A heterogeneous ozone oxidation catalyst composition and a process for wastewater treatment

Abstract

A kind of heterogeneous ozone oxidation catalyst composition and wastewater treatment process method, including catalyst I and catalyst II, catalyst I is supported solid catalyst, including transition metal and activated carbon, catalyst II includes soluble transition metal salt and soluble rare earth metal salt.Wastewater treatment process method includes: wastewater is entered into adjusting tank after being removed hard, is mixed with catalyst II and is entered into catalytic ozone oxidation unit after adjusting acidity, catalytic ozone oxidation unit is loaded with catalyst I;Effluent enters nanofiltration, nanofiltration concentrated water part enters single membrane electrodialysis treatment, part enters adjusting tank, mother liquor obtained from single membrane electrodialysis treatment enters adjusting tank, and circulation is formed;Single membrane electrodialysis anion liquid and nanofiltration effluent enter neutralization tank, then enter biochemical unit, effluent is merged into effluent monitoring tank, or according to water quality, effluent from neutralization tank is directly entered into effluent monitoring tank via auxiliary line.The nanofiltration and single membrane electrodialysis double membrane technology of the application solve the problem of active metal component loss in catalyst, especially the loss of metal in supported solid catalyst I, so that the use of liquid phase catalyst II and solid catalyst loaded with noble metal becomes possible, and the catalytic ozone oxidation process has higher treatment efficiency.

Description

Technical Field

[0001] This invention relates to a multiphase ozone oxidation catalyst composition and a process for wastewater treatment using the same, belonging to the field of wastewater treatment technology. Background Technology

[0002] With the rapid development of industries such as petroleum, chemical, and pharmaceutical, the amount of recalcitrant substances in industrial wastewater is increasing daily, making it difficult to meet environmental protection requirements using traditional water treatment methods. Advanced oxidation technologies (AOP) utilize various reactive free radicals to attack organic matter, effectively mineralizing or converting toxic and recalcitrant organic compounds into low-toxicity, easily biodegradable small-molecule organic compounds. These technologies mainly include the Fenton process, wet catalytic oxidation, photocatalysis, electrocatalysis, and catalytic ozone oxidation. Among these, catalytic ozone oxidation has developed more rapidly due to its lack of limitations imposed by wastewater color, colloidal substances, high temperature, and high pressure.

[0003] Catalytic ozone oxidation is divided into homogeneous catalytic oxidation and heterogeneous catalytic oxidation. Heterogeneous catalytic ozone oxidation is a technology that utilizes ozone oxidation and solid catalysts to achieve deep oxidation and maximize the removal of recalcitrant pollutants. Studies generally suggest that heterogeneous catalytic oxidation follows a surface hydroxyl mechanism dominated by hydroxyl radicals, with chemisorption on the catalyst surface being the controlling step. To improve ozone utilization, the specific surface area of ​​the catalyst support should be maximized to provide more active sites and reaction contact area. However, limited by the overall adsorption performance, wear resistance, and stability of the catalyst, existing heterogeneous catalysts suffer from low ozone utilization and short service life, and may even exhibit excessive ozone emissions after a period of use. Furthermore, when treating acidic wastewater, the leaching and loss of metal catalysts is significant.

[0004] The mechanisms of homogeneous catalytic ozone oxidation can be mainly attributed to two categories: the hydroxyl radical theory and the complex theory. The hydroxyl radical theory primarily involves adding a liquid catalyst to the ozone oxidation system to catalyze the decomposition of ozone, generating hydroxyl radicals with higher activity potentials, thereby degrading organic matter. The complex theory posits that the liquid catalyst forms complexes with organic matter, and these complexes are more readily degraded by ozone. Based on these theories, homogeneous catalytic ozone oxidation possesses advantages such as high catalytic activity, strong organic matter removal capacity, and high ozone utilization rate. However, it also suffers from disadvantages such as the difficulty in recovering metal salt catalysts and the potential for secondary pollution from metal ions.

[0005] In recent years, with the advancement of ecological civilization construction in China, the coordinated control of PM2.5 and ozone pollution has received further attention, and the development of catalytic ozone oxidation technology has also encountered enormous challenges. On the one hand, the development direction of catalytic ozone oxidation must be guided by improving ozone utilization and reducing ozone emissions; on the other hand, the purpose of catalytic ozone oxidation should not be limited to the removal of organic matter (decarbonization), but should also have other functions, such as denitrification. Summary of the Invention

[0006] To address the above shortcomings, this invention provides a multiphase ozone oxidation catalyst composition and a process for wastewater treatment using the same, which can significantly improve ozone utilization and organic matter removal rates, while simultaneously removing ammonia nitrogen and total nitrogen. The catalyst used can be recycled.

[0007] To achieve the above technical objectives, the technical solution adopted by this invention is as follows:

[0008] The technical objective of the first aspect of this invention is to provide a heterogeneous ozone oxidation catalyst composition, comprising catalyst I and catalyst II. Catalyst I is a supported solid catalyst, comprising an active component and a support. The active component comprises a transition metal selected from one or more of iron, copper, zinc, manganese, cobalt, and nickel. The support is activated carbon. Catalyst II comprises a soluble transition metal salt and a soluble rare earth metal salt. The soluble transition metal salt is selected from at least one of copper, zinc, manganese, and cobalt metal salts. The soluble rare earth metal salt is selected from at least one of cerium, praseodymium, lanthanum, and neodymium metal salts.

[0009] Furthermore, the catalyst I in the catalyst composition is loaded into the ozone catalytic oxidation unit, and its loading volume is 1 / 5 to 4 / 5 of the total volume of the reaction unit. The catalyst II, based on the metal element therein, is 1 / 500 to 1 / 2 of the weight of COD in the wastewater to be treated.

[0010] Furthermore, in the catalyst I, the transition metal accounts for 1% to 15% of the total mass of the catalyst by weight.

[0011] Furthermore, the catalyst I is also loaded with a noble metal, wherein the mass ratio of the noble metal element to the transition metal element is 1:5 to 1:200, and the noble metal is selected from one or more of platinum, palladium, rhodium, silver and ruthenium.

[0012] Furthermore, the catalyst I is also loaded with rare earth metals, and the mass ratio of rare earth metal elements to transition metal elements is 1:2 to 1:50. The rare earth metals are selected from one or more of cerium, praseodymium, lanthanum and neodymium.

