Sulfate purification process and system for high-salinity wastewater

Abstract

The invention relates to the field of industrial wastewater treatment, in particular to a sulfate purification process and system for high-salinity wastewater. The sulfate purification process comprises the following steps: carrying out denitrification nitrogen removal treatment, resin hardness removal treatment, reverse osmosis treatment, electrochemical oxidation treatment and sodium sulfate crystallization treatment on the high-salinity wastewater to finally obtain a sodium sulfate product. The system comprises a denitrification unit, a hardness removal unit, a reverse osmosis unit, an oxidation unit and a crystallization unit according to a material flow. According to the sulfate purification process and the sulfate purification system, a sulfur autotrophic biological fuel cell technology is adopted in denitrification treatment, so that the sulfate purification process and the sulfate purification system have the remarkable characteristics that an organic carbon source does not need to be additionally added, and meanwhile, a main byproduct is valuable sulfate. In addition, the process and the method have extremely high adaptability, can effectively treat a wastewater environment with high total nitrogen, high salt and heavy metal content, and realize resource utilization of industrial wastewater.

Description

Technical Field

[0001] The invention relates to the field of industrial wastewater treatment, and in particular to a sulfate purification process and system for high-salt wastewater. Background Art

[0002] The coal chemical industry generates a large amount of industrial by-product salts with sulfate and nitrate as the main components. These by-product salts are difficult to be treated by traditional biochemical degradation methods due to their high salt content. Although sulfates have potential application value, the heavy metal ions in them greatly limit their scope of application. Especially today when environmental protection standards are becoming increasingly stringent, waste sulfates generated by some industries are even classified as hazardous wastes, which hinders the road to resource utilization.

[0003] As a key impurity in the by-product sulfate, the impact of nitrate cannot be ignored. First, nitrate will significantly reduce the purity of sulfate, causing great difficulties for subsequent recycling; second, as a hazardous chemical, nitrate needs to be strictly landfilled, which undoubtedly increases the operating costs of the enterprise; finally, nitrate will also increase the energy consumption of wastewater treatment, especially in the evaporation crystallization process, its presence will lead to an increase in energy consumption of 30% to 50%.

[0004] There are currently many methods for treating nitrates, such as physical and chemical methods, biological denitrification, and catalytic reduction. However, these methods generally have problems such as high cost, pollution transfer, and the generation of large amounts of sludge, which limits the application of by-product sulfate in actual production.

[0005] Therefore, it is particularly important to develop a new sulfate purification process for high-salt wastewater environments. This process can effectively treat high-salt wastewater from coal chemical industry, realize resource utilization, reduce the output of impure salt, solve the problem of hazardous waste disposal, and reduce operating costs and energy consumption. Summary of the invention

[0006] The purpose of the present invention is to solve the problems raised in the background technology and to provide a sulfate purification process and system for high-salinity wastewater.

[0007] In order to achieve the above object, the first aspect of the present invention provides a sulfate purification process for high-salinity wastewater, comprising the following steps:

[0008] (S1) using a sulfur autotrophic microbial fuel cell system to perform denitrification treatment on the high-salinity wastewater to obtain denitrified effluent;

[0009] (S2) subjecting the denitrification effluent to a resin de-hardening treatment to obtain de-hardening effluent;

[0010] (S3) subjecting the de-hardened water to reverse osmosis treatment to obtain reverse osmosis concentrated water;

[0011] (S4) subjecting the reverse osmosis concentrated water to electrochemical oxidation treatment to obtain oxidized water;

[0012] (S5) subjecting the oxidation effluent to sodium sulfate crystallization to obtain a sodium sulfate product.

