Process method for treating degradation-resistant high-sulfate organic wastewater

Abstract

The invention relates to a process method for treating degradation-resistant high-sulfate organic wastewater. The process method comprises a pretreatment section, a reaction section and a catalyst regeneration section, the pretreatment section comprises an adjusting hardness removal unit, a tubular microfiltration unit, an electrodialysis unit, a concentration and salt separation system and a sludge concentration, dehydration and drying unit; the reaction section comprises a primary anaerobic unit, a secondary anaerobic unit and a Fenton oxidation unit; the catalyst regeneration section comprises a nanofiltration unit, a single-membrane electrodialysis unit, a regeneration unit, a neutralization unit and a methane storage tank; a modified anion exchange membrane is adopted for electrodialysis, separation of organic matter and salt and concentration of the salt are achieved, the anti-pollution capacity is greatly improved, follow-up anaerobic treatment is facilitated, the content of organic matter in the salt separation section is reduced, and the product purity of the salt separation section is improved. In the process method provided by the invention, wastewater is recycled, waste gas is stored and can be used as fuel, salt is converted into sodium sulfate and sodium chloride products, and water, gas and solid are integrally recycled.

Description

Technical Field

[0001] This invention relates to a method for treating recalcitrant high-sulfate organic wastewater, belonging to the field of wastewater treatment technology. Background Technology

[0002] High-sulfate organic wastewater exists in various industries such as chemical, pharmaceutical, papermaking, food processing, and mining. This type of wastewater has a high salt concentration, mainly sulfate, and also contains a certain concentration of organic matter (COD), some of which is difficult to biodegrade.

[0003] If the wastewater has a high organic content, anaerobic treatment is usually used to recover methane. However, high-sulfate organic wastewater contains a large amount of sulfate, which will be reduced to sulfur under anaerobic conditions by sulfate-reducing bacteria (SRB). 2- These ions possess strong biotoxicity and significantly inhibit microbial flora, severely impacting the removal of organic matter. Therefore, this method generally requires the sulfate concentration in the anaerobic reactor to be less than 2000 mg / L, as illustrated in patent CN103771670A. However, this method is not suitable for high-sulfate wastewater. Similarly, aerobic processes also face challenges such as excessively high salt concentrations leading to a limited variety of salt-tolerant bacterial species and low treatment efficiency. Furthermore, aerobic processes suffer from aeration dead zones and localized anaerobic processes, and excessively high sulfate concentrations can also result in high sulfide concentrations in the water.

[0004] Anaerobic biological treatment helps hydrolyze large organic molecules into smaller ones and improves the biodegradability of wastewater. However, its capacity for treating recalcitrant organic matter is limited. Therefore, to ensure wastewater meets discharge standards, advanced oxidation processes are typically added at the end of biological treatment. Common advanced oxidation processes include ozone catalytic oxidation, electrocatalytic oxidation, photocatalysis, and Fenton oxidation. Among these, electrocatalytic oxidation and photocatalysis are currently limited by high treatment costs, making industrial application difficult. The biggest problem with ozone catalytic oxidation is its low ozone utilization rate and the pollution it causes. Ozone pollution is now another complex pollution problem facing the world after acid rain and PM2.5. It is foreseeable that the application of ozone catalytic oxidation technology will be restricted as national regulations on ozone pollutants become more stringent. The biggest problem with Fenton oxidation is the loss of iron ions and the problem of iron sludge. This is because the Fenton reaction system is acidic, and ferrous ions act as catalysts for the generation of hydroxyl radicals. To meet discharge standards, the pH of the effluent needs to be adjusted to neutral by adding alkali, which generates a large amount of iron sludge. The proper treatment of this iron sludge has become a bottleneck in the development of Fenton oxidation technology. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a process for treating recalcitrant high-sulfate organic wastewater, ensuring that the effluent meets discharge and recycling standards, converting salts into sodium sulfate and sodium chloride products, and converting most organic matter into methane for resource recovery. The Fenton oxidation and catalyst regeneration combined process enables catalyst recycling and zero discharge of iron sludge.

[0006] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a process for treating recalcitrant high-sulfate organic wastewater, comprising a pretreatment section, a reaction section, and a catalyst regeneration section;

[0008] The pretreatment section includes a hardening and conditioning unit, a tubular microfiltration unit, an electrodialysis unit, a salt concentration and desalination system, and a sludge concentration, dewatering, and drying unit. Wastewater first undergoes hardening and conditioning in the hardening and conditioning unit, then passes through the tubular microfiltration unit for filtration before entering the electrodialysis unit. The concentrate from the electrodialysis unit enters the salt concentration and desalination system, while the desalinated solution enters the primary anaerobic digester of the reaction section. The chemical sludge produced by the hardening and conditioning unit and the tubular microfiltration unit enters the sludge concentration, dewatering, and drying unit. The dewatered water is returned to the inlet of the pretreatment section, and the dried sludge is sent off-site.

[0009] The reaction section sequentially includes a primary anaerobic unit, a secondary anaerobic unit, and a Fenton oxidation unit. The primary anaerobic unit mainly performs organic acidification and sulfate reduction, producing hydrogen sulfide gas. The secondary anaerobic unit mainly performs methanogenesis, and the generated methane is pumped to the primary anaerobic unit as stripping gas, carrying most of the hydrogen sulfide produced in the primary anaerobic unit out of the wastewater system. The mixed gas of methane and hydrogen sulfide produced in the primary anaerobic unit enters the regeneration unit of the catalyst regeneration section. Hydrogen peroxide is added to the Fenton oxidation unit, and the iron catalyst comes from the regeneration unit of the catalyst regeneration section. The effluent enters the nanofiltration unit of the catalyst regeneration section.

[0010] The catalyst regeneration section includes a nanofiltration unit, a single-membrane electrodialysis unit, a regeneration unit, a neutralization unit, and a methane storage tank. The effluent from the nanofiltration unit is divided into nanofiltration concentrate and nanofiltration permeate. The nanofiltration permeate enters the neutralization unit, where it is neutralized with alkali and then reused or discharged. The nanofiltration concentrate flows to the single-membrane electrodialysis unit. The effluent from the single-membrane electrodialysis unit is divided into mother liquor and anion exchange liquid. The anion exchange liquid is returned to the inlet of the primary anaerobic unit in the reaction section. The mother liquor enters the regeneration unit and reacts with the methane and hydrogen sulfide mixture generated by the primary anaerobic unit in the reaction section. The reacted water is returned to the Fenton oxidation unit in the reaction section, and the gas is recovered to the methane storage tank for later use.

