A homogeneous catalyst for ozone oxidation and a process for wastewater treatment

Abstract

A homogeneous catalyst for ozone oxidation and a process for wastewater treatment are disclosed. The catalyst includes an active component and an auxiliary agent. The active component is a transition metal salt, and the auxiliary agent is a rare earth metal salt. The wastewater treatment process includes: after hardening removal, the wastewater enters an equalization tank, is mixed with the homogeneous catalyst, and after acidity adjustment, it enters a catalytic ozone oxidation unit. The effluent enters a nanofiltration unit. Part of the nanofiltration concentrate enters a single-membrane electrodialysis unit, and part 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 and the nanofiltration permeate enter a neutralization tank, and then enter a biological treatment unit. The effluent from the biological treatment unit flows into an 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. The homogeneous catalyst for ozone oxidation of this invention adds rare earth metals as auxiliary agents to the transition metal catalyst, which improves the hydroxyl radical conversion rate and catalytic oxidation efficiency, thereby significantly improving the removal rate of organic matter and total nitrogen. At the same time, the improved ozone utilization rate significantly reduces the amount of ozone exhaust gas generated, and also reduces the environmental risks associated with ozone oxidation technology.

Description

Technical Field

[0001] This invention relates to a homogeneous catalyst for ozone oxidation and a process for wastewater treatment using the same catalyst, 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 homogeneous ozone oxidation catalyst and a process for wastewater treatment using the catalyst. This fully leverages the advantages of homogeneous catalytic ozone oxidation technology, such as high ozone utilization, strong organic matter removal capacity, and low ozone tail gas generation. Simultaneously, it achieves the simultaneous removal of ammonia nitrogen and total nitrogen, as well as the recycling of the catalyst, reducing the environmental risks associated with ozone oxidation technology and broadening its application scenarios.

[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 homogeneous ozone oxidation catalyst, comprising an active component and an auxiliary agent, wherein the active component is a transition metal salt selected from one or more metal salts of iron, copper, zinc, manganese, cobalt and nickel, preferably a composite metal salt of iron and copper, and the auxiliary agent is a rare earth metal salt selected from one or more metal salts of cerium, praseodymium, lanthanum and neodymium, preferably a metal salt of cerium.

[0009] Furthermore, the mass ratio of transition metal elements to rare earth metal elements in the homogeneous ozone oxidation catalyst is 2 to 50:1, preferably 5 to 10:1.

[0010] Furthermore, the homogeneous ozone oxidation catalyst exists in a water-soluble form.

[0011] The second aspect of the present invention aims to provide a method for wastewater treatment using the above-mentioned ozone oxidation homogeneous catalyst, comprising the step of contacting the homogeneous catalyst with COD-containing wastewater.

[0012] Furthermore, in the above method, the amount of homogeneous catalyst added is based on a mass ratio of COD in the wastewater to metal elements in the homogeneous catalyst of 500:1 to 2:1.

[0013] 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.

[0014] The technical objective of the third aspect of this invention is to provide a wastewater treatment process, comprising 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. After being mixed with a homogeneous ozone oxidation catalyst and having its acidity adjusted, the wastewater enters the catalytic ozone oxidation unit. Wastewater is treated under the action of the homogeneous ozone oxidation catalyst. The effluent from the catalytic ozone oxidation unit enters the nanofiltration tank. Part of the nanofiltration concentrate enters the single-membrane electrodialysis unit for treatment, 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 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.

[0015] 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.

[0016] Furthermore, the homogeneous ozone oxidation catalyst comprises an active component and an auxiliary agent. The active component is a transition metal salt, selected from one or more metal salts of iron, copper, zinc, manganese, cobalt, and nickel, preferably a composite metal salt of iron and copper. The auxiliary agent is a rare earth metal salt, selected from one or more metal salts of cerium, praseodymium, lanthanum, and neodymium, preferably a metal salt of cerium. The homogeneous ozone oxidation catalyst is added to the catalytic ozone oxidation unit in a water-soluble form.

