange membrane, lacking surface modification, is more susceptible to fouling by negatively charged organic matter as it passes through, reducing its lifespan. This ultimately leads to poorer separation of organic matter and salts, higher salt content in the anaerobic influent, and hindered anaerobic methanogenesis. The methane conversion rate of organic matter in this comparative example is 43.5%.

Claims

1. A method for treating high-sulfate organic wastewater, characterized in that, A modified anion exchange membrane is used as the anion exchange membrane in an electrodialysis unit to treat high-sulfate organic wastewater via electrodialysis. The modified anion exchange membrane is prepared through the following steps: Step a: Polyvinyl alcohol is added to water to prepare a polyvinyl alcohol aqueous solution. Then, a positively charged amine compound and β-cyclodextrin are added to the above solution respectively. After mixing and reacting, a casting solution is obtained. The positively charged amine compound is one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxychloropropaneamine, and quaternized chitosan. Step b: Cast the casting solution obtained in step a onto a horizontal panel, dry it, and obtain the base film; Step c: Immerse the base film obtained in step b in a crosslinking solution composed of crosslinking agent, sodium sulfate, sulfuric acid, and water; Step d: Wash the cross-linked membrane, alkalize it in an alkaline solution, and then soak it in water to obtain a polyvinyl alcohol anion exchange membrane; Step e: Dissolve the polyanionic modifier and sodium chloride in Tris–HCl buffer solution, and adjust the pH to 8-9 with hydrochloric acid to obtain a modified solution; the polyanionic modifier is one or more of sodium poly4-styrene sulfonate, sodium polyethylene sulfonate, and sodium polypropylene sulfonate. Step f: Place the anion exchange membrane obtained in step d in the middle of the DC electrodeposition apparatus to form two compartments. Put the modified solution prepared in step e into the compartment on the cathode side and put water into the compartment on the anode side to carry out the electrodeposition reaction and obtain the modified anion exchange membrane.

2. The method according to claim 1, characterized in that, The mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1 to 0.6:

1.

3. The method according to claim 1, characterized in that, The mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.05:1 to 0.4:

1.

4. The method according to claim 1, characterized in that, In step a, the mass fraction of the polyvinyl alcohol aqueous solution is 5% to 15%, and the reaction time with the positively charged amine compound and β-cyclodextrin is 2 to 10 hours.

5. The method according to claim 1, characterized in that, The crosslinking agent is selected from aldehyde or acid crosslinking agents.

6. The method according to claim 1, characterized in that, The crosslinking solution contains, by weight, 2%–8% crosslinking agent, 4%–15% sodium sulfate, and 1%–4% sulfuric acid, with the remainder being water.

7. The method according to claim 1, characterized in that, In step c, the base film is immersed in the crosslinking solution for 1 to 6 hours.

8. The method according to claim 1, characterized in that, In step e, the mass concentration of the polyanionic modifier in the modified solution is 1–10 g / L, and the mass concentration of sodium chloride is 3–30 g / L.

9. The method according to claim 1, characterized in that, The electrodeposition reaction time in step f is 0.2–2 h, and the current density is 1–50 mA / cm². 2 .

10. The method according to claim 1, characterized in that, The high-sulfate organic wastewater has a COD ≥ 2000 mg / L and a sulfate content ≥ 3000 mg / L.

11. The method according to claim 1, characterized in that, The electrodialysis treatment time is 0.5–5 hours, and the current density is 1–80 mA / cm². 2 .

12. A treatment process for high-sulfate organic wastewater, comprising a softening and conditioning unit, an electrodialysis unit, an anaerobic biological treatment unit, a methane purification unit, and a post-treatment unit; characterized in that, The electrodialysis unit employs the method described in claim 1.

13. The processing method according to claim 12, characterized in that, Specifically: High-sulfate organic wastewater first enters the softening and conditioning unit to remove calcium and magnesium hardness, and then enters the electrodialysis unit; the anion exchange membrane of the electrodialysis unit is a modified anion exchange membrane, and the cation exchange membrane is a general-purpose cation exchange membrane. The electrodialysis desalination solution enters the anaerobic biochemical unit, and the electrodialysis concentrate enters the post-treatment unit. The methane produced by the anaerobic biological treatment unit is recycled after being treated by the methane purification unit, and the effluent from the anaerobic biological treatment unit enters the post-treatment unit in the same way as the electrodialysis concentrate.

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