[0013] Furthermore, the activated carbon carrier of catalyst I is powdered activated carbon, prepared from various types of wood-based activated carbon, fruit shell activated carbon, and coal-based activated carbon, with a particle size of 150-300 mesh and a specific surface area of ​​500-3000 m². 2 / g, and pore volume 0.5~1.8cm 3 / g, with an average pore size of 0.5–4.0 nm, and pores with a pore size of 1–3 nm accounting for more than 90% of the total pore volume.

[0014] Furthermore, the mass ratio of transition metal elements to rare earth metal elements in catalyst II is 2:1 to 200:1, preferably 5:1 to 50:1. Catalyst II exists in a water-soluble form.

[0015] The second aspect of the present invention aims to provide a method for preparing the above-mentioned heterogeneous ozone oxidation catalyst composition, wherein the catalyst II forms a homogeneous catalyst after being dissolved in water, and the catalyst I is prepared by the following method: a carrier activated carbon, a necessary binder and water are mixed, dried, shaped and cured at low temperature to form a carrier material, the active components are loaded by impregnation, and the catalyst I is obtained by drying and calcination;

[0016] The two are mixed to obtain the heterogeneous ozone oxidation catalyst composition.

[0017] Furthermore, in the preparation process of catalyst I, the impregnation solution used during impregnation is a metal salt of the active component, or the reflux liquid from the ozone oxidation reaction catalyzed by the multiphase ozone oxidation catalyst composition, to recover and utilize the metals in catalyst II and the metals lost from catalyst I. This fully utilizes the active metals in the composition that have been lost or dissolved in the liquid phase due to long-term use, making it more economical. The impregnation time is 1–12 hours.

[0018] Furthermore, given that the reflux liquid after catalyst use contains many unwanted ions, the method for preparing the impregnation liquid from the reflux liquid is as follows: the reflux liquid is concentrated by nanofiltration to remove monovalent cations and chloride ions. The nanofiltration concentrate is then subjected to single-mode electrodialysis to remove sulfate ions and other high-valent anions. The mother liquor from the single-mode electrodialysis is then subjected to nanofiltration again. This process is repeated 1 to 5 times to obtain the final concentrate. After adding metal salts to the final concentrate, the impregnation liquid is obtained.

[0019] Furthermore, the adhesive is an inorganic adhesive, preferably one or more of silicate inorganic adhesives and phosphate inorganic adhesives; the silicate inorganic adhesive is selected from one or more of aluminum silicate, sodium silicate and calcium silicate; the phosphate inorganic adhesive is selected from one or more of aluminum phosphate, aluminum dihydrogen phosphate and sodium tripolyphosphate.

[0020] Furthermore, the activated carbon, binder, and water are mixed in a mass ratio of 50–80:2–10:20–50.

[0021] Furthermore, the drying temperature is 40–100°C, and the drying time is 2–24 hours.

[0022] Furthermore, the calcination is carried out under nitrogen or inert gas protection, with a calcination temperature of 400–700°C and a calcination time of 1–12 hours.

[0023] The technical objective of the third aspect of this invention is to provide a method for wastewater treatment using the above-mentioned multiphase ozone oxidation catalyst composition, comprising the step of contacting the catalyst composition with COD-containing wastewater.

[0024] Furthermore, in the above method, the catalyst I is loaded into the ozone catalytic oxidation unit, and its loading volume is 1 / 5 to 4 / 5 of the total volume of the reaction unit. The catalyst II, based on the metal elements therein, is 1 / 500 to 1 / 2 of the weight of COD in the wastewater to be treated.

[0025] Furthermore, in the above method, the amount of ozone used is 0.3 to 2 times the amount of oxidant required based on the COD value of the wastewater. The catalytic ozone oxidation reaction time is 10 to 120 minutes.

[0026] The fourth aspect of this invention aims to provide a wastewater treatment process, comprising a hardening tank, an equalization tank, a catalytic ozone oxidation unit, nanofiltration, single-membrane electrodialysis, a neutralization tank, a biochemical unit, and an effluent monitoring tank. Wastewater first undergoes hardening removal in the hardening tank and then enters the equalization tank. There, it is mixed with catalyst II from the multiphase ozone oxidation catalyst composition, and the pH is adjusted before entering the catalytic ozone oxidation unit, which is filled with catalyst I. The effluent from the catalytic ozone oxidation unit enters the nanofiltration tank. Part of the nanofiltration concentrate enters the single-membrane electrodialysis unit, and part directly enters the equalization tank. The mother liquor obtained from the single-membrane electrodialysis unit enters the equalization tank, forming a cycle. The single-membrane electrodialysis anion exchange solution enters the neutralization tank, and the nanofiltration permeate also enters the neutralization tank for mixing and pH adjustment. Then, it enters the biochemical unit. The effluent from the biochemical unit flows into the effluent monitoring tank, or, depending on the water quality, the effluent from the neutralization tank directly enters the effluent monitoring tank via a secondary line.

[0027] Furthermore, chemical agents are used to remove hardness in the hardening tank, preferably a combination of sodium hydroxide and sodium carbonate. Sodium hydroxide is added at 1 to 4 times the mass concentration of magnesium ions, and sodium carbonate is added at 1 to 3 times the mass concentration of calcium ions.

[0028] Furthermore, when the reaction system is started, catalyst II is added to the equalization tank at a mass ratio of COD in the wastewater to metal elements in catalyst II of 500:1 to 2:1.

[0029] Furthermore, in the catalytic ozone oxidation unit, the loading volume of catalyst I is 1 / 5 to 4 / 5 of the total volume of the reaction unit; the ozone dosage is 0.3 to 2 times the amount of oxidant required based on the wastewater COD value. The catalytic ozone oxidation reaction time is 10 to 120 minutes.

[0030] Furthermore, acid is added to the conditioning tank to adjust the pH to 5-7; the acid used is hydrochloric acid or sulfuric acid, preferably hydrochloric acid.

[0031] Furthermore, after pH adjustment, the chloride ion content in the conditioning tank should be no less than 1200 mg / L. If it is less than 1200 mg / L, chloride salts need to be added for further adjustment, preferably sodium chloride or potassium chloride.