[0011] The electrodialysis unit is composed of anion and cation exchange membranes, wherein the anion exchange membrane is a modified anion exchange membrane and the cation exchange membrane is a general-purpose cation exchange membrane.

[0012] The modification methods for anion exchange membranes are as follows:

[0013] Step a: Dissolve the linear polymer in an organic solvent, then add styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide and a hydrophilic modifier respectively, stir and react to obtain a polymer solution, wherein the hydrophilic modifier is selected from one or more of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin;

[0014] Step b: Add organic solvent to the polymer solution obtained in step a, add anhydrous zinc chloride and chloromethyl methyl ether, stir to react, then add precipitant, and then filter, dry and pulverize to obtain powdered chloromethylated polymer;

[0015] Step c: Dissolve the polymer obtained in step b in N,N-dimethylformamide, introduce trimethylamine gas, and carry out a quaternization reaction to obtain a quaternized polymer solution; prepare a membrane from the quaternized polymer solution; immerse the obtained membrane in sodium hydroxide solution for alkalization, and then wash it with deionized water until neutral to obtain an anion exchange membrane;

[0016] Step d: Dissolve the polyanionic modifier and sodium chloride in Tris-HCl buffer, and adjust the pH to 8-9 with hydrochloric acid to obtain the electrodeposition mother solution;

[0017] Step e: Place the anion exchange membrane obtained in step c in the middle of the DC electrodeposition apparatus to form two compartments. Put the electrodeposition mother solution prepared in step d 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.

[0018] Furthermore, the linear polymer mentioned in step a is selected from at least one of polyethylene, polypropylene, polyvinyl chloride, or polyvinylidene fluoride, preferably polyvinyl chloride.

[0019] Furthermore, the organic solvent mentioned in step a is one of dichloromethane, dichloroethane, or chloroform, preferably dichloromethane.

[0020] Furthermore, the linear polymer in step a has a mass-volume concentration of 30–100 mg / mL in the organic solvent, and the styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide, and hydrophilic modifier have mass-volume concentrations of 20–100 mg / mL, 20–100 mg / mL, 5–20 mg / mL, 2–10 mg / mL, and 30–80 mg / mL in the organic solvent, respectively.

[0021] Furthermore, the temperature of the stirring reaction in step a is 50–90°C, and the time is 0.5–6 h.

[0022] Furthermore, the amount of organic solvent added in step b is 0.5 to 1 times the amount of organic solvent used in step a.

[0023] Furthermore, in step b, the anhydrous zinc chloride in the organic solvent has a mass-volume concentration of 15–30 mg / mL, and the volume ratio of chloromethyl ether to the organic solvent is 0.5:1–2:1.

[0024] Furthermore, the temperature of the stirring reaction in step b is 30–55°C, and the time is 2–24 h.

[0025] Furthermore, the precipitant mentioned in step b is methanol and / or ethanol.

[0026] Furthermore, the mass-volume concentration of the polymer and N,N-dimethylformamide in step c is 15–40 mg / mL.

[0027] Furthermore, the trimethylamine gas in step c is obtained by heating and vaporizing an aqueous solution of trimethylamine, followed by drying with an alkaline drying agent. The alkaline drying agent is selected from at least one of potassium hydroxide, sodium hydroxide, quicklime, and soda lime.

[0028] Furthermore, the quaternization reaction in step c takes 10 to 120 minutes.

[0029] Furthermore, the quaternized polymer solution described in step c is used to form a film by casting or casting, and then dried at a temperature of 50–70°C for 12–24 hours.

[0030] Furthermore, the concentration of the sodium hydroxide solution used for alkalization in step c is 0.1–1 mol / L.

[0031] Furthermore, the concentration of the Tris–HCl buffer solution in step d is 10–50 mmol / L.

[0032] Furthermore, the polyanionic modifier mentioned in step d is selected from one or more of sodium poly4-styrene sulfonate, sodium p-styrene sulfonate, sodium polyethylene sulfonate, and sodium polypropylene sulfonate, with sodium poly4-styrene sulfonate being preferred.

[0033] Furthermore, in step d, the mass concentration of the polyanionic modifier in the electrodeposition mother liquor is 0.5–5 g / L, and the mass concentration of sodium chloride is 3–30 g / L.

[0034] Furthermore, the electrodeposition reaction time in step e is 0.2–2 h, and the current density is 1–50 mA / cm². 2 A polyanionic modifier is deposited on the surface of anion exchange membrane using an electrodeposition method, which simultaneously sulfonates and modifies the membrane surface.

[0035] Furthermore, the modified anion exchange membrane is then stored in a sodium chloride solution with a mass concentration of 5–20 g / L.

[0036] Those skilled in the art should understand that most polar organic pollutants present in natural water bodies or wastewater, such as surfactants, humic acids, and proteins, are negatively charged. Anion exchange membranes, after modification with polyanionic modifiers, have a negatively charged surface, exhibiting electrostatic repulsion against negatively charged organic matter in the water, thus inhibiting organic pollution of the anion exchange membrane. Those skilled in the art should also understand that while the negative surface charge prevents organic pollution through electrostatic interaction, it also affects the migration rate of inorganic anions. The greater the ion charge, the greater the impact; therefore, sulfate ions are more affected than chloride ions. Adding hydrophilic modifiers during the preparation of anion exchange membranes can impart strong hydrophilicity to the membrane and alter the migration rates between anions. Specifically, the migration rate of less hydrated anions, such as bromide and nitrate ions, relative to chloride ions decreases, while the migration rate of more hydrated anions, such as sulfate ions, increases relative to chloride ions. On the other hand, increased membrane hydrophilicity reduces van der Waals forces between the membrane and organic solutes, decreasing attractiveness. 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, the anion exchange membrane of this invention, through the combined action of polyanionic and hydrophilic modifiers, exhibits significantly increased antifouling ability and enhanced selective permeability to sulfate ions.

[0037] Furthermore, the hardening agent used in the hardening unit is preferably a combination of sodium hydroxide, sodium carbonate, and PAM. Sodium carbonate is added at 1 to 3 times the mass concentration of calcium ions, the amount of sodium hydroxide added is greater than the mass concentration of magnesium ions, and the amount of PAM added is 1 to 20 mg / L. Sodium hydroxide also acts as a pH adjuster, and the pH value should be greater than 8 after addition.

