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

Abstract

The application discloses a modified anion exchange membrane, which is prepared by crosslinking of polyvinyl alcohol, positively charged amine compounds and beta-cyclodextrin, then is subjected to surface modification by reaction in a dopamine Tris buffer solution containing copper sulfate, and finally is subjected to surface modification by electrodeposition in the presence of a polyanion modifier. The modified anion exchange membrane can effectively separate salt and organic matter in high-sulfate organic wastewater in an electrodialysis process, and solves the problem of long-term difficulty in treating high-sulfate organic wastewater. Further, most of the organic matter is converted into methane through subsequent anaerobic reaction, resource recycling is realized, and carbon dioxide emission and energy consumption are reduced. 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, and from the perspective of energy utilization, the carbon source is not effectively utilized.

[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 hydrophilic anion exchange membrane that is modified by dopamine polymerization deposition and polyanion electrodeposition. It is particularly suitable for treating high-sulfate organic wastewater, effectively separating salts and organic matter from the wastewater, facilitating further treatment of organic matter and resource utilization of 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:

[0008] 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:

[0009] Step a: Add polyvinyl alcohol to water to prepare a polyvinyl alcohol aqueous solution. Then add positively charged amine compounds, β-cyclodextrin, and crosslinking agents to the above solution respectively. Add inorganic acid to adjust the pH. After mixing and stirring, the casting solution is obtained.

[0010] Step b: Cast the casting solution obtained in step a onto a horizontal panel, dry it, and obtain the base film;

[0011] Step c: After washing the base membrane obtained in step b, place it in an alkaline solution for alkalization, and then soak it in water to obtain a polyvinyl alcohol anion exchange membrane;

[0012] Step d: Dissolve dopamine in Tris-HCl buffer and adjust the pH to 8-9 with hydrochloric acid to obtain dopamine Tris buffer solution;

[0013] Step e: Place the anion exchange membrane obtained in step c in a dopamine Tris buffer solution and add copper sulfate. Stir the reaction while maintaining air circulation. After the reaction is complete, a surface-modified anion exchange membrane is obtained.

[0014] Step f: 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 electrodeposition mother solution;

[0015] Step g: Place the anion exchange membrane obtained in step e in the middle of the DC electrodeposition apparatus to form two compartments. Put the electrodeposition mother solution prepared in step f 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.

[0016] Furthermore, the positively charged amine compound is selected from 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.

[0017] Furthermore, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.05:1 to 0.4:1.

[0018] Furthermore, the crosslinking agent is selected from aldehyde or acid crosslinking agents, preferably glutaraldehyde, and the mass ratio of the crosslinking agent to polyvinyl alcohol is 0.01:1 to 0.1:1.

[0019] Furthermore, in step a, the inorganic acid is sulfuric acid, hydrochloric acid, or nitric acid, and the pH of the solution is adjusted to 4-6.

[0020] Furthermore, in step a, the polyvinyl alcohol aqueous solution has a mass fraction of 5% to 15%, and the reaction time with the positively charged amine compound, β-cyclodextrin, and crosslinking agent is 4 to 16 hours.

[0021] Furthermore, the polyvinyl alcohol aqueous solution is prepared by stirring at 60–90°C to dissolve the polyvinyl alcohol in water.

[0022] 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.

[0023] Furthermore, the washing described in step c involves washing with water until the solution is neutral.

[0024] Furthermore, the alkalization is performed using a 0.5–3 mol / L sodium hydroxide aqueous solution for 12–24 hours.

[0025] Furthermore, the soaking time in step c is 12 to 24 hours.

[0026] Furthermore, the concentration of the Tris-HCl buffer solution in steps d and f is 10–50 mmol / L.

[0027] Furthermore, the dopamine concentration in step d is 0.3–3 g / L.

[0028] Furthermore, in step e, the concentration of copper sulfate is 1–15 mmol / L, and the stirring reaction time is 1–10 h. The copper sulfate can induce rapid polymerization of dopamine, forming a negatively charged polydopamine electrolyte layer on the surface of the anion exchange membrane, thus performing preliminary modification on the membrane surface.