[0032] Furthermore, the nanofiltration permeate has a permeate rate of 60%–85%, and a membrane pore size between 1 and 5 nm. It can retain metals in catalyst II, metals lost from catalyst I, high-valent salts (such as sulfates and carbonates), and large molecular organics (relative molecular mass greater than 200), etc. After retention, the water enters the concentrate side. The metals in catalyst II and those lost from catalyst I are eventually returned to the equalization tank. The nanofiltration permeate includes small molecular organics and monovalent salts, etc.

[0033] Furthermore, 1% to 40% of the nanofiltration concentrate effluent enters a single-membrane electrodialysis system. This single-membrane electrodialysis system uses only anion exchange membranes. Under the action of the electrode and the anion exchange membrane, high-valence anions such as sulfates and carbonates in the nanofiltration concentrate permeate through the anion exchange membrane into the concentrate side. It also includes small organic molecules that exhibit negative oxidation states. The cationic catalyst remains in the mother liquor and is reused. Those skilled in the art should understand that nanofiltration does not retain monovalent ions such as sodium, potassium, and chloride, but it has a high retention rate for divalent anions. Single-membrane electrodialysis effectively solves the problem of divalent anion enrichment and does not cause loss of metal catalysts. It also employs branched side-stream treatment, resulting in lower processing costs.

[0034] Furthermore, the pH of the neutralization tank is adjusted to 6-9 by adding one or more of sodium hydroxide, calcium hydroxide, or potassium hydroxide.

[0035] Furthermore, the biochemical unit adopts a combined A / O and post-denitrification process; in the A / O process, the A stage comes first and the O stage comes later. The A stage is mainly used to improve the biodegradability of wastewater and accelerate the biodegradation rate, while also having a certain denitrification function. The O stage is mainly used for the removal of organic matter and the nitrification reaction of residual ammonia nitrogen. The post-denitrification is used to remove total nitrogen and convert nitrate nitrogen and nitrite nitrogen into nitrogen gas for removal.

[0036] Furthermore, the influent salt concentration of the biological unit should not exceed 5000 mg / L. When the influent salt concentration is too high, in order to ensure the treatment effect of subsequent nitrification and denitrification bacteria, other low-salt wastewater should be used for dilution treatment, preferably domestic sewage, which has relatively low salt concentration and COD and is easy to treat.

[0037] Furthermore, the COD, ammonia nitrogen, and total nitrogen concentrations of the effluent from the neutralization tank meet the relevant emission standards. It is possible to bypass the biochemical unit and enter the effluent monitoring tank via a secondary line before discharging in compliance with the standards.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] (1) The nanofiltration and single-membrane electrodialysis dual-membrane technology of the present invention solves the problem of loss of active metal components in the catalyst, especially the loss of metal in the supported solid catalyst I, making it possible to use liquid-phase (homogeneous) catalyst II and solid catalysts supported with noble metals, etc. Specifically, in the slightly acidic environment of the ozone catalytic system, the metal contained in catalyst I will dissolve in the liquid phase after being lost, and mix with catalyst II which is already contained in the liquid phase to continue to exert catalytic effect. The dual-membrane technology is then used to realize the recycling of catalytic metals. At the same time, the dual-membrane technology also solves the problem of salt accumulation in the cyclic treatment of catalytic ozone oxidation. Specifically, the nanofiltration membrane removes monovalent cations, chloride ions and other monovalent ions, and the single-membrane electrodialysis removes sulfate ions and other high-valence anions.

[0040] (2) The catalytic ozone oxidation process of the present invention has higher treatment efficiency. Specifically, the liquid catalyst II itself has high catalytic activity and high ozone utilization rate. Secondly, the solid catalyst I can support expensive but superior precious metals and rare earth metals. Thirdly, the support of the solid catalyst I is activated carbon with high specific surface area and high adsorption performance. Due to the recycling of catalyst metals, there will be a large amount of adsorption and desorption phenomena on the activated carbon support. The migration of active components and the change of action mechanism have a certain promoting effect on the function of both solid catalyst I and liquid catalyst II.

[0041] (3) The catalyst composition and catalytic ozone oxidation process of the present invention also have better denitrification function. In the preferred embodiment, both the solid catalyst I and the liquid catalyst II of the present invention contain rare earth metals. By means of the unique 4f electron layer structure and lanthanide contraction characteristics of rare earth elements, a large number of oxidation active sites can be provided in the catalytic reaction, accelerating the electron transfer between the catalyst and the reactants. When chloride ions are added or there are a large number of chloride ions, it will promote the free residual chlorine (ClO in water). - The generation of chlorine (such as HClO and Cl2) and the decomposition of free residual chlorine into hydroxyl radicals and chlorine radicals accelerate the oxidative decomposition of organic matter while promoting the conversion of ammonia and the removal of total nitrogen.

[0042] (4) In the catalyst preparation method provided by the present invention, the reflux liquid generated by the catalytic ozone oxidation process can be fully utilized when preparing catalyst I. After simple physical concentration, it can become the impregnation liquid required for preparing catalyst I. This method greatly saves the investment cost of catalyst, especially catalysts containing precious metals and rare earth metals.

[0043] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0044] Figure 1 The process flow diagram for wastewater treatment according to the present invention. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0046] Example 1

[0047] The process flow diagram for wastewater treatment is as follows: Figure 1 As shown: Wastewater first undergoes hardness removal in a hardening tank before entering an equalization tank. It is then mixed with catalyst II and the pH is adjusted before entering the catalytic ozone oxidation unit, which is filled with catalyst I. The effluent from the catalytic ozone oxidation unit enters a nanofiltration tank. Part of the nanofiltration concentrate is treated by a single-membrane electrodialysis system, while the remainder is directly fed into the equalization tank. The mother liquor obtained from the single-membrane electrodialysis treatment also enters the equalization tank, forming a cycle. The single-membrane electrodialysis anion exchange solution enters a neutralization tank, and the nanofiltration permeate also enters the neutralization tank for pH adjustment before entering the biological treatment unit. The effluent from the biological treatment unit flows into the effluent monitoring tank. Depending on the water quality, the effluent from the neutralization tank can also directly enter the effluent monitoring tank via a branch line.