[0038] Furthermore, the tubular microfiltration unit is mainly used to filter suspended solids, colloids, etc., to prevent subsequent electrodialysis membrane clogging.

[0039] Furthermore, the electrodialysis unit has a treatment time of 0.2–3 hours and a current density of 1–80 mA / cm². 2 .

[0040] Furthermore, the concentration and salt separation system employs multi-effect evaporation or MVR for evaporation and concentration, concentrating the salt content to 200–300 g / L, before entering the nitrate crystallizer and salt crystallizer. The salt is separated by utilizing the temperature difference in solubility of sodium chloride and sodium sulfate. The temperature of the nitrate crystallizer is controlled at 100–130°C, and the temperature of the salt crystallizer is controlled at 70–90°C. The residual liquid is returned to the inlet of the concentration and salt separation system.

[0041] Furthermore, the dissolved oxygen in the primary anaerobic unit is controlled below 0.2 mg / L, the wastewater retention time is 1–12 h, the temperature is 25–35 °C, the pH is controlled at 5–6 by adding acid, and the bacterial strains are organic acidifying bacteria and sulfate-reducing bacteria.

[0042] Furthermore, the dissolved oxygen in the secondary anaerobic unit is controlled below 0.1 mg / L, the wastewater retention time is 2–36 h, the temperature is 30–40 °C, the pH is controlled at 7–9 by adding alkali, and the bacteria are methanogens.

[0043] Furthermore, the stripping gas from the primary anaerobic unit is methane produced by the secondary anaerobic unit, and the methane and hydrogen sulfide mixture produced after stripping enters the regeneration unit.

[0044] Furthermore, the amount of hydrogen peroxide added in the Fenton oxidation unit is 1 to 12:1 by mass ratio of hydrogen peroxide to wastewater COD, and the amount of iron added is 0.2 to 1.5:1 by mass ratio of iron to hydrogen peroxide, with a pH of 3 to 5; the iron is ferrous divalent, and the ferrous salt is selected from at least one of ferrous chloride, ferrous nitrate, and ferrous sulfate.

[0045] Furthermore, the nanofiltration unit has a water production rate of 60% to 95% and has a good retention effect on divalent and high-valence ions; specifically, after the Fenton oxidation effluent is treated by nanofiltration, iron ions, sulfate ions, etc. are retained and enter the concentrate side, while sodium ions, chloride ions, etc. pass through the nanofiltration membrane and enter the product water side.

[0046] Furthermore, the neutralization unit adjusts the pH to 6-9 by adding one or more of sodium hydroxide, calcium hydroxide, or potassium hydroxide to meet the requirements for water reuse or discharge.

[0047] Furthermore, the single-membrane electrodialysis unit uses a common anion exchange membrane. Under the action of electrode drive and the anion exchange membrane, sulfate ions in the nanofiltration concentrate permeate through the anion membrane into the concentrate side, including Fe. 2+ Fe 3+ The cations and most organic matter remain in the mother liquor; the single-membrane electrodialysis treatment time is 0.1–2 h, and the current density is 1–50 mA / cm². 2 .

[0048] Furthermore, the regeneration unit introduces a mixture of methane and hydrogen sulfide to process Fe. 3+ In the reduction and regeneration process, methane does not participate in the reaction and is insoluble in water; therefore, the regeneration unit also purifies methane gas. Furthermore, by controlling the reaction between hydrogen sulfide and Fe... 3+ By controlling the concentration of ions and utilizing the fact that hydrogen sulfide is slightly soluble in water, methane with a purity greater than 95% can be obtained and stored in methane storage tanks.

[0049] Furthermore, the recalcitrant high-sulfate organic wastewater of the present invention is wastewater with a sulfate concentration greater than 2000 mg / L and a COD concentration greater than 1000 mg / L, and is more suitable for treatment by the process method of the present invention.

[0050] Compared with the prior art, the present invention has the following advantages:

[0051] (1) The modified anion exchange membrane and improved electrodialysis of the present invention efficiently achieve the separation of organic matter and salt and the concentration of salt, greatly increasing the anti-pollution ability. After the improved electrodialysis treatment, most of the organic matter is retained in the desalination liquid and most of the salt is concentrated in the concentrate, which is beneficial to the subsequent anaerobic treatment, reduces the organic matter content in the salt separation section, and increases the purity of the salt separation product.

[0052] (2) The two-stage anaerobic process of the present invention not only reduces COD and sulfate, but also realizes the resource utilization of organic matter and sulfur. Specifically, sulfate is converted into hydrogen sulfide in the first-stage anaerobic unit and used as a reducing agent to regenerate the ferric ions generated by the Fenton oxidation unit. Organic matter is converted into methane in the second-stage anaerobic unit and purified by the regeneration unit to realize resource utilization.

[0053] (3) Since the wastewater contains some organic matter that is difficult to biodegrade, the present invention uses Fenton advanced oxidation to further treat the two-stage anaerobic biological effluent. Then, the ferric iron produced by Fenton oxidation is intercepted by nanofiltration, separated by single membrane electrodialysis, and regenerated by the regeneration unit, and returned to the Fenton oxidation unit in the form of ferrous iron, so as to realize the recycling of iron catalyst and zero generation of iron sludge. Nanofiltration further desalinates the Fenton oxidation effluent. Finally, the salt content and COD of the nanofiltration product are very low, and it can be reused or discharged after simple pH adjustment.

[0054] (4) The process method of this invention is used to recycle and reuse the recalcitrant high sulfate organic wastewater. The waste gas is stored in tanks and can be used as fuel. The salt is converted into sodium sulfate and sodium chloride products, realizing the overall resource utilization of water, gas and solids.

[0055] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0056] Figure 1 Flowchart of the treatment process for recalcitrant high-sulfate organic wastewater in Example 1;

[0057] Figure 2 Schematic diagram of anion exchange membrane electrodeposition modification in Example 1. Detailed Implementation

[0058] 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.

[0059] Example 1

[0060] The process flow diagram for treating recalcitrant high-sulfate organic wastewater is as follows: Figure 1 As shown, the wastewater first undergoes hardness removal in the regulating and hardening tank, then passes through a tubular microfiltration system before entering electrodialysis. The concentrated solution from the electrodialysis enters the concentration and desalination system to produce sodium sulfate and sodium chloride products. The chemical sludge generated by the regulating and hardening tank and the tubular microfiltration system enters the sludge concentration, dewatering and drying unit. The dewatered water is returned to the inlet of the pretreatment section, and the dried sludge is sent out.

