Process method for zero discharge of ethylene alkali residue wastewater

Abstract

The application discloses a process method for zero discharge of ethylene alkali residue wastewater, which comprises a wet oxidation section, a biochemical section and a salt treatment section; the wet oxidation section comprises a heat exchange unit, a wet oxidation reactor, a cooler and an adjusting tank; the biochemical section comprises an electrodialysis I, aerobic biochemical treatment, ozone catalytic oxidation, anaerobic biochemical treatment, secondary biochemical treatment, a recycled water pool and a methane purification unit; the salt treatment section comprises a tubular microfiltration, an electrodialysis II, a decarbonizer, a salt separation system, a biological reactor and a reverse osmosis; wherein the modified anion exchange membrane used in the electrodialysis has the characteristics of strong anti-pollution ability and high ion exchange rate, can effectively realize the separation of salt and organic matters in the wet oxidation effluent of the ethylene alkali residue, solves the problem of difficult treatment of the organic matters in the wet oxidation effluent of the ethylene alkali residue, and finally realizes zero discharge.

Description

TECHNICAL FIELD

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

[0002] Ethylene waste lye is wastewater generated in the process of alkali washing of cracking gas in ethylene production, and the pollutants therein are relatively complex, including high content of organic matter, sulfide and salt, and also containing malodorous gases such as mercaptan and sulfide. The most mainstream treatment method for ethylene alkali residue wastewater is wet oxidation method, which operates under high temperature (180-320℃) and high pressure (2.5-20 MPa), and uses gaseous oxygen as oxidant to oxidize and decompose organic matter in water into small molecular organic matter or inorganic matter. However, the traditional wet oxidation requires high temperature and pressure, has high operation cost per ton of water, has high requirement for equipment material, and also has high one-time investment.

[0003] Wastewater "zero discharge" means that after repeated use of industrial wastewater, the salts and pollutants in the water are discharged from the factory in the form of solid by concentration and crystallization, and the wastewater is recycled and utilized without any waste liquid discharged from the factory. Ethylene alkali residue wastewater has very high salt content, and with a substantial increase in the number and scale of ethylene devices, the amount of ethylene alkali residue wastewater is also very large. In the context of increasingly strict wastewater discharge, zero discharge will inevitably be the future direction of development.

[0004] The normal zero discharge approach is concentrated water pretreatment and concentration and crystallization. Membrane separation technology is a new technology that uses separation membranes as the core for separation, concentration and purification, and plays an indispensable role in wastewater zero discharge. The solubility of organic matter will restrict the separation efficiency and service life of the membrane. Electrodialysis is a new technology formed on the basis of membrane separation combined with electrochemistry, which has been widely used in seawater desalination, brackish water desalination, etc. The system desalination rate can be selected in the range of 30% to 99% as needed, and compared with multi-effect evaporation, the energy consumption of electrodialysis is much lower. However, for industrial wastewater, because the water contains not only soluble inorganic salts but also a large amount of organic matter, the ion exchange membrane will be polluted and scaled during separation and concentration, which affects the further application of electrodialysis technology.

[0005] The COD concentration of ethylene waste lye is as high as tens of thousands of mg / L, a large part of which 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, and to oxidize malodorous gases such as mercaptan and sulfide. Its treatment capacity for organic matter is limited, so wet oxidation can only be used as pretreatment, and the effluent still has high COD and a large amount of salt. SUMMARY

[0006] In order to solve the above problems, the application provides a process method for zero discharge of ethylene alkali residue wastewater, which can realize efficient treatment and zero discharge of ethylene alkali residue wastewater by using the combination of wet oxidation, improved electrodialysis, biological reinforcement and other processes, and can simultaneously produce high-purity sodium sulfate, sodium chloride and methane, and has the advantages of mild operation conditions and low energy consumption.

[0007] In order to achieve the above technical purposes, the technical scheme adopted by the application is as follows:

[0008] A process method for zero discharge of ethylene alkali residue wastewater, comprising a wet oxidation section, a biochemical section and a salt treatment section;

[0009] The wet oxidation section comprises a heat exchange unit, a wet oxidation reactor, a cooler and an adjusting tank; the ethylene alkali residue wastewater first enters the heat exchange unit, is heated by heat exchange and then enters the wet oxidation reactor, the water outlet of the wet oxidation reactor is heated by the heat exchange unit and then cooled by the cooler, and then enters the adjusting tank for pH adjustment, and the water outlet of the adjusting tank enters the electrodialysis I of the biochemical section;

[0010] The biochemical section comprises the electrodialysis I, aerobic biochemical treatment, ozone catalytic oxidation, anaerobic biochemical treatment, secondary biochemical treatment, a reuse water tank and a methane purification unit; the concentrated solution of the electrodialysis I enters the aerobic biochemical treatment, the dilute solution enters the anaerobic biochemical treatment, the water outlet of the anaerobic biochemical treatment is treated by the secondary biochemical treatment and then enters the reuse water tank, and the methane produced by the anaerobic biochemical treatment is treated by the methane purification unit and then recycled; the water outlet of the aerobic biochemical treatment enters the ozone catalytic oxidation, and then enters the tubular microfiltration of the salt treatment section;

[0011] The salt treatment section comprises the tubular microfiltration, the electrodialysis II, a decarbonator, a salt separation system, a biological reactor and reverse osmosis; the water outlet of the tubular microfiltration enters the electrodialysis II, the concentrated solution of the electrodialysis II is treated by the decarbonator and then enters the salt separation system, and the dilute solution of the electrodialysis II enters the biological reactor; the water outlet of the biological reactor enters the reverse osmosis, the concentrated water of the reverse osmosis is sent back to the ozone catalytic oxidation unit of the biochemical section, and the water produced by the reverse osmosis enters the anaerobic biochemical unit of the biochemical section.

