High-efficiency landfill leachate treatment process

Abstract

The application relates to the technical field of water treatment, and particularly discloses a high-efficiency landfill leachate treatment process. The high-efficiency landfill leachate treatment process comprises the following steps: pretreatment: adding a coagulant A into landfill leachate, then adding a coagulant B, carrying out sedimentation or subsidence treatment, and obtaining pretreated liquid; the coagulant A comprises polyferric sulfate; the coagulant B comprises polyaluminum chloride, cationic polyacrylamide, modified bentonite and activated carbon; A / O treatment: sequentially passing the pretreated liquid through an anoxic tank and an aerobic tank to obtain treatment liquid A; MBR treatment: carrying out MBR treatment on the treatment liquid A by using an MBR (membrane bioreactor), to obtain treatment liquid B; and DTRO treatment: carrying out DTRO treatment on the treatment liquid B, to obtain purified water. The treatment process is convenient, and the treatment effect on the landfill leachate is good.

Description

Technical Field

[0001] This application relates to the technical field of water treatment, and in particular to a highly efficient landfill leachate treatment process. Background Technology

[0002] With accelerated urbanization, the amount of municipal solid waste is increasing year by year. Sanitary landfill remains the mainstream treatment method due to its mature technology and low cost. However, during the landfill process, waste degradation and rainwater leaching produce leachate, which is extremely harmful: its composition is complex, containing carbohydrates, heavy metals, and persistent organic pollutants; pollutant concentrations are extremely high, with COD reaching 10,000-80,000 mg / L and ammonia nitrogen concentrations exceeding 1,000 mg / L; moreover, the water quality fluctuates greatly with the age of the landfill and the season. Fresh leachate has good biodegradability, while aged leachate often has a BOD5 / COD ratio below 0.2. If discharged without treatment, it will seriously pollute soil, groundwater, and surface water, threatening the ecosystem and human health.

[0003] Commonly used treatment methods include: physicochemical methods, such as membrane separation, which can efficiently retain pollutants and produce good effluent, but membrane modules are expensive, prone to fouling, and can generate difficult-to-treat concentrates; coagulation and sedimentation are simple to operate but struggle to remove dissolved organic matter and high concentrations of ammonia nitrogen. Biological treatment methods, such as anaerobic-aerobic combined processes, first remove large amounts of organic matter anaerobically, then remove residual pollutants aerobically, which is low-cost and environmentally friendly, but has poor treatment effect on aged leachate, and the system is easily affected by temperature and water quality fluctuations. Physicochemical-biological combined processes, such as "anaerobic-aerobic-membrane separation," can improve treatment efficiency, but suffer from complex process routes and high equipment and operating costs, making them unsuitable for small and medium-sized landfills, and they are ineffective in removing some pollutants from high-concentration, recalcitrant leachate. Therefore, there is an urgent need to develop a high-efficiency landfill leachate treatment process that offers good treatment results and is convenient. Summary of the Invention

[0004] To improve the treatment effect of landfill leachate, this application provides a high-efficiency landfill leachate treatment process.

[0005] This application provides a highly efficient landfill leachate treatment process, which adopts the following technical solution: A highly efficient landfill leachate treatment process includes the following steps: Pretreatment: Coagulant A is added to the landfill leachate first, followed by coagulant B, and sedimentation or settling is performed to obtain a pretreated liquid; Coagulant A includes polyferric sulfate; Coagulant B includes polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon; A / O treatment: The pretreated solution is passed sequentially through an anoxic tank and an aerobic tank to obtain treated solution A; MBR treatment: The treatment solution A is treated by MBR using an MBR membrane bioreactor to obtain treatment solution B; DTRO treatment: The treatment solution B is subjected to DTRO treatment to obtain purified water.