[0029] Furthermore, the polyanionic modifier in step f 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.

[0030] Furthermore, in step f, the mass concentration of the polyanionic modifier in the electrodeposition mother liquor is 1–5 g / L, and the mass concentration of sodium chloride is 3–30 g / L.

[0031] Furthermore, the electrodeposition reaction time in step g is 0.2–2 h, and the current density is 1–50 mA / cm². 2 A polyanionic modifier is deposited a second time on the surface of the anion exchange membrane using an electrodeposition method, which sulfonates and modifies the membrane surface.

[0032] Furthermore, the modified anion exchange membrane is then stored in a sodium chloride solution. The mass concentration of the sodium chloride solution is 5–20 g / L.

[0033] 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.

[0034] The technical objective of the third aspect of this invention is to provide a method for treating high-sulfate organic wastewater, which uses the modified anion exchange membrane as the anion exchange membrane in the electrodialysis unit to perform electrodialysis concentration treatment on the high-sulfate organic wastewater.

[0035] Furthermore, the high-sulfate organic wastewater has a COD ≥ 1500 mg / L and a sulfate content ≥ 2000 mg / L.

[0036] 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 .

[0037] Those skilled in the art should understand that most organic pollutants present in natural water bodies or wastewater, such as surfactants, humic acids, proteins, and aromatic hydrocarbon derivatives, are negatively charged. Dopamine has strong self-polymerization and adsorption capabilities, and can increase the negative charge density and membrane stability of the membrane surface. Therefore, after modification with polydopamine, the anion exchange membrane becomes negatively charged, exhibiting electrostatic repulsion against negatively charged organic matter in the water, thus inhibiting organic matter fouling of the anion exchange membrane. Further surface sulfonation and modification with polyanion modifiers can reduce the membrane surface roughness caused by dopamine adsorption, further increasing the negative charge density on the membrane surface. Those skilled in the art should also understand that while the negative surface charge prevents organic matter fouling through electrostatic interaction, it also affects the migration rate of inorganic anions. The greater the ionic 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. Specifically, the migration numbers of less hydrated anions, such as bromide and nitrate ions, relative to chloride ions decrease, while the migration numbers of more hydrated anions, such as sulfate ions, relative to chloride ions increase. Furthermore, the increased hydrophilicity of the membrane reduces van der Waals forces between the membrane and organic solutes, decreasing the attractive force. Simultaneously, a hydration layer forms between the hydrophilic membrane and water molecules due to hydrogen bonding, further hindering the adsorption of pollutants on the membrane surface. Therefore, the anion exchange membrane of this invention, after being co-modified with a polyanion modifier and β-cyclodextrin, exhibits significantly increased antifouling ability and enhanced selective permeability to sulfate ions.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Furthermore, the electrodialysis treatment time is 0.5–5 hours, and the current density is 1–80 mA / cm². 2 .

[0042] 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%.

[0043] 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.

[0044] By employing the above-described technology, the beneficial effects of the present invention compared to the prior art are as follows:

[0045] The modified anion exchange membrane of this invention, applied to electrodialysis, effectively separates salts and organic matter in the treatment of high-sulfate organic wastewater, solving the long-standing problem of its difficult treatment. The separated organic solution, due to its low salt content, can be subsequently converted into methane through anaerobic reaction, achieving resource utilization and reducing carbon dioxide emissions and energy consumption, aligning with the current dual-carbon development concept. Furthermore, the modified anion exchange membrane exhibits strong antifouling ability, high organic matter retention rate, and high ion exchange rate, especially sulfate ion exchange rate, making it highly valuable for application.

[0046] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0047] Figure 1 Schematic diagram of anion exchange membrane electrodeposition modification in Example 1;

[0048] Figure 2 Flowchart of high sulfate organic wastewater treatment in Example 1. Detailed Implementation

[0049] 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.