[0048] Wastewater from a certain EDTA treatment process has the following characteristics: COD concentration of 500 mg / L, sulfate ion concentration of 400 mg / L, chloride ion concentration of 600 mg / L, total salt content of 2200 mg / L, ammonia nitrogen concentration of 40 mg / L, total nitrogen concentration of 80 mg / L, calcium ion concentration of 20 mg / L, magnesium ion concentration of 10 mg / L, pH of 8, and influent flow rate of 2 t / h.

[0049] Catalyst I: Initial preparation of powdered activated carbon (wood-based activated carbon powder, 200 mesh, specific surface area 830 m²) 2 / g (average pore size 2.5nm), binder sodium silicate, and water are mixed in a mass ratio of 65:5:30, and then kneaded, dried, shaped, and cured at low temperature to form a carrier material; an impregnation solution is prepared using copper nitrate, cerium nitrate, and palladium chloride at elemental proportions of 6.0%, 1.0%, and 0.3% of the total mass of the catalyst, respectively; the catalyst is impregnated with an equal volume of this solution for 3 hours, then dried at 80℃ for 12 hours, calcined under nitrogen protection at 580℃ for 5 hours, and then removed after the temperature drops to room temperature to obtain catalyst I.

[0050] Secondary preparation of catalyst I: The reflux liquid generated from the catalytic ozone oxidation process was used as the impregnation liquid stock solution. The reflux liquid was concentrated and separated three times by nanofiltration and single-membrane electrodialysis to obtain the final concentrate. Soluble active metal salts (copper nitrate, cerium nitrate, palladium chloride) were added to the final concentrate to replenish the active metals lost by the membrane. After the addition of the soluble active metal salts, copper, cerium, and palladium (by element) accounted for 6.0%, 1.0%, and 0.3% of the total mass of the catalyst, respectively, to obtain the final impregnation liquid. The carrier material was impregnated with an equal volume of this impregnation liquid. The preparation of the carrier material was the same as that of the initial preparation of catalyst I. The drying and calcination after impregnation were also the same as those of the initial preparation of catalyst I, and finally catalyst I was obtained again.

[0051] Based on the EDTA wastewater quality, catalyst II is a composite catalyst of copper sulfate and cerium nitrate. It is added according to the mass ratio of metal elements in catalyst II to COD in the wastewater to be treated of 17:500. The mass concentration ratio of copper to cerium (by element) in catalyst II is 15:2. The calculated mass concentrations of copper and cerium (by element) are 15 mg / L and 2 mg / L, respectively.

[0052] The aforementioned EDTA wastewater first enters a hardening tank. Reagents are added at a concentration of 24 mg / L sodium hydroxide and 60 mg / L sodium carbonate. After clarification, the calcium ion concentration in the supernatant decreases to below 3 mg / L, and the magnesium ion concentration to below 2 mg / L, while other parameters remain unchanged. The effluent then enters a regulating tank. In the regulating tank, the solution is mixed with the effluent from the regeneration unit and liquid-phase catalyst II. The catalyst is added according to the above proportions, and hydrochloric acid is added to adjust the pH to 5.8, at which point the chloride ion concentration is 680 mg / L. Sodium chloride is then added at a concentration of 860 mg / L to bring the chloride ion concentration in the solution to approximately 1200 mg / L. The effluent from the regulating tank then enters the catalytic ozone oxidation unit. In the catalytic ozone oxidation unit, catalyst I is filled to 3 / 5 of the total unit volume, the reaction time is 30 minutes, and the ozone dosage is 300 mg / L. The ozone utilization rate is calculated based on the effluent ozone concentration. The utilization rate is 99.1%. The effluent from the catalytic ozone oxidation unit enters the nanofiltration membrane, which has a pore size of 1.3 nm and a permeate rate of 70.4%. Metal catalysts, sulfates, and large organic molecules are retained and enter the concentrate side, while the vast majority of sodium, potassium, chloride ions, ammonia nitrogen, and small organic molecules permeate through the nanofiltration membrane into the permeate side. 25% of the nanofiltration concentrate enters the single-mode electrodialysis, and the remainder flows to the equalization tank. The mother liquor from the single-mode electrodialysis is also sent to the equalization tank. The anion exchange solution, like the nanofiltration permeate, flows to the neutralization tank. The pH in the neutralization tank is adjusted to 6.5 by adding NaOH. At this point, the water quality COD is 38 mg / L, total salt content is 4331 mg / L, ammonia nitrogen is 7 mg / L, and total nitrogen is 24 mg / L, meeting the requirements of the "Emission Standard of Pollutants for Petroleum Refining Industry" (GB31570-2015). It can bypass the biological treatment unit's influent and effluent monitoring tank via a secondary line and be discharged in compliance with standards. The daily loss rate of metals through the dual membranes is less than 0.3%. In the initial stage of the entire process operation, the removal effect of pollutants in each unit is shown in Table 1, and the catalytic ozone oxidation treatment efficiency is shown in Table 2.

[0053] Table 1

[0054]

[0055] Table 2

[0056]

[0057] As shown in Table 2, for the difficult-to-treat MDEA wastewater, the catalytic ozone oxidation unit in this embodiment achieved a COD removal rate of 90.5%, a total nitrogen removal rate of 69.7%, and an ozone utilization rate of 99.1%. Based on the ozone dosage and COD removal efficiency of the ozone oxidation unit, approximately 1.14g of COD is removed per 1g of ozone.

[0058] Assuming the daily metal loss rate through the double membrane is 0.3%, and no catalyst II is replenished during the loss period, as the device operates, catalyst I will also experience metal loss, with the metal transferring to the liquid phase. The change in the treatment efficiency of the catalytic ozone oxidation unit with operating time is shown in Table 3.