[0061] The desalinated liquid from electrodialysis sequentially enters the primary anaerobic digester, secondary anaerobic digester, and Fenton oxidation. The methane gas produced in the secondary anaerobic digester is used as stripping gas and pumped to the primary anaerobic digester. Most of the hydrogen sulfide produced in the primary anaerobic digester is carried out of the wastewater system and enters the regeneration unit. Hydrogen peroxide is added to the Fenton oxidation unit, and the iron catalyst comes from the regeneration unit of the catalyst regeneration section. The effluent from the Fenton oxidation unit enters the nanofiltration unit. The nanofiltration permeate enters the neutralization tank, where alkali is added to adjust it to neutral, and the effluent is either reused or discharged. The nanofiltration concentrate flows to the single-membrane electrodialysis unit. The effluent from the single-membrane electrodialysis unit is divided into mother liquor and anion exchange liquid. The anion exchange liquid is returned to the primary anaerobic digester inlet, and the mother liquor enters the regeneration unit to react with the methane and hydrogen sulfide mixture produced in the primary anaerobic digester. The reacted water is returned to the Fenton oxidation unit, and the gas is recovered to the methane storage tank for later use.

[0062] The process method of this invention is used to treat recalcitrant high-sulfate organic wastewater.

[0063] A certain recalcitrant organic wastewater with high sulfate content has the following characteristics: COD 1550 mg / L, sulfate 5500 mg / L, chloride concentration 2500 mg / L, calcium ion concentration 120 mg / L, magnesium ion concentration 60 mg / L, total salt content 12600 mg / L, and pH 6.5.

[0064] The electrodialysis provided in this embodiment is a modified electrodialysis, wherein the anion exchange membrane is a modified anion exchange membrane with strong anti-fouling ability and high ion permeability, and the cation exchange membrane is a general-purpose cation exchange membrane (Hefei Capgemini Polymer Co., Ltd., China, model CJ-MC-3).

[0065] The modified anion exchange membrane described above was prepared by the following method:

[0066] Step a: Dissolve the linear polymer in one volume unit of organic solvent, with a mass-volume concentration of 65 mg / mL for both the linear polymer and the organic solvent. Add styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide, and a hydrophilic modifier at mass-volume concentrations of 45 mg / mL, 40 mg / mL, 9 mg / mL, 6 mg / mL, and 40 mg / mL, respectively. Stir the mixture at 70°C for 2.5 h to obtain a polymer solution. The linear polymer is polyvinyl chloride, the organic solvent is dichloromethane, and the hydrophilic modifier is β-cyclodextrin.

[0067] Step b: Add 0.6 volume units of organic solvent to the polymer solution prepared in step a, add anhydrous zinc chloride and chloromethyl methyl ether, the mass-volume concentration of anhydrous zinc chloride to solvent is 22 mg / mL, the volume ratio of chloromethyl methyl ether to solvent is 1.3:1, stir the reaction at 45℃ for 10 h, add precipitant methanol, filter, dry, and pulverize to obtain powdered chloromethylated polymer;

[0068] Step c: Dissolve the polymer obtained in step b in N,N-dimethylformamide, with a mass-volume concentration of 26 mg / mL for both polymer and N,N-dimethylformamide; heat and vaporize the trimethylamine aqueous solution, then pass the trimethylamine gas through an alkaline drying agent into the N,N-dimethylformamide solution of the polymer, reacting for 60 minutes to obtain a quaternized polymer solution; cast the quaternized polymer solution into a membrane using a casting method, and dry it at 65°C for 15 hours to form a membrane; immerse the obtained membrane in a 0.5 mol / L sodium hydroxide solution for alkalization, then wash it with deionized water until neutral to obtain an anion exchange membrane;

[0069] Step d: Dissolve the polyanionic modifier and sodium chloride in 20 mmol / L Tris–HCl buffer solution, adjust the pH to 8.5 with hydrochloric acid, and prepare an electrodeposition mother liquor with a polyanionic modifier mass concentration of 3 g / L and a sodium chloride mass concentration of 10 g / L; the polyanionic modifier is selected as sodium poly4-styrene sulfonate.

[0070] Step e: Take the anion exchange membrane prepared in step c, and perform surface modification and alteration using an electrodeposition method, such as... Figure 2 As shown, the preliminarily modified anion exchange membrane is placed in the middle of a DC electrodeposition apparatus to form two compartments. The electrodeposition mother solution prepared in step d is placed in the compartment on the cathode side, and water is placed in the compartment on the anode side. The electrodeposition time is 0.8 h, and the current density is 20 mA / cm². 2 Finally, the modified anion exchange membrane was obtained;

[0071] Step f: Take out the modified anion exchange membrane obtained in step e and place it in a sodium chloride solution with a mass concentration of 10 g / L for later use.

[0072] The specific operating parameters for treating recalcitrant, high-sulfate organic wastewater are as follows:

[0073] Wastewater first enters the equalization and hardening tank, where sodium hydroxide (150 mg / L), sodium carbonate (180 mg / L), and PAM (8 mg / L) are added to raise the solution pH to 8.5. After clarification, the calcium ion concentration in the supernatant decreases to below 10 mg / L, and the magnesium ion concentration decreases to below 5 mg / L. The effluent is then filtered through a tubular microfiltration system before entering electrodialysis. The chemical sludge produced in the equalization and hardening tank and the tubular microfiltration system enters the sludge thickening, dewatering, and drying unit. The dewatered water is returned to the inlet of the equalization and hardening tank, while the dried sludge is sent off-site. The electrodialysis treatment time is 0.5 hours, and the current density is 25 mA / cm³. 2 After treatment, the salt content of the electrodialysis concentrate was approximately 52.7 g / L, and the COD was 355 mg / L. The salt content of the desalination solution was 3.8 g / L, and the COD was 1795 mg / L. The water production rate (the percentage of desalination solution to total influent) was 82%. The sulfate ion selective permeability was 72.2%, the chloride ion selective permeability was 82.5%, and the organic matter rejection rate was 96.1%.