[0050] Example 1

[0051] Modified anion exchange membranes were prepared using the following method:

[0052] Step a: Add polyvinyl alcohol to deionized water to prepare an 11% aqueous solution. Stir at 85°C to dissolve it. Then add 2,3-epoxypropyltrimethylammonium chloride, β-cyclodextrin, and glutaraldehyde to the water. The mass ratio of 2,3-epoxypropyltrimethylammonium chloride to polyvinyl alcohol is 0.4:1, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.2:1, and the mass ratio of glutaraldehyde to polyvinyl alcohol is 0.04:1. Adjust the pH to 5 with hydrochloric acid and react for 8 hours to obtain a viscous liquid, which is the casting solution.

[0053] Step b: Cast the casting solution onto a horizontal glass plate and dry it at room temperature for 4 hours. Then, continue to dry the formed film under vacuum at 60°C for 6 hours to obtain the base film.

[0054] Step c: Wash the base membrane obtained in step b with deionized water until neutral, then place it in a 1 mol / L sodium hydroxide aqueous solution for alkalization for 15 h, and then soak it in deionized water for 18 h to obtain a polyvinyl alcohol anion exchange membrane.

[0055] Step d: Dissolve dopamine in 15 mmol / L Tris–HCl buffer, adjust the pH to 8.5 with hydrochloric acid to obtain a dopamine Tris buffer solution with a dopamine mass concentration of 0.7 g / L.

[0056] Step e: Place the polyvinyl alcohol anion exchange membrane to be modified in a dopamine Tris buffer solution and add 4 mmol / L copper sulfate. Stir and react for 5 hours. Keep the air circulating during the reaction. Copper sulfate can induce the rapid polymerization of dopamine and form a negatively charged polydopamine electrolyte layer on the surface of the anion exchange membrane. After the reaction is completed, the preliminarily modified anion exchange membrane is obtained.

[0057] Step f: 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 2 g / L, the mass concentration of sodium chloride is 8 g / L, and the polyanionic modifier is sodium poly4-styrene sulfonate, to obtain the electrodeposition mother liquor.

[0058] Step g: Surface sulfonation and modification are performed using electrodeposition methods, 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 electrodeposition mother solution, and the anode-side compartment contained deionized water. The electrodeposition time was 0.7 hours, and the current density was 20 mA / cm². 2 The final modified anion exchange membrane was obtained.

[0059] Step h: Take out the modified anion exchange membrane obtained in step g and place it in a sodium chloride solution with a mass concentration of 10 g / L for later use.

[0060] The modified anion exchange membrane prepared above was used for electrodialysis treatment of high-sulfate organic wastewater.

[0061] 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.

[0062] The high-sulfate organic wastewater used in this embodiment has the following characteristics: COD 5000 mg / L, sulfate 4000 mg / L, chloride concentration 2500 mg / L, calcium ion concentration 150 mg / L, magnesium ion concentration 50 mg / L, total salt content 10300 mg / L, and wastewater flow rate 10 t / h. The organic matter in the wastewater is mainly neutral (uncharged), classifying it as typical high-sulfate organic wastewater.

[0063] In this embodiment, the anion exchange membrane used in 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).

[0064] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows:

[0065] The wastewater is first softened and conditioned by adding a dehardening agent at a concentration of 100 mg / L sodium hydroxide and 290 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 treated electrodialysis desalination solution was 6321 mg / L, the salt content was 3237 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 1917 mg / L, the salt content was 26780 mg / L, and the flow rate was 3 t / h. The selective permeability of sulfate ions was 74.1%, the selective permeability of chloride ions was 84.2%, and the retention rate of organic matter was 88.5%.

[0066] Subsequently, the electrodialysis desalination solution enters the anaerobic biological treatment unit. The methane produced is purified to a purity of 98.4% after being purified by alkaline solution. The COD concentration of the effluent from the anaerobic biological treatment unit is 640 mg / L, and the salt content is 3266 mg / L. It then enters the post-treatment unit. The COD concentration of the mixed influent to the post-treatment unit is 1023 mg / L, and the salt content is 10351 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.

