A process for treating refinery caustic sludge wastewater

Abstract

A process method for treating refinery caustic sludge wastewater, comprising a wet oxidation section, an organic matter treatment section and a salt treatment section; the wet oxidation section comprises an adjusting tank, a heat exchange unit, a wet oxidation reactor, a cooler, an electrodialysis I and a nanofiltration I, the organic matter treatment section comprises an electrodialysis II, anaerobic biochemistry, secondary biochemistry, a reuse water tank and a methane purification unit; the salt treatment section comprises, in sequence, aerobic biochemistry, a decarbonizer, a nanofiltration II, ozone catalytic oxidation and a nitrate crystallizer; the electrodialysis all adopts a modified anion exchange membrane, which is prepared by crosslinking polyvinyl alcohol, a positively charged amine compound and beta-cyclodextrin, and performing surface modification by electrodeposition in the presence of a polyanion modifier. The application adopts a treatment process with homogeneous catalytic wet oxidation as the core, fully utilizes the characteristics of high catalytic activity and high treatment efficiency of homogeneous catalytic wet oxidation, and greatly improves the treatment capacity of wet oxidation.

Description

TECHNICAL FIELD

[0001] The application relates to a treatment method of oil refining alkali residue wastewater and belongs to the technical field of wastewater treatment. BACKGROUND

[0002] Alkali residue wastewater generated in the process of oil refining contains a large amount of neutral oil, organic acid, volatile phenol and sulfide and other toxic and harmful substances, the wastewater is black brown and has a foul odor, and the treatment is extremely difficult, which has been a problem troubling oil refining enterprises. The most mainstream treatment method of the oil refining alkali residue wastewater is a wet oxidation method, which operates under the conditions of high temperature (180-320 DEG C) and high pressure (2.5-20 MPa), utilizes gaseous oxygen as an oxidant to oxidize and decompose organic matters in water into small molecular organic matters or inorganic matters. However, the traditional wet oxidation needs higher temperature, pressure and relatively longer residence time, the operation cost per ton of water is high, the equipment material requirement is high, and the one-time investment is also high.

[0003] In order to reduce the required temperature and pressure of the reaction and improve the treatment effect, a catalytic wet air oxidation (CWAO) technology has become a research hotspot in recent years. CN201510274988.5 discloses a catalyst for catalytic wet air oxidation of refractory organic wastewater, the catalyst is a "noble metal-transition metal-rare earth" composite catalyst, the main component of the carrier FSC is alumina; CN201410340574.3 discloses a catalyst for catalytic wet air oxidation treatment and a preparation method thereof, the catalyst takes a noble metal-non-noble metal nano alloy as an active component and takes activated carbon as a carrier; CN201510661575.2 discloses a heterogeneous wet air oxidation catalyst, the components include a composite oxide carrier and a small amount of noble metal; and CN201310621017.4 discloses a preparation method of a catalyst carrier for catalytic wet air oxidation, the carrier takes activated carbon as a core and takes amorphous silicon aluminum as a shell.

[0004] The above patents all adopt heterogeneous catalytic wet air oxidation, which has advantages in the separation and recovery of the catalyst and metal loss, but is not necessarily suitable for the existing wet oxidation process. A paper "Alkali residue moderate wet air oxidation + SBR treatment technology industrial application" (2011) discloses an alkali residue moderate wet air oxidation process of Fushun Petrochemical Research Institute, the process has been popularized and applied in 28 refining enterprises and has strong representativeness. The wet oxidation reactor used in the process is a bubbling flow internal circulation reactor with an inner cylinder, if a heterogeneous catalyst is used in the reactor, it can be predicted that the gas-liquid circulation will be seriously affected, and even the reactor and pipeline will be blocked, if a fixed bed method is used, greater gas resistance will be caused, which is more unfavorable to the gas-liquid circulation, and the reaction rate will be greatly reduced.

[0005] Homogeneous catalysis has higher catalytic efficiency than heterogeneous catalysis because of no internal and external diffusion effects and high dispersion, and the preparation of catalyst is much simpler than that of heterogeneous catalyst, but the biggest problem of homogeneous catalysis applied to wet oxidation is the loss of metal catalyst.

[0006] The COD concentration of oil refining waste lye is as high as tens of thousands mg / L, and a large part of the COD is false COD caused by sodium sulfide and sodium thiosulfate. The purpose of wet oxidation treatment of waste lye is to convert sulfide and sodium thiosulfate into sodium sulfate, oxidize malodorous gases such as mercaptan and sulfide, and effectively remove organic matter. However, the effluent of wet oxidation still has a certain COD and a large amount of salt, and the proper disposal of COD and salt is still a problem to be solved. SUMMARY

[0007] In view of the above problems, the present application provides a treatment method for oil refining lye residue wastewater, which combines homogeneous wet oxidation, improved electrodialysis, nanofiltration and other processes to realize efficient treatment and zero discharge of oil refining lye residue wastewater, and to produce high-purity sodium sulfate and methane, while solving the problems of catalyst loss in homogeneous catalytic process and separation of organic matter and salt in wet oxidation effluent, and having the advantages of environmental protection and energy saving.

[0008] To achieve the above technical purposes, the technical scheme adopted by the present application is as follows:

[0009] A process method for treating oil refining lye residue wastewater, comprising a wet oxidation section, an organic matter treatment section and a salt treatment section;

[0010] The wet oxidation section comprises an adjusting tank, a heat exchange unit, a wet oxidation reactor, a cooler, electrodialysis I and nanofiltration I. The oil refining lye residue wastewater first enters the adjusting tank, is mixed with nanofiltration I concentrated water and homogeneous catalyst, and is adjusted in pH by adding acid, and then is heated by the heat exchange unit and then enters the wet oxidation reactor. The effluent of the wet oxidation reactor enters the heat exchange unit for heat exchange and cooling, and then enters the electrodialysis I after being cooled by the cooler. The dilute liquid of the electrodialysis I enters the electrodialysis II of the organic matter treatment section, the anode concentrated liquid of the electrodialysis I enters the aerobic biochemical unit of the salt treatment section, and the cathode concentrated liquid of the electrodialysis I enters the nanofiltration I. The concentrated water of the nanofiltration I enters the adjusting tank, and the produced water of the nanofiltration I is mixed with the anode concentrated liquid of the electrodialysis I.

