Method for treating EDTA wastewater by homogeneous catalytic wet oxidation

Abstract

The present invention discloses a method for treating EDTA wastewater by homogeneous catalytic wet oxidation, comprising a pretreatment section, a wet oxidation section, and an advanced treatment section; the EDTA wastewater is first subjected to calcium and magnesium hardness removal, and after being concentrated by a first-level nanofiltration, a wet oxidation catalytic treatment is carried out by a homogeneous catalyst to obtain wastewater with a high EDTA removal rate, and then concentrated by a second-level nanofiltration, and the concentrated water portion is returned for wet oxidation catalytic treatment, and part is treated by single-membrane electrodialysis. After treatment, the mother liquor returns to the wet oxidation for further treatment, and the anionic liquid is subjected to chemical denitrification and biochemical treatment, and finally reaches the discharge standard. In view of the characteristics of EDTA wastewater being difficult to degrade and high in nitrogen, the present invention adopts a treatment process with homogeneous catalytic wet oxidation as the core, and utilizes a combination of chemical denitrification and biological denitrification to ultimately achieve the discharge standard of EDTA wastewater.

Description

Technical Field

[0001] The invention relates to a method for treating EDTA wastewater by homogeneous catalytic wet oxidation, and belongs to the technical field of wastewater treatment. Background Art

[0002] EDTA, or ethylenediaminetetraacetic acid, is an important chelating agent with a wide range of applications, such as bleaching and fixing solutions for the processing of color photosensitive materials, dyeing auxiliaries, fiber processing auxiliaries, cosmetic additives, blood anticoagulants, stabilizers, detergents, synthetic rubber polymerization initiators, etc. EDTA wastewater refers to wastewater generated during the production or use of EDTA. Due to the unique molecular structure of EDTA, its chemical properties are very stable and difficult to biodegrade, so the treatment of EDTA wastewater becomes very difficult. Refractory wastewater is usually treated by advanced oxidation methods, such as ozone catalytic oxidation, electrocatalytic oxidation, photocatalysis, Fenton oxidation, etc. Among them, electrocatalytic oxidation and photocatalysis are still limited by high treatment costs and are difficult to apply in industry. Fenton oxidation has problems such as complex operation, unstable hydrogen peroxide, and loss of iron ions. As the country controls ozone pollutants, the application of ozone catalytic oxidation is also restricted.

[0003] Wet oxidation involves the use of gaseous oxygen as an oxidant under high temperature (120-320°C) and high pressure (0.5-20 MPa) conditions to decompose organic matter in water into small organic or inorganic molecules. This process is characterized by zero secondary pollution and low treatment costs. Drawing on its widespread application in treating alkali residue wastewater, a growing number of researchers are investigating wet oxidation technology for treating other challenging wastewaters. To improve its treatment effectiveness, research is focusing on catalytic wet oxidation.

[0004] CN201510274988.5 discloses a catalyst for catalytic wet oxidation of difficult-to-degrade organic wastewater, which is a "precious metal-transition metal-rare earth" composite catalyst, and the main component of the carrier FSC is alumina; CN201410340574.3 discloses a catalyst for catalytic wet oxidation treatment and its preparation method, which uses precious metal-non-precious metal nanoalloy as active ingredient and activated carbon as carrier; CN201510661575.2 discloses a multiphase wet oxidation catalyst, the components of which include a composite oxide carrier and a small amount of precious metal; CN201310621017.4 discloses a method for preparing a catalytic wet oxidation catalyst carrier, which uses activated carbon as a core and amorphous silicon aluminum as a shell.

[0005] The aforementioned patents all utilize heterogeneous catalytic wet oxidation, which offers advantages in catalyst separation and recovery and metal loss, but is not necessarily applicable to wet oxidation processes. The 2011 paper "Industrial Application of Alkali Residue Moderated Wet Oxidation + SBR Treatment Technology" discloses the Fushun Petrochemical Research Institute's alkali residue moderated wet oxidation process, which has been implemented in 28 refineries and petrochemical companies, making it a highly representative process. The wet oxidation reactor employed is a bubbling flow internal circulation reactor with an inner barrel. Using a heterogeneous catalyst in this reactor would severely impact gas-liquid circulation, potentially even blocking the reactor and piping. Using a fixed-bed method would result in greater gas resistance, further hindering gas-liquid circulation and significantly reducing the reaction rate.

[0006] Homogeneous catalysis has higher catalytic efficiency than heterogeneous catalysis due to its lack of internal and external diffusion effects and high dispersion. Catalyst preparation is also much simpler than heterogeneous catalysis. However, the biggest challenge in applying homogeneous catalysis to wet oxidation is the loss of metal catalysts. Currently, research in this area is limited. CN201210225873.3 provides a method for treating industrial wastewater by homogeneous catalytic wet oxidation. Ring gear packing is placed in a fixed-bed reactor, and the homogeneous catalyst is iron-based. However, the patent does not address catalyst loss or solutions. Summary of the Invention

[0007] In response to the above shortcomings, the present invention provides a method for treating EDTA wastewater in the prior art. By combining homogeneous catalytic wet oxidation and membrane technology, it ultimately achieves efficient treatment and standard discharge of EDTA wastewater, while solving the problem of catalyst loss and achieving catalyst recycling. The comprehensive operating cost is low and the economy and practicality are strong.