[0012] The electrodialysis I and the electrodialysis II are composed of anion exchange membranes and cation exchange membranes, wherein the anion exchange membranes are modified anion exchange membranes, and the cation exchange membranes are general cation exchange membranes;

[0013] The modification method of the anion exchange membrane is as follows:

[0014] Step a: taking the anion exchange membrane as a base film, washing with a hydrochloric acid solution and a sodium hydroxide solution respectively, and then rinsing with water to remove impurities on the surface of the film, to obtain a pretreated base film;

[0015] Step b: dissolving dopamine and β-cyclodextrin in a Tris-HCl buffer solution, adjusting the pH to 8-9, and fully dissolving them by stirring to obtain a modified solution;

[0016] Step c: placing the base film obtained in step a in a modification solution and adding copper sulfate, stirring the reaction under the condition of air flow, and obtaining a preliminarily modified anion exchange membrane after the reaction is completed;

[0017] Step d: dissolving the polyanion modifier and sodium chloride in a Tris-HCl buffer solution, adjusting the pH to 8-9, and obtaining an electrodeposition mother liquor;

[0018] Step e: placing the anion exchange membrane obtained in step c in the middle of a direct current electrodeposition device to form two compartments, placing the electrodeposition mother liquor prepared in step d in the cathode side compartment and water in the anode side compartment, and performing an electrodeposition reaction to obtain a finally modified anion exchange membrane.

[0019] Those skilled in the art should understand that the anion exchange membrane used before modification is a kind of high molecular polymer membrane with selective permeability to anions in the prior art, and the base material is a conventional ion exchange membrane high molecular material such as polyvinyl alcohol, polyethylene, polypropylene, polyvinyl chloride, and polystyrene.

[0020] Further, the concentration of hydrochloric acid in the hydrochloric acid solution in step a is 0.1-0.3 mol / L, and the concentration of sodium hydroxide in the sodium hydroxide solution is 0.1-0.3 mol / L.

[0021] Further, the concentration of the Tris-HCl buffer solution in steps b and d is 10-50 mmol / L.

[0022] Further, the mass concentration of dopamine in the modification solution in step b is 0.2-2 g / L, preferably 0.5-1 g / L, and the mass concentration of β-cyclodextrin is 0.3-3 g / L, preferably 0.5-1.2 g / L.

[0023] Further, the stirring time in step b is 1-10 h.

[0024] Further, the concentration of copper sulfate in the reaction solution formed in step c is 1-20 mmol / L, preferably 3-10 mmol / L, and the stirring reaction time is 1-20 h. Copper sulfate can induce rapid polymerization of dopamine and form an electrolyte layer containing β-cyclodextrin and polydopamine on the surface of the anion exchange membrane by using the adhesion of dopamine. After the reaction is completed, a preliminarily modified anion exchange membrane is obtained, which not only has a negative charge on the surface but also has a significantly increased hydrophilicity.

[0025] Further, the polyanion modifier in step d is selected from one or more of poly 4-sodium styrene sulfonate, p-sodium styrene sulfonate, polyvinyl sulfonate, and polypropylene sulfonate, and is preferably poly 4-sodium styrene sulfonate.

[0026] Further, the mass concentration of the polyanion modifier in the electrodeposition mother liquor of step d is 1-5 g / L, and the mass concentration of sodium chloride is 3-30 g / L.

[0027] Further, hydrochloric acid is used to adjust the pH in steps b and d.

[0028] Further, the electrodeposition reaction time of step e is 0.2-2 h, and the current density is 1-50 mA / cm 2 The polyanion modifier is secondarily deposited on the surface of the anion exchange membrane by the electrodeposition method, so as to sulfonate and modify the membrane surface.

[0029] Further, the finally modified anion exchange membrane is stored in a sodium chloride solution, and the mass concentration of the sodium chloride solution is 5-20 g / L.

[0030] As understood by those skilled in the art, the alkaline residue wet-oxidized water contains a small amount of negatively charged organic matter, dopamine has strong self-aggregation and adhesion capacity, and can improve the surface negative charge density and the membrane stability, so that the anion exchange membrane modified by the polydopamine has a negative charge on the surface, has electrostatic repulsion to the negatively charged organic matter in water, and can inhibit the organic matter from polluting the anion exchange membrane, the surface is sulfonated and modified by the polyanion modifier, the membrane surface roughness caused by the adsorption of dopamine is reduced, and the surface negative charge density is further improved. As also understood by those skilled in the art, the negative surface charge prevents the organic matter from being polluted by the electrostatic effect, and also affects the migration rate of inorganic anions, and the more the ion charge number, the greater the influence, so that the sulfate ion is more affected than the chloride ion. In the anion exchange membrane polymerization deposition modification, the β-cyclodextrin is added, the adhesion capacity of the polydopamine is utilized, the surface negative charge density of the membrane is increased, the surface of the membrane is endowed with strong hydrophilicity, and the migration rate of anions is changed, wherein the migration number of anions with low hydration degree such as bromide and nitrate relative to the chloride is reduced, and the migration number of the sulfate ion with high hydration degree relative to the chloride is increased. On the other hand, the membrane hydrophilicity is improved, the van der Waals force between the membrane and the organic matter solute is reduced, the attraction is reduced, and a hydration layer is formed between the hydrophilic membrane and water molecules due to the hydrogen bond effect, which further hinders the adsorption of the pollutants on the membrane surface. Therefore, after the anion exchange membrane of the present application is modified by dopamine, β-cyclodextrin and polyanion modifier, the anti-pollution capacity of the membrane is greatly increased, and the selective permeability of the sulfate ion is obviously improved.