[0017] Furthermore, the mass ratio of transition metal elements to rare earth metal elements in the homogeneous ozone oxidation catalyst is 2–50:1, preferably 5–10:1. The homogeneous ozone oxidation catalyst is added to the equalization tank at a wastewater COD to catalyst mass ratio of 500:1–2:1 during reaction system startup.

[0018] Furthermore, the ozone dosage 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.

[0019] Furthermore, the pH in the conditioning tank is adjusted to 3-6, preferably 4-5.5, using acid; the acid used is hydrochloric acid or sulfuric acid, preferably hydrochloric acid.

[0020] 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.

[0021] Those skilled in the art should understand that in catalytic ozone oxidation systems, rare earth elements, due to their unique 4f electron shell structure and lanthanide contraction characteristics, provide a large number of oxidation active sites in the catalytic reaction. Their combination with transition metals has a synergistic effect, accelerating electron transfer between the catalyst and reactants and promoting the continuous generation of hydroxyl radicals through a free radical chain reaction. In the presence of a large amount of chloride ions, it also promotes the generation of free residual chlorine (ClO₂ in water). - The generation of chlorine (such as HClO and Cl2) and the decomposition of free residual chlorine into hydroxyl radicals and chlorine radicals can accelerate the oxidative decomposition of organic matter and the conversion of ammonia.

[0022] 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, high-valent salts (such as sulfates and carbonates), and large-molecule organic matter (relative molecular mass greater than 200) from the homogeneous catalyst. After retention, the permeate enters the concentrate side, while the metals of the homogeneous catalyst are eventually returned to the equalization tank. The nanofiltration permeate includes small-molecule organic matter and monovalent salts.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) The ozone oxidation homogeneous catalyst of the present invention adds rare earth metals with controllable price as auxiliary agents on the basis of transition metals, which improves the conversion rate of hydroxyl radicals and catalytic oxidation efficiency, thereby greatly improving the organic matter removal rate. At the same time, the improvement of ozone utilization rate greatly reduces the amount of ozone tail gas generated, and also reduces the environmental risks brought about by ozone oxidation technology.

[0030] (2) This invention makes full use of the synergistic effect of rare earth metals and transition metals. By increasing or maintaining a certain chloride ion content in the ozone catalytic system, it better promotes the generation and conversion of free residual chlorine, thereby significantly improving the removal rate of ammonia nitrogen and total nitrogen and broadening the application scenarios of ozone oxidation technology.

[0031] (3) The process method for treating wastewater by catalytic ozone oxidation of the present invention achieves the recovery and recycling of metal catalysts through a combination of acidification (keeping metal salts in a soluble state), nanofiltration and single-membrane electrodialysis, and also achieves salt balance in the homogeneous catalytic ozone oxidation cycle treatment process, thus solving the bottleneck restricting the application and development of homogeneous catalytic ozone oxidation.

[0032] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0033] Figure 1 The process flow diagram for wastewater treatment according to the present invention. Detailed Implementation

[0034] 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.

[0035] Example 1

[0036] The process flow diagram of wastewater treatment is as follows: Figure 1As shown: Wastewater first undergoes hardness removal in a dehardening tank before entering an equalization tank. In the equalization tank, it is mixed with a homogeneous catalyst for ozone oxidation and the acidity is adjusted before entering the catalytic ozone oxidation unit. The effluent from the catalytic ozone oxidation unit enters nanofiltration. Part of the nanofiltration concentrate enters single-membrane electrodialysis treatment, and part enters directly into the equalization tank. The mother liquor obtained from single-membrane electrodialysis 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 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 enter the effluent monitoring tank directly via a branch line.

[0037] MDEA is a recalcitrant compound. A wastewater containing MDEA was treated with the following parameters: COD concentration of 400 mg / L, sulfate ion concentration of 300 mg / L, chloride ion concentration of 700 mg / L, total salt content of 2100 mg / L, ammonia nitrogen concentration of 70 mg / L, total nitrogen concentration of 110 mg / L, calcium ion concentration of 20 mg / L, magnesium ion concentration of 10 mg / L, pH of 9, and influent flow rate of 10 t / h.