[0011] The organic matter treatment section comprises electrodialysis II, anaerobic biochemical, secondary biochemical, reuse water tank and methane purification unit. The concentrated liquid of the electrodialysis II enters the aerobic biochemical unit of the salt treatment section, and the dilute liquid enters the anaerobic biochemical unit. The liquid phase produced by the anaerobic biochemical enters the secondary biochemical, and the effluent of the secondary biochemical enters the reuse water tank. The gas phase produced by the anaerobic biochemical enters the methane purification unit, and high-purity methane is obtained after purification.

[0012] The salt treatment section comprises, in sequence, aerobic biochemical treatment, decarbonizer, nanofiltration II, ozone catalytic oxidation and nitrate crystallizer; the concentrated water of the nanofiltration II enters the ozone catalytic oxidation, the water produced by the nanofiltration II is returned to the electrodialysis I of the wet oxidation section; the effluent of the ozone catalytic oxidation enters the nitrate crystallizer, the product sodium sulfate is obtained from the nitrate crystallizer, and the remaining mother liquor is returned to the electrodialysis I of the wet oxidation section or is discharged as a miscellaneous salt.

[0013] Further, the electrodialysis I and the electrodialysis II both use modified anion exchange membranes, and the cation exchange membrane is a general cation exchange membrane.

[0014] The modified anion exchange membrane is prepared by the following steps:

[0015] Step a: polyvinyl alcohol is added to water to prepare a polyvinyl alcohol aqueous solution, then a positively charged amine compound and β-cyclodextrin are added to the above solution, and a casting solution is obtained after mixing reaction;

[0016] Step b: the casting solution obtained in step a is cast on a horizontal panel and dried to obtain a base membrane;

[0017] Step c: the base membrane obtained in step b is further immersed in a crosslinking solution composed of a crosslinking agent, sodium sulfate, sulfuric acid and water;

[0018] Step d: the crosslinked membrane is washed, alkalized in a lye, and then soaked in water to obtain a polyvinyl alcohol anion exchange membrane;

[0019] Step e: a polyanion modifier and sodium chloride are dissolved in a Tris-HCl buffer solution, and the pH is adjusted to 8-9 with hydrochloric acid to obtain a modified solution;

[0020] Step f: the anion exchange membrane obtained in step d is placed in the middle of a direct current electrodeposition device to form two compartments, the modified solution obtained in step e is placed in the cathode side compartment, and water is placed in the anode side compartment, and an electrodeposition reaction is carried out to obtain a modified anion exchange membrane.

[0021] Further, the positively charged amine compound is one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxy chloropropane amine and quaternary ammonium chitosan, and is preferably 2,3-epoxypropyltrimethylammonium chloride; the mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1-0.6:1.

[0022] Further, the mass ratio of the β-cyclodextrin to polyvinyl alcohol is 0.05:1-0.4:1.

[0023] Further, the mass fraction of the polyvinyl alcohol aqueous solution in step a is 5%-15%, and the mixing reaction time of the positively charged amine compound and the β-cyclodextrin is 2-10 h.

[0024] Further, the polyvinyl alcohol aqueous solution is prepared by stirring the polyvinyl alcohol in water at 60-90℃ until the polyvinyl alcohol is dissolved.

[0025] Further, the drying in step b is performed at room temperature for 2-6h, and then at 40-80℃ under vacuum for 4-10h.

[0026] Further, the crosslinking agent is selected from aldehyde or acid crosslinking agents, and preferably is glutaraldehyde.

[0027] Further, the mass percentage of the crosslinking agent, sodium sulfate and sulfuric acid in the crosslinking solution is 2%-8%, 4%-15% and 1%-4% respectively, and the rest is water.

[0028] Further, the soaking time of the base film in the crosslinking solution in step c is 1-6h, and the crosslinking is formed in the film through acetal reaction.

[0029] Further, the washing in step d is performed with water until the film is neutral.

[0030] Further, the alkali treatment is performed with 0.5-3mol / L sodium hydroxide aqueous solution for 12-24h.

[0031] Further, the soaking time in step d is 12-24h.

[0032] Further, the polyanion modifier is one or more of poly(4-styrenesulfonic acid) sodium salt, p-styrenesulfonic acid sodium salt, polyvinylsulfonic acid sodium salt and polypropylene sulfonic acid sodium salt, and preferably is poly(4-styrenesulfonic acid) sodium salt.

[0033] Further, the mass concentration of the polyanion modifier in the modification solution in step e is 1-10g / L, and the mass concentration of sodium chloride is 3-30g / L.

[0034] Further, the concentration of the Tris-HCl buffer in step e is 10-50mmol / L.

[0035] Further, the electrodeposition reaction time in step f is 0.2-2h, and the current density is 1-50mA / cm 2 A layer of polyanion modifier is deposited on the surface of the anion exchange membrane by electrodeposition to modify the surface of the membrane.

[0036] Further, the modified anion exchange membrane is stored in a sodium chloride solution after being obtained, and the mass concentration of the sodium chloride solution is 5-20g / L.

[0037] The skilled in the art should understand that the alkali residue wet oxidation effluent contains a small amount of negatively charged organic matter, and the anion exchange membrane of the application is modified by a polyanion modifier, and the surface is negatively charged, which has electrostatic repulsion effect on the negatively charged organic matter in water, and can inhibit the pollution of the anion exchange membrane by the organic matter. The negative surface charge prevents the pollution of the organic matter by electrostatic effect, and also affects the migration rate of inorganic anions, and the more the ionic charge, the greater the influence, therefore, the influence on sulfate ions is greater than that on chloride ions. The addition of β-cyclodextrin in the anion exchange membrane can give the membrane strong hydrophilicity and change the migration rate of anions, among which the migration number of anions with low hydration degree such as bromide ions and nitrate ions is reduced relative to that of chloride ions, and the migration number of sulfate ions with high hydration degree is increased relative to that of chloride ions. On the other hand, the hydrophilicity of the membrane is improved, the van der Waals force between the membrane and the organic solute is reduced, the attraction is reduced, and at the same time, the hydrophilic membrane and water molecules can form a hydration layer due to hydrogen bonding, which can further hinder the adsorption of pollutants on the membrane surface. Therefore, after the anion exchange membrane of the application is modified by the polyanion modifier and β-cyclodextrin, the anti-pollution ability of the membrane is greatly increased, and the selective permeability of sulfate ions is significantly increased.