[0031] Further, the heat exchange unit is composed of multiple heat exchangers, which exchanges heat between the wet oxidation reactor outlet water and the ethylene alkali residue inlet water, and the temperature of the ethylene alkali residue inlet water is increased to 110-150℃ after heat exchange, and the temperature of the wet oxidation reactor outlet water is decreased to 50-75℃.

[0032] Further, the wet oxidation reactor is a bubbling flow internal loop reactor with an inner cylinder, the reaction temperature is 110-200℃, the reaction pressure is 1-3MPa, the liquid space velocity is 0.25-3h -1 , and the gas-liquid volume ratio is 20:1-400:1.

[0033] Further, the cooling medium of the cooler is circulating water, which further cools the wet oxidation reactor outlet water, and the temperature is decreased to 30-50℃, which meets the temperature requirement of the subsequent biochemical unit.

[0034] Further, acid is added to the adjusting tank to adjust the pH to 6-9, and the acid is hydrochloric acid or sulfuric acid, and the sulfuric acid is preferred.

[0035] Further, the treatment time of the electrodialysis I and the electrodialysis II is 0.5-3h, and the current density is 1-80mA / cm 2 .

[0036] Further, the aerobic biochemical process adopts salt-tolerant bacteria, and adopts full aerobic process, and the BAF or MBR is preferred.

[0037] Further, in the ozone catalytic oxidation, the ozone dosage is 0.1-2 times of the required oxidant dosage 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.

[0038] Further, the dissolved oxygen of the anaerobic biochemical unit is controlled to be below 0.1mg / L, the hydraulic retention time is controlled to be 2-96h, and the water temperature is controlled to be 25-38℃.

[0039] Further, the methane purification unit adopts one of the solid desulfurizer adsorption, biological desulfurization, alkali desulfurization and amine liquid desulfurization technology to purify the gas produced by the anaerobic biochemical unit, and the purity of the obtained methane is greater than 96%.

[0040] Further, the secondary biochemical process adopts ordinary biological bacteria, and adopts one of the BAF, MBR, contact oxidation tank and MBBR aerobic processes.

[0041] Further, the tubular microfiltration is mainly used for filtering suspended solids, colloids, microorganisms and the like.

[0042] Further, the biological reactor adopts the BAF or MBR process, and the biological bacteria adopt salt-tolerant bacteria.

[0043] The salt-tolerant bacteria involved in aerobic biochemical and bioreactor are salt-tolerant, especially sulfate-tolerant strains, and have strong tolerance to sulfides, preferably the salt-tolerant bacteria GXNYJ-DL-1 disclosed in CN114686391A, with the preservation number of CGMCC No. 20350.

[0044] Further, the reverse osmosis operating pressure is 1.0-3.0 Mpa, and the water production rate is 50%-80%.

[0045] Further, the decarbonator removes carbonate and bicarbonate by adding acid, the acid is hydrochloric acid or sulfuric acid, preferably sulfuric acid, and the addition amount is determined according to the pH reduction to 4-6.

[0046] Further, the salt separation system is a multi-effect evaporation crystallization system or an MVR evaporation crystallization system, and sodium sulfate and sodium chloride products with a purity of more than 99% are obtained.

[0047] Compared with the prior art, the present application has the following advantages:

[0048] (1) The traditional wet oxidation has high operating temperature, pressure and treatment cost, but the effluent of wet oxidation still contains high organic matter, and the salt content of the effluent is too high, so the treatment difficulty is still great. Based on this, the modified anion exchange membrane and the improved electrodialysis provided by the present application have the characteristics of strong anti-pollution ability and high ion exchange rate, which can effectively realize the separation of salt and organic matter in the effluent of ethylene caustic sludge wet oxidation, solve the problem of difficult treatment of organic matter in the effluent of ethylene caustic sludge wet oxidation, and finally realize zero discharge.

[0049] (2) Since the improved electrodialysis can effectively separate salt and organic matter, the organic matter can be efficiently removed by biochemical reaction, so it is not necessary to pursue the technical route of high temperature, high pressure and high energy consumption for wet oxidation. While ensuring efficient conversion of sulfides and efficient treatment of malodorous substances, the operating conditions of wet oxidation are more moderate, and the energy consumption is moderate. The increased organic matter in the effluent can be converted into methane through anaerobic reaction in the biochemical section, that is, carbon emission is reduced, and resource utilization of wastewater organic matter is realized.

[0050] (3) In the salt treatment section, the modified anion exchange membrane and the improved electrodialysis of the present application not only realize the concentration of salt, but also purify the water quality, that is, most of the organic matter is intercepted in the desalination liquid and returned to the treatment, thereby reducing the organic matter content of the salt separation system. Combined with the further removal of carbonates by the decarbonator, the purity of sodium sulfate and sodium chloride products in the salt separation system is greatly increased.