[0013] The second aspect of the present invention provides a system for the sulfate purification process, wherein the system comprises the following units according to the material flow:

[0014] A denitrification unit is used to perform denitrification treatment on the high-salinity wastewater to obtain denitrified effluent;

[0015] a hardness removal unit, used for performing resin hardness removal treatment on the denitrification effluent to obtain hardness-removed effluent;

[0016] A reverse osmosis unit, used for performing reverse osmosis treatment on the de-hardened water to obtain reverse osmosis concentrated water;

[0017] An oxidation unit, used for electrochemically oxidizing the reverse osmosis concentrated water to obtain oxidized effluent;

[0018] The crystallization unit is used to perform sodium sulfate crystallization treatment on the oxidation effluent to obtain a sodium sulfate product.

[0019] The present invention has the following beneficial effects:

[0020] 1. The present invention effectively treats high-salt coal chemical wastewater with high total nitrogen, high salt and heavy metal content by sequentially performing denitrification, hardness removal, reverse osmosis concentration, oxidation removal of COD and sodium sulfate crystallization, and realizes the resource utilization of industrial wastewater.

[0021] Second, the present invention uses sulfur autotrophic coupled biofuel cells for denitrification treatment, which not only efficiently utilizes sulfide and oxygen, with the main byproduct being the target product sulfate, but also realizes the biological conversion of sulfide to electrical energy, significantly reducing the potential threat of sulfide to the environment.

[0022] 3. The sulfur autotrophic coupled biofuel cell of the present invention uses inorganic carbon as the carbon source and sulfur as the electron donor, and does not require the addition of an organic carbon source, thus overcoming the disadvantages of high operating costs and secondary pollution caused by the addition of an external carbon source to traditional microbial fuel cells. In addition, the denitrification process in which the fuel cell participates does not generate CO2 and NO X It fully demonstrates the advantages of environmental protection and resource utilization in the high-salt wastewater sulfate purification process, and also saves energy for the subsequent sodium sulfate crystallization process. DETAILED DESCRIPTION

[0023] The present invention is described in detail below in conjunction with specific embodiments, but such description is not intended to limit the scope of protection of the present invention. Those skilled in the art should know that certain process steps and equipment used in the specific embodiments of the present invention can be properly adjusted or replaced without affecting the implementation of the present invention.

[0024] The first aspect of the present invention provides a sulfate purification process for high-salinity wastewater, comprising the following steps:

[0025] (S1) using a sulfur autotrophic microbial fuel cell system to perform denitrification treatment on the high-salinity wastewater to obtain denitrified effluent;

[0026] (S2) subjecting the denitrification effluent to a resin de-hardening treatment to obtain de-hardening effluent;

[0027] (S3) subjecting the de-hardened water to reverse osmosis treatment to obtain reverse osmosis concentrated water;

[0028] (S4) subjecting the reverse osmosis concentrated water to electrochemical oxidation treatment to obtain oxidized water;

[0029] (S5) subjecting the oxidation effluent to sodium sulfate crystallization to obtain a sodium sulfate product.

[0030] The high-salt wastewater is wastewater obtained after various types of wastewater generated in coal chemical industry have been subjected to quality separation treatment, biochemical treatment and various forms of primary concentration treatment in this field. The parameters of the high-salt wastewater include: pH 6-9, COD content ≤200mg / L, total nitrogen content ≤230mg / L, total hardness content ≤500mg / L, ammonia nitrogen content ≤30mg / L, and TDS content of 5000-11000mg / L.

[0031] In step (S1), the denitrification treatment refers to the use of sulfur autotrophic microbial fuel cell technology, which integrates sulfur autotrophic denitrification and microbial fuel cells to convert chemical energy in wastewater into electrical energy and simultaneously remove nitrogen in high-salinity wastewater.

[0032] In some embodiments, in step (S1), the sulfur autotrophic microbial fuel cell system includes a cathode chamber and an anode chamber, and the two chambers are separated by a proton exchange membrane, and the anode electrode and the cathode electrode are connected by wires and loaded in series.