[0038] Further, an acid is added to the adjusting tank to adjust the pH to 2-6; the acid is hydrochloric acid or sulfuric acid, preferably sulfuric acid.

[0039] Further, the heat exchange unit is composed of multiple heat exchangers, which are used to exchange heat between the wet oxidation reactor effluent and the adjusting tank effluent, and after heat exchange, the temperature of the adjusting tank effluent is increased to 130-160℃, and the temperature of the wet oxidation reactor effluent is reduced to 50-75℃.

[0040] Further, the homogeneous catalyst is a transition metal catalyst selected from one or more of copper, iron, manganese, zinc and nickel, preferably a copper catalyst; the transition metal in the homogeneous catalyst exists in the form of a metal salt compound or a complex, and is dissolved in the liquid phase.

[0041] Further, the homogeneous catalyst is added according to the ratio of COD mass concentration to metal ion mass concentration of 10000:1-20:1, and is appropriately supplemented according to the catalyst loss rate and the change of the concentration of the reaction liquid during normal operation.

[0042] Further, the wet oxidation reactor is a bubbling flow internal cylinder reactor, which uses gaseous oxygen (air) as oxidant to oxidize general organic matters in water into small molecular organic matters or inorganic matters under high temperature and high pressure conditions; those skilled in the art should understand that the refinery alkali residue wastewater is a typical difficult-to-treat wastewater, and the wet oxidation alone has strong removal capacity for sulfides in the wastewater, but relatively weak removal capacity for organic matters; however, under the condition of catalyst, oxygen under high temperature and high pressure is more likely to have free radical reaction, and the free radical strong oxidation greatly improves the decomposition conversion capacity and reaction rate of organic matters. On the other hand, the homogeneous catalyst itself has high activity and high selectivity, and is more rapid and effective in treating special pollutants, and the problem of easy loss is solved through membrane technology.

[0043] Further, the reaction temperature of the wet oxidation reactor is 150-250℃, the reaction pressure is 1-5 MPa, the liquid space velocity is 0.25-4 h -1 , and the gas-liquid volume ratio is 20:1-500:1.

[0044] Further, the cooling medium of the cooler is circulating water, which further cools the outlet water of the wet oxidation reactor, and the temperature is reduced to 30-50℃, meeting the temperature requirement of the subsequent biochemical unit.

[0045] Further, the treatment time of the electrodialysis I and the electrodialysis II is 0.5-3 h, and the current density is 1-80 mA / cm 2 .

[0046] Further, the concentrated solution of the electrodialysis I is divided into anode concentrated solution and cathode concentrated solution, the anode concentrated solution mainly contains anions such as sulfate ions and chloride ions, and the cathode concentrated solution mainly contains cations such as sodium, potassium, copper and iron.

[0047] Further, the water production rate of the nanofiltration I and the nanofiltration II is 45%-75%; the nanofiltration I is mainly used for intercepting high-valence cations, so as to separate monovalent ions such as sodium and potassium from high-valence metal ions such as copper, iron and zinc, and realize the recycling of metal catalysts; and the nanofiltration II is mainly used for intercepting sulfate ions, so as to concentrate sodium sulfate.

[0048] Further, the anaerobic biochemical unit adds alkali to adjust the pH value to 6-9, the alkali is one of sodium hydroxide, calcium hydroxide and potassium hydroxide, the dissolved oxygen is controlled to be below 0.1 mg / L, the hydraulic retention time is controlled to be 2-48 h, and the water temperature is controlled to be 25-38℃.

[0049] Further, the methane purification unit adopts one of solid desulfurizer adsorption, biological desulfurization, alkali desulfurization and amine liquid desulfurization technology to purify the gas generated by the anaerobic biochemical unit, and methane with purity greater than 96% is obtained.

[0050] Further, the secondary biochemical process adopts one of anoxic and aerobic process, and the residence time is 6-36h, and the sludge adopts common biological bacteria, which is well known by those skilled in the art.

[0051] Further, the aerobic biochemical process adds alkali to adjust the pH value to 6-9, the alkali is preferably sodium hydroxide, the aerobic biochemical biological bacteria adopts salt-tolerant bacteria, and at least one of BAF, MBR, contact oxidation tank and MBBR is selected as the aerobic process.

[0052] Further, the decarbonizer removes carbonate and bicarbonate by adding acid, the acid is hydrochloric acid or sulfuric acid, preferably sulfuric acid, and the adding amount is controlled according to the pH value of 4-6.

[0053] Further, in the ozone catalytic oxidation, the ozone amount is 0.1-2 times of the required oxidant amount calculated according to the COD value of the wastewater, the reaction time is 10-120 minutes, and the catalyst is a conventional solid-supported metal catalyst.

[0054] Further, the operation temperature of the nitrate crystallizer is controlled at 40-110 DEG C, the purity of the sodium sulfate product of the nitrate crystallizer is greater than 98.5%, further, the mother liquor generated by the nitrate crystallizer is refluxed to the electrodialysis I for recycling treatment, when the sodium chloride concentration in the mother liquor is increased to 250-350g / L after multiple recycling, the mother liquor is discharged in the form of mixed salt.

[0055] Compared with the prior art, the present application has the following advantages:

[0056] (1) According to the characteristics of high COD, high salt content, high toxicity and difficult degradation of the refinery alkali residue wastewater, the present application adopts a treatment process with homogeneous catalytic wet oxidation as the core, fully utilizes the characteristics of high catalytic activity and high treatment efficiency of the homogeneous catalytic wet oxidation, and greatly improves the treatment capacity of the wet oxidation.

[0057] (2) The present application solves the problem of catalyst loss in the homogeneous catalytic wet oxidation by combining wet oxidation with improved electrodialysis and nanofiltration membrane technology, and realizes the recycling use of the catalyst.

[0058] (3) The modified anion exchange membrane and improved electrodialysis of the present application can effectively realize the separation of salt and organic matter in the effluent of oil refining alkali residue wet oxidation, solve the problem of difficult treatment of organic matter in the effluent of oil refining alkali residue wet oxidation, reduce the treatment pressure of the wet oxidation unit, and help to alleviate the relatively harsh treatment conditions of wet oxidation; most of the separated organic matter is converted into methane under anaerobic reaction conditions, realizing resource recycling; the modified electrodialysis has the characteristics of strong anti-pollution ability and high ion exchange rate, and has high application value.