[0074] The electrodialysis desalination solution enters the primary anaerobic stage, where dissolved oxygen is controlled below 0.15 mg / L, pH is maintained at 5.4 by adding sulfuric acid, wastewater retention time is 4 h, temperature is 30℃, and the bacterial strains are organic acidifying bacteria and sulfate-reducing bacteria. The effluent COD is reduced to 1622 mg / L, and the salt content is reduced to 2903 mg / L. In the secondary anaerobic stage, dissolved oxygen is controlled below 0.1 mg / L, pH is maintained at 8 by adding sodium hydroxide, wastewater retention time is 12 h, temperature is 35℃, and the bacterial strains are methanogenic bacteria. The effluent COD is reduced to 1622 mg / L, and the salt content is reduced to 2903 mg / L. The OD is 255 mg / L, and the salt content is 2690 mg / L. The electrodialysis concentrate enters the multi-effect evaporator, where the salt content is further concentrated to 245 g / L. Then, it enters the nitrate crystallizer, where the operating temperature is controlled at 114℃, to crystallize and obtain sodium sulfate. The effluent enters the salt crystallizer, where the operating temperature is controlled at 86℃, to crystallize and obtain sodium chloride. The residual liquid is returned to the inlet of the multi-effect evaporator. The methane gas produced by the secondary anaerobic digester is pumped to the primary anaerobic digester as stripping gas. The methane and hydrogen sulfide composite gas produced by the primary anaerobic digester enters the regeneration unit.

[0075] The Fenton oxidation unit adds hydrogen peroxide at a 4:1 COD-to-wastewater mass ratio, specifically 1020 mg / L. The iron-based catalyst is derived from recycled water from the regeneration unit, resulting in an iron ion concentration of 980 mg / L after mixing. The pH is adjusted to 3.5 by adding sulfuric acid, ultimately reducing the COD from 255 mg / L to 58 mg / L. The effluent then enters a nanofiltration system; the nanofiltration permeate yield is 89%, with iron and sulfate ion rejection rates both exceeding 98%. The nanofiltration permeate enters a neutralization tank, where sodium hydroxide is added to adjust the pH to 6.5, resulting in a final effluent with a COD of 54 mg / L and a salt content of 1340 mg / L, meeting discharge and reclaimed water quality requirements. The nanofiltration concentrate enters a single-membrane electrodialysis system, with a treatment time of 0.3 hours and a current density of 20 mA / cm². 2 The anion exchange membrane used is a product of Asahi Glass Corporation of Japan (SELEMION AMV), with a sulfate ion selective permeability of 66.5% and an iron ion rejection rate of over 98%. The anion solution is returned to the primary anaerobic inlet, and the mother liquor enters the regeneration unit. The total iron content of the influent to the regeneration unit is less than 10% ferrous ions. After reacting with the hydrogen sulfide mixture, the total iron content of the effluent from the regeneration unit is greater than 95% ferrous ions. The effluent is then returned to the Fenton oxidation unit, and the insoluble gas from the regeneration unit is sent to the methane storage tank. The methane purity is 96.3%.

[0076] As demonstrated in this embodiment, the present invention can effectively treat recalcitrant high-sulfate organic wastewater. Electrodialysis, with a modified anion exchange membrane as its core, efficiently separates organic matter from salts and concentrates the salts. Most of the organic matter is retained in the desalination solution, and most of the salts are concentrated in the concentrate, which is beneficial for subsequent anaerobic treatment. The salts are eventually converted into sodium sulfate and sodium chloride, and most of the organic matter is eventually converted into methane and realized as a resource. Since the wastewater contains some recalcitrant organic matter, the present invention uses Fenton advanced oxidation to further treat the effluent from the two-stage anaerobic biological treatment. The ferric iron produced by Fenton oxidation is then retained by nanofiltration, separated by single-membrane electrodialysis, and regenerated by a regeneration unit, and returned to the Fenton oxidation unit in the form of ferrous iron, realizing the recycling of the iron-based catalyst. No iron sludge is generated during the process. Nanofiltration further desalinates the Fenton oxidation effluent. The final nanofiltration product has very low salt content and COD, and can be reused or discharged after simple pH adjustment.

[0077] Example 2

[0078] use Figure 1 The process shown is for treating a type of recalcitrant high-sulfate organic wastewater.

[0079] A certain recalcitrant organic wastewater with high sulfate content has the following water quality: COD 2800 mg / L, sulfate 9000 mg / L, chloride concentration 4000 mg / L, calcium ion concentration 150 mg / L, magnesium ion concentration 100 mg / L, total salt content 20800 mg / L, and pH 7.

[0080] The process route and implementation steps for treating this wastewater in this embodiment are the same as in Example 1. The electrodialysis in the process route is the same as in Example 1, being a modified electrodialysis method. The anion exchange membrane is a modified anion exchange membrane, and the cation exchange membrane is a general-purpose cation exchange membrane (Hefei Kaijie Polymer Co., Ltd., China, model CJ-MC-3). In the preparation of the modified anion exchange membrane, except that the linear polymer in step a is polyethylene, the β-cyclodextrin mass-volume concentration is 60 mg / ml, the volume ratio of chloromethyl ether to solvent in step b is 1.4:1, and the stirring reaction time is 12 h, everything else is the same as in Example 1.

[0081] The specific operating parameters for treating recalcitrant, high-sulfate organic wastewater are as follows:

[0082] Wastewater first enters the equalization and hardening tank, where sodium hydroxide (200 mg / L), sodium carbonate (200 mg / L), and PAM (9 mg / L) are added. The solution pH rises to 8.6. After clarification, the calcium ion concentration in the supernatant decreases to below 10 mg / L, and the magnesium ion concentration decreases to below 5 mg / L. The effluent is then filtered through a tubular microfiltration system before entering electrodialysis. The chemical sludge produced in the equalization and hardening tank and the tubular microfiltration system enters the sludge thickening, dewatering, and drying unit. The dewatered water is returned to the inlet of the equalization and hardening tank, while the dried sludge is sent off-site. The electrodialysis treatment time is 0.6 hours, and the current density is 30 mA / cm³. 2 After treatment, the salt content of the electrodialysis concentrate was approximately 87.2 g / L, and the COD was 628 mg / L. The salt content of the desalination solution was approximately 4.2 g / L, and the COD was 3343 mg / L. The water production rate (the percentage of desalination solution to the total influent) was 80%. The sulfate ion selective permeability was 81.1%, the chloride ion selective permeability was 90.6%, and the organic matter rejection rate was 95.5%.