[0038] Based on the above wastewater quality, the homogeneous catalyst for the catalytic ozone oxidation unit is a composite catalyst of ferric chloride, copper sulfate, and cerium chloride. The amount of homogeneous catalyst added is based on a mass ratio of COD in the wastewater to the metal elements in the homogeneous catalyst of 80:7. Specifically, the mass concentrations of iron, copper, and cerium are calculated and added at 15 mg / L, 15 mg / L, and 5 mg / L, respectively. The mass ratio of transition metal elements iron and copper to rare earth metal element cerium is 6:1.

[0039] The aforementioned MDEA 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 an equalization tank. In the equalization tank, the solution is mixed with the effluent from the regeneration unit and a homogeneous catalyst. The catalyst is added according to the aforementioned ratio, and hydrochloric acid is added to adjust the pH to 5. At this point, the chloride ion concentration is 780 mg / L. Sodium chloride is then added at a concentration of 650 mg / L to bring the chloride ion concentration in the solution to approximately 1200 mg / L. The effluent from the equalization tank then enters a catalytic ozone oxidation unit. The catalytic ozone oxidation reaction time is 30 minutes, and the ozone dosage is 240 mg / L. Based on the effluent ozone concentration, the ozone utilization rate is calculated to be 96%. The effluent from the catalytic ozone oxidation unit then enters a nanofiltration unit. The filter membrane has a pore size of 1.5 nm and a water production rate of 70.4%. 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. 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 flows to the neutralization tank in the same way as the nanofiltration permeate. The pH in the neutralization tank is adjusted to 6.5 by adding NaOH. The biological treatment tank adopts the A / O process plus post-denitrification. The final effluent COD is 45 mg / L, total salt content is 3895 mg / L, ammonia nitrogen is 4 mg / L, and total nitrogen is 16 mg / L, which meets the requirements of the "Emission Standard of Pollutants for Petroleum Refining Industry" (GB31570-2015) and can be discharged from the effluent monitoring tank in compliance with standards. The daily loss rate of the metal catalyst is less than 0.5%. The removal efficiency of pollutants in each unit is shown in Table 1, and the catalytic ozone oxidation treatment efficiency is shown in Table 2.

[0040] Table 1

[0041]

[0042] Table 2

[0043]

[0044] As shown in Table 2, for difficult-to-treat wastewater containing MDEA, the catalytic ozone oxidation unit in this embodiment achieved a COD removal rate of 72.1%, a total nitrogen removal rate of 66.3%, and an ozone utilization rate of 96%.

[0045] As can be seen from this embodiment, the homogeneous catalyst and process method provided by the present invention can not only maintain the high-efficiency operation of homogeneous catalytic ozone oxidation and achieve effective removal of COD, ammonia nitrogen and total nitrogen, but also achieve catalyst recycling.

[0046] Example 2

[0047] use Figure 1The process shown is used to treat a reverse osmosis concentrate.

[0048] A certain reverse osmosis concentrate has the following characteristics: COD concentration of 180 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 45 mg / L, ammonia nitrogen calcium ion concentration of 40 mg / L, magnesium ion concentration of 20 mg / L, pH of 7, and influent flow rate of 10 t / h.

[0049] Based on the above-mentioned reverse osmosis concentrate water quality, the homogeneous catalyst of the catalytic ozone oxidation unit is a composite catalyst of ferric chloride, copper sulfate and cerium nitrate. The amount of homogeneous catalyst added is based on a mass ratio of COD in the wastewater to the metal elements in the homogeneous catalyst of 10:1. Specifically, the mass concentrations of iron, copper and cerium are added at 8 mg / L, 8 mg / L and 2 mg / L respectively, and the mass ratio of transition metal elements iron and copper to rare earth metal element cerium is 8:1.