[0059] (4) In the salt treatment section, the present application removes carbonates through a decarbonator, separates sodium chloride through nanofiltration II, and further removes organic matter through ozone catalytic oxidation, and high-purity sodium sulfate products are prepared in a nitration crystallizer, realizing efficient treatment and zero discharge of oil refining alkali residue wastewater.

[0060] Other features and advantages of the present application will be described in detail in the subsequent specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 The treatment flow chart of oil refining alkali residue wastewater in Example 1 is shown in the following figure.

[0062] Figure 2 The schematic diagram of anion exchange membrane electrodeposition modification in Example 1 is shown in the following figure. DETAILED DESCRIPTION

[0063] The present application will be further described in detail below in combination with specific embodiments. The embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0064] Example 1

[0065] Treatment of oil refining alkali residue wastewater by the process method of the present application

[0066] The process flow chart for treating oil refining alkali residue wastewater is shown in the following figure. Figure 1As shown: the refinery alkali residue wastewater first enters the adjusting tank, is mixed with the nanofiltration I concentrated water and the homogeneous catalyst, pH is adjusted by adding acid, then is heated by the heat exchange unit and enters the wet oxidation reactor; the wet oxidation reactor effluent enters the heat exchange unit for heat exchange and cooling, then is cooled by the cooler and enters the electrodialysis I, the electrodialysis I dilute liquid enters the electrodialysis II, the electrodialysis I anode concentrated liquid enters the aerobic biochemical unit, the electrodialysis I cathode concentrated liquid enters the nanofiltration I, the nanofiltration I concentrated water enters the adjusting tank, and the nanofiltration I produced water is mixed with the electrodialysis I anode concentrated liquid; the electrodialysis I dilute liquid enters the anaerobic biochemical unit after further desalination by the electrodialysis II, and the electrodialysis II concentrated liquid enters the aerobic biochemical unit; the liquid phase produced by the anaerobic biochemical treatment enters the reuse water pool after secondary biochemical treatment, and the gas phase enters the methane purification unit, and high-purity methane is obtained after purification; the aerobic biochemical effluent enters the nanofiltration II for further concentration after decarburization treatment, the nanofiltration II produced water is returned to the wet oxidation section electrodialysis I, and the nanofiltration II concentrated water enters the ozone catalytic oxidation and then enters the nitrate crystallizer after removing COD; the nitrate crystallizer obtains product sodium sulfate, and the remaining mother liquor is returned to the wet oxidation section electrodialysis I, and when the mother liquor chloride salt concentration is high, it is discharged in the form of mixed salt.

[0067] A certain stock of refinery alkali residue wastewater has the following water quality: COD 50250mg / L, chloride ion 1605mg / L, sulfate ion 12500mg / L, total salt content 36126mg / L, sulfide 5500mg / L, ammonia nitrogen 73mg / L, total nitrogen 1850mg / L, and pH 12.1, with an influent flow rate of 10t / h.

[0068] The electrodialysis I and the electrodialysis II provided in this embodiment are both modified electrodialysis, wherein the anion exchange membrane is a modified anion exchange membrane, which has strong anti-pollution ability and high ion permeability, and the cation exchange membrane is a general cation exchange membrane (CJ-MC-3, China Hefei Kaitai Polymer Co., Ltd.).

[0069] The above modified anion exchange membrane is prepared by the following method:

[0070] Step a: polyvinyl alcohol is added to deionized water to prepare a 10% water solution, which is stirred at 80°C until dissolved, then epoxypropyltrimethylammonium chloride and β-cyclodextrin are added to the water, the mass ratio of polyvinyl alcohol to epoxypropyltrimethylammonium chloride is 1:0.5, and the mass ratio of polyvinyl alcohol to β-cyclodextrin is 1:0.3, and the reaction is carried out for 6h to obtain a viscous liquid, which is the casting solution;

[0071] Step b: the casting solution is cast on a horizontal glass plate, dried at room temperature for 3h, and then the formed membrane is further dried at 60°C under vacuum for 6h to obtain the base membrane;

[0072] Step c: the vacuum dried membrane is continuously immersed in a mixed solution composed of glutaraldehyde, sodium sulfate, sulfuric acid, and deionized water, with mass percentages of 6%, 8%, and 2% for glutaraldehyde, sodium sulfate, and sulfuric acid, respectively, and the remaining being deionized water, for 4 hours to form cross-linking in the membrane through acetalization;

[0073] Step d: the cross-linked membrane is washed with deionized water until neutral, then alkalinized in a 1 mol / L sodium hydroxide aqueous solution for 16 hours, and then soaked in deionized water for 16 hours to obtain a modified anion exchange membrane.

[0074] Step e: a polyanion modifier and sodium chloride are dissolved in a 20 mmol / L Tris-HCl buffer, and the pH is adjusted to 8.5 with hydrochloric acid, with a mass concentration of 2.5 g / L for the polyanion modifier and a mass concentration of 10 g / L for sodium chloride; the polyanion modifier is selected from poly-4-styrene sulfonic acid sodium;

[0075] Step f: surface modification is performed by electrodeposition, as shown in Figure 2 , the modified anion exchange membrane is placed in the middle of a direct current electrodeposition device to form two compartments, the modification solution is placed in the cathode side compartment, and water is placed in the anode side compartment, the electrodeposition time is 0.8 h, and the current density is 20 mA / cm 2 .

[0076] Step g: the modified anion exchange membrane is taken out and placed in a 10 g / L sodium chloride solution for use.

[0077] The schematic diagram of electrodeposition modification in the preparation process of the above-mentioned anion exchange membrane is shown in Figure 2 .