[0051] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 The treatment flow chart of ethylene caustic sludge wastewater in Example 1 is shown in the following figure:

[0053] Figure 2 The schematic diagram of anion exchange membrane electrodeposition modification in Example 1 is shown in the following figure. DETAILED DESCRIPTION

[0054] The application will be further described in detail below in combination with specific examples. The examples are implemented on the premise of the technical scheme of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following examples.

[0055] Example 1

[0056] Treatment of ethylene caustic sludge wastewater by the process method of the application

[0057] The process flow chart for treating ethylene caustic sludge wastewater is shown in the following figure: Figure 1 The ethylene caustic sludge wastewater first enters a heat exchange unit, is heated by heat exchange, and then enters a wet oxidation reactor. The water from the wet oxidation reactor is heated by the heat exchange unit, cooled by a cooler, and then enters a pH adjustment tank for pH adjustment. The water from the pH adjustment tank enters the electrodialysis I. The water from the electrodialysis I is divided into concentrated liquid and diluted liquid. The concentrated liquid enters aerobic biochemical treatment, and the diluted liquid enters anaerobic biochemical treatment. The water from the anaerobic biochemical treatment is treated by secondary biochemical treatment and then enters a reuse water pool. Methane produced by the anaerobic biochemical treatment is treated by a methane purification unit and then recycled. The water from the aerobic biochemical treatment is treated by ozone catalytic oxidation, then filtered by a tubular microfiltration, and then enters the electrodialysis II. The water from the electrodialysis II is divided into concentrated liquid and diluted liquid. The concentrated liquid enters a decarbonizer, and the diluted liquid enters a biological reactor. The water from the biological reactor enters reverse osmosis. The concentrated water from the reverse osmosis is sent back to the ozone catalytic oxidation unit in the biochemical section. The produced water from the reverse osmosis enters the anaerobic biochemical unit in the biochemical section. The water from the decarbonizer enters a salt separation system, and the salt separation system produces product sodium sulfate and sodium chloride.

[0058] A certain stock of ethylene caustic sludge wastewater has the following water quality: COD 14950 mg / L, chloride ion 1580 mg / L, sulfate ion 6550 mg / L, total salt content 19550 mg / L, sulfide 2080 mg / L, and pH 12.2. The water inflow is 20 t / h.

[0059] The electrodialysis I and the electrodialysis II provided in this example are both modified electrodialysis. The anion exchange membrane is a modified anion exchange membrane, which has strong anti-pollution ability and high ion permeability. The cation exchange membrane is a general cation exchange membrane (CJ-MC-3, China Hefei Kaitie Polymer Co., Ltd.).

[0060] The modified anion exchange membrane is prepared by the following method:

[0061] Step a: using a commercial anion exchange membrane (SELEMION AMV, product of Asahi Glass, Japan) as a base membrane, rinsing with 0.2 mol / L hydrochloric acid solution and 0.2 mol / L sodium hydroxide solution respectively, and then rinsing with deionized water to remove impurities on the surface of the membrane, to obtain a pretreated base membrane;

[0062] Step b: configuring a 20 mmol / L Tris-HCl buffer solution, adjusting the pH to 8.5 with hydrochloric acid, adding dopamine and β-cyclodextrin, and stirring for 4 h to fully dissolve, to obtain a dopamine Tris buffer solution, wherein the mass concentration of dopamine in the dopamine Tris buffer solution is 0.5 g / L, and the mass concentration of β-cyclodextrin is 0.8 g / L;

[0063] Step c: placing the base membrane prepared in step a in the dopamine Tris buffer solution, and adding 4 mmol / L copper sulfate, and stirring for 8 h, and keeping the air flowing during the reaction, to obtain an anion exchange membrane with a preliminarily modified surface;

[0064] Step d: dissolving a polyanion modifier and sodium chloride in a 20 mmol / L Tris-HCl buffer solution, adjusting the pH to 8.5 with hydrochloric acid, and the mass concentration of the polyanion modifier is 1.5 g / L, and the mass concentration of sodium chloride is 10 g / L, and the polyanion modifier is selected from poly-4-styrene sulfonic acid sodium, to obtain an electrodeposition mother liquor;

[0065] Step e: performing surface sulfonation and modification by an electrodeposition method, as shown in Figure 2 , placing the anion exchange membrane obtained in step c in the middle of a direct current electrodeposition device to form two compartments, placing the electrodeposition mother liquor prepared in step d in the cathode side compartment, and placing water in the anode side compartment, and the electrodeposition time is 0.6 h, and the current density is 20 mA / cm 2 , to obtain a final modified anion exchange membrane;

[0066] Step f: taking out the modified anion exchange membrane prepared in step e and placing it in a 10 g / L sodium chloride solution for use.