[0050] The reverse osmosis concentrate first enters the hardening tank, where 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 the equalization tank. In the equalization tank, the solution is mixed with the effluent from the regeneration unit and a homogeneous catalyst. The catalyst is added according to the above proportions, and hydrochloric acid is added to adjust the pH to 5.2. At this point, the chloride ion concentration is 3715 mg / L, requiring no additional chloride addition. The effluent from the equalization tank then enters the catalytic ozone oxidation unit. The catalytic ozone oxidation reaction time is 35 minutes, and the ozone dosage is 150 mg / L. Based on the effluent ozone concentration, the ozone utilization rate is calculated to be 94%. The effluent from the catalytic ozone oxidation unit then enters the nanofiltration unit, where the nanofiltration membrane has a pore size of 1.5 nm. The water production rate was 67.2%. Metal catalysts, sulfates, and large molecular organic matter were retained and flowed into the concentrate side, while most sodium, potassium, chloride ions, ammonia nitrogen, and small molecular organic matter permeated through the nanofiltration membrane and entered the product water side. 33.3% of the nanofiltration concentrate entered the single-mode electrodialysis, and the remainder flowed to the equalization tank. The mother liquor from the single-mode electrodialysis was also sent to the equalization tank. The anion exchange solution flowed to the neutralization tank in the same way as the nanofiltration product water. The pH in the neutralization tank was adjusted to 6.4 by adding NaOH. At this point, the COD in the neutralization tank was 45 mg / L, the total salt content was 7212 mg / L, the ammonia nitrogen was 5 mg / L, and the total nitrogen was 13 mg / L, which met the requirements of the "Emission Standard of Pollutants for Petroleum Refining Industry" (GB31570-2015). It can be discharged from the effluent monitoring tank via a bypass line, bypassing the biological treatment unit. The daily loss rate of the metal catalyst was less than 0.5%. The removal efficiency of pollutants in each unit is shown in Table 3, and the catalytic ozone oxidation treatment efficiency is shown in Table 4.

[0051] Table 3

[0052]

[0053] Table 4

[0054]

[0055] 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, and single-membrane electrodialysis operation parameters, and the effluent meets the requirements of the "Emission Standard of Pollutants for Petroleum Refining Industry" (GB31570-2015).

[0056] Example 3

[0057] use Figure 1 The process shown is for treating a certain large red 3R wastewater.

[0058] A certain type of wastewater (specifically, a 3R type) has the following characteristics: COD concentration of 500 mg / L, sulfate ion concentration of 300 mg / L, chloride ion concentration of 3500 mg / L, total salt content of 6100 mg / L, ammonia nitrogen concentration of 50 mg / L, total nitrogen concentration of 150 mg / L, calcium ion concentration of 20 mg / L, magnesium ion concentration of 10 mg / L, pH of 9, and influent flow rate of 10 t / h. Based on the wastewater quality, the same catalyst and dosage concentration as in Example 1 were selected.

[0059] The wastewater treatment process is basically the same as in Example 1, except that the chloride ion content of the Dahong 3R wastewater is 3500 mg / L, and no additional chloride salt needs to be added to the equalization tank. The treatment efficiency of the catalytic ozone oxidation unit is shown in Table 5, where the COD removal rate, total nitrogen removal rate, and ozone utilization rate are slightly higher than in Example 1. After further treatment by nanofiltration, single-membrane electrodialysis, and neutralization tank, the final COD of the wastewater in the neutralization tank is 115 mg / L, ammonia nitrogen is 15 mg / L, total nitrogen is 33 mg / L, and total salt content is 6850 mg / L. To ensure the treatment effect of the subsequent nitrification and denitrification bacteria in the biological unit, domestic sewage is added at a rate of 10 t / h for salt dilution. The domestic sewage has a COD of approximately 400 mg / L, ammonia nitrogen of 20 mg / L, total nitrogen of 42 mg / L, and total salt content of 2100 mg / L. Finally, the wastewater is discharged in compliance with standards through the A / O and post-denitrification processes of the biological unit.

[0060] Table 5

[0061]

[0062] Example 4

[0063] The water quality of the MDEA wastewater treated was the same as in Example 1, and the process route, implementation steps, and reaction parameters were also basically the same as in Example 1, except for the type of catalyst, as shown in Table 6. The catalytic ozone oxidation treatment efficiency is shown in Table 6.