[0008] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0009] A method for treating EDTA wastewater by homogeneous catalytic wet oxidation, comprising a pretreatment section, a wet oxidation section, and an advanced treatment section;

[0010] The pretreatment section includes a hardness removal tank, a first-level nanofiltration and an intermediate water tank; the EDTA wastewater first enters the hardness removal tank to remove calcium and magnesium hardness, and when the EDTA concentration in the wastewater is ≤10000 mg / L, it enters the first-level nanofiltration concentration treatment, and after treatment, the first-level nanofiltration concentrated water and the first-level nanofiltration produced water are obtained, and the first-level nanofiltration produced water enters the intermediate water tank; when the EDTA concentration in the wastewater is greater than 10000 mg / L, it directly enters the wet oxidation section;

[0011] The wet oxidation section includes a wet oxidation reactor, a heat exchange unit, a cooler, a secondary nanofiltration, and a single membrane electrodialysis; the primary nanofiltration concentrated water or wastewater with an EDTA concentration greater than 10,000 mg / L is mixed with a homogeneous catalyst and then enters the heat exchange unit; the heat exchange unit uses a heat exchanger to perform heat exchange on the effluent from the wet oxidation reactor and the primary nanofiltration concentrated water, the effluent from the wet oxidation reactor goes through the tube side, the primary nanofiltration concentrated water goes through the shell side, and the primary nanofiltration concentrated water after heat exchange and temperature increase enters the wet oxidation reactor; the effluent from the wet oxidation reactor is heat exchanged by the heat exchange unit and then cooled by the cooler, and the effluent enters the secondary nanofiltration treatment to obtain secondary nanofiltration concentrated water and secondary nanofiltration produced water, part of the secondary nanofiltration concentrated water is mixed with the primary nanofiltration concentrated water, and then returned to the heat exchange unit and enters the wet oxidation reactor, and part of it enters the single membrane electrodialysis to obtain single membrane electrodialysis mother liquor and anionic liquid, and the single membrane electrodialysis mother liquor is returned to the heat exchange unit;

[0012] The deep treatment section includes a chemical denitrification tank, a biochemical tank and an effluent monitoring tank; the secondary nanofiltration water and the single membrane electrodialysis anion liquid enter the chemical denitrification tank, mainly for the removal of ammonia nitrogen and COD; the effluent from the chemical denitrification tank enters the biochemical tank, for further treatment by biological methods, and after the treatment is completed, it is discharged to the effluent monitoring tank and finally meets the discharge standards; according to the nature of the effluent from the intermediate water tank, it may first enter the biochemical tank for treatment or be directly discharged into the effluent monitoring tank.

[0013] Furthermore, chemical agents are used in the de-hardening pool to remove hardness, preferably a combination of sodium hydroxide and sodium carbonate, with sodium hydroxide added at 1 to 4 times the mass concentration of magnesium ions and sodium carbonate added at 1 to 3 times the mass concentration of calcium ions.

[0014] Furthermore, the primary nanofiltration water production rate is 60% to 85%, which has a concentrating effect on EDTA wastewater, reduces the subsequent wet oxidation unit treatment load, and solves the problem of poor economic efficiency in treating low-concentration, high-flow wastewater.

[0015] Furthermore, the pore size of the first-level nanofiltration membrane is between 1 and 3 nm, which can separate organic matter with a relative molecular mass greater than 200, and at the same time can intercept high-valent salts. For EDTA wastewater, EDTA and high-valent salts in the wastewater are intercepted and enter the concentrated water side, while the organic matter concentration on the water production side is lower, the salt content is lower, and the main component of the salt is monovalent salt.

[0016] Furthermore, the heat exchange unit is composed of multiple heat exchangers. After multiple heat exchanges, the temperature of the primary nanofiltration concentrated water rises to 130-160°C, and the outlet water temperature of the wet oxidation reactor drops to 45-75°C.

[0017] Furthermore, the homogeneous catalyst is a composite catalyst of precious metals and transition metals; the precious metal is selected from one or more of platinum, palladium, rhodium, silver and ruthenium, and the transition metal is selected from one or more of copper, iron, manganese, zinc and nickel. The mass percentage of precious metals in the homogeneous catalyst is 2% to 20%, preferably a platinum-iron composite catalyst; the precious metals and transition metals exist in the form of metal salt compounds or complexes and are dissolved in the liquid phase.