[0059] Table 3

[0060]

[0061] As shown in Tables 2 and 3, after two months of overall operation, the COD removal rate, total nitrogen removal rate, and ozone utilization rate did not decrease but instead slightly increased. This is because the metals lost from catalyst I were transferred to the liquid phase, especially precious metals and rare earth metals, thus promoting the treatment efficiency of the liquid phase catalyst and improving the overall treatment efficiency. As the operating time increased, the amount of metal lost from catalyst I into the liquid phase gradually increased. Since the daily metal loss rate of the dual-membrane system was 0.3%, the overall amount of metal catalyst decreased, leading to a decrease in COD removal rate, total nitrogen removal rate, and ozone utilization rate. Because catalyst II was not replenished, it was completely lost after 12 months based on the daily metal loss rate. However, at 12 and 24 months, the catalytic ozone oxidation still maintained a COD removal rate of over 60%, indicating that a large amount of active metal components remained in the system. Testing revealed that the content of precious metals and rare earth metals in the active components remained at a high level. This is because noble metals and rare earth metals have large relative molecular masses and atomic radii, making them less prone to loss through the double membrane than transition metals. In this case, the reflux liquid in the system should be used for secondary preparation of catalyst I. This serves two purposes: first, to improve the catalytic efficiency of the solid catalyst; and second, to better protect the noble metals and rare earth metals by utilizing the loading of the solid catalyst, thereby reducing their loss.

[0062] As can be seen from this embodiment, the multiphase catalytic ozone oxidation method provided by the present invention can treat highly difficult EDTA wastewater very efficiently, and effectively remove COD, ammonia nitrogen and total nitrogen. The catalyst used can be basically recycled.

[0063] Example 2

[0064] use Figure 1 The process shown is for treating MDEA wastewater.

[0065] A certain MDEA wastewater has the following characteristics: COD concentration of 800 mg / L, sulfate ion concentration of 600 mg / L, chloride ion concentration of 3500 mg / L, total salt content of 6500 mg / L, ammonia nitrogen concentration of 20 mg / L, total nitrogen concentration of 150 mg / L, calcium ion concentration of 40 mg / L, magnesium ion concentration of 20 mg / L, pH of 9, and influent flow rate of 2 t / h.

[0066] Initial preparation of catalyst I: Powdered activated carbon (fruit shell activated carbon powder, 250 mesh, specific surface area 900 m²) was prepared. 2 / g (average pore size 2.9nm), binder aluminum dihydrogen phosphate, and water were mixed in a mass ratio of 63:7:30, and then kneaded, dried, shaped, and cured at low temperature to form a carrier material; an impregnation solution was prepared using copper nitrate, cerium nitrate, and palladium chloride at elemental proportions of 8.0%, 1.5%, and 0.4% of the total mass of the catalyst, respectively; the catalyst was impregnated with this solution in equal volume for 4 hours, then dried at 90℃ for 13 hours, and then calcined under nitrogen protection at 550℃ for 6 hours. After the temperature was reduced to room temperature, the catalyst was removed to obtain catalyst I.

[0067] Secondary preparation of catalyst I: The reflux liquid generated from the catalytic ozone oxidation process was used as the impregnation liquid stock solution. The reflux liquid was concentrated and separated three times by nanofiltration and single-membrane electrodialysis to obtain the final concentrate. Soluble active metal salts (copper nitrate, cerium nitrate, palladium chloride) were added to the final concentrate to compensate for the active metals lost by the membrane. After the addition of soluble active metal salts, copper, cerium, and palladium (by element) accounted for 8.0%, 1.5%, and 0.4% of the total mass of the catalyst, respectively, to obtain the final impregnation liquid. The carrier material was impregnated with an equal volume of this impregnation liquid. The preparation of the carrier material was the same as that of the initial preparation of catalyst I. The drying and calcination after impregnation were also the same as those of the initial preparation of catalyst I, and finally catalyst I was obtained again.

[0068] Based on the EDTA wastewater quality, catalyst II uses copper sulfate and cerium nitrate. The catalyst is added at a mass ratio of 9:400 between the metal elements in catalyst II and the COD in the wastewater to be treated. The mass concentration ratio of copper to cerium (by element) in catalyst II is 8:1. The calculated mass concentrations of copper and cerium (by element) are 16 mg / L and 2 mg / L, respectively.

[0069] The aforementioned EDTA wastewater first enters a hardening tank. Reagents are added at a concentration of 50 mg / L sodium hydroxide and 100 mg / L sodium carbonate. After clarification, the calcium ion concentration in the supernatant decreases to below 5 mg / L, and the magnesium ion concentration to below 3 mg / L, while other parameters remain unchanged. The effluent then enters a regulating tank. In the regulating tank, the solution is mixed with the effluent from the regeneration unit and liquid-phase catalyst II. The catalyst is added according to the above proportions, and hydrochloric acid is added to adjust the pH to 5.7. At this point, the chloride ion concentration is 3715 mg / L, requiring no additional chloride addition. The effluent from the regulating tank then enters the catalytic ozone oxidation unit. In the catalytic ozone oxidation unit, catalyst I is filled to 4 / 5 of the total unit volume, the reaction time is 30 minutes, and the ozone dosage is 400 mg / L. The ozone utilization rate was calculated to be 99.3% based on the ozone concentration in the effluent. The effluent from the catalytic ozone oxidation unit enters the nanofiltration membrane, which has a pore size of 1.3 nm and a permeate rate of 66.7%. Metal catalysts, sulfates, and large molecular organic matter are retained and enter the concentrate side, while most sodium, potassium, chloride ions, ammonia nitrogen, and small molecular organic matter permeate through the nanofiltration membrane and enter the permeate side. 38.9% of the nanofiltration concentrate enters the single-mode electrodialysis, and the remainder flows to the equalization tank. The mother liquor from the single-mode electrodialysis is also sent to the equalization tank. The anion exchange solution flows to the neutralization tank in the same way as the nanofiltration permeate. The pH in the neutralization tank is adjusted to 6.4 by adding NaOH. At this point, the wastewater COD is 120 mg / L, ammonia nitrogen is 6 mg / L, total nitrogen is 42 mg / L, and total salt content is 7505 mg / L. To ensure the treatment efficiency of the subsequent nitrification and denitrification bacteria in the biological treatment unit, domestic sewage was added at a rate of 3 t / h for salt dilution. The domestic sewage contained approximately 400 mg / L COD, 20 mg / L ammonia nitrogen, 42 mg / L total nitrogen, 300 mg / L sulfate, and a total salt content of 2100 mg / L. The wastewater ultimately met discharge standards after passing through the A / O and post-denitrification processes in the biological treatment unit. The daily metal loss rate through the dual membrane was less than 0.3%. The removal efficiency of pollutants in each unit during the initial operation of the entire process is shown in Table 4, and the catalytic ozone oxidation treatment efficiency is shown in Table 5.