[0006] By adopting the above technical solution, polyferric sulfate is first added, utilizing the rapid reaction of iron ions with phosphate and colloidal particles in the leachate to generate ferric phosphate precipitate. Then, polyaluminum chloride is added, using aluminum ions to expand the floc volume. Cationic polyacrylamide combines with the formed flocs, accelerating growth and improving sedimentation and filtration. Modified bentonite not only adsorbs pollutants, but its particles also serve as the "skeleton" for floc growth, improving floc structure and exhibiting electrochemical synergistic effects with other components. Activated carbon adsorbs recalcitrant molecular organic matter. Therefore, the combined effect of these components improves the pretreatment effect of landfill leachate. A / O treatment is then used, with alternating anoxic and aerobic operation to improve the organic matter removal rate and nitrogen and phosphorus removal efficiency. MBR treatment further removes residual organic matter and microorganisms, improving effluent quality. DTRO treatment, as a deep treatment unit, effectively removes recalcitrant organic matter, ammonia nitrogen, and salt, ensuring that the effluent meets discharge standards. The process is convenient and has a good treatment effect on landfill leachate.

[0007] In one specific implementation scheme, the weight ratio of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon in the coagulant B is 100:(1-5):(200-300):(10-15).

[0008] By adopting the above technical solution, the proportions of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon in coagulant B are further limited, thereby further improving the pretreatment effect on landfill leachate.

[0009] In one specific implementation, the method for preparing the modified bentonite includes the following steps: Preparation of modified clay A: Bentonite was dispersed in deionized water at 60°C and stirred until a homogeneous slurry was formed; hexadecyltrimethylammonium bromide was dissolved in deionized water at 60°C and slowly added dropwise to the slurry; the reaction was continuously stirred at 60°C for 4 hours; after the reaction was completed, the mixture was centrifuged, washed with hot water at 60°C until no bromide ions were found, dried at 105°C, and ground to obtain modified clay A; Preparation of modified soil B: Chitosan was dissolved in a 1% (w / w) glacial acetic acid solution to prepare a 2% (w / w) chitosan solution; modified soil A was dispersed in the chitosan solution and stirred at 50°C for 3 hours; after the reaction was completed, the mixture was centrifuged, and the washing solution was adjusted to neutral with a 0.1 mol / L sodium hydroxide solution to precipitate and fix the chitosan. Finally, the mixture was washed with deionized water and dried at 60°C to obtain modified soil B. Preparation of modified bentonite: Ferric chloride hexahydrate and ferrous chloride tetrahydrate were dissolved in deionized water, and oxygen was simultaneously removed by passing N2 to obtain an iron salt solution; modified clay B was dispersed in the iron salt solution, and under the protection of N2, the mixture was vigorously stirred in a 40°C water bath, and 25% ammonia solution was slowly added dropwise to adjust the pH to 10-11, and the reaction was continued for 1 hour; the temperature was raised to 80°C for 30 minutes for aging, and after the aging was completed, the solid was separated with the assistance of a magnet, washed with deionized water until neutral, and dried under vacuum at 60°C to obtain modified bentonite.

[0010] By adopting the above technical solution, bentonite is first cationically modified using hexadecyltrimethylammonium bromide, then chitosan is grafted onto it, and finally magnetic iron oxide nanoparticles are loaded onto the surface of the bentonite using ferric chloride hexahydrate and ferrous chloride tetrahydrate to obtain modified bentonite. When using this modified bentonite for pretreatment, hexadecyltrimethylammonium bromide provides positive charge to quickly neutralize colloids, the long chains of chitosan capture and bridge destabilized particles and suspended solids to form large and dense flocs, resulting in a high removal rate of suspended solids and colloids. Iron oxide causes the flocs to rapidly magnetically aggregate and settle, improving the pretreatment effect of landfill leachate.

[0011] In one specific implementation, in the modified clay A preparation step, the weight ratio of bentonite to hexadecyltrimethylammonium bromide is 100:(15-25); in the modified clay B preparation step, the weight ratio of modified clay A to chitosan is 100:(4-6); in the modified bentonite preparation step, the weight ratio of modified clay B, ferric chloride hexahydrate, and ferrous chloride tetrahydrate is 2:(5.2-5.6):(1.8-2.2).

[0012] By adopting the above technical solution, the ratio of bentonite and hexadecyltrimethylammonium bromide, the ratio of modified clay A and chitosan, and the ratio of modified clay B, ferric chloride hexahydrate, and ferrous chloride tetrahydrate were further defined, thereby improving the modification effect of bentonite.

