A comprehensive treatment method for leachate from aging landfills

Abstract

This invention relates to the field of landfill leachate treatment and discloses a comprehensive treatment method for leachate from aging landfills, comprising two parts: denitrification and deep decarbonization. Denitrification employs an "OAO+UF" process, while deep decarbonization utilizes a "coagulation sedimentation + Fenton + built-in MBR + ozone + carbon filtration" process. The OAO unit of this invention achieves ammonia nitrogen and total nitrogen levels sufficient for municipal solid waste landfill pollution control standards, and eliminates the need for nitrification liquid return pumps or internal return pumps, resulting in lower energy consumption. The deep treatment section employs a two-stage AOP-based process, which can utilize a combination of Fenton and ozone processes, leading to higher COD compliance stability. This method offers advantages such as smaller footprint, stable operation, good treatment effect, low operating cost, and no concentrate production. The treated effluent consistently meets discharge standards, making it particularly suitable for treating leachate from closed or near-closed aging landfills.

Description

Technical Field

[0001] This invention relates to the field of landfill leachate treatment technology, and in particular to a comprehensive treatment method for leachate from aging landfills. Background Technology

[0002] Landfilling was the mainstream process for municipal solid waste treatment in my country for a long time. However, due to land scarcity and the increasing environmental risks of landfilling, with the implementation of waste sorting and collection, resource utilization technologies such as waste incineration have become the main means of municipal solid waste treatment. Nevertheless, landfills will still have a long-term impact on the environment. As landfills reach the end of their service life or cease landfilling, leachate will exhibit "aging" characteristics, specifically high concentrations of ammonia nitrogen and total nitrogen, low organic matter concentration, low B / C ratio, poor biodegradability, weak alkalinity, and high alkalinity. Furthermore, due to the reinjection of large amounts of concentrate from the previous dual-membrane process, the leachate has high conductivity, making it impossible for existing treatment facilities to achieve compliant discharge of leachate.

[0003] Currently, the mainstream treatment processes on the market include: two-stage AO + dual-membrane (NF+RO) process, high-pressure disc tube membrane (DTRO) process, and MVR process. Among these, the two-stage AO + dual-membrane (NF+RO) process is effective for treating early and mid-stage leachate, but for aging leachate, the two-stage AO denitrification is ineffective, and the membrane's retention rate for ammonia and nitrate nitrogen is limited. Therefore, two or more stages of RO are needed to ensure compliance, resulting in large footprints, high energy consumption, and the generation of large amounts of concentrate due to the membrane process. The high-pressure disc tube membrane (DTRO) process also produces a large amount of concentrate. MVR requires an additional heat source, and the mother liquor from evaporation is difficult to dispose of.

[0004] Patent CN109851182A discloses a method for treating landfill leachate, which uses OAO + acidification flotation + Fenton oxidation + AO + MBR to treat the leachate. This method eliminates the need for nanofiltration or RO, avoiding the generation of concentrated water, and is suitable for treating leachate from middle-aged and older landfills. However, this method has the following limitations when treating leachate from aging landfills: ① Due to the lack of advanced treatment equipment, the stability of COD compliance is poor;

[0005] ② Its OAO process requires the installation of nitrification liquor return pump and sludge return pump, resulting in high operating energy consumption;

[0006] ③ The Fenton technology it uses is the first generation Fenton technology. In addition to hydrogen peroxide as an oxidant, it requires the addition of ferrous ions as a homogeneous catalyst and produces a large amount of sludge, which is not conducive to practical application. Summary of the Invention

[0007] This invention aims to overcome the aforementioned problems existing in the treatment of leachate from aging landfills using existing technologies, and provides a comprehensive treatment method for leachate from aging landfills. This method has the advantages of requiring less land, stable operation, good treatment effect, low operating cost, and no concentrated liquid production. The treated effluent quality can stably meet the emission limit standards of the "Standard for the Control of Municipal Solid Waste Landfills" (GB 16889-2008), and is particularly suitable for the treatment of leachate from aging landfills that have been closed or are close to closure.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for the full-volume treatment of leachate from aging landfills includes the following steps:

[0010] (1) After the leachate is removed from floating matter by the solid-liquid separation device, it enters the OAO unit and passes through the O1 aerobic tank, the A facultative anaerobic tank and the O2 aerobic tank in sequence for denitrification.

[0011] (2) The effluent from the OAO unit enters the UF unit for ultrafiltration treatment, and the sludge is intercepted. The intercepted sludge is then returned to the O1 aerobic tank and the O2 aerobic tank.