[0018] Furthermore, the homogeneous catalyst is only added in large quantities when the device is started up, and is added according to the mass ratio of EDTA to metal ions of 2000:1 to 2:1; during normal operation, it is appropriately supplemented according to the catalyst loss rate and the change in EDTA concentration.

[0019] Furthermore, the wet oxidation reactor is a bubbling flow inner circulation reactor in an inner tube, which uses gaseous oxygen (air) as an oxidant under conditions of high temperature and high pressure to oxidize general organic matter in water into small molecular organic matter or inorganic matter; those skilled in the art should understand that EDTA is a chemically stable and difficult-to-degrade organic matter, and wet oxidation alone has limited ability to remove EDTA. However, under the conditions of a catalyst, oxygen under high temperature and high pressure is more likely to undergo free radical reactions, and the strong oxidizing property of free radicals greatly improves the decomposition and conversion ability and reaction rate of EDTA. On the other hand, the composite homogeneous catalyst used in the present invention itself has high activity and high selectivity, and its treatment of special pollutants is faster and more effective, and the problem of large-scale loss of homogeneous catalysts is also solved by membrane technology.

[0020] Furthermore, the reaction temperature of the wet oxidation reactor is 150-300°C, the reaction pressure is 2MPa-8MPa, and the liquid space velocity is 0.25-4h -1 , the gas-liquid volume ratio is 20:1 to 300:1.

[0021] Furthermore, the cooling medium of the cooler is circulating water, which further cools the outlet water of the wet oxidation reactor to 25-40°C, meeting the temperature requirements of the subsequent nanofiltration membrane.

[0022] Furthermore, the secondary nanofiltration can intercept metal catalysts, high-valent salts, unreacted EDTA, macromolecular organic matter, etc., which enter the concentrated water side after interception, are mixed with the primary nanofiltration concentrated water, and return to the wet oxidation reactor for secondary treatment after heat exchange and temperature increase, while realizing the recycling of metal catalysts.

[0023] Furthermore, the secondary nanofiltration water production rate is 50% to 70%, and the pore size of the secondary nanofiltration membrane is between 1 and 3 nm.

[0024] Furthermore, 1% to 50% of the secondary nanofiltration concentrated water enters the single membrane electrodialysis; the single membrane electrodialysis only uses an anion membrane. Under the action of the electrode drive and the anion membrane, some high-valent anion salts such as sulfate and carbonate in the secondary nanofiltration concentrated water pass through the anion membrane into the concentrated water side, and also include small molecular organic matter that presents negative, and the cationic catalyst remains in the mother liquor and is reused again; It should be understood by those skilled in the art that the secondary nanofiltration does not intercept monovalent ions such as sodium, potassium, and chloride, but has a high retention rate for divalent anions, and the single membrane electrodialysis solves the problem of divalent anion enrichment very well, and does not cause the loss of metal catalysts. The branched side line treatment is adopted, and its treatment cost is also low;

[0025] Furthermore, the chemical denitrification tank adds hypochlorous acid or sodium hypochlorite, and according to the principle of breakpoint chlorination, the molar ratio of chlorine to ammonia is controlled at 1:1 to 2:1. Those skilled in the art should understand that under the action of EDTA catalytic wet oxidation, macromolecular organic matter will be converted into small molecular organic matter and inorganic matter, among which organic nitrogen will be converted into nitrogen, nitrate nitrogen (nitrite nitrogen is unstable) and ammonia nitrogen. Breakpoint chlorination is to use chlorine-based oxidants to oxidize ammonia nitrogen into chloramines, and then oxidize and decompose into nitrogen, thereby achieving the purpose of removing ammonia nitrogen and total nitrogen. At the same time, COD will also be partially removed under the action of chlorine-based oxidants.

[0026] Furthermore, the biochemical pool adopts an A / O and post-denitrification combined process; the A / O process has the A section in front and the O section in the back, the A section is mainly used to improve the biodegradability of wastewater and accelerate the biodegradation rate, the O section is mainly used for the removal of organic matter and the nitrification reaction of residual ammonia nitrogen, and the post-denitrification is used to remove total nitrogen and convert nitrate nitrogen and nitrite nitrogen into nitrogen gas for removal.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) In view of the characteristics of EDTA wastewater being difficult to degrade and containing high nitrogen, the present invention adopts a treatment process with homogeneous catalytic wet oxidation as the core, giving full play to the characteristics of high catalytic activity and strong treatment capacity of homogeneous catalytic wet oxidation, and using a combination of chemical denitrification and biological denitrification to ultimately achieve the discharge of EDTA wastewater in compliance with the standards.

[0029] (2) The present invention solves the problem of homogeneous catalyst loss in homogeneous catalytic wet oxidation by combining wet oxidation with membrane technologies such as nanofiltration membrane and electrodialysis single anion membrane, realizes the recycling of catalyst, and realizes the reflux and secondary treatment of large molecular organic matter, thereby greatly improving the processing capacity of the wet oxidation process.