[0013] In one specific implementation scheme, the pretreatment step includes: adding coagulant A to the landfill leachate first, followed by coagulant B, for sedimentation or settling treatment; then extracting the supernatant of the landfill leachate for electrocatalytic oxidation treatment to obtain the pretreated liquid; the electrode material is selected as a Ti / RuO2-IrO2 electrode, and the current density is 10-30 mA / cm². 2 .

[0014] By adopting the above technical solution and adding an electrocatalytic unit, the BOD / COD ratio is increased to above 0.3 through the oxidation and decomposition of recalcitrant organic matter by hydroxyl radicals.

[0015] In one specific implementation scheme, in the A / O treatment step, the dissolved oxygen content in the anoxic tank is 0.2-0.5 mg / L, and the hydraulic retention time is 12-24 h; denitrifying bacteria are used for nitrogen removal, and the COD / N ratio is 3:1-5:1; the dissolved oxygen content in the aerobic tank is 2.0-3.0 mg / L, and the hydraulic retention time is 24-48 h.

[0016] In one specific implementation, in the MBR treatment step, the membrane in the MBR membrane bioreactor comprises a polyvinylidene fluoride membrane with a pore size of 0.1 μm.

[0017] By adopting the above technical solution and using a polyvinylidene fluoride membrane with a pore size of 0.1 μm for MBR treatment, the treatment effect of landfill leachate can be further improved.

[0018] In one specific implementation scheme, the MBR treatment steps are as follows: the treatment solution B is first treated with a disc tube reverse osmosis membrane module for primary DTRO treatment, and then treated with an antifouling spiral membrane module for secondary DTRO treatment, so that the amount of concentrate reinjected is reduced to less than 10% of the total treatment volume, and purified water is obtained; wherein the operating pressure during primary DTRO treatment is 2.5-3 MPa, and the operating pressure during secondary DTRO treatment is 5.0-7.0 MPa.

[0019] In summary, this application includes at least one of the following beneficial technical effects: The treatment process described in this application first involves adding polyferric sulfate, which utilizes the rapid reaction of iron ions with phosphate and colloidal particles in the leachate to generate ferric phosphate precipitate. Then, polyaluminum chloride is added, which expands the floc volume through aluminum ions. Cationic polyacrylamide combines with the formed flocs, accelerating growth and improving settling and filtration properties. Modified bentonite not only adsorbs pollutants, but its particles also serve as a "skeleton" for floc growth, improving floc structure and exhibiting electrochemical synergistic effects with other components. Activated carbon adsorbs recalcitrant molecular organic matter. Therefore, the combined effect of these components improves the pretreatment effect of landfill leachate. A / O treatment further enhances organic matter removal rate and nitrogen and phosphorus removal efficiency through alternating anoxic and aerobic operation. MBR treatment further removes residual organic matter and microorganisms, improving effluent quality. DTRO treatment, as a deep treatment unit, effectively removes recalcitrant organic matter, ammonia nitrogen, and salts, ensuring effluent meets discharge standards. The process is convenient and has a good treatment effect on landfill leachate. In this application, bentonite is first cationic modified using hexadecyltrimethylammonium bromide, then chitosan is grafted onto it, and finally magnetic iron oxide nanoparticles are loaded onto the surface of the bentonite using ferric chloride hexahydrate and ferrous chloride tetrahydrate to obtain modified bentonite. When using this modified bentonite for pretreatment, hexadecyltrimethylammonium bromide provides a positive charge to quickly neutralize colloids, the long chains of chitosan capture and bridge destabilized particles and suspended solids to form large and dense flocs, resulting in a high removal rate of suspended solids and colloids. Iron oxide causes the flocs to rapidly magnetically aggregate and settle, improving the pretreatment effect of landfill leachate. In this application, an electrocatalytic unit is added during pretreatment to decompose recalcitrant organic matter through hydroxyl radical oxidation, thereby increasing the BOD / COD ratio to above 0.3. Detailed Implementation

[0020] The present application will be further described in detail below with reference to the embodiments.