[0033] Furthermore, the material of the anode electrode is selected from at least one of carbon felt, carbon cloth, carbon nanotubes or graphite, which not only have excellent electrical conductivity, but also promote the attachment of microorganisms and electron transfer; in the anode chamber, sulfur autotrophic denitrifying bacteria oxidize low-valent sulfur (such as hydrogen sulfide and sulfur in organic matter) into sulfate and release electrons, and use these electrons to reduce nitrate and nitrite to nitrogen gas, thereby achieving denitrification of high-salinity wastewater. That is, the main electron donors in the anode chamber are low-valent sulfur (such as hydrogen sulfide) and organic matter in high-salinity wastewater, and the main carbon source is organic pollutant COD in wastewater.

[0034] Furthermore, the material of the cathode electrode is selected from at least one of platinum, platinum alloy or metal oxide (such as manganese dioxide), which has high catalytic activity and stability. These materials serve as the "terminal station" of electrons in the cathode chamber, where the electrons react with electron acceptors (such as dissolved oxygen) to generate water or other products, completing the closure of the electrochemical reaction. In addition, the reaction efficiency can be further enhanced by optimizing the shape, structure and surface modification of the cathode material.

[0035] Furthermore, the proton exchange membrane plays a vital role in the sulfur autotrophic microbial fuel cell system. It allows protons to pass freely to maintain electrical neutrality, while effectively preventing direct penetration of electrons, ensuring that current can only flow through the external circuit. This design not only improves the energy conversion efficiency of the system, but also ensures the stable operation of the system.

[0036] In some embodiments, in step (S1), sulfur autotrophic denitrifying bacteria participate in the denitrification and denitrification treatment, wherein the sulfur autotrophic denitrifying bacteria are selected from at least one of Thiobacillus denitrificans, Thiobacillusthioparus, Beggiatoa alba, Desulfurispirillumindicum, Paracoccus denitrificans, Desulfovibrio vulgaris, Desulfovibrio desulfuricans, Achromatium oxaliferum, and Acidithiobacillus ferrooxidans in the genus Thiobacillus. Compared with common sulfur autotrophic denitrifying bacteria, the above-mentioned strains have higher salt tolerance and excellent metabolic capacity, and have strong adaptability to the treatment of high-salt wastewater from coal chemical industry.

[0037] In some embodiments, in step (S1), the denitrification denitrification treatment not only achieves effective removal of nitrogen (the total nitrogen content of the denitrification effluent is less than 100 mg / L), but also reduces part of the COD (chemical oxygen demand) to less than 200 mg / L. Compared with traditional activated sludge treatment, this technology exhibits stronger adaptability to load and environmental changes and is suitable for treating high-salinity wastewater with large fluctuations. At the same time, the denitrification process uses sulfide as an electron donor to efficiently reduce nitrate to nitrogen gas, avoiding the common problem of nitrite accumulation, and also realizing energy recovery in the wastewater treatment process, with significant environmental and economic benefits.

[0038] In step (S2), the resin hardness removal treatment refers to reducing the hardness of the denitrification effluent by using ion exchange resin. In some embodiments, the ion exchange resin is a strong acidic cation exchange resin, such as a sulfonic acid resin, which has a strong anti-pollution ability and can resist the influence of pollutants in the water on its performance to a certain extent.

[0039] Furthermore, the operating conditions of the ion exchange resin include: the flow rate is controlled at 30-60m 3 / m 2 ·h, water temperature 25℃, pH 7.5-8.5, exchange capacity 2-4meq / mL.

[0040] Furthermore, the total hardness content of the de-hardening effluent is ≤20 mg / L.

[0041] The inventors have found that strongly acidic sulfonic acid groups have low chemical reactivity and adsorption tendency to most organic pollutants and complex ions, so they are not easily covered or inactivated by pollutants. In contrast, weakly acidic or weakly basic functional groups are more likely to react with or be adsorbed by organic pollutants, resulting in performance degradation.

[0042] In step (S3), the reverse osmosis treatment refers to concentrating the de-hardening water using a high-pressure reverse osmosis device in the art to reduce the scale of subsequent sodium sulfate crystallization treatment to obtain reverse osmosis concentrated water.