[0030] (3) The method of the present invention solves the problem of poor economic efficiency in treating low-concentration, high-flow wastewater. EDTA wastewater is efficiently concentrated using a nanofiltration membrane with a special pore size. Heat exchange is used to raise the temperature before entering the reactor. A catalyst is introduced into the wet oxidation reactor to increase the reaction rate, thereby keeping the overall wet oxidation process cost low.

[0031] (4) The method of the present invention solves the problem of high salt content in wastewater after concentration and the scaling and clogging of reactors and process pipelines caused by it. The de-hardening tank first solves the impact of calcium and magnesium hardness of wastewater on subsequent membrane processes; two-stage nanofiltration removes most of the monovalent salts such as sodium chloride and potassium chloride in the wastewater, reducing the accumulation of salts during the wet oxidation cycle treatment; single-membrane electrodialysis removes most of the anionic salts such as sulfate and carbonate in the wastewater, achieving salt balance during the wet oxidation cycle treatment.

[0032] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 . Flow chart of the treatment of EDTA wastewater of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below with reference to specific examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0035] Example 1

[0036] use Figure 1 The process method shown is used to treat EDTA wastewater: EDTA wastewater first enters a de-hardness tank to remove calcium and magnesium hardness, and then enters a primary nanofiltration treatment. After treatment, the primary nanofiltration concentrated water is mixed with a homogeneous catalyst and enters a heat exchange unit. After heat exchange with the effluent of a wet oxidation reactor and heating, it enters a wet oxidation reactor. The primary nanofiltration produced water enters an intermediate water tank. EDTA wastewater is efficiently treated under the action of high temperature, high pressure and catalyst in the wet oxidation reactor. The effluent is first cooled by heat exchange in a heat exchange unit, then cooled by a cooler, and finally enters a secondary nanofiltration. The metal catalyst is recovered to concentrated water. The secondary nanofiltration concentrate is mixed with the primary nanofiltration concentrate, and a small part enters the single membrane electrodialysis through the side line. The single membrane electrodialysis mother liquor is mixed with the two nanofiltration concentrates, and the anion liquid is sent to the chemical denitrification tank. The secondary nanofiltration produced water is also sent to the chemical denitrification tank; the chemical denitrification tank uses the inflection point chlorination principle to remove ammonia nitrogen, total nitrogen, and COD by adding chlorine oxides. The effluent enters the biochemical tank for further treatment, and is discharged to the effluent monitoring tank after the treatment, and finally meets the discharge standards; the intermediate water tank can be directly discharged into the effluent monitoring tank or incorporated into the biochemical tank for further treatment depending on the water quality.

[0037] The water quality of a certain EDTA wastewater is as follows: EDTA concentration 3000mg / L, COD 3800mg / L, total salt content 3500mg / L, sulfate ion concentration 400mg / L, calcium ion concentration 300mg / L, magnesium ion concentration 100mg / L, ammonia nitrogen 10mg / L, total nitrogen 300mg / L, and wastewater flow rate 20t / h.