[0012] (3) The effluent from the UF unit enters the coagulation sedimentation tank, where coagulant is added for coagulation and sedimentation;

[0013] (4) The effluent from the coagulation sedimentation tank enters the Fenton treatment unit for primary AOP treatment; in the Fenton treatment unit, acid is first added to adjust the pH to 2-4, then Fenton reagent is added to react, and then alkali is added to adjust the pH to 7.0-9.0 before sedimentation.

[0014] (5) The effluent from the Fenton treatment unit enters the built-in MBR reactor for microbial treatment;

[0015] (6) The effluent from the built-in MBR reactor enters the ozone treatment unit for secondary AOP treatment;

[0016] (7) The effluent from the ozone treatment unit enters the carbon filter unit, and after adsorption by activated carbon, the effluent quality meets the discharge standards.

[0017] The comprehensive treatment method of this invention includes two parts: denitrification and deep decarbonization. Denitrification employs an "OAO+UF" process, while deep decarbonization uses a "coagulation sedimentation + Fenton + built-in MBR + ozone + carbon filtration" process. In the denitrification section, leachate from aged landfills undergoes solid-liquid separation and first enters the OAO unit. Complete nitrification occurs in the O1 aerobic tank, removing ammonia nitrogen from the water. It then enters the A facultative anaerobic tank for complete denitrification, removing nitrate nitrogen from the wastewater. Any excess carbon source is removed in the O2 aerobic tank. Finally, the leachate enters the UF unit. The UF membrane traps and recirculates sludge, increasing the sludge concentration in the OAO unit to improve treatment efficiency. Simultaneously, alkalinity is added to the O1 tank to enhance its nitrification effect. After denitrification, the wastewater undergoes further decarbonization. It first enters a coagulation and sedimentation tank, where chemical reaction, coagulation, and sedimentation remove small amounts of colloidal substances, reducing the dosage of strong oxidants in subsequent units. Then, it undergoes primary AOP treatment, utilizing the strong oxidizing effect of Fenton's reagent to decompose recalcitrant large organic molecules into easily degradable small organic molecules. The Fenton effluent then enters an internal MBR reactor, where microorganisms convert the small organic molecules decomposed by Fenton's strong oxidation into carbon dioxide and water, thus removing organic matter from the wastewater. The MBR reactor uses an internal membrane to increase sludge concentration, thereby improving treatment efficiency. After MBR biochemical treatment, the wastewater enters the ozone treatment unit for secondary AOP treatment. The strong oxidizing effect of ozone converts all the residual recalcitrant organic matter in the water into small molecule organic matter, carbon dioxide, and water. Finally, the wastewater passes through the carbon filter unit, where the adsorption and filtration effect of activated carbon removes the residual organic matter in the water. The effluent quality can stably meet the emission limits of the "Standard for the Control of Municipal Solid Waste Landfills" (GB16889-2008).

[0018] This invention employs an OAO+UF process in the denitrification section, achieving high total nitrogen compliance. Total nitrogen levels are met in the biological treatment stage, eliminating the need for further total nitrogen removal in the advanced treatment phase; only the removal of recalcitrant organic matter is required. Compared to other two-stage AO+membrane processes, the biological stage omits an A tank, resulting in a smaller footprint and lower investment. Furthermore, the denitrification section of this invention, apart from the UF recirculation, eliminates the need for a separate internal recirculation system. The O1 tank replenishes sludge concentration and alkalinity required for nitrification through UF recirculation, saving operational energy. In addition, the advanced carbon removal section utilizes two-stage strong oxidation—Fenton and ozone—to convert recalcitrant organic matter into readily biodegradable organic matter in stages. Combined with an integrated MBR biological treatment and carbon filtration, this ensures that the effluent COD consistently meets discharge standards. The entire process generates no concentrate, resulting in lower operating costs. It is particularly suitable for treating leachate from closed or near-closed aging landfills.

[0019] Preferably, the solid-liquid separation device in step (1) is one of a filter, a bar screen, or a coagulation sedimentation tank; the leachate entering the OAO unit has a COD of 1000–3000 mg / L, a B / C ratio of less than 0.2, a C / N ratio of ≤1, an ammonia nitrogen ratio of 500–2000 mg / L, a total nitrogen ratio of 500–3000 mg / L, a Kjeldahl nitrogen ratio of no more than 40 mg / L, and a pH of 7.5–8.0. Compared with ordinary landfill leachate, the leachate from the aging landfill in this invention has typical water quality, with a low raw COD concentration, a high total nitrogen concentration, and very poor biodegradability, making it difficult to meet treatment standards using traditional processes.

[0020] Preferably, in step (1), the dissolved oxygen in the O1 aerobic tank and the O2 aerobic tank is controlled at 2-6 mg / L, and a carbon source is added in the A facultative tank at a carbon-to-nitrogen ratio of 3-5:1 to carry out a complete denitrification reaction. The carbon source is selected from one or more of methanol, glucose, and sodium acetate. The residence time in the O1 aerobic tank is 48-96 h, the residence time in the A facultative tank is 60-120 h, and the residence time in the O2 aerobic tank is 12-18 h.