[0021] All raw materials used in the examples were commercially available. The cationic polyacrylamide was provided by Gongyi Teli Water Treatment Materials Factory, model GB / T13940-92; the bentonite was 200-mesh sodium bentonite, CAS number: 85049-30-5; and the activated carbon was 200-mesh. Preparation Example

[0022] Preparation Example 1 Preparation Example 1 provides a method for preparing modified bentonite, comprising the following steps: Preparation of modified clay A: Bentonite was dispersed in deionized water at 60℃ with a solid-liquid ratio of 1:20 and stirred for 30 min until a homogeneous slurry was formed. Hexadecyltrimethylammonium bromide was dissolved in deionized water at 60℃ and slowly added dropwise to the slurry. The reaction was continuously stirred at 60℃ for 4 h. After the reaction was completed, the mixture was centrifuged, washed with hot water at 60℃ until no bromide ions were found, dried at 105℃, and ground to obtain modified clay A. The weight ratio of bentonite to hexadecyltrimethylammonium bromide was 100:15. The bentonite was sodium-based bentonite with a mesh size of 200. Preparation of modified soil B: Chitosan was dissolved in a 1% (w / w) glacial acetic acid solution to prepare a 2% (w / w) chitosan solution; modified soil A was dispersed in the chitosan solution, and the mixture was stirred at 50°C for 3 hours; after the reaction was completed, the mixture was centrifuged, and the washing solution was adjusted to neutral with a 0.1 mol / L sodium hydroxide solution to precipitate and fix the chitosan. Finally, the mixture was washed with deionized water and dried at 60°C to obtain modified soil B; the weight ratio of modified soil A to chitosan was 100:4. Preparation of modified bentonite: Ferric chloride hexahydrate and ferrous chloride tetrahydrate were dissolved in deionized water at a solid-liquid ratio of 7.4:100, and oxygen was simultaneously removed by passing N2 to obtain an iron salt solution; modified clay B was dispersed in the iron salt solution, and under N2 protection, the mixture was vigorously stirred in a 40°C water bath, and 25% ammonia solution was slowly added dropwise to adjust the pH to 10, and the reaction was continued for 1 hour; the temperature was raised to 80°C for 30 minutes for aging, and after aging, the solid was separated with the aid of a magnet, washed with deionized water until neutral, and dried under vacuum at 60°C to obtain modified bentonite; wherein the weight ratio of modified clay B, ferric chloride hexahydrate, and ferrous chloride tetrahydrate was 2:5.2:1.8.

[0023] Preparation Example 2 Preparation Example 2 provides a method for preparing modified bentonite, comprising the following steps: Preparation of modified clay A: Bentonite was dispersed in deionized water at 60℃ with a solid-liquid ratio of 1:20 and stirred for 30 min until a homogeneous slurry was obtained; hexadecyltrimethylammonium bromide was dissolved in deionized water at 60℃ and slowly added dropwise to the slurry; the reaction was continuously stirred at 60℃ for 4 h; after the reaction was completed, the mixture was centrifuged, washed with hot water at 60℃ until no bromide ions were found, dried at 105℃, and ground to obtain modified clay A; wherein the weight ratio of bentonite to hexadecyltrimethylammonium bromide was 100:20; the bentonite was sodium-based bentonite with a mesh size of 200. Preparation of modified soil B: Chitosan was dissolved in a 1% (w / w) glacial acetic acid solution to prepare a 2% (w / w) chitosan solution; modified soil A was dispersed in the chitosan solution, and the mixture was stirred at 50°C for 3 hours; after the reaction was completed, the mixture was centrifuged, and the washing solution was adjusted to neutral with a 0.1 mol / L sodium hydroxide solution to precipitate and fix the chitosan. Finally, the mixture was washed with deionized water and dried at 60°C to obtain modified soil B; the weight ratio of modified soil A to chitosan was 100:5. Preparation of modified bentonite: Ferric chloride hexahydrate and ferrous chloride tetrahydrate were dissolved in deionized water at a solid-liquid ratio of 7.4:100, and oxygen was simultaneously removed by passing N2 to obtain an iron salt solution; modified clay B was dispersed in the iron salt solution, and under N2 protection, the mixture was vigorously stirred in a 40°C water bath, and 25% ammonia solution was slowly added dropwise to adjust the pH to 10, and the reaction was continued for 1 hour; the temperature was raised to 80°C for 30 minutes for aging, and after aging, the solid was separated with the aid of a magnet, washed with deionized water until neutral, and vacuum dried at 60°C to obtain modified bentonite; wherein the weight ratio of modified clay B, ferric chloride hexahydrate, and ferrous chloride tetrahydrate was 2:5.4:2.