[0038] The specific operating conditions for EDTA wastewater treatment are as follows: the above-mentioned EDTA wastewater first enters the de-hardening tank, and reagents are added according to the mass concentration of sodium hydroxide 250 mg / L and the mass concentration of sodium carbonate 800 mg / L. After clarification, the calcium ion concentration of the supernatant is reduced to below 20 mg / L, and the magnesium ion concentration is below 5 mg / L. Other factors remain unchanged, and the effluent enters the first-stage nanofiltration; the first-stage nanofiltration water production rate is 75%, and EDTA is concentrated to 12000 mg / L and enters the concentrated water side of the nanofiltration with a flow rate of 5t / h. The COD on the water production side is 160 mg / L, and the EDTA concentration is less than 10 mg / L, which does not reach the direct According to the emission standards, it needs to enter the biochemical pool for further treatment with a flow rate of 15t / h. Before entering the heat exchange unit, the primary nanofiltration concentrate is mixed with the secondary nanofiltration concentrate, the single membrane electrodialysis mother liquor, and the homogeneous catalyst. After mixing, the flow rate becomes 7.5t / h. The homogeneous catalyst uses a platinum-iron catalyst, which is a mixed salt of platinum chloride and ferric chloride. After mixing, the platinum metal ion concentration in the liquid is about 10mg / L, and the iron metal ion concentration is about 200mg / L. After heat exchange, the liquid temperature rises to 150℃ and enters the wet oxidation reactor. The reaction temperature of the wet oxidation reactor is 205℃, the pressure is 4MPa, and the liquid space velocity is 2h -1, the gas-liquid volume ratio is 100:1, and the EDTA concentration of the reaction effluent is less than 100 mg / L; the wet oxidation effluent is cooled to 55°C by the heat exchange unit, and then cooled to 35°C by the cooler, and enters the secondary nanofiltration. The metals, EDTA, macromolecular organic matter, sulfates, carbonates, etc. in the homogeneous catalyst are intercepted again and enter the concentrated water side. The secondary nanofiltration water production rate is 60%, and the EDTA concentration of the produced water is less than 5 mg / L, flowing into the chemical denitrification tank. The EDTA concentration on the concentrated water side is 242 mg / L; 33% of the secondary nanofiltration concentrated water enters the single-mode electrodialysis treatment, and the remaining 67% is directly merged into the primary nanofiltration concentrated water. The anion liquid EDTA concentration in the single-mode electrodialysis effluent is less than 50 mg / L and flows to the chemical denitrification tank. The mother liquor, with an EDTA concentration of approximately 420 mg / L, is mixed with the nanofiltration concentrate and then re-enters the wet oxidation unit for treatment. The chemical denitrification tank has an influent flow rate of 5 t / h, with ammonia nitrogen content of 186 mg / L and total nitrogen content of 430 mg / L. Sodium hypochlorite is added, with a chlorine-to-ammonia molar ratio of 1.2:1, reducing the ammonia nitrogen content in the effluent to 24 mg / L and the total nitrogen content to 255 mg / L. The biochemical tank, which incorporates the effluent from the chemical denitrification tank and the intermediate tank, has an influent flow rate of 20 t / h. The biochemical tank utilizes an A / O process with post-denitrification. The final effluent has a COD content of 46 mg / L, a total salt content of 3750 mg / L, ammonia nitrogen content of 2 mg / L, and total nitrogen content of 14 mg / L, meeting discharge standards and allowing for discharge from the effluent monitoring tank. The daily loss rate of the metal catalyst is less than 0.5%, virtually achieving full recovery. The reaction parameters and treatment efficiency of each unit are shown in Tables 1 and 2.

[0039] Table 1

[0040]

[0041] Table 2

[0042]

[0043] It can be seen from this embodiment that the process method of the present invention realizes the efficient operation of homogeneous catalytic wet oxidation, solves the loss problem of homogeneous catalyst through membrane technology, maintains the salt balance of the reaction system, solves the problems of high COD, difficult degradation and high nitrogen in EDTA wastewater, and finally achieves the discharge standard of EDTA wastewater.

[0044] Example 2

[0045] use Figure 1 The process shown treats EDTA wastewater.

[0046] The water quality of a certain EDTA wastewater is as follows: EDTA concentration 10300mg / L, COD 12000mg / L, total salt content 5000mg / L, sulfate ion concentration 600mg / L, calcium ion concentration 400mg / L, magnesium ion concentration 100mg / L, ammonia nitrogen 25mg / L, total nitrogen 1044mg / L, and wastewater flow rate 5t / h.

[0047] The specific operating conditions for EDTA wastewater treatment are as follows: the above-mentioned EDTA wastewater first enters the de-hardening tank, and reagents are added according to the mass concentration of sodium hydroxide 300 mg / L and the mass concentration of sodium carbonate 900 mg / L. After clarification, the calcium ion concentration of the supernatant is reduced to below 22 mg / L, and the magnesium ion concentration is below 3 mg / L. Other factors remain unchanged. The effluent directly bypasses the first-stage nanofiltration and is directly mixed with the secondary nanofiltration concentrate, the single-membrane electrodialysis mother liquor, and the homogeneous catalyst. After mixing, the flow rate becomes 7.6 t / h; the homogeneous catalyst uses a platinum-iron catalyst, which is a mixed salt of platinum chloride and ferric chloride. After mixing, the platinum metal ion concentration in the liquid is 9 mg / L, and the iron metal ion concentration is 220 mg / L. After heat exchange, the liquid temperature rises to 148°C and enters the wet oxidation reactor; the reaction temperature of the wet oxidation reactor is 215°C, the pressure is 3.5 MPa, and the liquid space velocity is 1.5h -1 The gas-liquid volume ratio is 90:1, and the EDTA concentration of the reaction effluent is less than 100 mg / L; the wet oxidation effluent is cooled to 52°C by the heat exchange unit, and then cooled to 32°C by the cooler, and enters the secondary nanofiltration. The metals, EDTA, macromolecular organic matter, sulfates, carbonates, etc. in the homogeneous catalyst are retained again and enter the concentrated water side. The secondary nanofiltration water production rate is 62.5%, and the EDTA concentration of the produced water is less than 5 mg / L, flowing into the chemical denitrification tank. The EDTA concentration on the concentrated water side is 187 mg / L; 17.5% of the secondary nanofiltration concentrated water enters the single-mode electrodialysis treatment, and the remaining 82.5% is directly collected into the de-hardness pool effluent. The anionic liquid EDTA concentration in the single-mode electrodialysis effluent is less than 50 mg / L The effluent flows to the chemical denitrification tank, where the mother liquor has an EDTA concentration of approximately 350 mg / L. After mixing with the nanofiltration concentrate, it enters the wet oxidation unit for further treatment. The influent flow rate to the chemical denitrification tank is 5.1 t / h, with ammonia nitrogen concentration of 199 mg / L and total nitrogen of 398 mg / L. Sodium hypochlorite is added, and the molar ratio of chlorine to ammonia is controlled at 1.3:1. This reduces the ammonia nitrogen concentration in the effluent to 21 mg / L and the total nitrogen concentration to 192 mg / L. The influent to the biochemical tank is the effluent from the chemical denitrification tank, which utilizes an A / O process with post-denitrification. The final effluent has a COD of 48 mg / L, a total salt content of 5286 mg / L, ammonia nitrogen of 4 mg / L, and total nitrogen of 26 mg / L, meeting discharge standards and allowing for discharge from the effluent monitoring tank. The daily loss rate of the metal catalyst is less than 0.5%, essentially achieving full recovery. The reaction parameters and treatment efficiency of each unit are shown in Tables 3 and 4.