[0021] Preferably, in step (2), the sludge return ratio of the O1 aerobic tank is 100-300%, and the sludge return ratio of the O2 aerobic tank is 600-800%.

[0022] Preferably, the coagulant in step (3) includes PAC and PAM, with PAC added at a dosage of 80-200 ppm and PAM added at a dosage of 1-2 ppm.

[0023] Preferably, the Fenton reagent in step (4) includes hydrogen peroxide and a heterogeneous catalyst, and the preparation method of the heterogeneous catalyst includes the following steps:

[0024] A) Dissolve ferric chloride in DMF, then add terephthalic acid, and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:0.7-0.8; the mixed solution is subjected to hydrothermal reaction at 100-110℃ for 12-24h to obtain Fe-MOF; B) Calcine Fe-MOF at 700-800℃ for 1-3h in an inert atmosphere to obtain a porous support;

[0025] C) The porous carrier is mixed and ground with ferric chloride, cobalt nitrate and glucose in a mass ratio of 1:1~2:0.3~0.5:20~25. Then urea is added, and the mass ratio of porous carrier to urea is 1:50~80. After further grinding, the precursor powder is obtained.

[0026] D) The precursor powder is calcined at 700–900°C for 1–3 h in an inert atmosphere to obtain the heterogeneous catalyst.

[0027] In traditional homogeneous Fenton technology, Fe is generally used. 2+ When using hydrogen peroxide as the oxidant and soluble metal ions as the catalyst, the catalyst is difficult to recover, resulting in waste and the reaction generates a large amount of iron sludge, causing secondary pollution. This invention uses a heterogeneous catalyst as the Fenton reaction catalyst, which can greatly reduce the generation of iron sludge, and the catalyst after the reaction can be recovered and recycled, reducing treatment costs.

[0028] In the preparation of the heterogeneous catalyst of the present invention, Fe is first used 3+ Using terephthalic acid as a ligand and terephthalic acid as a metal ion, an iron-based metal-organic framework (Fe-MOF) is prepared via a hydrothermal reaction. The metal-organic framework material has high porosity and large specific surface area. After calcination in step B), a porous carbon support loaded with iron oxides is obtained. Then, in steps C) and D), urea is used as a nitrogen source to introduce N atoms into the porous carbon support. Through the strong coordination between N and metal atoms, iron and cobalt are fixed on the porous carbon support. An iron-cobalt bimetallic single-atom catalyst is then loaded onto the porous carbon support loaded with iron oxides. The heterogeneous catalyst of this invention, which combines iron oxide and iron-cobalt bimetallic single-atom catalyst, exhibits high catalytic activity and can efficiently catalyze the decomposition of H2O2 into ·OH, thereby oxidizing and decomposing recalcitrant organic pollutants in wastewater. The porous support made of MOF structure has high porosity and large specific surface area, which can accelerate the mass transfer of reactants and provide abundant sites for the subsequent anchoring of the iron-cobalt bimetallic single-atom catalyst. The iron-cobalt bimetallic single-atom catalyst is highly dispersed on the surface of the porous support, exposing more catalytic sites and exhibiting high catalytic efficiency.

[0029] Preferably, the mass ratio of hydrogen peroxide added in step (4) to COD in the influent is 0.5 to 1.2:1, and the mass ratio of hydrogen peroxide to heterogeneous catalyst is 4 to 6:1.

[0030] Preferably, in step (5), the dissolved oxygen in the built-in MBR reactor is greater than 2 mg / L, and the residence time in the built-in MBR reactor is 8 to 12 h.

[0031] Preferably, in step (6), the mass ratio of ozone to COD in the ozone treatment unit is 3 to 5:1, and the treatment time in the ozone treatment unit is 60 to 120 minutes.

[0032] Preferably, in the carbon filter unit of step (7), the empty bed filtration rate is 8-10 m / h, the filter bed thickness is 1.5-2.0 m, and the iodine value is ≥950.

[0033] Therefore, the present invention has the following beneficial effects:

[0034] (1) The effluent ammonia nitrogen and total nitrogen of the OAO unit of this invention can meet the discharge standards of Table 2 of the Pollution Control Standard for Municipal Solid Waste Landfills (GB16889-2008), and there is no nitrification liquid return pump or internal return pump, so the operating energy consumption is more economical;

[0035] (2) The deep treatment section adopts a two-stage AOP-based treatment process. The AOP process can use a combination of Fenton and ozone processes, resulting in higher COD compliance stability.

[0036] (3) No concentrate is generated during the entire process, which will not lead to salt accumulation in the landfill.