[0078] The specific operation parameters for treating refinery caustic sludge wastewater are as follows:

[0079] The above-mentioned 10 t / h of refinery caustic sludge wastewater first enters the adjustment tank, is mixed with nanofiltration concentrated water and homogeneous catalyst, and is adjusted to a pH of 5 by adding sulfuric acid; the homogeneous catalyst is a copper catalyst, specifically copper sulfate, and the concentration of copper metal ions in the mixed liquid is about 400 mg / L; the wastewater temperature is raised to 150℃ after heat exchange, and then the wastewater enters the wet oxidation reactor, the reaction temperature of the wet oxidation reactor is 200℃, the pressure is 3 MPa, and the liquid space velocity is 1h -1, the gas-liquid volume ratio is 150:1; the effluent of the wet oxidation is cooled to 65°C by a heat exchange unit, and then cooled to 45°C by a cooler before entering the adjusting tank, at this time, the COD of the wastewater is 5210 mg / L, the total salt content is 47556 mg / L, the sulfide is 0.3 mg / L, the total nitrogen is 206 mg / L, the sulfide removal rate is greater than 99%, the COD removal rate is 88.5%, and the total nitrogen removal rate is 87.4%, and the effluent enters the electrodialysis I. The treatment time of the electrodialysis I is 1.2 h, and the current density is 35 mA / cm 2 , after the treatment, the COD concentration of the dilution liquid in the electrodialysis I is 6980 mg / L, the total salt content is 11355 mg / L, the dilution liquid flow accounts for 70% of the water flow of the electrodialysis I; the COD concentration of the anode concentrated liquid is 1954 mg / L, the total salt content is 169262 mg / L, the anode concentrated liquid accounts for 16% of the water flow of the electrodialysis I; the COD concentration of the cathode concentrated liquid is 81 mg / L, the total salt content is 89468 mg / L, and the cathode concentrated liquid accounts for 14% of the water flow of the electrodialysis I; the total sulfate ion selective permeation rate of the electrodialysis I is 82.8%, the total chloride ion selective permeation rate is 83.9%, and the organic matter interception rate is 93.8%; the cathode concentrated liquid of the electrodialysis I enters the nanofiltration treatment, the nanofiltration water yield is 65%, the copper catalyst interception rate is 94%, the copper catalyst is returned to the adjusting tank with the nanofiltration concentrated water for recycling, and the total loss rate of the catalyst is 19.8%, and the catalyst of the adjusting tank is supplemented at 79 mg / L.

[0080] The dilution liquid in the electrodialysis I enters the electrodialysis II, the treatment time of the electrodialysis II is 1 h, and the current density is 30 mA / cm 2 ; after the treatment, the COD concentration of the concentrated liquid in the electrodialysis II is 1216 mg / L, the total salt content is 37245 mg / L, the concentrated water accounts for 25% of the total water, the COD concentration of the dilution liquid is 8901 mg / L, the total salt content is 2725 mg / L, and the dilution liquid accounts for 75% of the total water; the organic matter interception rate of the electrodialysis II is 95.6%, the concentrated liquid of the electrodialysis II enters the aerobic biochemical treatment, and the dilution liquid of the electrodialysis II enters the anaerobic biochemical treatment; sodium hydroxide is added to the anaerobic biochemical treatment to adjust the pH to 7.5, the residence time is 40 h, the water temperature is 32°C, the dissolved oxygen is less than 0.1 mg / L, the produced methane is purified by alkali liquid, and the purity reaches 98.4%, the COD concentration of the effluent of the anaerobic biochemical unit is 588 mg / L, the salt content is 2559 mg / L, and the effluent enters the secondary biochemical treatment; the secondary biochemical treatment adopts the A / O process, and the conventional activated sludge is added, the residence time is 20 h, the COD concentration of the final effluent is 55 mg / L, and the effluent enters the reuse water pool.

[0081] The influent COD concentration of aerobic biochemical treatment is 1231 mg / L, and the total salt content is 97846 mg / L. The aerobic biochemical treatment adopts a contact oxidation tank process, salt-tolerant bacteria are added, the high-efficiency salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A is selected, the preservation number is CGMCC No. 20350, sodium hydroxide is added to adjust the pH to 6.5, the residence time is 48 h, and the effluent COD is as low as 98 mg / L after mud-water separation; the aerobic biochemical effluent enters a decarbonizer, sulfuric acid is added to adjust the pH to 5.5 to remove carbonate and bicarbonate in the solution, the decarbonizer effluent enters nanofiltration II; the nanofiltration water production rate is 65%, the nanofiltration concentrated water total salt content is 38663 mg / L, and the COD is 67 mg / L, which is returned to the electrodialysis I for further concentration, the nanofiltration concentrated water total salt content is 207757 mg / L, and the COD is 155 mg / L, which enters ozone catalytic oxidation; the ozone catalytic oxidation ozone dosage concentration is 60 mg / L, the reaction time is 30 min, the effluent COD is as low as 78 mg / L, which enters the nitrate crystallizer; the temperature of the nitrate crystallizer is controlled at 85 DEG C, and the crystallization product purity is 99.6% sodium sulfate, and the remaining mother liquor returns to the electrodialysis I for secondary treatment, the sodium chloride in the mother liquor is still in a dissolved state, which does not affect the purity of the sodium sulfate product, and when the sodium chloride concentration in the mother liquor rises to 320 g / L after multiple cycles, the sodium chloride is discharged in the form of a mixed salt.

[0082] It can be known from the embodiment that the process method of the application realizes efficient operation of homogeneous catalytic wet oxidation. In view of the problems of high COD, high toxicity and difficult degradation of oil refining alkali residue wastewater, the COD removal rate of the wet oxidation unit in the embodiment is as high as 88.5%, the total nitrogen removal rate is 87.4%, and the sulfide removal rate is greater than 99%, so that the oil refining alkali residue wastewater is finally zero discharged, and high-purity sodium sulfate is prepared. At the same time, the modified electrodialysis plays an important role. It solves the problem of loss of homogeneous catalyst in combination with nanofiltration technology, and the catalyst recovery rate in the embodiment is 80.2%; in combination with anaerobic technology, high-purity methane is prepared, and the wastewater is recycled.

[0083] Embodiment 2

[0084] By using Figure 1 The process shown in the figure is used to treat certain oil refining alkali residue wastewater

[0085] A certain oil refining alkali residue wastewater has the following water quality: COD 80500 mg / L, chloride ion 2110 mg / L, sulfate ion 18500 mg / L, total salt content 53350 mg / L, sulfide 8500 mg / L, ammonia nitrogen 15 mg / L, total nitrogen 2250 mg / L, and pH 12.2. The influent flow rate is 10 t / h.

[0086] The process route and implementation steps of treating the refinery alkali residue wastewater are the same as those of Example 1. The electrodialysis I and the electrodialysis II in the process route are both modified electrodialysis, wherein the anion exchange membrane is a modified anion exchange membrane, and the cation exchange membrane is a general cation exchange membrane (Hefei Kaijie Polymer Co., Ltd., China, Model CJ-MC-3). In the preparation of the modified anion exchange membrane, in addition to the positive electric amine compound in step a being polyethyleneimine, the mass ratio of polyvinyl alcohol to polyethyleneimine being 1:0.55, and the mass ratio of polyvinyl alcohol to β-cyclodextrin being 1:0.35, the reaction time of step a being 8 h, the others are the same as those of Example 1.