[0048] Table 3

[0049]

[0050] Table 4

[0051]

[0052] It can be seen from this embodiment that the process method of the present invention can treat EDTA wastewater of different concentrations. By adjusting the dosage of the dehardening agent, the first-level nanofiltration water production ratio, the amount of catalyst added, the wet oxidation reaction parameters, the second-level nanofiltration water production ratio, the second-level nanofiltration concentrated water side line desalination rate, the chemical denitrification dosage and other methods, the EDTA wastewater can finally achieve the discharge standards of various indicators.

[0053] Example 3

[0054] The water quality of EDTA wastewater treated in Example 3 is the same as that in Example 1, and the process route, implementation steps, and reaction parameters are also the same as those in Example 1, except that a platinum-copper catalyst is used as the catalyst. The results of the wet oxidation stage treatment are shown in Table 5.

[0055] Table 5

[0056]

[0057] This example shows that when a platinum-copper composite catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is reduced to 84.5% and the total nitrogen removal rate is increased to 78.2% compared with Example 1. The corresponding treatment pressure of the chemical denitrification tank is reduced and the treatment pressure of the biochemical unit is increased.

[0058] Example 4

[0059] The water quality of EDTA wastewater treated in Example 4 is the same as that in Example 1, and the process route, implementation steps, and reaction parameters are also the same as those in Example 1, except that a platinum-nickel catalyst is used as the catalyst. The results of the wet oxidation stage treatment are shown in Table 6.

[0060] Table 6

[0061]

[0062] This example shows that when a platinum-nickel composite catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is reduced to 82.6% and the total nitrogen removal rate is reduced to 50.2% compared with Example 1.

[0063] Example 5

[0064] The water quality of EDTA wastewater treated in Example 5 is the same as that in Example 1, and the process route, implementation steps, and reaction parameters are also the same as those in Example 1, except that a platinum-nickel catalyst is used as the catalyst. The results of the wet oxidation stage treatment are shown in Table 7.

[0065] Table 7

[0066]

[0067] This example shows that when a platinum-nickel composite catalyst is used and the nickel dosage is increased to 300 mg / L, the COD removal rate of the homogeneous catalytic wet oxidation is increased to 91.2% and the total nitrogen removal rate is increased to 63.5% compared with Example 1.

[0068] Example 6

[0069] The water quality of EDTA wastewater treated in Example 6 is the same as that in Example 1, and the process route, implementation steps, and reaction parameters are also the same as those in Example 1, except that a palladium iron catalyst is used as the catalyst. The results of the wet oxidation stage treatment are shown in Table 8.

[0070] Table 8

[0071]

[0072] This example shows that when the palladium-iron composite catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is reduced to 86.8% and the total nitrogen removal rate is increased to 69.5% compared with Example 1.

[0073] Example 7

[0074] The water quality of EDTA wastewater treated in Example 7 is the same as that in Example 1, and the process route, implementation steps, and reaction parameters are also the same as those in Example 1, except that a palladium-copper catalyst is used as the catalyst. The results of the wet oxidation stage treatment are shown in Table 9.

[0075] Table 9

[0076]

[0077] This example shows that when the palladium-copper composite catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is reduced to 81.2% and the total nitrogen removal rate is increased to 83.5% compared with Example 1.

[0078] Example 8

[0079] The water quality of EDTA wastewater treated in Example 8 is the same as that in Example 1, and the process route, implementation steps, and reaction parameters are also the same as those in Example 1, except that a rhodium-iron catalyst is used as the catalyst. The results of the wet oxidation stage treatment are shown in Table 10.

[0080] Table 10

[0081]

[0082] This example demonstrates that, using a rhodium-iron composite catalyst at the same dosage, the COD removal rate for homogeneous catalytic wet oxidation increased to 92.6% and the total nitrogen removal rate increased to 76.7%, compared to Example 1. Considering that the price of the precious metal rhodium is much higher than that of platinum, and that the platinum-iron catalyst meets the treatment requirements, the platinum-iron catalyst is preferred.