[0037] (4) The Fenton treatment unit uses a heterogeneous catalyst, which can save a lot of hydrogen peroxide and ferrous oxide dosage compared with the traditional Fenton, and greatly reduce the generation of iron sludge. Furthermore, the catalyst after the reaction can be recovered and recycled, resulting in lower investment and operating costs. Attached Figure Description

[0038] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0039] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0040] In this invention, unless otherwise specified, all raw materials are available from the market or commonly used in the industry. The methods in the following embodiments are conventional methods in the field unless otherwise specified.

[0041] General Implementation Examples:

[0042] A comprehensive treatment method for leachate from aging landfills, such as... Figure 1 As shown, the steps include:

[0043] (1) After solid-liquid separation, the leachate enters the OAO unit and undergoes denitrification in sequence through the O1 aerobic tank, the A facultative tank, and the O2 aerobic tank. The leachate has a COD of 1000-3000 mg / L, a B / C ratio of less than 0.20, a C / N ratio of ≤1, an ammonia nitrogen of 500-2000 mg / L, a total nitrogen of 500-3000 mg / L, a Kjeldahl nitrogen of no more than 40 mg / L, and a pH of 7.5-8.0. The dissolved oxygen in the O1 and O2 aerobic tanks is controlled at 2-6 mg / L. In the A facultative tank, a carbon source is added at a carbon-to-nitrogen ratio of 3-5:1 to carry out complete denitrification. The carbon source is selected from one or more of methanol, glucose, and sodium acetate. The residence time in the O1 aerobic tank is 48-96 h, the residence time in the A facultative tank is 60-120 h, and the residence time in the O2 aerobic tank is 12-18 h.

[0044] (2) The effluent from the OAO unit enters the UF unit for ultrafiltration treatment to intercept the sludge. The intercepted sludge is then returned to the O1 aerobic tank and the O2 aerobic tank. The sludge return ratio of the O1 aerobic tank is 100-300%, and the sludge return ratio of the O2 aerobic tank is 600-800%.

[0045] (3) The effluent from the UF unit enters the coagulation sedimentation tank, where coagulants PAC and PAM are added for coagulation and sedimentation; the dosage of PAC is 80-200 ppm and the dosage of PAM is 1-2 ppm.

[0046] (4) The effluent from the coagulation sedimentation tank enters the Fenton treatment unit for primary AOP treatment; in the Fenton treatment unit, acid is first added to adjust the pH to 2-4, then Fenton reagent is added for reaction, and then alkali is added to adjust the pH to 7.0-9.0 for precipitation; the Fenton reagent includes hydrogen peroxide and a heterogeneous catalyst, the mass ratio of hydrogen peroxide to COD in the influent is 0.5-1.2:1, and the mass ratio of hydrogen peroxide to heterogeneous catalyst is 4-6:1; the preparation method of the heterogeneous catalyst includes the following steps:

[0047] A) Dissolve ferric chloride in DMF, then add terephthalic acid, and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:0.7-0.8; the mixed solution is subjected to hydrothermal reaction at 100-110℃ for 12-24h to obtain Fe-MOF; B) Calcine Fe-MOF at 700-800℃ for 1-3h in an inert atmosphere to obtain a porous support;

[0048] C) The porous carrier is mixed and ground with ferric chloride, cobalt nitrate and glucose in a mass ratio of 1:1~2:0.3~0.5:20~25. Then urea is added, and the mass ratio of porous carrier to urea is 1:50~80. After further grinding, the precursor powder is obtained.

[0049] D) The precursor powder is calcined at 700–900°C for 1–3 h in an inert atmosphere to obtain the heterogeneous catalyst;

[0050] (5) The effluent from the Fenton treatment unit enters the built-in MBR reactor for microbial treatment; the dissolved oxygen in the built-in MBR reactor is greater than 2 mg / L, and the residence time in the built-in MBR reactor is 8 to 12 h.

[0051] (6) The effluent from the built-in MBR reactor enters the ozone treatment unit for secondary AOP treatment; the mass ratio of ozone to COD in the ozone treatment unit is 3-5:1, and the treatment time in the ozone treatment unit is 60-120 min.

[0052] (7) The effluent from the ozone treatment unit enters the carbon filter unit. In the carbon filter unit, the empty bed filtration rate is 8-10 m / h, the filter bed thickness is 1.5-2.0 m, and the iodine value is ≥950. After adsorption by activated carbon, the effluent quality meets the discharge standards.