[0067] The specific operation parameters for treating ethylene alkali residue wastewater are as follows:

[0068] The above ethylene alkali residue wastewater 20 t / / h first enters a heat exchange unit, and after heat exchange, the wastewater temperature rises to 120℃, and enters a wet oxidation reactor; the reaction temperature of the wet oxidation reactor is 150℃, the pressure is 2 MPa, and the liquid space velocity is 1 h -1, gas-liquid volume ratio of 80:1; wet oxidation effluent is cooled to 70°C by heat exchange unit, then cooled to 45°C by cooler and enters the adjusting tank, at this time the wastewater COD is 6603 mg / L, total salt content is 25195 mg / L, sulfide is 10.6 mg / L, pH is 11.6, the removal rate of wet oxidation unit COD is 55.8%, the removal rate of sulfide is 99.5%; the adjusting tank adds sulfuric acid to adjust the pH value to 8, the total salt content increases to 26523 mg / L, the effluent enters the electrodialysis I.

[0069] The treatment time of electrodialysis I is 1.2 h, the current density is 30 mA / cm 2 , after treatment, the dilution liquid in electrodialysis I has a COD concentration of 10135 mg / L, a total salt content of 4330 mg / L, a flow rate of 12 t / h, the concentrated liquid has a COD concentration of 1305 mg / L, a total salt content of 59813 mg / L, a flow rate of 8 t / h, a sulfate ion selective permeability of 89.5%, a chloride ion selective permeability of 92.3%, and an organic matter interception rate of 92.1%; the electrodialysis I dilution liquid enters the anaerobic biochemical unit, and the reverse osmosis produced water also enters the anaerobic biochemical unit, which has a good dilution effect on salt; the anaerobic biochemical unit has a residence time of 50 h, a water temperature of 32°C, and a dissolved oxygen of less than 0.1 mg / L, and the generated methane has a purity of 98.3% after being purified by alkali liquid; the anaerobic biochemical unit effluent has a COD concentration of 455 mg / L and a salt content of 3380 mg / L, which enters the secondary biochemical unit; the secondary biochemical unit adopts BAF process, adds conventional activated sludge, and has a residence time of 18 h; the final effluent has a COD concentration of 56 mg / L and enters the reuse water tank; the electrodialysis concentrated liquid enters the aerobic biochemical unit, the aerobic biochemical unit adopts MBR process, the salt concentration is close to 60 g / L, salt-tolerant bacteria are added, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A is selected, the preservation number is CGMCC No.20350, the residence time is 20 h, the effluent COD is as low as 245 mg / L, then enters the ozone catalytic oxidation unit, the ozone addition concentration is 60 mg / L, the reaction time is 30 min, the effluent COD is 175 mg / L, the total salt content is 55255 mg / L, and after being filtered by a tubular microfiltration, it enters the electrodialysis II.

[0070] The treatment time of electrodialysis II is 0.9 h, the current density is 30 mA / cm 2COD concentration of the concentrated solution in the post-treatment electrodialysis II is 35 mg / L, the total salt content is 164581 mg / L, the concentrated water accounts for 25% of the total inflow, the COD concentration of the dilute solution is 221 mg / L, the total salt content is 18813 mg / L, and the dilute water accounts for 75% of the total inflow; the dilute solution of the electrodialysis II enters the biological reactor, the BAF process is adopted, the salt-tolerant bacteria are added, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A is selected, the preservation number is CGMCC No. 20350, the residence time is 8 h, the effluent COD is as low as 65 mg / L, the reverse osmosis is entered, the reverse osmosis water production rate is 68%, the salt content is less than 2200 mg / L after the reverse osmosis treatment, the anaerobic biochemical unit is entered, the reverse osmosis concentrated water is sent back to the ozone catalytic oxidation for further treatment; the electrodialysis II concentrated solution enters the decarbonizer, sulfuric acid is added to adjust the pH to 5.3, so as to remove the carbonate and bicarbonate in the solution, the decarbonizer effluent enters the salt separation system; the salt separation system adopts the multi-effect evaporation salt separation crystallization process, and finally the sodium sulfate with a purity of 99.3% and the sodium chloride with a purity of 99.2% are obtained.

[0071] It can be seen from the embodiment that the ethylene caustic sludge wastewater can be effectively treated, the wastewater is finally zero discharged, and high-purity sodium sulfate, aluminum chloride and methane are prepared. The reaction temperature of the traditional ethylene caustic sludge wet oxidation is about 200°C, and the operation pressure is between 3-3.5 MPa. The reaction temperature of the wet oxidation in the embodiment is reduced by 25% compared with the traditional wet oxidation reaction temperature, and the operation pressure is reduced by more than 33%, which greatly reduces the energy consumption of the wet oxidation reaction.

[0072] Example 2

[0073] By using Figure 1 the process shown in the figure to treat certain ethylene caustic sludge wastewater

[0074] A certain ethylene caustic sludge wastewater has the following water quality: COD 24050 mg / L, chloride ion 2010 mg / L, sulfate ion 8520 mg / L, total salt content 25120 mg / L, sulfide 3050 mg / L, pH 12.4, and inflow flow rate 20 t / h.

[0075] The process route and implementation steps of the ethylene alkali residue wastewater in this example are the same as those in 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 type cation exchange membrane (Hefei Kaijie Polymer Co., Ltd., China, model CJ-MC-3). In the preparation process of the modified anion exchange membrane, except that the mass concentration of dopamine in the dopamine Tris buffer solution in step b is 0.6 g / L, the addition amount of copper sulfate in step c is 4.5 mmol / L, and the stirring reaction is 9 h, the mass concentration of the polyanion modifier in step d is 1.7 g / L, and the electrodeposition time in step e is 0.7 h, the other steps are the same as those in Example 1.