[0024] Preparation Example 3 Preparation Example 3 provides a method for preparing modified bentonite, comprising the following steps: Preparation of modified clay A: Bentonite was dispersed in deionized water at 60℃ with a solid-liquid ratio of 1:20 and stirred for 30 min until a homogeneous slurry was formed. Hexadecyltrimethylammonium bromide was dissolved in deionized water at 60℃ and slowly added dropwise to the slurry. The reaction was continuously stirred at 60℃ for 4 h. After the reaction was completed, the mixture was centrifuged, washed with hot water at 60℃ until no bromide ions were found, dried at 105℃, and ground to obtain modified clay A. The weight ratio of bentonite to hexadecyltrimethylammonium bromide was 100:25. The bentonite was sodium-based bentonite with a mesh size of 200. Preparation of modified soil B: Chitosan was dissolved in a 1% (w / w) glacial acetic acid solution to prepare a 2% (w / w) chitosan solution; modified soil A was dispersed in the chitosan solution, and the mixture was stirred at 50°C for 3 hours; after the reaction was completed, the mixture was centrifuged, and the washing solution was adjusted to neutral with a 0.1 mol / L sodium hydroxide solution to precipitate and fix the chitosan. Finally, the mixture was washed with deionized water and dried at 60°C to obtain modified soil B; the weight ratio of modified soil A to chitosan was 100:6. Preparation of modified bentonite: Ferric chloride hexahydrate and ferrous chloride tetrahydrate were dissolved in deionized water at a solid-liquid ratio of 7.4:100, and oxygen was simultaneously removed by passing N2 to obtain an iron salt solution. Modified bentonite B was dispersed in the iron salt solution and stirred vigorously in a 40°C water bath under N2 protection. Ammonia solution with a mass concentration of 25% was slowly added dropwise to adjust the pH to 10, and the reaction was continued for 1 hour. The temperature was raised to 80°C for 30 minutes for aging. After aging, the solid was separated with the aid of a magnet, washed with deionized water until neutral, and dried under vacuum at 60°C to obtain modified bentonite. The weight ratio of modified bentonite B, ferric chloride hexahydrate, and ferrous chloride tetrahydrate was 2:5.6:2.2. Example

[0025] Example 1 Example 1 provides a highly efficient landfill leachate treatment process, including the following steps: Pretreatment: Coagulant A was added to the landfill leachate first, and then coagulant B was added after 3 minutes. The mixture was allowed to settle or settle for 12 days to obtain the pretreated liquid. The dosage of coagulant A was 200 mg / L, and coagulant A was polyferric sulfate. The dosage of coagulant B was 200 mg / L, and coagulant B was a mixture of polyaluminum chloride, cationic polyacrylamide, modified bentonite from Preparation Example 1, and activated carbon. The weight ratio of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon was 100:1:200:10. A / O treatment: The pretreated liquid is passed sequentially through an anoxic tank and an aerobic tank to obtain treated liquid A; the dissolved oxygen content in the anoxic tank is 0.2 mg / L, and the hydraulic retention time is 24 h; denitrification is carried out using denitrifying bacteria, and the COD / N ratio is 3:1; the dissolved oxygen content in the aerobic tank is 2.0 mg / L, and the hydraulic retention time is 48 h. MBR treatment: Treatment solution A is treated by MBR using an MBR membrane bioreactor to obtain treatment solution B; wherein the membrane in the MBR membrane bioreactor is a polyvinylidene fluoride membrane with a pore size of 0.1 μm. DTRO treatment: The treated solution B is first treated with a disc tube reverse osmosis membrane module for primary DTRO treatment, and then treated with an antifouling spiral membrane module for secondary DTRO treatment, so that the amount of concentrate reinjected is reduced to less than 10% of the total treatment volume, resulting in purified water; the operating pressure during primary DTRO treatment is 2.5 MPa, and the operating pressure during secondary DTRO treatment is 5.0 MPa.