[0053] Example 1:

[0054] The leachate from a closed landfill in Ningbo has the following raw water characteristics: COD 1000–2500 mg / L, B / C ratio less than 0.2, ammonia nitrogen 1200–2000 mg / L, total nitrogen 1300–2500 mg / L, C / N ≤ 1, Kjeldahl nitrogen < 40 mg / L, pH 7.5–8.0. It is treated using a comprehensive treatment method for leachate from an aging landfill, as described in this invention. The specific steps are as follows:

[0055] (1) The leachate enters the OAO unit and passes through the O1 aerobic tank, the A facultative tank and the O2 aerobic tank in sequence for denitrification. The dissolved oxygen in the O1 aerobic tank and the O2 aerobic tank is controlled at 2-6 mg / L. In the A facultative tank, a carbon source is added at a carbon-nitrogen ratio of 4:1 to carry out a complete denitrification reaction. The carbon source is methanol. The residence time in the O1 aerobic tank is 84 h, the residence time in the A facultative tank is 108 h, and the residence time in the O2 aerobic tank is 18 h.

[0056] (2) The effluent from the OAO unit enters the UF unit for ultrafiltration treatment to intercept the sludge. The intercepted sludge is then returned to the O1 aerobic tank and the O2 aerobic tank. The sludge return ratio of the O1 aerobic tank is 300%, and the sludge return ratio of the O2 aerobic tank is 600%. The COD of the effluent from the UF unit is 400-800 mg / L, the ammonia nitrogen is less than 5 mg / L, and the total nitrogen is less than 40 mg / L.

[0057] (3) The effluent from the UF unit enters the coagulation sedimentation tank, where coagulants PAC and PAM are added for coagulation and sedimentation. The dosage of PAC is 150 ppm and the dosage of PAM is 1.5 ppm. After coagulation and sedimentation, the effluent COD is 350-600 mg / L, and the ammonia nitrogen and total nitrogen remain basically unchanged.

[0058] (4) The effluent from the coagulation sedimentation tank enters the Fenton treatment unit for primary AOP treatment. In the Fenton treatment unit, acid is first added to adjust the pH to 3, and then Fenton reagent is added for reaction. Fenton reagent includes hydrogen peroxide and heterogeneous catalyst. The mass ratio of hydrogen peroxide added to COD in the influent is 1:1, and the mass ratio of hydrogen peroxide to heterogeneous catalyst is 5:1. Then, alkali is added to adjust the pH to 7 for precipitation. The supernatant is sent to the built-in MBR reactor. The heterogeneous catalyst obtained from precipitation can be recycled.

[0059] The preparation method of the heterogeneous catalyst includes the following steps:

[0060] A) Ferric chloride was dissolved in DMF, and then terephthalic acid was added. After stirring evenly, a mixed solution was obtained. The molar ratio of ferric chloride to terephthalic acid was 1:0.8. The mixed solution was subjected to hydrothermal reaction at 105℃ for 18h to obtain Fe-MOF.

[0061] B) The Fe-MOF was calcined at 800℃ for 1 h in a nitrogen atmosphere to obtain a porous support;

[0062] C) The porous carrier is mixed and ground with ferric chloride, cobalt nitrate and glucose in a mass ratio of 1:1.5:0.4:24. Then urea is added, and the mass ratio of porous carrier to urea is 1:65. After further grinding, the precursor powder is obtained.

[0063] D) The precursor powder was calcined at 800°C for 2 hours in a nitrogen atmosphere to obtain the heterogeneous catalyst;

[0064] (5) The effluent from the Fenton treatment unit enters the built-in MBR reactor for microbial treatment; the dissolved oxygen in the built-in MBR reactor is greater than 2 mg / L, and the residence time in the built-in MBR reactor is 10 h; after MBR treatment, the effluent COD is 180-300 mg / L, ammonia nitrogen is less than 1 mg / L, and total nitrogen is less than 30 mg / L.

[0065] (6) The effluent from the built-in MBR reactor enters the ozone treatment unit for secondary AOP treatment; the mass ratio of ozone to COD in the ozone treatment unit is controlled at 3:1, and the treatment time in the ozone treatment unit is 100 min.

[0066] (7) The effluent from the ozone treatment unit enters the carbon filter unit. In the carbon filter unit, the empty bed filtration rate is 9 m / h, the filter bed thickness is 1.8 m, and the iodine value is 1000. After adsorption by activated carbon, the COD of the final effluent is 80 mg / L, which meets the emission limit standard of the "Standard for the Control of Municipal Solid Waste Landfills" (GB 16889-2008).