[0076] The specific operation parameters for treating the ethylene alkali residue wastewater are as follows:

[0077] The above-mentioned 20 t / h of ethylene alkali residue wastewater first enters the heat exchange unit, and after heat exchange, the wastewater temperature rises to 125°C, and then enters the wet oxidation reactor; the reaction temperature of the wet oxidation reactor is 165°C, the pressure is 2.5 MPa, the liquid space velocity is 1 h -1 , and the gas-liquid volume ratio is 90:1; the wet oxidation effluent is cooled to 72°C by the heat exchange unit, and then cooled to 44°C by the cooler before entering the adjusting tank, at this time, the wastewater COD is 7512 mg / L, the total salt content is 31232 mg / L, the sulfide is 1.8 mg / L, the pH is 11.8, the COD removal rate of the wet oxidation unit is 68.7%, and the sulfide removal rate is 99.9%; the pH value is adjusted to 8.1 by adding sulfuric acid in the adjusting tank, the total salt content increases to 33255 mg / L, and the effluent enters the electrodialysis I.

[0078] The treatment time of the electrodialysis I is 1.3 h, the current density is 35 mA / cm 2, the COD concentration of the diluted liquid in the electrodialysis I after treatment is 13761 mg / L, the total salt content is 4835 mg / L, the flow rate is 10 t / h, the COD concentration of the concentrated liquid is 1263 mg / L, the total salt content is 61675 mg / L, the flow rate is 10 t / h, the selective permeation rate of sulfate ions is 91.5%, the selective permeation rate of chloride ions is 93.5%, and the rejection rate of organic matter is 91.6%; the diluted liquid in the electrodialysis I enters the anaerobic biochemical unit, and the reverse osmosis produced water also enters the anaerobic biochemical unit, and the reverse osmosis produced water has a good dilution effect on salt; the residence time is 72 h, the water temperature is 32°C, the dissolved oxygen is less than 0.1 mg / L, the produced methane is purified by alkali liquor, and the purity reaches 98.8%, the COD concentration of the water out of the anaerobic biochemical unit is 532 mg / L, the salt content is 3671 mg / L, and the water enters the secondary biochemical unit; the secondary biochemical unit adopts the MBR process, conventional activated sludge is added, the residence time is 20 h, the COD concentration of the final effluent is 58 mg / L, and the effluent enters the reuse water tank; the electrodialysis concentrated liquid enters the aerobic biochemical unit, the aerobic biochemical unit adopts the MBR process, the salt concentration is close to 62 g / L, salt-tolerant bacteria are added, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A are selected, the preservation number is CGMCC No. 20350, the residence time is 24 h, the COD concentration of the effluent is as low as 288 mg / L, then the effluent enters the ozone catalytic oxidation unit, the ozone addition concentration is 70 mg / L, the reaction time is 30 min, the COD concentration of the effluent is 182 mg / L, the total salt content is 58210 mg / L, and the effluent enters the electrodialysis II after being filtered by a tubular microfiltration.

[0079] The treatment time of the electrodialysis II is 0.9 h, the current density is 35 mA / cm 2 , the COD concentration of the concentrated liquid in the electrodialysis II after treatment is 37 mg / L, the total salt content is 172195 mg / L, the concentrated water accounts for 25% of the total inflow, the COD concentration of the diluted liquid is 230 mg / L, the total salt content is 20125 mg / L, and the diluted liquid accounts for 75% of the total inflow; the diluted liquid in the electrodialysis II enters the biological reactor, adopts the BAF process, salt-tolerant bacteria are added, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A are selected, the preservation number is CGMCC No. 20350, the residence time is 8 h, the COD concentration of the effluent is as low as 66 mg / L, the effluent enters the reverse osmosis, the reverse osmosis produced water rate is 65%, the salt content of the effluent after being treated by the reverse osmosis is lower than 2600 mg / L, the effluent enters the anaerobic biochemical unit, and the reverse osmosis concentrated water is sent back to the ozone catalytic oxidation unit for further treatment; the electrodialysis II concentrated liquid enters the decarbonizer, sulfuric acid is added to adjust the pH to 5.5, so as to remove carbonate and bicarbonate in the solution, the effluent of the decarbonizer enters the salt separation system; the salt separation system adopts the multi-effect evaporation salt separation crystallization process, and finally sodium sulfate with a purity of 99.4% and sodium chloride with a purity of 99.2% are obtained.

[0080] It can be seen from the embodiment that the application can effectively treat ethylene caustic sludge wastewater with different concentrations, and finally achieve zero discharge of wastewater, and high-purity sodium sulfate, sodium chloride and methane are prepared. The reaction temperature of traditional ethylene caustic sludge wet oxidation is about 200°C, and the operation pressure is between 3-3.5 MPa. In the embodiment, the reaction temperature of wet oxidation is reduced by 17.5% compared with the traditional wet oxidation reaction temperature, and the operation pressure is reduced by more than 16.7%. The reaction condition is more moderate, and the energy consumption is lower.

[0081] Comparative Example 1

[0082] The wastewater treated in Comparative Example 1 has the same quality as that in Example 1, the process route and implementation steps are the same as those in Example 1, and the difference is that the anion and cation exchange membranes of electrodialysis I are general membranes without modification treatment. The anion exchange membrane is a product of Asahi Glass Company in Japan (SELEMION AMV), and the cation exchange membrane is a product of Hefei Kaitai Polymer Co., Ltd. in China (model CJ-MC-3).