[0067] 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 achieves excellent separation of organic matter and salt, with high organic matter retention rate and high resource utilization rate. Among them, 79.5% 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.

[0068] Example 2

[0069] Modified anion exchange membranes were prepared using the following method:

[0070] Except that the dopamine concentration in the buffer solution in step d is 0.8 g / L, the amount of copper sulfate added in step e is 4.5 mmol / L, and the stirring reaction time is 5.5 h, the polyanionic modifier concentration in step f is 2.3 g / L, and the electrodeposition time in step g is 0.8 h, everything else is the same as in Example 1.

[0071] 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 2500 mg / L, chloride concentration 2000 mg / L, calcium ion concentration 100 mg / L, magnesium ion concentration 100 mg / L, total salt content 7400 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.

[0072] 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).

[0073] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows:

[0074] The wastewater is first softened and conditioned by adding a dehardening agent at a concentration of 180 mg / L sodium hydroxide and 210 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 treated electrodialysis desalination solution was 4037 mg / L, the salt content was 2854 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 580 mg / L, the salt content was 18006 mg / L, and the flow rate was 3 t / h. The selective permeability of sulfate ions was 70.1%, the selective permeability of chloride ions was 78.8%, and the retention rate of organic matter was 94.2%.

[0075] The electrodialysis desalination solution then enters the anaerobic biological treatment unit. The methane produced is purified to a purity of 98.5% after being purified with alkaline solution. The COD concentration of the effluent from the anaerobic biological treatment unit is 490 mg / L, and the salt content is 2875 mg / L. It then enters the post-treatment unit. The COD concentration of the mixed influent to the post-treatment unit is 517 mg / L, and the salt content is 7866 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.

[0076] 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 94.2%, of which 82.8% of the organic matter is utilized as methane, which has a higher organic matter rejection rate and a higher resource utilization rate.

[0077] Example 3

[0078] Modified anion exchange membranes were prepared using the following method:

[0079] Except that the positively charged amine compound in step a is polyethyleneimine, the mass ratio of polyethyleneimine to polyvinyl alcohol is 0.45:1, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.25:1, the mass ratio of glutaraldehyde to polyvinyl alcohol is 0.05:1, and the reaction time in step a is 10 hours, everything else is the same as in Example 1.

[0080] The modified anion exchange membrane prepared above was used for electrodialysis treatment of high-sulfate organic wastewater:

[0081] The wastewater quality is as follows: COD 6500 mg / L, sulfate 5000 mg / L, chloride concentration 3500 mg / L, calcium ion concentration 150 mg / L, magnesium ion concentration 100 mg / L, total salt content 13800 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.

[0082] 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).

[0083] The specific operating parameters for treating wastewater with high sulfate and high organic content are as follows:

[0084] The wastewater is first softened and conditioned by adding a dehardening agent at a concentration of 210 mg / L sodium hydroxide and 300 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. 2 Data from one week of stable operation of the electrodialysis unit showed that the COD concentration of the treated electrodialysis desalination solution was 8680 mg / L, the salt content was 3560 mg / L, and the flow rate was 6.5 t / h. The COD concentration of the concentrate was 2451 mg / L, the salt content was 32817 mg / L, and the flow rate was 3.5 t / h. The sulfate ion selective permeability was 77.2%, the chloride ion selective permeability was 88.7%, and the organic matter rejection rate was 86.8%.

[0085] The electrodialysis desalination solution then enters the anaerobic biological treatment unit. The methane produced is purified to a purity of 98.8% by alkaline solution. The COD concentration of the effluent from the anaerobic biological treatment unit is 815 mg / L, and the salt content is 3589 mg / L. It then enters the post-treatment unit. The COD concentration of the mixed influent to the post-treatment unit is 1387 mg / L, and the salt content is 13855 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.