[0083] The electrodialysis desalination solution enters the primary anaerobic stage, where dissolved oxygen is controlled below 0.15 mg / L, pH is maintained at 5.5 by adding sulfuric acid, wastewater retention time is 5 h, temperature is 31℃, and the bacterial strains are organic acidifying bacteria and sulfate-reducing bacteria. The effluent COD is reduced to 2956 mg / L, and the salt content is reduced to 3112 mg / L. In the secondary anaerobic stage, dissolved oxygen is controlled below 0.1 mg / L, pH is maintained at 7.9 by adding sodium hydroxide, wastewater retention time is 18 h, temperature is 35℃, and the bacterial strain is methanogenic bacteria. The effluent... The COD is 342 mg / L and the salt content is 2850 mg / L. The electrodialysis concentrate enters the MVR, where the salt content is further concentrated to 250 g / L. Then it enters the nitrate crystallizer, where the operating temperature is controlled at 115℃, and the product sodium sulfate is obtained by crystallization. The effluent enters the salt crystallizer, where the operating temperature is controlled at 88℃, and the product sodium chloride is obtained by crystallization. The residual liquid is recycled to the inlet of the multi-effect evaporator. The methane gas produced by the secondary anaerobic digester is pumped to the primary anaerobic digester as stripping gas. The methane and hydrogen sulfide composite gas produced by the primary anaerobic digester enters the regeneration unit.

[0084] The Fenton oxidation unit adds hydrogen peroxide at a mass ratio of 3.8:1 to wastewater COD, specifically at a dosage of 1300 mg / L. The iron-based catalyst is derived from recycled water from the regeneration unit, resulting in an iron ion concentration of 1230 mg / L after mixing. The pH is adjusted to 3.6 by adding sulfuric acid, ultimately reducing the COD from 342 mg / L to 63 mg / L. The effluent then enters a nanofiltration system; the nanofiltration permeate yield is 88%, with iron and sulfate ion rejection rates both exceeding 98%. The nanofiltration permeate enters a neutralization tank, where sodium hydroxide is added to adjust the pH to 7. The final effluent has a COD of 58 mg / L and a salt content of 1512 mg / L, meeting discharge and reclaimed water quality requirements. The nanofiltration concentrate enters a single-membrane electrodialysis system, with a treatment time of 0.35 h and a current density of 25 mA / cm². 2 The anion exchange membrane used is a product of Asahi Glass Corporation of Japan (SELEMION AMV). The sulfate ion selective permeability is 69.3%, and the iron ion rejection rate is greater than 98%. The anion solution is returned to the primary anaerobic inlet, and the mother liquor enters the regeneration unit. The total iron ion content of the influent to the regeneration unit is less than 10% ferrous ions. After reacting with the hydrogen sulfide mixture, the total iron ion content of the effluent from the regeneration unit is greater than 95% ferrous ions. The effluent is recycled to the Fenton oxidation unit, and the insoluble gas from the regeneration unit is sent to the methane storage tank. The methane purity is 96.6%.

[0085] As can be seen from this embodiment, the present invention can effectively treat recalcitrant high-sulfate organic wastewater of different concentrations, and the treatment process realizes the resource utilization of water, air and solids.

[0086] Comparative Example 1

[0087] The treatment of recalcitrant high-sulfate organic wastewater was the same as in Example 1, and the process route and implementation steps were also the same as in Example 1. The difference was that the anion and cation exchange membranes used in the electrodialysis were both general-purpose membranes. The anion exchange membrane was a product of Asahi Glass Co., Ltd. (SELEMION AMV) from Japan, and the cation exchange membrane was a product of Hefei Kaijie Polymer Co., Ltd. (model CJ-MC-3) from China. No modification treatment was performed.

[0088] Specifically, as in Example 1, the wastewater, after being treated by a regulating and hardening tank and tubular microfiltration, enters the electrodialysis process. The electrodialysis treatment time is 0.5 hours, and the current density is 25 mA / cm². 2 After treatment, the electrodialysis concentrate had a salt content of approximately 44.5 g / L and a COD of 1094 mg / L, while the desalinated solution had a salt content of approximately 5.6 g / L and a COD of 1650 mg / L. The permeate yield (percentage of desalinated solution to total influent) was 82%, the sulfate ion selective permeation rate was 61.1%, the chloride ion selective permeation rate was 72.5%, and the organic matter rejection rate was 87.3%. The electrodialysis desalinated solution entered the primary anaerobic digester, with dissolved oxygen controlled below 0.15 mg / L. Sulfate was added to control the dissolved oxygen levels. The pH was controlled at 5.4, the wastewater retention time was extended to 6 hours, the temperature was 30℃, and the bacterial strains were organic acidifying bacteria and sulfate-reducing bacteria. The effluent COD was reduced to 1511 mg / L, and the salt content was reduced to 4115 mg / L. The dissolved oxygen in the secondary anaerobic system was controlled below 0.1 mg / L, the pH was controlled at 8 by adding sodium hydroxide, the wastewater retention time was extended to 16 hours, the temperature was 35℃, and the bacterial strains were methanogenic bacteria. The effluent COD was 653 mg / L, and the salt content was 3550 mg / L.

[0089] This comparative example shows that electrodialysis using unmodified cation and anion exchange membranes has poor ability to separate organic matter and salts. Furthermore, the anion exchange membrane is easily fouled by organic matter, ultimately leading to a COD concentration of 1094 mg / L in the concentrate, severely affecting the purity of subsequent salt products. The desalination solution also has an excessively high salt concentration (5.3 g / L). Subsequent primary anaerobic treatment, even with extended retention time, still resulted in an effluent salt content as high as 4115 mg / L, especially with relatively high sulfate levels. This also affected the biological activity of methanogenic bacteria in the secondary anaerobic process. Even with extended secondary anaerobic retention time, the effluent COD remained as high as 653 mg / L, and the salt content reached 3550 mg / L. This significantly increased the processing load on subsequent units such as Fenton oxidation, nanofiltration, and catalyst regeneration, easily leading to substandard nanofiltration permeate. Moreover, the catalyst usage in the Fenton oxidation unit increased dramatically, resulting in a relative insufficiency in hydrogen sulfide production during primary anaerobic treatment, decreased catalyst regeneration efficiency, and ultimately, a decline in the treatment efficiency of the Fenton oxidation unit, creating a vicious cycle.

[0090] Comparative Example 2

[0091] The treatment of recalcitrant high-sulfate organic wastewater is the same as in Example 1, and the process route and implementation steps are also basically the same as in Example 1. The difference is that the nanofiltration concentrate directly enters the regeneration unit, without single-membrane electrodialysis.