[0083] Specifically, the wastewater is introduced into the wet oxidation reactor after heat exchange, and the effluent is cooled and pH adjusted by a cooler before being introduced into the ordinary electrodialysis I. The operation parameters of each unit before entering the ordinary electrodialysis I are the same as those in Example 1. The treatment time of the ordinary electrodialysis I is 1.2 h, the current density is 30 mA / cm 2 , the COD concentration of the dilute liquid in the electrodialysis I after treatment is 8671 mg / L, the salt content is 9407 mg / L, the flow rate is 12 t / h, the COD concentration of the concentrated liquid is 3501 mg / L, the salt content is 52197 mg / L, the flow rate is 8 t / h, the sulfate ion selective permeability is 77.5%, and the chloride ion selective permeability is 80.4%. Compared with Example 1, the membrane flux decreases significantly, which may be related to membrane clogging. In addition, the organic matter retention rate decreases to 78.8%, indicating that a large amount of negatively charged organic matter passes through the anion membrane, increasing the possibility of membrane clogging. The dilute liquid after treatment by the electrodialysis I is mixed with the reverse osmosis produced water before being introduced into the anaerobic biochemical unit. The residence time of the anaerobic biochemical unit is 50 h, the water temperature is 32°C, and the dissolved oxygen is less than 0.1 mg / L. The COD concentration of the effluent of the anaerobic biochemical unit is 5896 mg / L, and the salt content is 8850 mg / L, which is introduced into the secondary biochemical unit. The secondary biochemical unit adopts the BAF process, and the conventional activated sludge is added, and the residence time is 18 h. The COD concentration of the final effluent is 4513 mg / L, and the salt content is 8815 mg / L, which cannot be reused and still needs further treatment. The reason is that the high salt concentration, especially the high sulfate concentration, leads to poor treatment efficiency of the anaerobic biochemical unit and the secondary biochemical unit.

[0084] It can be seen from the comparative example that the unmodified anion and cation exchange membranes used in the electrodialysis I cannot effectively separate organic matter and salt, resulting in high salt content in the biochemical unit, and the wastewater cannot be treated for reuse.

[0085] Comparative Example 2

[0086] Comparative Example 2

[0087] Specifically, the same as Example 1, the wastewater was pretreated by wet oxidation, electrodialysis I and aerobic biochemistry, and then entered the ozone catalytic oxidation unit. The ozone dosage concentration was 60 mg / L, and the reaction time was 30 min. The COD of the effluent was 175 mg / L, and the total salt content was 55255 mg / L. After microfiltration by a tubular filter, the wastewater entered electrodialysis II. The treatment time of electrodialysis II was 0.9 h, and the current density was 30 mA / cm 2 . After treatment, the COD concentration of the concentrated solution in electrodialysis I was 115 mg / L, the total salt content was 113170 mg / L, the concentrated water accounted for 25% of the total amount of the influent, the COD concentration of the dilute solution was 195 mg / L, the total salt content was 35950 mg / L, and the dilute solution accounted for 75% of the total amount of the influent. The dilute solution of electrodialysis II entered the biological reactor, and the BAF process was used. The salt-tolerant bacteria GXNYJ-DL-1 were added, and the residence time was 8 h. The COD of the effluent was as low as 57 mg / L. The effluent entered the reverse osmosis, and the water production rate of the reverse osmosis was 68%. The COD of the effluent of the reverse osmosis was less than 40 mg / L, and the salt content was 4012 mg / L. The salt content was relatively high, which indirectly affected the COD treatment efficiency and the reuse rate of the effluent in the biochemical section. The salt content of the concentrated solution of electrodialysis II was 113170 mg / L, which was relatively low, increasing the energy consumption of the salt separation system. The COD was slightly increased, and the purity of the sodium sulfate and sodium chloride products was 98.8% and 98.7%, respectively.

[0088] From this comparative example, it can be seen that the unmodified cation and anion exchange membranes used in electrodialysis II have poor separation ability for organic matter and salt. The anion exchange membrane is easily contaminated by organic matter, resulting in high salt content in the dilute solution of electrodialysis II, poor reverse osmosis water production, low salt content in the concentrated solution of electrodialysis II, high COD, and increased energy consumption of the salt separation system, which reduces the purity of the sodium sulfate and sodium chloride products.