[0070] Table 4

[0071]

[0072] Table 5

[0073]

[0074] As shown in Table 5, for the difficult-to-treat MDEA wastewater, the catalytic ozone oxidation unit in this embodiment achieved a COD removal rate of 81.5%, a total nitrogen removal rate of 71.3%, and an ozone utilization rate of 99.3%. Based on the ozone dosage and COD removal efficiency of the ozone oxidation unit, approximately 1.26g of COD was removed per 1g of ozone.

[0075] Assuming a daily metal loss rate of 0.3% through the dual membrane, copper, a lower-priced transition metal, is replenished daily at 0.3% of the total mass concentration of catalyst II (18 mg / L), without replenishment of rare earth metal cerium. The change in the treatment efficiency of the catalytic ozone oxidation unit with operating time is shown in Table 6.

[0076] Table 6

[0077]

[0078] As shown in Tables 5 and 6, similar to Example 1, after two months of overall operation, the COD removal rate, total nitrogen removal rate, and ozone utilization rate did not decrease but instead increased slightly. With longer operation time, the COD removal rate, total nitrogen removal rate, and ozone utilization rate all decreased to varying degrees, but the decrease was less than in Example 1. This is because transition metal copper was replenished during operation according to the loss rate. To improve the catalytic efficiency of the solid catalyst and better protect precious and rare earth metals by utilizing the loading of the solid catalyst, the reflux liquid within the system should be used for secondary preparation of catalyst I after 24 months of operation.

[0079] As can be seen from this embodiment, for wastewater under different working conditions, this embodiment achieves efficient treatment of specific wastewater by adjusting a series of methods such as catalyst dosage, catalytic ozone reaction parameters, nanofiltration membrane water production rate, single membrane electrodialysis operation parameters, and biochemical deep treatment, and the effluent meets the requirements of the "Emission Standard of Pollutants for Petroleum Refining Industry" (GB31570-2015).

[0080] Example 3

[0081] The water quality for treating EDTA wastewater was the same as in Example 1. The carrier material for the initial preparation of catalyst I was the same as in Example 1, and the impregnation and calcination methods were also the same. The difference was that the impregnation solution was prepared using copper nitrate and palladium chloride at 7.0% and 0.3% of the total catalyst mass, respectively. The secondary preparation method for catalyst I was the same as in Example 1. Catalyst II was the same as in Example 1, using copper sulfate and cerium nitrate, added at elemental copper and cerium mass concentrations of 15 mg / L and 2 mg / L, respectively.

[0082] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 1. The treatment efficiency of catalytic ozone oxidation is shown in Table 7.

[0083] Table 7

[0084]

[0085] As shown in Table 7, compared with Example 1, the COD removal rate and ozone utilization rate of homogeneous catalytic wet oxidation did not change much, only slightly decreased, but the total nitrogen removal rate decreased from 69.7% to 56.6%.

[0086] Example 4

[0087] The water quality for treating EDTA wastewater was the same as in Example 1. The carrier material for the initial preparation of catalyst I was the same as in Example 1, as were the impregnation and calcination methods. The difference was that the impregnation solution was prepared using copper nitrate and cerium nitrate at concentrations of 6.2% and 1.1% of the total catalyst mass, respectively. The secondary preparation method for catalyst I was the same as in Example 1. Catalyst II was the same as in Example 1, using copper sulfate and cerium nitrate, added at concentrations of 15 mg / L and 2 mg / L of elemental copper and cerium, respectively.

[0088] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 1. The treatment efficiency of catalytic ozone oxidation is shown in Table 8.

[0089] Table 8

[0090]

[0091] As shown in Table 8, compared with Example 1, the total nitrogen removal rate and ozone utilization rate of homogeneous catalytic wet oxidation did not change much, only slightly decreased, and the COD removal rate decreased from 90.5% to 79.4%.

[0092] Example 5

[0093] The water quality for treating EDTA wastewater was the same as in Example 1. The carrier material for the initial preparation of catalyst I was the same as in Example 1, as were the impregnation and calcination methods. The difference was that the impregnation solution was prepared using copper nitrate, cerium nitrate, and platinum chloride at concentrations of 6.0%, 1.0%, and 0.3% of the total catalyst mass, respectively. The secondary preparation method for catalyst I was the same as in Example 1. Catalyst II was the same as in Example 1, using copper sulfate and cerium nitrate, added at concentrations of 15 mg / L and 2 mg / L of elemental copper and cerium, respectively.

[0094] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 1. The treatment efficiency of catalytic ozone oxidation is shown in Table 9.

[0095] Table 9

[0096]

[0097] As shown in Table 9, compared with Example 1, the COD removal rate of homogeneous catalytic wet oxidation increased slightly, the ozone utilization rate remained basically unchanged, and the total nitrogen removal rate decreased from 69.7% to 54.6%.

[0098] Example 6

[0099] The water quality for treating EDTA wastewater was the same as in Example 1. The carrier material for the initial preparation of catalyst I was the same as in Example 1, as were the impregnation and calcination methods. The difference was that the impregnation solution was prepared using ferric chloride, cerium nitrate, and palladium chloride at elemental iron, cerium, and palladium concentrations of 6.0%, 1.0%, and 0.3% of the total catalyst mass, respectively. The secondary preparation method for catalyst I was the same as in Example 1. Catalyst II was the same as in Example 1, using copper sulfate and cerium nitrate, added at elemental copper and cerium mass concentrations of 15 mg / L and 2 mg / L, respectively.

[0100] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 1. The treatment efficiency of catalytic ozone oxidation is shown in Table 10.

[0101] Table 10

[0102]

[0103] As shown in Table 10, compared with Example 1, the COD removal rate of homogeneous catalytic wet oxidation increased slightly, the ozone utilization rate remained basically unchanged, and the total nitrogen removal rate decreased from 69.7% to 55.3%.

[0104] Example 7

[0105] The water quality for treating EDTA wastewater was the same as in Example 1. Catalyst I was the same as in Example 1. The secondary preparation method for Catalyst I was the same as in Example 1. Catalyst II consisted of manganese chloride and cerium nitrate, added at elemental manganese and cerium concentrations of 15 mg / L and 2 mg / L, respectively.