[0087] The specific operation parameters for treating the refinery alkali residue wastewater are as follows:

[0088] The above refinery alkali residue wastewater 10 t / h first enters the adjustment tank, is mixed with the nanofiltration concentrated water and the homogeneous catalyst in the adjustment tank, and is adjusted to pH 5 by adding sulfuric acid. The homogeneous catalyst is a copper catalyst, specifically copper sulfate. The concentration of copper metal ions in the mixed liquid is about 600 mg / L. The effluent from the adjustment tank is heated to a temperature of 150°C, enters the wet oxidation reactor, and the reaction temperature of the wet oxidation reactor is 210°C, the pressure is 3 MPa, the liquid space velocity is 1 h -1 , and the gas-liquid volume ratio is 180:1. The effluent from the wet oxidation is cooled to 65°C by a heat exchange unit, and then is cooled to 45°C by a cooler before entering the adjustment tank. At this time, the COD of the wastewater is 8860 mg / L, the total salt content is 70855 mg / L, the sulfide is 0.4 mg / L, the total nitrogen is 253 mg / L, the sulfide removal rate is greater than 99%, the COD removal rate is 88.3%, and the total nitrogen removal rate is 88.2%. The effluent enters the electrodialysis I.

[0089] The treatment time of the electrodialysis I is 1.4 h, and the current density is 40 mA / cm 2 . After treatment, the COD concentration of the dilute liquid in the electrodialysis I is 12881 mg / L, the total salt content is 14171 mg / L, the dilute liquid flow accounts for 65% of the water flow of the electrodialysis I. The COD concentration of the anode concentrated liquid is 2581 mg / L, the total salt content is 233919 mg / L, the anode concentrated liquid accounts for 18% of the water flow of the electrodialysis I. The COD concentration of the cathode concentrated liquid is 134 mg / L, the total salt content is 114931 mg / L, and the cathode concentrated liquid accounts for 17% of the water flow of the electrodialysis I. The total sulfate ion selective permeation rate of the electrodialysis I is 86.7%, the chloride ion selective permeation rate is 87.8%, and the organic matter interception rate is 94.5%. The cathode concentrated liquid of the electrodialysis I enters the nanofiltration treatment, the nanofiltration water production rate is 60%, the copper catalyst interception rate is 95%, the copper catalyst is returned to the adjustment tank with the nanofiltration concentrated water for recycling, the total loss rate of the catalyst is 17.4%, and the catalyst in the adjustment tank is supplemented at 104 mg / L.

[0090] The dilute liquid in the electrodialysis I enters the electrodialysis II, the treatment time of the electrodialysis II is 1.1 h, and the current density is 35 mA / cm 2 ; the COD concentration of the concentrated liquid in the electrodialysis II after treatment is 1550 mg / L, the total salt content is 40334 mg / L, the concentrated water accounts for 30% of the total water, the COD concentration of the dilute liquid is 17737 mg / L, the total salt content is 2958 mg / L, and the dilute liquid accounts for 70% of the total water; the organic matter retention rate of the electrodialysis II is 96.3%, the concentrated liquid of the electrodialysis II enters the aerobic biochemical treatment, and the dilute liquid of the electrodialysis II enters the anaerobic biochemical treatment; sodium hydroxide is added in the anaerobic biochemical treatment to adjust the pH to 8, the residence time is 72 h, the water temperature is 32 DEG C, the dissolved oxygen is less than 0.1 mg / L, the purity of the generated methane after being purified by the lye reaches 98.5%, the COD concentration of the effluent of the anaerobic biochemical unit is 655 mg / L, the salt content is 2866 mg / L, and the effluent enters the secondary biochemical treatment; the secondary biochemical treatment adopts the SBR process, the conventional activated sludge is added, the residence time is 24 h, the COD concentration of the final effluent is 53 mg / L, and the final effluent enters the reuse water tank.

[0091] The COD concentration of the influent of the aerobic biochemical treatment is 1609 mg / L, the total salt content is 129084 mg / L, the aerobic biochemical treatment adopts the MBBR process, the high-efficiency salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A is added, the preservation number is CGMCC No.20350, sodium hydroxide is added to adjust the pH to 7, the residence time is 72 h, and the COD of the effluent after mud-water separation is as low as 135 mg / L; the effluent of the aerobic biochemical treatment enters the decarbonizer, sulfuric acid is added to adjust the pH to 5.5, so that the carbonate and bicarbonate in the solution are removed, the effluent of the decarbonizer enters the nanofiltration II; the nanofiltration water production rate is 60%, the total salt content of the nanofiltration water is 53350 mg / L, the COD is 88 mg / L, the nanofiltration water is returned to the electrodialysis I for further concentration, the total salt content of the nanofiltration concentrated water is 242685 mg / L, the COD is 206 mg / L, and the concentrated water enters the ozone catalytic oxidation; the ozone concentration in the ozone catalytic oxidation is 80 mg / L, the reaction time is 30 min, the COD of the effluent is as low as 98 mg / L, and the effluent enters the nitrate crystallizer; the temperature of the nitrate crystallizer is controlled at 90 DEG C, the product sodium sulfate with a purity of 99.7% is obtained by crystallization, the remaining mother liquor is returned to the electrodialysis I for secondary treatment, the sodium chloride in the mother liquor is still in a dissolved state, and the purity of the sodium sulfate product is not affected; when the sodium chloride concentration in the mother liquor rises to 300 g / L after multiple cycles, the sodium chloride is discharged in the form of a mixed salt.

[0092] It can be known from the embodiment that the process method can treat higher-concentration oil refining alkali residue wastewater, finally realizes zero discharge of the oil refining alkali residue wastewater, and high-purity sodium sulfate and methane and low-salt reuse water are prepared.

[0093] Example 3

[0094] The water quality of the refinery caustic sludge wastewater treated is the same as that of Example 1, the process route, implementation steps and reaction parameters are also the same as those of Example 1, and only the type of catalyst is different, i.e., the iron salt catalyst is used. The treatment effect of the wet oxidation unit is shown in Table 1.