[0043] In some embodiments, the operating conditions of the high-pressure reverse osmosis device include: working pressure of 2-50 MPa, water inlet pressure of 2.0-3.0 MPa, interstage pressure of 0.2-0.5 MPa, recovery rate of 75-83%, membrane flux of 10-50 L / (m 2 h).

[0044] Furthermore, the TDS content of the reverse osmosis concentrated water is 20000-50000 mg / L.

[0045] In step (S4), the electrochemical oxidation treatment refers to reducing organic pollutants (i.e., reducing COD) in the reverse osmosis concentrated water by using an electrolysis device. The electrode material of the electrolysis device is an inert electrode material selected from at least one of silver, platinum, palladium, rhodium, iridium, osmium, and ruthenium.

[0046] Furthermore, the operating conditions of the electrolysis device include: a current density of 1-5A / dm 2 , time is 30-90min.

[0047] Furthermore, the COD content of the oxidation effluent is ≤50 mg / L.

[0048] In this scheme, no additional oxidant needs to be added in the electrochemical oxidation treatment, thus avoiding secondary pollution caused by the oxidant. The reaction conditions can be adjusted at any time as needed, with strong controllability. The hydroxyl radicals generated during the reaction have non-selective strong oxidizing properties and can directly degrade almost all types of organic pollutants. It also has good adaptability.

[0049] In step (S5), the sodium sulfate crystallization process is well known in the art, and refers to separating the sodium sulfate in the oxidized water by utilizing the difference in solubility of sodium sulfate in the solution at different temperatures, and comprises the following steps:

[0050] (S5a) evaporating and concentrating the oxidation water to obtain evaporated concentrated water;

[0051] (S5b) subjecting the evaporated concentrated water to sodium sulfate crystallization to obtain a sodium sulfate product.

[0052] In some embodiments, in step (S5a), the temperature of the evaporation concentration is 50-100°C; and the soluble solid content in the evaporated concentrated water is ≤30%.

[0053] In some embodiments, in step (S5b), the temperature of the sodium sulfate crystallization treatment is 0-30°C.

[0054] The sodium sulfate product can be subjected to conventional operations such as recrystallization, flash evaporation, and drying in the art to improve the purity of the sodium sulfate product.

[0055] Furthermore, the sodium sulfate content in the sulfate product is ≥98%, reaching Class A first-class product in the standard of "Industrial Sodium Sulfate as a By-product of Coal Chemical Industry" (T / CCT001-2019).

[0056] The second aspect of the present invention provides a system for the above-mentioned sulfate purification process, wherein the system comprises the following units according to the material flow:

[0057] A denitrification unit is used to perform denitrification treatment on the high-salinity wastewater to obtain denitrified effluent;

[0058] a hardness removal unit, used for performing resin hardness removal treatment on the denitrification effluent to obtain hardness-removed effluent;

[0059] A reverse osmosis unit, used for performing reverse osmosis treatment on the de-hardened water to obtain reverse osmosis concentrated water;

[0060] An oxidation unit, used for electrochemically oxidizing the reverse osmosis concentrated water to obtain oxidized effluent;

[0061] The crystallization unit is used to perform sodium sulfate crystallization treatment on the oxidation effluent to obtain a sodium sulfate product.

[0062] In some embodiments, the denitrification unit uses a sulfur autotrophic microbial fuel cell to treat the high-salinity wastewater;

[0063] The hardness removal unit uses an ion exchanger filled with a strong acidic cationic resin to treat the denitrification effluent;

[0064] The reverse osmosis unit uses a high-pressure reverse osmosis device to treat the de-hardened effluent;

[0065] The oxidation unit uses an electrolytic cell to treat the reverse osmosis concentrated water;

[0066] The crystallization unit uses a sodium sulfate crystallizer to treat the oxidation effluent.

[0067] In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention will be described in detail below through specific embodiments and comparative examples.

[0068] In the following examples and comparative examples, the water quality characteristics of the high-salinity wastewater are as follows: the total dissolved solids (TDS) content is 10625 mg / L, the total nitrogen content is 200 mg / L, and the COD content is 200 mg / L.