[0092] Specifically, as in Example 1, the wastewater sequentially passes through a molybdenum removal tank, a hardening and equalization tank, tubular microfiltration, electrodialysis, two-stage oxidation, Fenton oxidation, and nanofiltration before entering the regeneration unit. The COD of the effluent from the two-stage oxidation is 255 mg / L, and the salt content is 2690 mg / L. After Fenton oxidation, the COD decreases to 58 mg / L. Due to the addition of iron ions (980 mg / L) and sulfuric acid in the Fenton oxidation unit, the salt content increases to 4512 mg / L. The nanofiltration permeate rate is 89%, and the iron ion and sulfate ion rejection rates are both greater than 98%. The nanofiltration permeate enters the neutralization tank, where sodium hydroxide is added to adjust the pH to 6.5. The final effluent has a COD of 255 mg / L. The concentration of COD in the nanofiltration concentrate is 54 mg / L, and the salt content is 1340 mg / L, which meets the requirements for discharge and reuse water quality. The COD of the nanofiltration concentrate is 90 mg / L, and the salt content is 30176 mg / L, of which the iron ion concentration is 8856 mg / L and the sulfate concentration is 13150 mg / L. The nanofiltration concentrate flows to the regeneration unit, is regenerated by hydrogen sulfide mixed gas, and then flows back to Fenton oxidation to complete the local circulation. Since there is no sulfate removal unit during the circulation process, the sulfate concentration of the nanofiltration concentrate rises to 26300 mg / L after the second circulation.

[0093] As can be seen from this comparative example, without single-membrane electrodialysis, there is no sulfate removal process in the local circulation process of Fenton oxidation, nanofiltration, and regeneration units, which leads to an increasing sulfate concentration in the wastewater, eventually resulting in salt precipitation and scaling, and ultimately system failure.

[0094] Comparative Example 3

[0095] The water quality of the flue gas desulfurization wastewater treated is the same as in Example 1, and the process route and implementation steps are also basically the same as in Example 1. The difference is that there is no regeneration unit.

[0096] Specifically, as in Example 1, the wastewater is sequentially treated through a molybdenum removal tank, a hardening and equalization tank, tubular microfiltration, electrodialysis, two-stage oxidation, Fenton oxidation, nanofiltration, and single-membrane electrodialysis. After the above unit treatments, the iron ion concentration of the single-membrane electrodialysis mother liquor is 8756 mg / L, the proportion of ferrous ions in the total iron ions is less than 10%, mainly ferric ions, the salt content is 16500 mg / L, and the pH is 3.1. Considering that the mother liquor does not meet the discharge standards, it should be returned to the electrodialysis inlet for further treatment. Most of the iron ions enter the electrodialysis concentrate, but the iron ion content is too high, which will seriously affect the purity of the salt product. Fenton oxidation requires the addition of ferrous salt. The methane and hydrogen sulfide mixture produced by the primary anaerobic digestion cannot be properly treated. According to calculations, the methane purity in the methane storage tank is as low as 66.5% at this time.

[0097] As can be seen from this comparative example, compared with Example 1, the purity of both salt and methane is severely affected by the lack of a regeneration unit, and Fenton oxidation requires the continued addition of ferrous salt, which not only fails to produce qualified products but also significantly increases processing costs.

Claims

1. A process for treating recalcitrant high-sulfate organic wastewater, including a pretreatment section, a reaction section, and a catalyst regeneration section; The pretreatment section includes a hardening and conditioning unit, a tubular microfiltration unit, an electrodialysis unit, a salt concentration and desalination system, and a sludge concentration, dewatering, and drying unit. Wastewater first undergoes hardening and conditioning in the hardening and conditioning unit, then passes through the tubular microfiltration unit for filtration before entering the electrodialysis unit. The concentrate from the electrodialysis unit enters the salt concentration and desalination system, while the desalinated solution enters the primary anaerobic digester of the reaction section. The chemical sludge produced by the hardening and conditioning unit and the tubular microfiltration unit enters the sludge concentration, dewatering, and drying unit. The dewatered water is returned to the inlet of the pretreatment section, and the dried sludge is sent off-site. The reaction section sequentially includes a primary anaerobic unit, a secondary anaerobic unit, and a Fenton oxidation unit. The primary anaerobic unit mainly performs organic acidification and sulfate reduction, producing hydrogen sulfide gas. The secondary anaerobic unit mainly performs methanogenesis, and the generated methane is pumped to the primary anaerobic unit as stripping gas, carrying most of the hydrogen sulfide produced in the primary anaerobic unit out of the wastewater system. The mixed gas of methane and hydrogen sulfide produced in the primary anaerobic unit enters the regeneration unit of the catalyst regeneration section. Hydrogen peroxide is added to the Fenton oxidation unit, and the iron catalyst comes from the regeneration unit of the catalyst regeneration section. The effluent enters the nanofiltration unit of the catalyst regeneration section. The catalyst regeneration section includes a nanofiltration unit, a single-membrane electrodialysis unit, a regeneration unit, a neutralization unit, and a methane storage tank. The effluent from the nanofiltration unit is divided into nanofiltration concentrate and nanofiltration permeate. The nanofiltration permeate enters the neutralization unit, where it is neutralized with alkali and then reused or discharged. The nanofiltration concentrate flows to the single-membrane electrodialysis unit. The effluent from the single-membrane electrodialysis unit is divided into mother liquor and anion exchange liquid. The anion exchange liquid is returned to the inlet of the primary anaerobic unit in the reaction section. The mother liquor enters the regeneration unit and reacts with the methane and hydrogen sulfide mixture generated by the primary anaerobic unit in the reaction section. The reacted water is returned to the Fenton oxidation unit in the reaction section, and the gas is recovered to the methane storage tank for later use. in, The electrodialysis unit is composed of anion and cation exchange membranes, wherein the anion exchange membrane is a modified anion exchange membrane and the cation exchange membrane is a general-purpose cation exchange membrane. The modification methods for anion exchange membranes are as follows: Step a: Dissolve the linear polymer in an organic solvent, then add styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide and a hydrophilic modifier respectively, stir and react to obtain a polymer solution, wherein the hydrophilic modifier is selected from one or more of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin; Step b: Add organic solvent to the polymer solution obtained in step a, add anhydrous zinc chloride and chloromethyl methyl ether, stir to react, then add precipitant, and then filter, dry and pulverize to obtain powdered chloromethylated polymer; Step c: Dissolve the polymer obtained in step b in N,N-dimethylformamide, introduce trimethylamine gas, and carry out a quaternization reaction to obtain a quaternized polymer solution; prepare a membrane from the quaternized polymer solution; immerse the obtained membrane in sodium hydroxide solution for alkalization, and then wash it with deionized water until neutral to obtain an anion exchange membrane; Step d: Dissolve the polyanionic modifier and sodium chloride in Tris-HCl buffer, and adjust the pH to 8-9 with hydrochloric acid to obtain the electrodeposition mother solution; Step e: Place the anion exchange membrane obtained in step c in the middle of the DC electrodeposition apparatus to form two compartments. Put the electrodeposition mother solution prepared in step d 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 process method according to claim 1, characterized in that, In the modification process of the anion exchange membrane, the linear polymer in step a is selected from at least one of polyethylene, polypropylene, polyvinyl chloride or polyvinylidene fluoride, and the mass-volume concentration of the linear polymer in the organic solvent is 30-100 mg / mL.