[0067] Example 2:

[0068] The leachate from a landfill in Pujiang, Jinhua, has the following characteristics: COD 1000–1500 mg / L, B / C ratio less than 0.2, ammonia nitrogen 500–1200 mg / L, total nitrogen 600–1500 mg / L, C / N ≤ 1, Kjeldahl nitrogen < 40 mg / L, and pH 7.5–8.0. This invention provides a comprehensive treatment method for leachate from an aging landfill. The specific steps are as follows:

[0069] (1) The leachate enters the OAO unit and passes through the O1 aerobic tank, the A facultative tank and the O2 aerobic tank in sequence for denitrification. The dissolved oxygen in the O1 aerobic tank and the O2 aerobic tank is controlled at 2-6 mg / L. In the A facultative tank, a carbon source is added at a carbon-nitrogen ratio of 4:1 to carry out a complete denitrification reaction. The carbon source is methanol. The residence time in the O1 aerobic tank is 50 h, the residence time in the A facultative tank is 65 h, and the residence time in the O2 aerobic tank is 14 h.

[0070] (2) The effluent from the OAO unit enters the UF unit for ultrafiltration treatment to intercept the sludge. The intercepted sludge is then returned to the O1 aerobic tank and the O2 aerobic tank. The sludge return ratio of the O1 aerobic tank is 200%, and the sludge return ratio of the O2 aerobic tank is 700%. The COD of the effluent from the UF unit is 400-650 mg / L, the ammonia nitrogen is less than 1 mg / L, and the total nitrogen is less than 35 mg / L.

[0071] (3) The effluent from the UF unit enters the coagulation sedimentation tank, where coagulants PAC and PAM are added for coagulation and sedimentation. The dosage of PAC is 100 ppm and the dosage of PAM is 1.2 ppm. After coagulation and sedimentation, the effluent COD is 350-520 mg / L, while the ammonia nitrogen and total nitrogen remain basically unchanged.

[0072] (4) The effluent from the coagulation sedimentation tank enters the Fenton treatment unit for primary AOP treatment. In the Fenton treatment unit, acid is first added to adjust the pH to 3, and then Fenton reagent is added for reaction. Fenton reagent includes hydrogen peroxide and heterogeneous catalyst. The mass ratio of hydrogen peroxide added to COD in the influent is 2:1, and the mass ratio of hydrogen peroxide to heterogeneous catalyst is 5:1. Then, alkali is added to adjust the pH to 9 for precipitation. The supernatant is sent to the built-in MBR reactor. The heterogeneous catalyst obtained from precipitation can be recycled.

[0073] The preparation method of the heterogeneous catalyst includes the following steps:

[0074] A) Ferric chloride was dissolved in DMF, and then terephthalic acid was added. After stirring until homogeneous, a mixed solution was obtained. The molar ratio of ferric chloride to terephthalic acid was 1:0.7. The mixed solution was subjected to hydrothermal reaction at 110℃ for 12 h to obtain Fe-MOF.

[0075] B) The Fe-MOF was calcined at 700℃ for 3 hours in a nitrogen atmosphere to obtain a porous support;

[0076] C) The porous carrier is mixed and ground with ferric chloride, cobalt nitrate and glucose in a mass ratio of 1:1:0.5:20. Then urea is added, and the mass ratio of porous carrier to urea is 1:50. After further grinding, the precursor powder is obtained.

[0077] D) The precursor powder was calcined at 800°C for 2 hours in a nitrogen atmosphere to obtain the heterogeneous catalyst;

[0078] (5) The effluent from the Fenton treatment unit enters the built-in MBR reactor for microbial treatment; the dissolved oxygen in the built-in MBR reactor is greater than 2 mg / L, and the residence time in the built-in MBR reactor is 10 h; after MBR treatment, the effluent COD is 150-260 mg / L, ammonia nitrogen is less than 1 mg / L, and total nitrogen is less than 25 mg / L.

[0079] (6) The effluent from the built-in MBR reactor enters the ozone treatment unit for secondary AOP treatment; the mass ratio of ozone to COD in the ozone treatment unit is controlled at 3.5:1, and the treatment time in the ozone treatment unit is 80 min.

[0080] (7) The effluent from the ozone treatment unit enters the carbon filter unit. In the carbon filter unit, the empty bed filtration rate is 8 m / h, the filter bed thickness is 2.0 m, and the iodine value is 1000. After adsorption by activated carbon, the COD of the final effluent is 60 mg / L, which meets the emission limit standard of the "Standard for the Control of Municipal Solid Waste Landfills" (GB 16889-2008).

[0081] Comparative Example 1 (Heterogeneous catalyst without iron-cobalt bimetallic single-atom catalyst):

[0082] The preparation method of the heterogeneous catalyst used in step (4) of Comparative Example 1 is as follows:

[0083] A) Ferric chloride was dissolved in DMF, and then terephthalic acid was added. After stirring evenly, a mixed solution was obtained. The molar ratio of ferric chloride to terephthalic acid was 1:0.8. The mixed solution was subjected to hydrothermal reaction at 105℃ for 18h to obtain Fe-MOF.

[0084] B) The Fe-MOF was calcined at 800°C for 1 h in a nitrogen atmosphere to obtain the heterogeneous catalyst; the remaining steps were the same as in Example 1.