[0069] The sulfur autotrophic denitrifying bacteria are selected from Thiobacillus denitrificans, which are taken from groundwater rich in nitrate and sulfide, especially in areas with sulfide deposits. The strain number of the ATCC deposit is ATCC 29518, and the strain number of the DSMZ deposit is DSM 2003. (See DP Kelly, and AP Wood, Confirmation of Thiobacillus denitrificans as a species of the genus Thiobacillus, in the beta-subclass of the Proteobacteria, with strain NCIMB 9548 as the typestrain. International Journal of Systematic & Evolutionary Microbiology 50 Pt 2 (2000) 547)

[0070] Example 1

[0071] Step (S1): using a sulfur autotrophic microbial fuel cell to perform denitrification treatment on high-salinity wastewater to obtain denitrified effluent, comprising the following steps:

[0072] (S1a) In the anode chamber of the sulfur autotrophic coupled microbial fuel cell, the high-salt wastewater enters the anode chamber and is ready to undergo electron release and denitrification reactions; the sulfur autotrophic denitrifying bacteria oxidize the low-valent sulfur in the high-salt wastewater into sulfate ions and release electrons, and at the same time utilize the electrons released during the sulfur oxidation process to reduce the nitrate and nitrite in the high-salt wastewater into nitrogen gas, thereby completing the denitrification process; wherein,

[0073] In the anode chamber, the pH is 7, the temperature is 30°C, the dissolved oxygen content is 0.3 mg / L, and the anode material is a graphite electrode.

[0074] (S1b) In the cathode chamber of the sulfur autotrophic microbial fuel cell, electrons transferred from the anode chamber enter the cathode chamber and undergo a reduction reaction with oxygen to generate water; wherein,

[0075] In the cathode chamber, the pH is 7.5, the temperature is set at 30°C, the dissolved oxygen content is 0.8 mg / L, and the cathode material is MnO2 metal electrode;

[0076] The total nitrogen content of the denitrification effluent is 60 mg / L, and the COD content is 150 mg / L.

[0077] Step (S2): in an ion exchanger filled with a sulfonic acid type strong acidic cationic resin, the denitrification effluent is subjected to resin de-hardening treatment to obtain de-hardening effluent with a hardness of 10 mg / L; wherein,

[0078] The operating conditions of the ion exchanger include: the flow rate is controlled at 30m 3 / m 2 ·h, water temperature is 25℃, pH is 8, and exchange capacity is 2meq / mL.

[0079] Step (S3): In a high-pressure reverse osmosis device equipped with a reverse osmosis membrane assembly, the water inlet pressure is 2.0 MPa, the interstage pressure is 0.2 MPa, and the membrane flux is 30 L / (m 2 h), under the condition of a recovery rate of 80%, the de-hardening water is subjected to reverse osmosis treatment to obtain reverse osmosis concentrated water; wherein,

[0080] The TDS content of the reverse osmosis concentrated water is 30000 mg / L.

[0081] Step (S4): In an electrolytic cell whose electrode material is silver, at a current density of 3A / dm 2 , and the time is 60 minutes, the reverse osmosis concentrated water is subjected to electrochemical oxidation treatment to obtain oxidized water; wherein,

[0082] The COD content of the oxidation effluent is 30 mg / L.

[0083] Step (S5): the oxidation effluent is subjected to sodium sulfate crystallization to obtain a sodium sulfate product, comprising the following steps:

[0084] (S5a) In an MVR evaporator, the oxidation water is evaporated and concentrated to obtain evaporated concentrated water with a solid content of 30%; wherein:

[0085] Before the evaporation and concentration, the nitrate removal rate of the oxidized water is 90%;

[0086] The power consumption of evaporation for producing sodium sulfate product is maintained in the working range of 25-35kWh.

[0087] (S5b) in a sodium sulfate crystallizer, subjecting the evaporated concentrated water to sodium sulfate crystallization to obtain a sodium sulfate product and miscellaneous salts; wherein,

[0088] The purity of the sodium sulfate product is 94%, and the output of qualified grade sodium sulfate (purity above 92%) is 103.7t / d;

[0089] The sodium nitrate content in the miscellaneous salt is 6%.