[0086] 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 86.8%, of which 78.6% 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.

[0087] Comparative Example 1

[0088] 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.

[0089] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows:

[0090] 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. 2 Data from one week of stable operation of the electrodialysis unit showed that the COD concentration of the treated electrodialysis desalination solution was 5592 mg / L, the salt content was 5738 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 3618 mg / L, the salt content was 20943 mg / L, and the flow rate was 3 t / h. The sulfate ion selective permeation rate was 58.5%, and the chloride ion selective permeation rate was 65.1%, which were significantly lower than in Example 1. The decrease in membrane flux may be related to membrane fouling. The organic matter rejection rate decreased to 78.3%, indicating that a large amount of negatively charged organic matter passed through the anion exchange membrane, increasing the possibility of membrane fouling. The desalination solution after electrodialysis entered the anaerobic biological treatment unit. The COD concentration of the effluent from the anaerobic biological treatment unit was 3850 mg / L. This is because the salt content of the anaerobic unit water (electrodialysis desalination solution) was as high as 5738 mg / L, mainly sulfate, which easily generates sulfur dioxide (S₂O₃) in anaerobically. 2- These ions severely affect the methanogenesis reaction.

[0091] 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 24.4% 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.

[0092] Comparative Example 2

[0093] 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.

[0094] 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).

[0095] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows:

[0096] 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. 2 Data from one week of stable operation of the electrodialysis unit showed that the COD concentration of the treated electrodialysis desalination solution was 6800 mg / L, the salt content was 6101 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 802 mg / L, the salt content was 20100 mg / L, and the flow rate was 3 t / h. The sulfate ion selective permeability was 44.3%, the chloride ion selective permeability was 75.5%, and the organic matter rejection rate was 95.2%. Compared with Example 1, the sulfate ion selective permeability was significantly lower. The desalination solution after electrodialysis entered the anaerobic biological treatment unit. The COD concentration of the effluent from the anaerobic biological treatment unit was 5250 mg / L. This was because the salt content of the anaerobic unit water (electrodialysis desalination solution) was as high as 6101 mg / L, and it was mainly sulfate, which easily generated sulfur dioxide (S₂O₃) in an anaerobic environment. 2- These ions severely affect the methanogenesis reaction.

[0097] 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 95.2%, 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 21.7% of organic matter being utilized as methane.

[0098] Comparative Example 3

[0099] Preparation of anion exchange membranes:

[0100] Polyvinyl alcohol anion exchange membranes were prepared using the same procedures as steps a-c in Example 1, without any subsequent surface modification.

[0101] 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).

[0102] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows:

[0103] 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. 2 Data from one week of stable operation of the electrodialysis unit were collected. The COD concentration of the treated electrodialysis desalination solution was 5201 mg / L, the salt content was 4708 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 4531 mg / L, the salt content was 23346 mg / L, and the flow rate was 3 t / h. The sulfate ion selective permeation rate was 64.9%, and the chloride ion selective permeation rate was 72.3%, 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 72.8%, indicating that a large amount of negatively charged organic matter passed through the anion exchange membrane, increasing the possibility of membrane fouling. The desalination solution after electrodialysis entered the anaerobic biological treatment unit. The COD concentration of the effluent from the anaerobic biological treatment unit was 2511 mg / L. The low COD removal rate was related to the high salt content of the anaerobic unit water (electrodialysis desalination solution), which was mainly sulfate.

[0104] 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. Ultimately, this 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 37.66%.

[0105] Comparative Example 4

[0106] Preparation of anion exchange membranes:

[0107] A preliminarily modified polyvinyl alcohol anion exchange membrane was prepared by the same operation as steps a-e in Example 1, without subsequent electrodeposition treatment.

[0108] 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).