[0085] The leachate treated in the same way as in Example 1 was treated in step (5) by the built-in MBR reactor, and the COD of the effluent was 330-460 mg / L. After the activated carbon adsorption in step (7), the COD of the final effluent was 150 mg / L, which did not meet the emission limit standard of the "Standard for the Control of Municipal Solid Waste Landfills" (GB 16889-2008).

[0086] Comparative Example 2 (Heterogeneous catalyst supported only on iron single-atom catalyst):

[0087] The preparation method of the heterogeneous catalyst used in step (4) of Comparative Example 2 is as follows:

[0088] A) Ferric chloride was dissolved in DMF, and then terephthalic acid was added. After stirring evenly, a mixed solution was obtained. The molar ratio of ferric chloride to terephthalic acid was 1:0.8. The mixed solution was subjected to hydrothermal reaction at 105℃ for 18h to obtain Fe-MOF.

[0089] B) The Fe-MOF was calcined at 800℃ for 1 h in a nitrogen atmosphere to obtain a porous support;

[0090] C) The porous carrier is mixed and ground with ferric chloride and glucose at a mass ratio of 1:1.5:24, and then urea is added. The mass ratio of porous carrier to urea is 1:65. After further grinding, the precursor powder is obtained.

[0091] D) The precursor powder was calcined at 800°C for 2 hours in a nitrogen atmosphere to obtain the heterogeneous catalyst; the remaining steps were the same as in Example 1.

[0092] The leachate treated in the same way as in Example 1 was treated in step (5) by the built-in MBR reactor, and the COD of the effluent was 250-360 mg / L. After the activated carbon adsorption in step (7), the COD of the final effluent was 110 mg / L, which did not meet the emission limit standard of the "Standard for the Control of Municipal Solid Waste Landfills" (GB 16889-2008).

[0093] Comparative Example 3 (changing the type of metal in the porous carrier):

[0094] The preparation method of the heterogeneous catalyst used in step (4) of Comparative Example 3 is as follows:

[0095] A) Dissolve copper nitrate in DMF, then add terephthalic acid, and stir until homogeneous to obtain a mixed solution; the molar ratio of copper nitrate to terephthalic acid is 1:0.8; the mixed solution is subjected to hydrothermal reaction at 105℃ for 18h to obtain Cu-MOF;

[0096] B) Cu-MOF was calcined at 800℃ for 1 h in a nitrogen atmosphere to obtain a porous support;

[0097] C) The porous carrier is mixed and ground with ferric chloride, cobalt nitrate and glucose in a mass ratio of 1:1.5:0.4:24. Then urea is added, and the mass ratio of porous carrier to urea is 1:65. After further grinding, the precursor powder is obtained.

[0098] D) The precursor powder was calcined at 800°C for 2 hours in a nitrogen atmosphere to obtain the heterogeneous catalyst;

[0099] The leachate treated in the same way as in Example 1 was treated in step (5) by the built-in MBR reactor, and the COD of the effluent was 310-400 mg / L. After the activated carbon adsorption in step (7), the COD of the final effluent was 130 mg / L, which did not meet the emission limit standard of the "Standard for the Control of Municipal Solid Waste Landfills" (GB 16889-2008).

[0100] As can be seen from the treatment results of the above embodiments and comparative examples, after adopting the method of the present invention in Examples 1 and 2, the ammonia nitrogen and total nitrogen in the effluent of the "OAO+UF" denitrification process section and the COD in the effluent of the "coagulation sedimentation + Fenton + built-in MBR + ozone + carbon filtration" deep decarbonization process section all met the expected removal requirements of the process. Finally, all indicators of the effluent met the emission standard limits in Table 2 of the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB16889-2008). However, in Comparative Example 1, the heterogeneous catalyst used in the Fenton treatment did not support an iron-cobalt bimetallic single-atom catalyst; it only used porous carbon material loaded with iron oxides obtained after Fe-MOF calcination as the catalyst. Its catalytic activity was poor, and the recalcitrant large organic molecules in the wastewater could not be fully decomposed into easily degradable small organic molecules, resulting in a high COD content after MBR treatment, and the final effluent COD could not stably meet the emission standards. In Comparative Example 2, the heterogeneous catalyst only supported iron single-atom catalysts and did not support cobalt atoms. Its catalytic activity was also lower than that in Example 1, and it similarly failed to achieve stable COD compliance in the effluent. In Comparative Example 3, a porous support for calcined Cu-MOF supporting an iron-cobalt bimetallic single-atom catalyst was used as the heterogeneous catalyst for the Fenton treatment unit. The catalytic effect was also lower than that in Example 1, indicating that the morphology of the porous support and the type of metal oxidant supported on it both affect the catalytic performance of the heterogeneous catalyst.