[0095] Example 4

[0096] The water quality of the refinery caustic sludge wastewater treated is the same as that of Example 1, the process route, implementation steps and reaction parameters are also the same as those of Example 1, and only the type of catalyst is different, i.e., the nickel salt catalyst is used. The treatment effect of the wet oxidation unit is shown in Table 1.

[0097] Example 5

[0098] The water quality of the refinery caustic sludge wastewater treated is the same as that of Example 1, the process route, implementation steps and reaction parameters are also the same as those of Example 1, and only the type of catalyst is different, i.e., the zinc salt catalyst is used. The treatment effect of the wet oxidation unit is shown in Table 1.

[0099] Comparative Example 1

[0100] The water quality of the refinery caustic sludge wastewater treated is the same as that of Example 1, the process route, implementation steps and reaction parameters are also the same as those of Example 1, and the difference is that no catalyst is added in the wet oxidation. The treatment effect of the wet oxidation unit is shown in Table 1.

[0101] Table 1

[0102]

[0103] Comparative Example 2

[0104] The water quality of the refinery caustic sludge wastewater treated is the same as that of Example 1, the process route, implementation steps are also the same as those of Example 1, and the difference is that the anion exchange membrane of the electrodialysis I and the cation exchange membrane of the electrodialysis II are both general type membranes. The anion exchange membrane is the product of Japan Asahi Glass Company (SELEMION AMV) and is not modified, and the cation exchange membrane is the product of China Hefei Kaitai Polymer Co., Ltd. (Model CJ-MC-3).

[0105] Specifically, the wastewater is adjusted by the adjusting tank and then enters the wet oxidation reactor, and the effluent is cooled by the cooler and then enters the ordinary electrodialysis I. The COD of the wastewater is 5210 mg / L, and the total salt content is 47556 mg / L. The treatment time of the electrodialysis I is 1.2 h, the current density is 35 mA / cm 2COD concentration of the diluate in the electrodialysis I was 6214 mg / L, total salt content was 19022 mg / L, the diluate flow accounted for 70% of the water flow of the electrodialysis I; the COD concentration of the anode concentrate was 5263 mg / L, total salt content was 149671 mg / L, the anode concentrate accounted for 16% of the water flow of the electrodialysis I; the COD concentration of the cathode concentrate was 125 mg / L, total salt content was 73523 mg / L, the cathode concentrate accounted for 14% of the water flow of the electrodialysis I, the cathode concentrate entered the nanofiltration treatment, the nanofiltration water yield was 65%; the total sulfate ion selective permeation rate of the electrodialysis I was 71.8%, the chloride ion selective permeation rate was 72.5%, which was obviously lower than that of Example 1, the membrane flux decreased obviously, which might be related to the membrane blockage; the organic matter retention rate was 83.5%, which was about 10 percentage points lower than that of Example 1, which indicated that a large amount of negatively charged organic matter passed through the anion membrane, increasing the possibility of membrane blockage.

[0106] The diluate in the electrodialysis I entered the electrodialysis II, the treatment time of the electrodialysis II was 1 h, the current density was 30 mA / cm 2 ; the COD concentration of the concentrate of the electrodialysis II after treatment was 3840 mg / L, total salt content was 55011 mg / L, the concentrated water accounted for 25% of the total water, the COD concentration of the diluate was 7005 mg / L, total salt content was 7026 mg / L, the diluate water accounted for 75% of the total water; the organic matter retention rate of the electrodialysis II was 84.5%, the sulfate ion selective permeation rate was 72.3%, which was obviously lower than that of Example 1; the electrodialysis II concentrate entered the aerobic biochemical treatment, the electrodialysis II diluate entered the anaerobic biochemical treatment; the anaerobic biochemical treatment was adjusted to pH 7.5 by sodium hydroxide, the residence time was 40 h, the water temperature was 32℃, the dissolved oxygen was lower than 0.1 mg / L, the COD concentration of the effluent of the anaerobic biochemical unit was 5486 mg / L, the salt content was 6559 mg / L, which entered the secondary biochemical treatment; the secondary biochemical treatment adopted A / O process, the conventional activated sludge was added, the residence time was 20 h, the COD concentration of the final effluent was 4838 mg / L, the salt content was 6356 mg / L, which could not meet the requirement of entering the reuse water pool.

[0107] The COD concentration of the influent of the aerobic biochemical treatment was 3580 mg / L, total salt content was 92518 mg / L, the aerobic biochemical treatment adopted the contact oxidation tank process, the salt-tolerant bacteria GXNYJ-DL-1 was added, and sodium hydroxide was added to adjust the pH to 6.5, the residence time was 48 h, the COD was reduced to 1835 mg / L after the effluent was separated by the sludge; the effluent of the aerobic biochemical treatment entered the ozone catalytic oxidation after acid decarburization treatment, the ozone dosage concentration in the ozone catalytic oxidation was 60 mg / L, the reaction time was 30 min, the COD of the effluent was 1715 mg / L, which entered the nitrate crystallizer; the temperature of the nitrate crystallizer was controlled at 85℃, the purity of the sodium sulfate product was reduced to 97.4%.

[0108] It can be seen from the present comparative example that the separation ability of the unmodified cation and anion exchange membranes for organic matter and salt is poor, the anion exchange membrane is easily polluted by organic matter, which leads to the high salt content of the diluting liquid and the high organic matter content of the concentrated liquid, the effluent from the organic matter treatment section cannot meet the reuse requirement, the purity of sodium sulfate obtained from the salt treatment section is decreased, and the freezing crystallization efficiency is decreased.