[0064] Table 6

[0065]

[0066] As can be seen from this example, by using an iron-cerium composite catalyst with the same dosage, compared with Example 1, the COD removal rate of homogeneous catalytic wet oxidation increased to 78.1%, the total nitrogen removal rate decreased to 53.5%, and the ozone utilization rate decreased to 94%.

[0067] Example 5

[0068] The water quality of the MDEA wastewater treated was the same as in Example 1, and the process route, implementation steps, and reaction parameters were also basically the same as in Example 1, except for the type of catalyst, as shown in Table 7. The catalytic ozone oxidation treatment efficiency is shown in Table 7.

[0069] Table 7

[0070]

[0071] As can be seen from this example, by using a copper-cerium composite catalyst with the same dosage, compared with Example 1, the COD removal rate of homogeneous catalytic wet oxidation decreased to 63.2%, the total nitrogen removal rate increased to 73.5%, and the ozone utilization rate decreased to 94.5%.

[0072] Example 6

[0073] The water quality of the MDEA wastewater treated was the same as in Example 1, and the process route, implementation steps, and reaction parameters were also basically the same as in Example 1, except for the type of catalyst, as shown in Table 8. The catalytic ozone oxidation treatment efficiency is shown in Table 8.

[0074] Table 8

[0075]

[0076] As can be seen from this example, by using a manganese-cerium composite catalyst with the same dosage, compared with Example 1, the COD removal rate of homogeneous catalytic wet oxidation decreased to 66.3%, the total nitrogen removal rate decreased to 38.4%, and the ozone utilization rate was further improved to 99.5%.

[0077] Example 7

[0078] The water quality of the MDEA wastewater treated was the same as in Example 1, and the process route, implementation steps, and reaction parameters were also basically the same as in Example 1, except for the type of catalyst, as shown in Table 9. The catalytic ozone oxidation treatment efficiency is shown in Table 9.

[0079] Table 9

[0080]

[0081] As can be seen from this example, by using a zinc-cerium composite catalyst with the same dosage, compared with Example 1, the COD removal rate of homogeneous catalytic wet oxidation decreased to 62.9%, the total nitrogen removal rate decreased to 56.6%, and the ozone utilization rate decreased to 93.2%.

[0082] Example 8

[0083] The water quality of the MDEA wastewater treated was the same as in Example 1, and the process route, implementation steps, and reaction parameters were also basically the same as in Example 1, except for the amount of catalyst added, as shown in Table 10. The catalytic ozone oxidation treatment efficiency is shown in Table 10.

[0084] Table 10

[0085]

[0086] As can be seen from this embodiment, the iron-copper-cerium composite catalyst is still used, but the dosage is increased. Compared with Example 1, the homogeneous catalytic wet oxidation COD removal rate, total nitrogen removal rate and ozone utilization rate are improved to a certain extent, but the improvement is small.

[0087] Example 9

[0088] The water quality of the MDEA wastewater treated was the same as in Example 1. The process route, implementation steps, and reaction parameters were also basically the same as in Example 1, except for the type of catalyst, as shown in Table 11. The catalytic ozone oxidation treatment efficiency is shown in Table 11.

[0089] Table 11

[0090]

[0091] As can be seen from this embodiment, the COD removal rate, total nitrogen removal rate, and ozone utilization rate of homogeneous catalytic wet oxidation using the iron-copper-praseodymium composite catalyst are basically the same as those in Example 1, with little difference.

[0092] Example 10

[0093] The water quality of the MDEA wastewater treated was the same as in Example 1, and the process route, implementation steps, and reaction parameters were also basically the same as in Example 1, except for the type of catalyst, as shown in Table 12. The catalytic ozone oxidation treatment efficiency is shown in Table 12.