[0106] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 1. The treatment efficiency of catalytic ozone oxidation is shown in Table 11.

[0107] Table 11

[0108]

[0109] As shown in Table 11, compared with Example 1, the COD removal rate and ozone utilization rate of homogeneous catalytic wet oxidation increased slightly, while the total nitrogen removal rate decreased from 69.7% to 58.5%.

[0110] Example 8

[0111] The water quality for treating EDTA wastewater was the same as in Example 1. The carrier material for the initial preparation of catalyst I was the same as in Example 1, as were the impregnation and calcination methods. The difference was that the impregnation solution was prepared using copper nitrate, cerium nitrate, and rhodium chloride at concentrations of 6.0%, 1.0%, and 0.3% of the total catalyst mass, respectively. The secondary preparation method for catalyst I was the same as in Example 1. Catalyst II was the same as in Example 1, using copper sulfate and cerium nitrate, added at concentrations of 15 mg / L and 2 mg / L of elemental copper and cerium, respectively.

[0112] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 1. The treatment efficiency of catalytic ozone oxidation is shown in Table 12.

[0113] Table 12

[0114]

[0115] As shown in Table 12, compared with Example 1, the COD removal rate, total nitrogen removal rate and ozone utilization rate of homogeneous catalytic wet oxidation all increased, but the increase was small.

[0116] Example 9

[0117] The water quality for treating EDTA wastewater was the same as in Example 1. The carrier material for the initial preparation of catalyst I was the same as in Example 1, as were the impregnation and calcination methods. The difference was that the impregnation solution was prepared using copper nitrate, lanthanum nitrate, and palladium chloride at concentrations of 6.0%, 1.0%, and 0.3% of the total catalyst mass, respectively. The secondary preparation method for catalyst I was the same as in Example 1. Catalyst II used copper sulfate and lanthanum nitrate, added at concentrations of 15 mg / L for copper and 2 mg / L for lanthanum.

[0118] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 1. The treatment efficiency of catalytic ozone oxidation is shown in Table 13.

[0119] Table 13

[0120]

[0121] As shown in Table 13, compared with Example 1, the COD removal rate and total nitrogen removal rate of homogeneous catalytic wet oxidation were slightly improved, while the ozone utilization rate remained basically unchanged.

[0122] Example 10

[0123] The water quality for treating MDEA wastewater was the same as in Example 2. The carrier material for the initial preparation of catalyst I was the same as in Example 2, as were the impregnation and calcination methods. The difference was that the impregnation solution was prepared using copper nitrate, cerium nitrate, and palladium chloride at concentrations of 10.0%, 2%, and 0.5% of the total catalyst mass, respectively. The secondary preparation method for catalyst I was the same as in Example 2. Catalyst II used copper sulfate and cerium nitrate, added at concentrations of 20 mg / L and 3 mg / L of elemental copper and cerium, respectively.

[0124] The process route, implementation steps, and reaction parameters of catalytic ozone oxidation are the same as those in Example 2. The treatment efficiency of catalytic ozone oxidation is shown in Table 14.

[0125] Table 14

[0126]

[0127] As shown in Table 14, compared with Example 2, increasing the amount of catalyst added did not significantly improve the COD removal rate, total nitrogen removal rate, and ozone utilization rate of homogeneous catalytic wet oxidation.

[0128] Example 11

[0129] The water quality of the treated MDEA wastewater was the same as in Example 2. Catalysts I and II were also the same as in Example 2. The process route, implementation steps, and reaction parameters of catalytic ozone oxidation were basically the same as in Example 2, the only difference being that the ozone dosage was increased to 500 mg / L. The catalytic ozone oxidation treatment efficiency is shown in Table 15.

[0130] Table 15

[0131]

[0132] As shown in Table 15, compared with Example 2, increasing the ozone dosage of the catalytic ozone oxidation unit improved the COD removal rate of homogeneous catalytic wet oxidation to a certain extent, but the improvement in total nitrogen removal rate was small, and the ozone utilization rate was slightly reduced.

[0133] Comparative Example 1

[0134] The water quality of the treated EDTA wastewater was the same as in Example 1. Catalyst I was the same as in Example 1. The difference was that no liquid-phase catalyst was added, and the catalytic ozone oxidation process did not include nanofiltration and single-membrane electrodialysis, nor could it recover and utilize the active metals. Other implementation steps and reaction parameters were the same as in Example 1. The catalytic ozone oxidation treatment efficiency is shown in Table 16.

[0135] Table 16

[0136]

[0137] As shown in Table 16, compared with Example 1, the lack of liquid-phase catalyst supplementation resulted in a decrease in COD removal rate, total nitrogen removal rate, and ozone utilization rate of the catalytic ozone oxidation unit, but overall they still remained at a high level. Furthermore, Table 17 shows the change in the treatment efficiency of the catalytic ozone oxidation unit with operating time.

[0138] Table 17

[0139]

[0140] As shown in Tables 16 and 17, after two months of overall operation, the COD removal rate, total nitrogen removal rate, and ozone utilization rate all showed a slight decrease. With continued operation, the loss rate of solid catalyst I gradually increased. Due to the lack of dual-membrane recovery of active metals, the overall treatment efficiency of the catalytic ozone oxidation unit gradually declined. After 24 months, both the COD removal rate and total nitrogen removal rate were at low levels, and the ozone utilization rate was only 66.2%, resulting in a relatively high ozone concentration in the effluent from the catalytic ozone oxidation unit.

[0141] Comparative Example 2

[0142] The water quality of the EDTA wastewater treated was the same as in Example 1. No solid-phase catalyst was used; only a liquid-phase catalyst was added. Catalyst II consisted of copper sulfate and cerium nitrate, added at elemental copper and cerium mass concentrations of 15 mg / L and 2 mg / L, respectively. The process route, implementation steps, and reaction parameters for catalytic ozone oxidation were the same as in Example 1. The catalytic ozone oxidation treatment efficiency is shown in Table 18.

[0143] Table 18

[0144]

[0145] As shown in Table 18, compared with Example 1, the COD removal rate, total nitrogen removal rate and ozone utilization rate of the catalytic ozone oxidation unit all decreased to varying degrees.