[0026] Example 2 The difference between Example 2 and Example 1 is that the coagulant B is a mixture of polyaluminum chloride, cationic polyacrylamide, modified bentonite and activated carbon used in Example 2; the remaining steps are the same as in Example 1.

[0027] Example 3 The difference between Example 3 and Example 1 is that the coagulant B is a mixture of polyaluminum chloride, cationic polyacrylamide, modified bentonite and activated carbon used in Example 3; the remaining steps are the same as in Example 1.

[0028] Example 4 The difference between Example 4 and Example 2 is that the coagulant B is a mixture of polyaluminum chloride, cationic polyacrylamide, modified bentonite from Example 2, and activated carbon, and the weight ratio of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon is 100:3:250:12.5; the remaining steps are the same as in Example 2.

[0029] Example 5 The difference between Example 5 and Example 2 is that the coagulant B is a mixture of polyaluminum chloride, cationic polyacrylamide, modified bentonite from Preparation Example 3, and activated carbon, and the weight ratio of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon is 100:5:300:15; the remaining steps are the same as in Example 2.

[0030] Example 6 The difference between Example 6 and Example 4 is the pretreatment: coagulant A is added to the landfill leachate first, followed by coagulant B after 3 minutes, and the mixture is allowed to settle or precipitate for 12 days. Then, the supernatant of the landfill leachate is extracted and subjected to electrocatalytic oxidation to obtain the pretreated solution. The electrode material used is a Ti / RuO2-IrO2 electrode, and the current density is 10 mA / cm². 2The dosage of coagulant A is 200 mg / L, and coagulant A is polyferric sulfate; the dosage of coagulant B is 200 mg / L, and coagulant B is a mixture of polyaluminum chloride, cationic polyacrylamide, modified bentonite from Preparation Example 2, and activated carbon, and the weight ratio of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon is 100:3:250:12.5; the remaining steps are consistent with those in Example 4.

[0031] Example 7 The difference between Example 7 and Example 6 is the pretreatment: coagulant A is added to the landfill leachate first, followed by coagulant B after 3 minutes, and the mixture is allowed to settle or precipitate for 12 days. Then, the supernatant of the landfill leachate is extracted and subjected to electrocatalytic oxidation to obtain the pretreated solution. The electrode material used is a Ti / RuO2-IrO2 electrode, and the current density is 20 mA / cm². 2 ; A / O treatment: The pretreated liquid is passed sequentially through an anoxic tank and an aerobic tank to obtain treated liquid A; the dissolved oxygen content in the anoxic tank is 0.3 mg / L, and the hydraulic retention time is 18 h; denitrification is carried out using denitrifying bacteria, and the COD / N ratio is 4:1; the dissolved oxygen content in the aerobic tank is 2.5 mg / L, and the hydraulic retention time is 36 h. DTRO treatment: The treated solution B is first treated with a disc tube reverse osmosis membrane module for primary DTRO treatment, and then treated with an antifouling spiral membrane module for secondary DTRO treatment, so that the amount of concentrate reinjected is reduced to less than 10% of the total treatment volume, and purified water is obtained; the operating pressure during primary DTRO treatment is 2.8 MPa, and the operating pressure during secondary DTRO treatment is 6.0 MPa; the remaining steps are the same as in Example 6.