3. The process method according to claim 1, characterized in that, In the modification process of the anion exchange membrane, the organic solvent in step a is one of dichloromethane, dichloroethane or chloroform, and the mass-volume concentrations of styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide and hydrophilic modifier in the organic solvent are 20-100 mg / mL, 20-100 mg / mL, 5-20 mg / mL, 2-10 mg / mL and 30-80 mg / mL, respectively.

4. The process method according to claim 1, characterized in that, During the modification of the anion exchange membrane, the stirring reaction in step a is carried out at a temperature of 50–90°C for 0.5–6 hours.

5. The process method according to claim 1, characterized in that, In the modification process of the anion exchange membrane, the amount of organic solvent added in step b is 0.5 to 1 times the amount of organic solvent used in step a, the mass-volume concentration of anhydrous zinc chloride in the organic solvent is 15 to 30 mg / mL, and the volume ratio of chloromethyl ether to organic solvent is 0.5:1 to 2:1; the precipitant in step b is methanol and / or ethanol.

6. The process method according to claim 1, characterized in that, In the modification process of the anion exchange membrane, the stirring reaction in step b is carried out at a temperature of 30–55°C for 2–24 hours.

7. The process method according to claim 1, characterized in that, In the modification process of the anion exchange membrane, the mass-volume concentration of the polymer and N,N-dimethylformamide in step c is 15-40 mg / mL; the trimethylamine gas is obtained by heating and vaporizing a trimethylamine aqueous solution and then drying it with an alkaline drying agent, wherein the alkaline drying agent is selected from at least one of potassium hydroxide, sodium hydroxide, quicklime and soda lime.

8. The process method according to claim 1, characterized in that, In the modification process of the anion exchange membrane, the quaternization reaction in step c takes 10 to 120 minutes; the quaternization polymer solution is prepared by casting or casting, and then dried at a temperature of 50 to 70°C for 12 to 24 hours; the concentration of sodium hydroxide solution used for alkalization is 0.1 to 1 mol / L.

9. The process method according to claim 1, characterized in that, In the modification process of the anion exchange membrane, the concentration of the Tris-HCl buffer in step d is 10-50 mmol / L; the polyanion modifier is selected from one or more of sodium poly4-styrene sulfonate, sodium p-styrene sulfonate, sodium polyethylene sulfonate, and sodium polypropylene sulfonate; the mass concentration of the polyanion modifier in the electrodeposition mother liquor is 0.5-5 g / L, and the mass concentration of sodium chloride is 3-30 g / L.

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

11. The process method according to claim 1, characterized in that, The hardening agent in the hardening unit is a combination of sodium hydroxide, sodium carbonate, and PAM. Sodium carbonate is added at 1 to 3 times the mass concentration of calcium ions, the amount of sodium hydroxide added is greater than the mass concentration of magnesium ions, and the amount of PAM added is 1 to 20 mg / L. Sodium hydroxide also acts as a pH adjuster, and the pH value should be greater than 8 after addition.

12. The process method according to claim 1, characterized in that, The electrodialysis unit has a treatment time of 0.2–3 hours and a current density of 1–80 mA / cm². 2 .

13. The process method according to claim 1, characterized in that, The concentration and separation system uses multi-effect evaporation or MVR for evaporation and concentration, concentrating the salt content to 200-300 g / L, and then enters the nitrate crystallizer and salt crystallizer. The salt is separated by utilizing the temperature difference in the solubility of sodium chloride and sodium sulfate. The temperature of the nitrate crystallizer is controlled at 100-130℃, and the temperature of the salt crystallizer is controlled at 70-90℃. The residual liquid is returned to the inlet of the concentration and separation system.

14. The process method according to claim 1, characterized in that, The dissolved oxygen in the primary anaerobic unit is controlled below 0.2 mg / L, the wastewater retention time is 1–8 h, the temperature is 25–35 °C, the pH is controlled at 5–6 by adding acid, and the bacterial strains are organic acidifying bacteria and sulfate reducing bacteria.

15. The process method according to claim 1, characterized in that, The dissolved oxygen in the secondary anaerobic unit is controlled below 0.1 mg / L, the wastewater retention time is 2–36 h, the temperature is 30–40 °C, the pH is controlled at 7–9 by adding alkali, and the bacteria are methanogens.

16. The process method according to claim 1, characterized in that, The amount of hydrogen peroxide added in the Fenton oxidation unit is 1-12:1 by mass ratio of hydrogen peroxide to COD of wastewater, and the amount of iron added is 0.2-1.5:1 by mass ratio of iron to hydrogen peroxide, with a pH of 3-5. The iron is ferrous iron, and the iron salt is selected from at least one of ferrous chloride, ferrous nitrate, and ferrous sulfate.

17. The process method according to claim 1, characterized in that, The nanofiltration unit has a water production rate of 60% to 95%; the neutralization unit adjusts the pH to 6 to 9 by adding one or more of sodium hydroxide, calcium hydroxide or potassium hydroxide to meet the requirements for water reuse or discharge.

18. The process method according to claim 1, characterized in that, The single-membrane electrodialysis unit uses a common anion exchange membrane. Under the action of electrode drive and anion exchange membrane, sulfate ions in the nanofiltration concentrate permeate through the anion exchange membrane into the concentrate side, including Fe. 2+ 、Fe 3+ The cations and most organic matter remain in the mother liquor; the single-membrane electrodialysis treatment time is 0.1–2 h, and the current density is 1–50 mA / cm². 2 .

19. The process method according to claim 1, characterized in that, Recalcitrant high-sulfate organic wastewater is wastewater with a sulfate concentration greater than 2000 mg / L and a COD concentration greater than 1000 mg / L.

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