[0083] Example 9

[0084] The implementation steps and reaction parameters of each unit in Example 9 are the same as those in Example 1, and the type and concentration of the catalyst are also the same. The difference is the water quality of the EDTA wastewater. Compared with Example 1, the concentration of the EDTA wastewater is relatively lower, as shown in Table 11.

[0085] Table 11

[0086]

[0087] As shown in Table 11, the COD of the first-stage nanofiltration water production is 58 mg / L, the ammonia nitrogen is 5 mg / L, and the total nitrogen is 12 mg / L, which meets the discharge standards. It can be discharged directly through the effluent monitoring pool, or partially enter the biochemical pool to dilute the salt content in the biochemical pool.

[0088] Comparative Example 1

[0089] The water quality of EDTA wastewater treated in Comparative Example 1 is the same as that in Example 1. The process route, implementation steps, and reaction parameters are also the same as those in Example 1, but no precious metal catalyst is added, only transition metal catalyst is added. The results of the wet oxidation stage treatment are shown in Table 12.

[0090] Table 12

[0091]

[0092] It can be seen from this comparative example that without adding precious metal catalysts and only adding iron metal catalysts, the COD removal rate and total nitrogen removal rate of homogeneous catalytic wet oxidation decreased significantly, with the COD removal rate being only 68.5% and the total nitrogen removal rate being only 43.4%.

[0093] Comparative Example 2

[0094] The water quality of the EDTA wastewater treated in Comparative Example 2 was the same as that in Example 1. The process route, implementation steps, and reaction parameters were also the same as those in Example 1, but no catalyst was added. The reaction temperature of the wet oxidation reactor was 205°C, the pressure was 4 MPa, and the liquid space velocity was 2 h -1 , the gas-liquid volume ratio is 100:1, and the wet oxidation stage treatment results are shown in Table 13.

[0095] Table 13

[0096]

[0097] It can be seen from this comparative example that without adding a catalyst and using conventional wet oxidation, the final COD removal rate is only 31.6%, and the total nitrogen removal rate is only 9.3%.

[0098] Comparative Example 3

[0099] The water quality of the EDTA wastewater treated in Comparative Example 3 was the same as that in Example 1. The process route, implementation steps, and reaction parameters were also basically the same as those in Example 1, but no catalyst was added. The reaction temperature of the wet oxidation reactor was 260°C, the pressure was 6 MPa, and the liquid space velocity was 2 h -1 , the gas-liquid volume ratio is 100:1, and the wet oxidation stage treatment results are shown in Table 14.

[0100] Table 14

[0101]

[0102] This comparative example shows that, without adding a catalyst and using conventional wet oxidation, the reaction temperature was increased to 260°C and the pressure was 6 MPa, with all other factors remaining unchanged. The final COD removal rate was 62.8%, and the total nitrogen removal rate was only 14.5%. The significant increase in wet oxidation reaction temperature and pressure means a significant increase in operating costs, while the final treatment effect is unsatisfactory. In particular, the total nitrogen removal rate did not show a significant improvement compared to Comparative Example 2, and was significantly lower than that of Example 1.