[0146] Comparative Example 3

[0147] The water quality of the EDTA wastewater treated was the same as in Example 1. The solid-phase catalyst and liquid-phase catalyst were the same as in Example 1. The process route, implementation steps, and reaction parameters of catalytic ozone oxidation were the same as in Example 1, the only difference being that no chloride salt was added, i.e., the chloride ion concentration was maintained at 680 mg / L. The catalytic ozone oxidation treatment efficiency is shown in Table 19.

[0148] Table 19

[0149]

[0150] As shown in Table 19, compared with Example 1, the total nitrogen removal rate of the catalytic ozone oxidation unit decreased significantly, while the COD removal rate and ozone utilization rate decreased slightly.

[0151] Comparative Example 4

[0152] The water quality of the treated EDTA wastewater was the same as in Example 1. No solid-phase catalyst or liquid-phase catalyst was used; ozone oxidation alone was employed to treat the EDTA wastewater. The reaction parameters for ozone oxidation alone were the same as in Example 1, and the ozone oxidation treatment efficiency is shown in Table 20.

[0153] Table 20

[0154]

[0155] As shown in Table 20, compared with Example 1, the COD removal rate, total nitrogen removal rate and ozone utilization rate of the catalytic ozone oxidation unit are very low. This is because EDTA is a recalcitrant organic compound, and ozone alone cannot effectively remove it.

Claims

1. A wastewater treatment process, characterized in that, It includes a hardening tank, an equalization tank, a catalytic ozone oxidation unit, nanofiltration, a single-membrane electrodialysis unit, a neutralization tank, a biochemical unit, and an effluent monitoring tank. Wastewater first undergoes hardening removal in the hardening tank and then enters the equalization tank. It is mixed with catalyst II from the multiphase ozone oxidation catalyst composition and the pH is adjusted before entering the catalytic ozone oxidation unit, which is filled with catalyst I. The effluent from the catalytic ozone oxidation unit enters the nanofiltration tank. Part of the nanofiltration concentrate is treated by single-membrane electrodialysis, and part is directly entered into the equalization tank. The mother liquor obtained from single-membrane electrodialysis is also entered into the equalization tank, forming a cycle. The single-membrane electrodialysis anion solution enters the neutralization tank, and the nanofiltration permeate also enters the neutralization tank for mixing and pH adjustment. Then it enters the biological unit. The effluent from the biological unit flows into the effluent monitoring tank, or, depending on the water quality, the effluent from the neutralization tank enters the effluent monitoring tank directly via a branch line. The chloride ion content in the pH-adjusted tank should be no less than 1200 mg / L. If it is less than 1200 mg / L, chloride salts are added for further adjustment. The nanofiltration process has a water production rate of 60%–85%, with a membrane pore size between 1 and 5 nm. It retains metals from catalyst II, metals lost from catalyst I, high-valence salts, and large-molecule organic matter, which then enter the concentrate side. 1%–40% of the nanofiltration concentrate enters a single-membrane electrodialysis system. The single-membrane electrodialysis system uses only anion exchange membranes. Under the action of the electrode and the anion exchange membrane, high-valence anions and small-molecule organic matter in the nanofiltration concentrate permeate through the anion exchange membrane into the concentrate side, while the cationic catalyst remains in the mother liquor for reuse. Catalyst I is a supported solid catalyst, comprising an active component and a support. The active component includes a transition metal selected from one or more of iron, copper, zinc, manganese, cobalt, and nickel. The support is activated carbon. Based on the total weight of catalyst I, the transition metal accounts for 1% to 15% of the total catalyst weight. Catalyst I also contains a noble metal, with a mass ratio of noble metal element to transition metal element of 1:5 to 1:

200. The noble metal is selected from one or more of platinum, palladium, rhodium, silver, and ruthenium. The catalyst is loaded with rare earth metals, wherein the mass ratio of rare earth metal elements to transition metal elements is 1:2 to 1:50, and the rare earth metals are selected from one or more of cerium, praseodymium, lanthanum, and neodymium; the catalyst II comprises a soluble transition metal salt and a soluble rare earth metal salt, wherein the soluble transition metal salt is selected from at least one of copper, zinc, manganese, and cobalt metal salts, and the soluble rare earth metal salt is selected from at least one of cerium, praseodymium, lanthanum, and neodymium metal salts; the mass ratio of transition metal elements to rare earth metal elements in the catalyst II is 5:1 to 50:1; When the reaction system is started, catalyst II is added to the equalization tank at a mass ratio of COD in wastewater to metal elements in catalyst II of 500:1 to 2:1; the loading volume of catalyst I is 1 / 5 to 4 / 5 of the total volume of the reaction unit; the ozone dosage is 0.3 to 2 times the amount of oxidant required based on the COD value of the wastewater. The heterogeneous ozone oxidation catalyst composition is prepared by the following method: catalyst II is dissolved in water to form a homogeneous catalyst, and catalyst I is prepared by the following method: activated carbon, necessary binder and water are mixed, dried, shaped and cured at low temperature to form a carrier material, the active components are loaded by impregnation, and the catalyst I is obtained by drying and calcination; the two are mixed to obtain the heterogeneous ozone oxidation catalyst composition. In the preparation of catalyst I, the impregnation solution used during impregnation is the reaction reflux liquid after the ozone oxidation reaction catalyzed by the multiphase ozone oxidation catalyst composition; the method for preparing the impregnation solution from the reflux liquid is as follows: the reflux liquid is concentrated by nanofiltration to remove monovalent cations and chloride ions, the nanofiltration concentrate is then subjected to single-mode electrodialysis to remove sulfate ions and other high-valent anions, the single-mode electrodialysis mother liquor is taken and subjected to nanofiltration again, and this method is repeated to concentrate 1 to 5 times to obtain the final concentrate; after adding metal salt to the final concentrate, the impregnation solution is obtained.

2. The process method according to claim 1, characterized in that, The catalyst II exists in a form dissolved in water.

3. The process method according to claim 1, characterized in that, The catalytic ozone oxidation reaction time is 10 to 120 minutes.

4. The process method according to claim 1, characterized in that, The biological unit adopts a combination of A / O and post-denitrification processes, and the influent salt concentration of the biological unit does not exceed 5000 mg / L.

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