[0032] Example 8 The difference between Example 8 and Example 6 is the pretreatment: coagulant A is added to the landfill leachate first, followed by coagulant B after 3 minutes, and the mixture is allowed to settle or precipitate for 12 days. Then, the supernatant of the landfill leachate is extracted and subjected to electrocatalytic oxidation to obtain the pretreated solution. The electrode material used is a Ti / RuO2-IrO2 electrode, and the current density is 30 mA / cm². 2 ; A / O treatment: The pretreated liquid is passed sequentially through an anoxic tank and an aerobic tank to obtain treated liquid A; the dissolved oxygen content in the anoxic tank is 0.5 mg / L, and the hydraulic retention time is 12 h; denitrification is carried out using denitrifying bacteria, and the COD / N ratio is 5:1; the dissolved oxygen content in the aerobic tank is 3.0 mg / L, and the hydraulic retention time is 24 h. DTRO treatment: The treated solution B is first treated with a disc tube reverse osmosis membrane module for primary DTRO treatment, and then treated with an antifouling spiral membrane module for secondary DTRO treatment, so that the amount of concentrate reinjected is reduced to less than 10% of the total treatment volume, and purified water is obtained; the operating pressure of primary DTRO treatment is 3 MPa, and the operating pressure of secondary DTRO treatment is 7.0 MPa; the remaining steps are the same as in Example 6. Comparative Example

[0033] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the coagulant B is polyaluminum chloride; the remaining steps are the same as in Example 1.

[0034] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the coagulant B is a mixture of polyaluminum chloride, cationic polyacrylamide, bentonite, and activated carbon, and the weight ratio of polyaluminum chloride, cationic polyacrylamide, bentonite, and activated carbon is 100:1:200:10; the bentonite is sodium bentonite with a mesh size of 200; the remaining steps are the same as in Example 1. Performance testing experiment

[0035] Treatment effect: The same batch of landfill leachate was stirred and dispersed, then divided into 10 equal groups. Each group was treated using the treatment processes in the respective examples and comparative examples. The purified water was tested to obtain the concentrations of SS, COD and ammonia nitrogen.

[0036] Table 1 Performance test results of purified water

[0037] Combining Example 1 and Comparative Examples 1-2, Example 1 showed the best treatment effect for landfill leachate. This demonstrates that when using coagulant B for pretreatment of landfill leachate, the composite coagulant B, composed of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon, effectively utilizes the following: polyaluminum chloride contains aluminum ions that expand the floc volume; cationic polyacrylamide binds to the formed flocs, accelerating growth and improving sedimentation and filtration; modified bentonite not only adsorbs pollutants but its particles also serve as a "skeleton" for floc growth, improving floc structure and exhibiting electrochemical synergistic effects with other components; activated carbon adsorbs recalcitrant molecular organic matter. Therefore, the combined effect of these components enhances the pretreatment effect of landfill leachate.

[0038] Based on Examples 1-3, it can be seen that when preparing modified bentonite, the ratio of raw materials in Examples 1-3 all resulted in good modification effects on bentonite.

[0039] Combining Examples 2, 4, and 5, Example 4 showed the best treatment effect for landfill leachate. This indicates that when using coagulant B for pretreatment of landfill leachate, the ratio of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon in coagulant B was optimal in Example 4.

[0040] Combining Examples 4 and 6, Example 6 showed better treatment effect of landfill leachate. It can be seen that when using coagulants to pretreat landfill leachate, adding an electrocatalytic unit to decompose recalcitrant organic matter through hydroxyl radical oxidation can further improve the treatment effect of landfill leachate.

[0041] In combination with Examples 6-8, Example 7 showed the best treatment effect for landfill leachate, indicating that the treatment conditions in Example 7 were optimal when treating landfill leachate.

[0042] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A highly efficient landfill leachate treatment process, characterized in that: Includes the following steps: Pretreatment: Coagulant A is added to the landfill leachate first, followed by coagulant B, and sedimentation or settling is performed to obtain a pretreated liquid; Coagulant A includes polyferric sulfate; Coagulant B includes polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon; A / O treatment: The pretreated solution is passed sequentially through an anoxic tank and an aerobic tank to obtain treated solution A; MBR treatment: The treatment solution A is treated by MBR using an MBR membrane bioreactor to obtain treatment solution B; DTRO treatment: The treatment solution B is subjected to DTRO treatment to obtain purified water.