[0109] The specific operating parameters and results for treating high-sulfate organic wastewater are as follows:

[0110] 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. 2 Data from one week of stable operation of the electrodialysis unit were collected. The COD concentration of the treated electrodialysis desalination solution was 5992 mg / L, the salt content was 3745 mg / L, and the flow rate was 7 t / h. The COD concentration of the concentrate was 2685 mg / L, the salt content was 25593 mg / L, and the flow rate was 3 t / h. The sulfate ion selective permeability was 72.8%, and the chloride ion selective permeability was 80.1%, which was slightly lower than that in Example 1. The organic matter rejection rate was 83.9%. The desalination solution after electrodialysis treatment entered the anaerobic biological treatment unit. The COD concentration of the effluent from the anaerobic biological treatment unit was 1511 mg / L, and the methane conversion rate of organic matter was 62.7%.

[0111] As can be seen from this comparative example, compared with Example 1, the prepared anion exchange membrane, due to the lack of electrodeposition surface sulfonation and modification, only underwent preliminary surface modification, resulting in a slight decrease in the ion exchange rate and antifouling ability of the anion exchange membrane, which in turn leads to a shorter membrane lifespan and a lower organic matter rejection rate.

Claims

1. A method for treating high-sulfate organic wastewater, characterized in that, The modified anion exchange membrane is used as the anion exchange membrane in the electrodialysis unit to concentrate 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, β-cyclodextrin, and a crosslinking agent are added to the above solution respectively. An inorganic acid is added to adjust the pH. After mixing and stirring, a casting solution is obtained. The positively charged amine compound is selected from 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: After washing the base membrane obtained in step b, place it in an alkaline solution for alkalization, and then soak it in water to obtain a polyvinyl alcohol anion exchange membrane; Step d: Dissolve dopamine in Tris-HCl buffer and adjust the pH to 8-9 with hydrochloric acid to obtain dopamine Tris buffer solution; Step e: Place the anion exchange membrane obtained in step c in a dopamine Tris buffer solution and add copper sulfate. Stir the reaction while maintaining air circulation. After the reaction is complete, a surface-modified anion exchange membrane is obtained. Step f: 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 electrodeposition mother solution; the polyanionic modifier is selected from one or more of sodium poly4-styrene sulfonate, sodium polyethylene sulfonate and sodium polypropylene sulfonate; Step g: Place the anion exchange membrane obtained in step e in the middle of the DC electrodeposition apparatus to form two compartments. Put the electrodeposition mother solution prepared in step f 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 final modified anion exchange membrane.

2. The processing 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.

3. The processing method according to claim 1, characterized in that, The crosslinking agent is glutaraldehyde, and the mass ratio of the crosslinking agent to polyvinyl alcohol is 0.01:1 to 0.1:

1.

4. The processing method according to claim 1, characterized in that, The inorganic acid mentioned in step a is sulfuric acid, hydrochloric acid, or nitric acid, and the pH of the solution is adjusted to 4-6.

5. The processing method according to claim 1, characterized in that, The reaction time in step a is 4 to 16 hours.

6. The processing method according to claim 1, characterized in that, The drying process described 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.

7. The processing method according to claim 1, characterized in that, The alkalization time is 12 to 24 hours.

8. The processing method according to claim 1, characterized in that, The concentration of the Tris–HCl buffer solution mentioned in step d is 10–50 mmol / L.

9. The processing method according to claim 1, characterized in that, The dopamine Tris buffer solution in step d has a dopamine concentration of 0.3–3 g / L.

10. The processing method according to claim 1, characterized in that, In step e, the concentration of copper sulfate is 1–15 mmol / L, and the stirring reaction time is 1–10 h. Copper sulfate induces rapid polymerization of dopamine, forming a negatively charged polydopamine electrolyte layer on the surface of the anion exchange membrane, thus performing preliminary modification on the membrane surface.

11. The processing method according to claim 1, characterized in that, In step f, the mass concentration of the polyanionic modifier in the electrodeposition mother liquor is 1–5 g / L, and the mass concentration of sodium chloride is 3–30 g / L.

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

13. 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 processing method described in claim 1.

14. The processing method according to claim 13, 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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