[0090] Comparative Example 1

[0091] Refer to Example 1, the only difference is:

[0092] In step (S1), the denitrification process is changed from sulfur autotrophic denitrification to traditional AO denitrification process, resulting in a 10-fold increase in the total nitrogen content of the denitrification effluent (about 600 mg / L).

[0093] In step (S5a), due to the increase in total nitrogen content (which can be regarded as nitrate content), the boiling point of the oxidized water increases significantly, and the evaporation unit power consumption working range increases from 25 to 35 kWh to 33 to 46 kWh.

[0094] In step (S5b), the output of the sodium sulfate product is reduced from 103.7 t / d to 103.02 t / d (i.e., reduced by 0.68 t / d); and the nitrate content in the impurity salt is increased from 6% to 30%.

[0095] In summary, in Comparative Example 1, since the heterotrophic denitrification process of the AO denitrification process requires organic matter, compared with the sulfur autotrophic denitrification unit, the microorganisms in this process need to use the absorbed CO2 as an inorganic carbon source for assimilation, and the AO process will lead to an increase in CO2 and the production of N2O during the denitrification process. Comprehensive calculations show that the emission of greenhouse gases in Comparative Example 1 increased by 290t CO2eq.

[0096] Comparative Example 2

[0097] The only difference from Example 1 is that:

[0098] In step (S1), the sulfur autotrophic denitrifying bacteria is Sulfurimonas denitrificans, which is more suitable for sulfur autotrophic denitrification in a low-salinity environment. Higher salinity may inhibit its denitrification ability, causing the total nitrogen in the denitrification effluent to increase from 60 mg / L to 120 mg / L.

[0099] In step (S5a), before the evaporation concentration, the nitrate removal rate is reduced from 90% to 40%.

[0100] In step (S5b), since the boiling point of the evaporated concentrated water is affected by nitrates, the boiling point is greatly increased, and the evaporation unit power consumption working range is increased from 25 to 35 kWh to 105 to 125 kWh.

[0101] The purity of the sodium sulfate product is reduced from 94% to 39%, and the total output of qualified grade sodium sulfate (92%) is reduced from 103.7t to 40.1t.

[0102] In summary, in Comparative Example 2, due to the selection of non-salt-tolerant sulfur autotrophic denitrifying bacteria, the nitrate content in the water increased significantly, resulting in a serious reduction in the qualified rate of the final sodium sulfate product.

[0103] The present invention has described in detail the preferred embodiments of the present invention, but the embodiments are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other simple modifications and combinations within the scope of the present invention, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the scope of protection of the present invention.

Claims

1. A sulfate purification process for high-salinity wastewater, characterized in that: The steps include: (S1) using a sulfur autotrophic microbial fuel cell system to perform denitrification treatment on the high-salinity wastewater to obtain denitrified effluent; (S2) subjecting the denitrification effluent to a resin de-hardening treatment to obtain de-hardening effluent; (S3) subjecting the de-hardened water to reverse osmosis treatment to obtain reverse osmosis concentrated water; (S4) subjecting the reverse osmosis concentrated water to electrochemical oxidation treatment to obtain oxidized water; (S5) subjecting the oxidation effluent to sodium sulfate crystallization to obtain a sodium sulfate product.

2. The sulfate purification process according to claim 1, characterized in that: In step (S1), the sulfur autotrophic microbial fuel cell system comprises a cathode chamber and an anode chamber, and the two chambers are separated by a proton exchange membrane, and the anode electrode and the cathode electrode are connected by a wire and loaded in series; The material of the anode electrode is selected from at least one of carbon felt, carbon cloth, carbon nanotubes or graphite; The material of the cathode electrode is selected from at least one of platinum, platinum alloy or metal oxide, and the metal oxide is preferably manganese dioxide.