Claims

1. A process for zero discharge of ethylene caustic sludge wastewater, comprising a wet oxidation section, a biochemical section and a salt treatment section; The wet oxidation section comprises a heat exchange unit, a wet oxidation reactor, a cooler and a regulating tank; ethylene caustic sludge wastewater first enters the heat exchange unit, is heated and then enters the wet oxidation reactor, the water from the wet oxidation reactor is exchanged by the heat exchange unit, then is cooled by the cooler, and then enters the regulating tank for pH adjustment, and the water from the regulating tank enters the electro-dialysis I of the biochemical section; The biochemical section comprises electro-osmosis I, aerobic biochemical reaction, ozone catalytic oxidation, anaerobic biochemical reaction, secondary biochemical reaction, recycled water pool and methane purification unit. The concentrated solution of the electro-dialysis I enters aerobic biochemical treatment, the dilute solution enters anaerobic biochemical treatment, the water from the anaerobic biochemical treatment is treated by secondary biochemical treatment and then enters a reuse water tank, and the methane produced by the anaerobic biochemical treatment is treated by a methane purification unit and then is recycled; the water from the aerobic biochemical treatment enters ozone catalytic oxidation, and then enters the tubular microfiltration of the salt treatment section; The salt treatment section comprises a tubular microfiltration, an electro-dialysis II, a decarbonator, a salt separation system, a biological reactor and a reverse osmosis unit; the water from the tubular microfiltration enters the electro-dialysis II, the concentrated solution of the electro-dialysis II is treated by the decarbonator and then enters the salt separation system, and the dilute solution of the electro-dialysis II enters the biological reactor; the water from the biological reactor enters the reverse osmosis unit, the concentrated water from the reverse osmosis unit is sent back to the ozone catalytic oxidation unit of the biochemical section, and the water produced by the reverse osmosis unit enters the anaerobic biochemical unit of the biochemical section; The electro-dialysis I and the electro-dialysis II are composed of anion exchange membranes and cation exchange membranes, wherein the anion exchange membranes are modified anion exchange membranes, and the cation exchange membranes are general cation exchange membranes; The modification method of the anion exchange membrane is as follows: Step a: using an anion exchange membrane as a base film, washing with a hydrochloric acid solution and a sodium hydroxide solution respectively, and then rinsing with water to remove impurities on the surface of the film to obtain a pretreated base film; Step b: dissolving dopamine and β-cyclodextrin in a Tris-HCl buffer solution, adjusting the pH to 8-9, and stirring to fully dissolve them to obtain a modification solution; Step c: placing the base film obtained in step a in the modification solution, adding copper sulfate, stirring under the condition of air flow, and obtaining a preliminarily modified anion exchange membrane after the reaction; Step d: dissolving a polyanion modifier and sodium chloride in a Tris-HCl buffer solution, adjusting the pH to 8-9, and obtaining an electrodeposition mother liquor; Step e: placing the anion exchange membrane obtained in step c in the middle of a direct current electrodeposition device to form two compartments, placing the electrodeposition mother liquor prepared in step d in the cathode side compartment, placing water in the anode side compartment, and performing electrodeposition reaction to obtain a finally modified anion exchange membrane.

2. The process of claim 1, wherein, The mass concentration of dopamine in the modification solution in step b is 0.2-2 g / L, and the mass concentration of β-cyclodextrin is 0.3-3 g / L.

3. The process of claim 2, wherein, The mass concentration of dopamine in the modification solution in step b is 0.5-1 g / L.

4. The process of claim 1, wherein, In the reaction solution formed in step c, the concentration of copper sulfate is 1-20 mmol / L, and the stirring time is 1-20 h.

5. The process of claim 1, wherein, The polyanion modifier in step d is selected from one or more of sodium poly-4-styrenesulfonate, sodium p-styrenesulfonate, sodium polyvinylsulfonate and sodium polypropylenesulfonate, the mass concentration of the polyanion modifier in the electrodeposition mother liquor of step d is 1-5 g / L, and the mass concentration of sodium chloride is 3-30 g / L.

6. The process of claim 1, wherein, The heat exchange unit increases the temperature of the ethylene lye to 110-150 DEG C, and the temperature of the effluent from the wet oxidation reactor is reduced to 50-75 DEG C.

7. The process of claim 1, wherein, The reaction temperature of the wet oxidation reactor is 110-200℃, the reaction pressure is 1-3 MPa, the liquid space velocity is 0.25-3 h -1 , and the gas-liquid volume ratio is 20:1-400:

1.

8. The process of claim 1, wherein, The treatment time of the electrodialysis I and the electrodialysis II is 0.5-3h, and the current density is 1-80mA / cm 2 .

9. The process of claim 1, wherein, The aerobic biochemical reaction adopts a BAF or MBR full-aerobic process.

10. The process of claim 1, wherein, In the catalytic ozone oxidation, the ozone dosage is 0.1-2 times the amount of the required oxidant calculated according to the COD value of the wastewater, and the reaction time is 10-120 minutes.

11. The process of claim 1, wherein, The dissolved oxygen in the anaerobic biochemical unit is controlled to be below 0.1 mg / L, the hydraulic retention time is controlled to be 2-96 h, and the water temperature is controlled to be 25-38 DEG C.

12. The process of claim 1, wherein, The methane purification unit adopts one of the solid desulfurizer adsorption, biological desulfurization, alkali desulfurization and amine desulfurization technologies to purify the gas produced by the anaerobic biochemical unit, and the purity of the obtained methane is greater than 96%.

13. The process of claim 1, wherein, The secondary biochemical reaction adopts one of a BAF, MBR, contact oxidation tank and MBBR aerobic process.

14. The process of claim 1, wherein, The bioreactor adopts a BAF or MBR process.

15. The process of claim 1, wherein, The operating pressure of the reverse osmosis is 1.0-3.0 Mpa, and the water production rate is 50%-80%.

16. The process of claim 1, wherein, The decarbonator removes the carbonate and bicarbonate by adding acid, the acid is hydrochloric acid or sulfuric acid, and the amount of the acid added is determined according to the pH value being reduced to 4-6.

17. The process of claim 1, wherein, The salt separation system is a multi-effect evaporation crystallization system or a MVR evaporation crystallization system, and sodium sulfate and sodium chloride products are obtained.

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