Claims

1. A method for treating EDTA wastewater by homogeneous catalytic wet oxidation, comprising a pretreatment section, a wet oxidation section, and an advanced treatment section; The pretreatment section includes a hardness removal tank, a first-level nanofiltration and an intermediate water tank; the EDTA wastewater first enters the hardness removal tank to remove calcium and magnesium hardness, and when the EDTA concentration in the wastewater is ≤10000 mg / L, it enters the first-level nanofiltration concentration treatment, and after treatment, the first-level nanofiltration concentrated water and the first-level nanofiltration produced water are obtained, and the first-level nanofiltration produced water enters the intermediate water tank; when the EDTA concentration in the wastewater is greater than 10000 mg / L, it directly enters the wet oxidation section; The wet oxidation section includes a wet oxidation reactor, a heat exchange unit, a cooler, a secondary nanofiltration, and a single membrane electrodialysis; the primary nanofiltration concentrated water or wastewater with an EDTA concentration greater than 10,000 mg / L is mixed with a homogeneous catalyst and then enters the heat exchange unit; the heat exchange unit uses a heat exchanger to perform heat exchange on the effluent from the wet oxidation reactor and the primary nanofiltration concentrated water, the effluent from the wet oxidation reactor goes through the tube side, the primary nanofiltration concentrated water goes through the shell side, and the primary nanofiltration concentrated water after heat exchange and temperature increase enters the wet oxidation reactor; the effluent from the wet oxidation reactor is heat exchanged by the heat exchange unit and then cooled by the cooler, and the effluent enters the secondary nanofiltration treatment to obtain secondary nanofiltration concentrated water and secondary nanofiltration produced water, part of the secondary nanofiltration concentrated water is mixed with the primary nanofiltration concentrated water, and then returned to the heat exchange unit and enters the wet oxidation reactor, and part of it enters the single membrane electrodialysis to obtain single membrane electrodialysis mother liquor and anionic liquid, and the single membrane electrodialysis mother liquor is returned to the heat exchange unit; The deep treatment section includes a chemical denitrification tank, a biochemical tank and an effluent monitoring tank; the secondary nanofiltration water and the single membrane electrodialysis anion liquid enter the chemical denitrification tank, mainly for the removal of ammonia nitrogen and COD; the effluent from the chemical denitrification tank enters the biochemical tank, and is further treated by biological methods. After the treatment, it is discharged to the effluent monitoring tank and finally meets the discharge standards; according to the properties of the effluent from the intermediate water tank, it may first enter the biochemical tank for treatment or be directly discharged into the effluent monitoring tank; in, The homogeneous catalyst is a composite catalyst of precious metals and transition metals; the precious metal is selected from one or more of platinum, palladium, rhodium, silver and ruthenium, and the transition metal is selected from one or more of copper, iron, manganese, zinc and nickel, and the mass percentage of precious metals in the homogeneous catalyst is 2% to 20%; the precious metals and transition metals exist in the form of metal salt compounds or complexes and are dissolved in the liquid phase; The secondary nanofiltration water production rate is 50% to 70%, and the pore size of the secondary nanofiltration membrane is between 1 and 3 nm; 1% to 50% of the secondary nanofiltration concentrated water enters the single membrane electrodialysis, and the single membrane electrodialysis only uses an anion membrane. Under the action of the electrode drive and the anion membrane, the high-valent anion salts and negative small molecular organic matter in the secondary nanofiltration concentrated water pass through the anion membrane into the concentrated water side, and the cationic catalyst remains in the mother liquor and is reused again.

2. The method according to claim 1, characterized in that In the de-hardening pool, a combination of sodium hydroxide and sodium carbonate is used to remove hardness. Sodium hydroxide is added at a mass concentration of 1 to 4 times that of magnesium ions, and sodium carbonate is added at a mass concentration of 1 to 3 times that of calcium ions.

3. The method according to claim 1, characterized in that The first-stage nanofiltration water production rate is 60% to 85%.

4. The method according to claim 1, wherein The pore size of the first-stage nanofiltration membrane is between 1 and 3 nm, and EDTA and high-valent salts in the wastewater are intercepted and enter the concentrated water side.

5. The method according to claim 1, wherein The heat exchange unit is composed of multiple heat exchangers. After multiple heat exchanges, the temperature of the primary nanofiltration concentrated water rises to 130-160°C, and the outlet water temperature of the wet oxidation reactor drops to 45-75°C.

6. The method according to claim 1, wherein The homogeneous catalyst is a platinum-iron composite catalyst.

7. The method according to claim 1, characterized in that The homogeneous catalyst is added in large quantities only when the device is started up, and is added according to the mass ratio of EDTA to metal ions of 2000:1 to 2:1; during normal operation, it is appropriately supplemented according to the catalyst loss rate and the change of EDTA concentration.

8. The method according to claim 1, characterized in that The wet oxidation reactor is a bubbling flow internal circulation reactor with an inner tube. Under high temperature and high pressure conditions, it uses oxygen as an oxidant to oxidize organic matter in water into small molecular organic matter or inorganic matter.

9. The method according to claim 8, characterized in that The reaction temperature of the wet oxidation reactor is 150-300°C, the reaction pressure is 2MPa-8MPa, and the liquid space velocity is 0.25-4h -1 , the gas-liquid volume ratio is 20:1 to 300:

1.

10. The method according to claim 1, characterized in that The outlet water of the wet oxidation reactor is cooled to 25-40°C by a cooler.

11. The method according to claim 1, wherein The secondary nanofiltration can intercept metal catalysts, high-valent salts, unreacted EDTA, and macromolecular organic matter, which enter the concentrated water side after interception and are mixed with the primary nanofiltration concentrated water. After heat exchange and temperature increase, they return to the wet oxidation reactor for secondary treatment, while realizing the recycling of metal catalysts.

12. The method according to claim 1, characterized in that Hypochlorous acid or sodium hypochlorite is added to the chemical denitrification pool.

13. The method according to claim 1, wherein The biochemical pool adopts an A / O and post-denitrification combined process; the A / O process has the A section in front and the O section in the back, the A section is mainly used to improve the biodegradability of wastewater and accelerate the biodegradation rate, the O section is mainly used for the removal of organic matter and the nitrification reaction of residual ammonia nitrogen, and the post-denitrification is used to remove total nitrogen and convert nitrate nitrogen and nitrite nitrogen into nitrogen gas for removal.

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