Claims

1. A process for treating refinery alkali residue wastewater, comprising a wet oxidation section, an organic matter treatment section, and a salt treatment section; The wet oxidation section includes a regulating tank, a heat exchange unit, a wet oxidation reactor, a cooler, electrodialysis I, and nanofiltration I. The oil refining alkali residue wastewater first enters the regulating tank, mixes with nanofiltration I concentrate and homogeneous catalyst, and is pH adjusted by adding acid. Then, it is heated by the heat exchange unit and enters the wet oxidation reactor. The effluent from the wet oxidation reactor enters the heat exchange unit for heat exchange and cooling, and then is cooled by the cooler before entering electrodialysis I. The desalinated solution from electrodialysis I enters electrodialysis II in the organic matter treatment section. The anode concentrate from electrodialysis I enters the aerobic biochemical unit in the salt treatment section. The cathode concentrate from electrodialysis I enters nanofiltration I. The concentrate from nanofiltration I enters the regulating tank, and the permeate from nanofiltration I is mixed with the anode concentrate from electrodialysis I. The organic matter treatment section includes electrodialysis II, anaerobic biochemical treatment, secondary biochemical treatment, a reclaimed water tank, and a methane purification unit; The concentrate from electrodialysis II enters the aerobic biochemical unit of the salt treatment section, and the desalination solution enters the anaerobic biochemical unit. The liquid phase produced by the anaerobic biochemical process enters the secondary biochemical process, the effluent from the secondary biochemical process enters the reclaimed water tank, and the gas phase produced by the anaerobic biochemical process enters the methane purification unit, where high-purity methane is obtained after purification. The salt treatment section sequentially includes an aerobic biochemical treatment unit, a decarbonizer, nanofiltration II, ozone catalytic oxidation, and a nitrification crystallizer. The concentrate from nanofiltration II enters the ozone catalytic oxidation unit, and the permeate from nanofiltration II is returned to the electrodialysis I unit of the wet oxidation section. The effluent from the ozone catalytic oxidation unit enters the nitrification crystallizer, from which sodium sulfate is obtained. The remaining mother liquor is returned to the electrodialysis I unit of the wet oxidation section or discharged as miscellaneous salts. Both electrodialysis I and electrodialysis II use modified anion exchange membranes, while the cation exchange membrane is a general-purpose cation exchange membrane. The modified anion exchange membrane is prepared by the following steps: Step a: Add polyvinyl alcohol to water to prepare a polyvinyl alcohol aqueous solution, then add positively charged amine compounds and β-cyclodextrin to the above solution respectively, mix and react to obtain a casting solution; Step b: Cast the casting solution obtained in step a onto a horizontal panel, dry it, and obtain the base film; Step c: Immerse the base film obtained in step b in a crosslinking solution composed of crosslinking agent, sodium sulfate, sulfuric acid, and water; Step d: Wash the cross-linked membrane, alkalize it in an alkaline solution, and then soak it in water to obtain a polyvinyl alcohol anion exchange membrane; Step e: Dissolve the polyanionic modifier and sodium chloride in Tris-HCl buffer solution, and adjust the pH to 8-9 with hydrochloric acid to obtain the modified solution; Step f: Place the anion exchange membrane obtained in step d in the middle of the DC electrodeposition apparatus to form two compartments. Put the modified solution prepared in step e into the compartment on the cathode side and put water into the compartment on the anode side to carry out the electrodeposition reaction and obtain the modified anion exchange membrane.

2. The process method according to claim 1, characterized in that, The positively charged amine compound is one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxychloropropaneamine, and quaternized chitosan. The mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1 to 0.6:1, and the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.05:1 to 0.4:

1.

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

4. The process method according to claim 1, characterized in that, The crosslinking agent is selected from aldehyde or acid crosslinking agents. In the crosslinking solution, the mass percentages of crosslinking agent, sodium sulfate and sulfuric acid are 2%–8%, 4%–15% and 1%–4% respectively, with the remainder being water.

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

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

7. The process method according to claim 1, characterized in that, Acid is added to the regulating tank to adjust the pH to 2-6. The heat exchange unit exchanges heat between the effluent from the wet oxidation reactor and the effluent from the regulating tank. After multiple heat exchanges, the effluent temperature from the regulating tank rises to 130-160℃, while the effluent temperature from the wet oxidation reactor decreases to 50-75℃.

8. The process method according to claim 1, characterized in that, The homogeneous catalyst is selected from one or more of copper, iron, manganese, zinc and nickel. The transition metal in the homogeneous catalyst exists in the form of metal salt compounds or complexes and is dissolved in the liquid phase.

9. The process method according to claim 1, characterized in that, The homogeneous catalyst is added at a COD mass concentration to metal ion mass concentration ratio of 10000:1 to 20:1, and is replenished during the wastewater treatment process.

10. The process method according to claim 1, characterized in that, The wet oxidation reactor has a reaction temperature of 150–250°C, a reaction pressure of 1–5 MPa, and a liquid hourly space velocity of 0.25–4 h⁻¹. -1 The gas-liquid volume ratio is 20:1 to 500:

1.

11. The process method according to claim 1, characterized in that, The cooler further cools the effluent from the wet oxidation reactor to 30–50°C.

12. The process method according to claim 1, characterized in that, The treatment time for electrodialysis I and electrodialysis II is 0.5–3 hours, and the current density is 1–80 mA / cm². 2 .

13. The process method according to claim 1, characterized in that, The anaerobic biochemical unit is equipped with alkali to adjust the pH value to 6-9. The alkali is one of sodium hydroxide, calcium hydroxide and potassium hydroxide. The dissolved oxygen is controlled below 0.1 mg / L, the hydraulic retention time is controlled between 2 and 48 h, and the water temperature is controlled between 25 and 38 °C.

14. The process method according to claim 1, characterized in that, The methane purification unit employs one of the following technologies: solid desulfurizing agent adsorption, biological desulfurization, alkaline desulfurization, and amine desulfurization, to purify the gas generated by the anaerobic biochemical unit and obtain methane with a purity greater than 96%.

15. The process method according to claim 1, characterized in that, The secondary biochemical process employs anoxic-aerobic technology, selecting either A / O or SBR, with a residence time of 6–36 hours.

16. The process method according to claim 1, characterized in that, The aerobic biochemical process involves adding alkali to adjust the pH value to 6-9, and the process uses at least one of BAF, MBR, contact oxidation tank and MBBR aerobic processes.

17. The process method according to claim 1, characterized in that, The decarbonator removes carbonate and bicarbonate ions by adding hydrochloric acid or sulfuric acid, with the amount added adjusted to reduce the pH to 4-6.

18. The process method according to claim 1, characterized in that, In the ozone catalytic oxidation process, the amount of ozone used is 0.1 to 2 times the amount of oxidant required based on the COD value of the wastewater, and the reaction time is 10 to 120 minutes.

19. The process method according to claim 1, characterized in that, The operating temperature of the nitrate crystallizer is controlled at 40-110℃. The mother liquor generated by the nitrate crystallizer is returned to the electrodialysis I cycle for treatment. When the sodium chloride concentration in the mother liquor rises to 250-350 g / L after multiple cycles, it is completely discharged in the form of miscellaneous salts.

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