3. The sulfate purification process according to claim 1 or 2, characterized in that: In step (S1), sulfur autotrophic denitrifying bacteria participate in the denitrification treatment; Preferably, the sulfur autotrophic denitrifying bacteria is at least one selected from Thiobacillus denitrificans, Thiobacillus thioparus, Beggiatoa alba, Desulfurispirillumindicum, Paracoccus denitrificans, Desulfovibrio vulgaris, Desulfovibrio desulfuricans, Achromatium oxaliferum, and Acidithiobacillus ferrooxidans.

4. The sulfate purification process according to any one of claims 1 to 3, characterized in that: In step (S2), the resin hardness removal treatment refers to using a strong acid ion exchange resin to reduce the hardness of the denitrification effluent; Preferably, the strongly acidic ion exchange resin is a sulfonic acid resin; Preferably, the operating conditions of the strongly acidic ion exchange resin include: a flow rate of 30-60 m / s. 3 / m 2 ·h, pH 7.5-8.5, exchange capacity 2-4meq / mL.

5. The sulfate purification process according to any one of claims 1 to 4, characterized in that: In step (S3), the reverse osmosis treatment refers to using a high-pressure reverse osmosis device to perform reverse osmosis concentration on the de-hardened water to obtain reverse osmosis concentrated water; Preferably, the operating conditions of the high-pressure reverse osmosis device include: working pressure of 2-50MPa, water inlet pressure of 2.0-3.0MPa, interstage pressure of 0.2-0.5MPa, recovery rate of 75-83%, membrane flux of 10-50L / (m 2 h).

6. The sulfate purification process according to any one of claims 1 to 5, characterized in that: In step (S4), the electrochemical oxidation treatment refers to using an electrolysis device to reduce the content of organic pollutants in the reverse osmosis concentrated water; Preferably, the current density of the electrolysis device is 1-5A / dm 2 , the working time of the electrolysis device is 30-90min; Preferably, the electrode material of the electrolysis device is selected from at least one of silver, platinum, palladium, rhodium, iridium, osmium and ruthenium.

7. The sulfate purification process according to any one of claims 1 to 6, characterized in that: In step (S5), the sulfate crystallization process comprises the following steps: (S5a) evaporating and concentrating the oxidation water to obtain evaporated concentrated water; (S5b) subjecting the evaporated concentrated water to sodium sulfate crystallization to obtain a sodium sulfate product; Preferably, the temperature of the evaporation concentration is 40-100° C., and the soluble solid content in the evaporated concentrated water is ≤30%; Preferably, the temperature of the sodium sulfate crystallization treatment is 0-30°C.

8. The sulfate purification process according to claim 7, characterized in that: After the sodium sulfate crystallization treatment, recrystallization, flash evaporation and drying operations are performed to improve the product purity to obtain a sodium sulfate product.

9. A system for the sulfate purification process according to any one of claims 1 to 8, characterized in that: The system includes the following units according to the material flow: A denitrification unit is used to perform denitrification treatment on the high-salinity wastewater to obtain denitrified effluent; a hardness removal unit, used for performing resin hardness removal treatment on the denitrification effluent to obtain hardness-removed effluent; A reverse osmosis unit, used for performing reverse osmosis treatment on the de-hardened water to obtain reverse osmosis concentrated water; An oxidation unit, used for electrochemically oxidizing the reverse osmosis concentrated water to obtain oxidized effluent; The crystallization unit is used to perform sodium sulfate crystallization treatment on the oxidation effluent to obtain a sodium sulfate product.

10. The sulfate purification system according to claim 9, characterized in that: The denitrification unit uses a sulfur autotrophic microbial fuel cell system to treat the high-salinity wastewater; The hardness removal unit uses an ion exchanger filled with a strong acidic cationic resin to treat the denitrification effluent; The reverse osmosis unit uses a high-pressure reverse osmosis device to treat the de-hardened effluent; The oxidation unit uses an electrolytic cell to treat the reverse osmosis concentrated water; The crystallization unit uses a sodium sulfate crystallizer to treat the oxidation effluent.