2. The efficient landfill leachate treatment process according to claim 1, characterized in that: The weight ratio of polyaluminum chloride, cationic polyacrylamide, modified bentonite, and activated carbon in the coagulant B is 100:(1-5):(200-300):(10-15).

3. The efficient landfill leachate treatment process according to claim 1, characterized in that: The method for preparing the modified bentonite includes the following steps: Preparation of modified clay A: Bentonite was dispersed in deionized water at 60°C and stirred until a homogeneous slurry was formed; hexadecyltrimethylammonium bromide was dissolved in deionized water at 60°C and slowly added dropwise to the slurry; the reaction was continuously stirred at 60°C for 4 hours; after the reaction was completed, the mixture was centrifuged, washed with hot water at 60°C until no bromide ions were found, dried at 105°C, and ground to obtain modified clay A; Preparation of modified soil B: Chitosan was dissolved in a 1% (w / w) glacial acetic acid solution to prepare a 2% (w / w) chitosan solution; modified soil A was dispersed in the chitosan solution and stirred at 50°C for 3 hours; after the reaction was completed, the mixture was centrifuged, and the washing solution was adjusted to neutral with a 0.1 mol / L sodium hydroxide solution to precipitate and fix the chitosan. Finally, the mixture was washed with deionized water and dried at 60°C to obtain modified soil B. Preparation of modified bentonite: Ferric chloride hexahydrate and ferrous chloride tetrahydrate were dissolved in deionized water, and oxygen was simultaneously removed by passing N2 to obtain an iron salt solution; modified clay B was dispersed in the iron salt solution, and under the protection of N2, the mixture was vigorously stirred in a 40°C water bath, and 25% ammonia solution was slowly added dropwise to adjust the pH to 10-11, and the reaction was continued for 1 hour; the temperature was raised to 80°C for 30 minutes for aging, and after the aging was completed, the solid was separated with the assistance of a magnet, washed with deionized water until neutral, and dried under vacuum at 60°C to obtain modified bentonite.

4. The efficient landfill leachate treatment process according to claim 3, characterized in that: In the preparation step of modified clay A, the weight ratio of bentonite to hexadecyltrimethylammonium bromide is 100:(15-25); in the preparation step of modified clay B, the weight ratio of modified clay A to chitosan is 100:(4-6); in the preparation step of modified bentonite, the weight ratio of modified clay B, ferric chloride hexahydrate, and ferrous chloride tetrahydrate is 2:(5.2-5.6):(1.8-2.2).

5. The efficient landfill leachate treatment process according to claim 1, characterized in that: The pretreatment step involves: first adding coagulant A to the landfill leachate, then adding coagulant B, and performing sedimentation or settling treatment. The supernatant of the landfill leachate is then extracted and subjected to electrocatalytic oxidation treatment to obtain the pretreated solution. The electrode material used is a Ti / RuO2-IrO2 electrode, with a current density of 10-30 mA / cm². 2 .

6. The efficient landfill leachate treatment process according to claim 1, characterized in that: In the A / O treatment step, the dissolved oxygen content in the anoxic tank is 0.2-0.5 mg / L, and the hydraulic retention time is 12-24 h; denitrifying bacteria are used for nitrogen removal, and the COD / N ratio is 3:1-5:1; the dissolved oxygen content in the aerobic tank is 2.0-3.0 mg / L, and the hydraulic retention time is 24-48 h.

7. The efficient landfill leachate treatment process according to claim 1, characterized in that: In the MBR treatment step, the membrane in the MBR membrane bioreactor includes a polyvinylidene fluoride membrane with a pore size of 0.1 μm.

8. The efficient landfill leachate treatment process according to claim 1, characterized in that: The MBR treatment steps are as follows: the treatment solution B is first treated with a disc tube reverse osmosis membrane module for primary DTRO treatment, and then treated with an antifouling spiral membrane module for secondary DTRO treatment, so that the amount of concentrate reinjected is reduced to less than 10% of the total treatment volume, and purified water is obtained; wherein the operating pressure during primary DTRO treatment is 2.5-3 MPa, and the operating pressure during secondary DTRO treatment is 5.0-7.0 MPa.

Images