[0094] Table 12

[0095]

[0096] This embodiment demonstrates that using the iron-copper-lanthanum composite catalyst, the homogeneous catalytic wet oxidation COD removal rate, total nitrogen removal rate, and ozone utilization rate are slightly improved compared to Example 1, but the improvement is minimal. Considering that the rare earth metal praseodymium used in Example 9 and the rare earth metal lanthanum used in Example 10 are more expensive than the rare earth metal cerium, it is recommended to prioritize the use of cerium catalysts.

[0097] Comparative Example 1

[0098] The water quality of the MDEA wastewater treated was the same as in Example 1, and the process route, implementation steps, and reaction parameters were also basically the same as in Example 1. The difference was that only iron-copper composite metal was used as the catalyst, and no rare earth metals were added. The catalytic ozone oxidation treatment efficiency is shown in Table 13.

[0099] Table 13

[0100]

[0101] As can be seen from this embodiment, compared with Example 1, the reduction in COD removal rate, total nitrogen removal rate and ozone utilization rate of homogeneous catalytic wet oxidation is significant when using only iron-copper composite catalyst.

[0102] Comparative Example 2

[0103] The water quality of the MDEA wastewater treated was the same as in Example 1. The process route, implementation steps, and reaction parameters were also basically the same as in Example 1. The type and dosage of the catalyst were also the same. The only difference was that no chloride salt was added, that is, the chloride ion concentration was maintained at 780 mg / L. The catalytic ozone oxidation treatment efficiency is shown in Table 14.

[0104] Table 14

[0105]

[0106] This embodiment shows that the homogeneous catalytic wet oxidation COD removal rate was 71.2%, a slight decrease; the total nitrogen removal rate decreased to 45.3%, a significant decrease; and the ozone utilization rate decreased slightly to 92.2%. This is because a certain amount of chloride ions in the ozone catalytic oxidation system promotes the removal of free residual chlorine (ClO₂ in water). - The generation of free residual chlorine (such as HClO and Cl2) can further enhance the oxidation capacity, especially the removal of ammonia nitrogen and total nitrogen.

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 before entering the equalization tank. It is then mixed with a homogeneous ozone oxidation catalyst and its acidity is adjusted before entering the catalytic ozone oxidation unit. After pH adjustment, the chloride ion content in the equalization tank should be no less than 1200 mg / L. If it is less than 1200 mg / L, chloride salts are added for further adjustment. Wastewater is treated under the action of the homogeneous ozone oxidation catalyst. 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 solution enters the neutralization tank, and the nanofiltration permeate also enters the neutralization tank for pH adjustment, and then 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 is directly sent to the effluent monitoring tank via a branch line. The homogeneous ozone oxidation catalyst comprises an active component and an auxiliary agent. The active component is a transition metal salt selected from one or more metal salts of iron, copper, zinc, manganese, cobalt, and nickel. The auxiliary agent is a rare earth metal salt selected from one or more metal salts of cerium, praseodymium, lanthanum, and neodymium. The mass ratio of the transition metal element to the rare earth metal element in the homogeneous ozone oxidation catalyst is 5 to 10:

1. The homogeneous ozone oxidation catalyst is added to the catalytic ozone oxidation unit in the form of a solution dissolved in water. The homogeneous ozone oxidation catalyst is added to the equalization tank at the start-up of the reaction system at a mass ratio of COD in the wastewater to catalyst of 500:1 to 2:

1. 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 nanofiltration process has a water production rate of 60%–85%, with a membrane pore size between 1 and 5 nm. It retains metals, high-valence salts, and large-molecule organic matter from the homogeneous catalyst, which then enter the concentrate side. 1%–40% of the nanofiltration concentrate enters a single-membrane electrodialysis process. This single-membrane electrodialysis process uses only anion exchange membranes. Under the action of the electrode and the anion exchange membrane, sulfates, carbonates, and high-valence anions in the nanofiltration concentrate permeate through the anion exchange membrane into the concentrate side. It also includes small-molecule organic matter that is negatively charged. The cationic catalyst remains in the mother liquor and can be reused.

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

3. The process method according to claim 1, characterized in that, The pH in the conditioning tank is adjusted to 3-6 using acid; the acid used is hydrochloric acid or sulfuric acid.

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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