[0101] The specific embodiments and experiments of the present invention have been described in detail above. However, some modifications or improvements can be made to the present invention, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for full-scale treatment of aged landfill leachate, characterized by the steps of Comprise: (1) the leachate after removal of floating matter by solid-liquid separation device enters OAO unit, and is sequentially subjected to nitrogen removal by O1 aerobic tank, A facultative tank and O2 aerobic tank; (2) the effluent of step (1) is subjected to ultrafiltration in UF unit, and sludge is intercepted, and the intercepted sludge is backflowed to O1 aerobic tank and O2 aerobic tank; (3) the effluent of step (2) enters coagulation sedimentation tank, and coagulation and sedimentation are carried out after adding coagulant; (4) the effluent of step (3) enters Fenton treatment unit to carry out primary AOP treatment; first, pH is adjusted to 2~4 by adding acid, then H2O2 and heterogeneous catalyst are added, and then pH is adjusted to 7.0~9.0 by adding alkali and then sedimentation is carried out; the preparation method of the heterogeneous catalyst is as follows: A) FeCl3 is dissolved in DMF, then terephthalic acid with a molar ratio of 0.7~0.8:1 to FeCl3 is added, and a mixed solution is obtained by stirring, and the mixed solution is subjected to hydrothermal reaction at 100~110℃ for 12~24h to obtain Fe-MOF; B) the Fe-MOF is calcined at 700~800℃ for 1~3h in an inert atmosphere to obtain a porous carrier; C) the porous carrier is mixed with FeCl3, Co(NO3)2 and glucose according to a mass ratio of 1:1~2:0.3~0.5:20~25, and then grinding is carried out, then urea with a mass ratio of 50~80:1 to the porous carrier is added, and then grinding is carried out to obtain a precursor powder; D) the precursor powder is calcined at 700~900℃ for 1~3h in an inert atmosphere to obtain the heterogeneous catalyst; (5) the effluent of step (4) enters an MBR reactor to carry out microbial treatment; (6) the effluent of step (5) enters an ozone treatment unit to carry out secondary AOP treatment; (7) the effluent of step (6) enters a carbon filter unit, and the effluent water quality reaches the discharge standard after being adsorbed by activated carbon.

2. The method for full-scale treatment of aged landfill leachate according to claim 1, characterized in that, The solid-liquid separation device in step (1) is one of a filter, a grating machine and a coagulation sedimentation tank; the leachate entering the OAO unit has a COD of 1000~3000mg / L, a B / C less than 0.2, a C / N≤1, an ammonia nitrogen of 500~2000mg / L, a total nitrogen of 500~3000mg / L, a Kjeldahl nitrogen not higher than 40mg / L and a pH of 7.5~8.

0.

3. The method according to claim 1, wherein the method is characterized by, In the O1 aerobic tank and the O2 aerobic tank in step (1), the dissolved oxygen is controlled at 2~6mg / L, and complete denitrification reaction is carried out by adding a carbon source according to a carbon-nitrogen ratio of 3~5:1 in the A facultative tank, and the carbon source is selected from one or more of methanol, glucose and sodium acetate; the residence time of the O1 aerobic tank is 48~96h, the residence time of the A facultative tank is 60~120h, and the residence time of the O2 aerobic tank is 12~18h.

4. The method for full-scale treatment of aged landfill leachate according to claim 1, characterized in that, In step (2), the sludge backflow ratio of the O1 aerobic tank is 100~300%, and the sludge backflow ratio of the O2 aerobic tank is 600~800%.

5. The method for full-scale treatment of aged landfill leachate according to claim 1, characterized in that, In step (3), the coagulant includes PAC and PAM, the PAC is added in an amount of 80~200ppm, and the PAM is added in an amount of 1~2ppm.

6. The method for full-scale treatment of aged landfill leachate according to claim 1, characterized in that, In step (4), the mass ratio of hydrogen peroxide to COD in the influent is 0.5~1.2:1, and the mass ratio of hydrogen peroxide to heterogeneous catalyst is 4~6:

1.

7. The method for full-scale treatment of aged landfill leachate according to claim 1, characterized in that, The dissolved oxygen in the built-in MBR reactor in step (5) is greater than 2 mg / L, and the residence time in the built-in MBR reactor is 8-12 h.

8. The method for full-scale treatment of aged landfill leachate according to claim 1, characterized in that, In step (6), the mass ratio of ozone to COD in the influent in the ozone treatment unit is 3-5:1, and the treatment time in the ozone treatment unit is 60-120 min.

9. The method for full-scale treatment of aged landfill leachate according to claim 1, characterized in that, In the carbon filter unit of step (7), the empty bed filtration rate is 8-10 m / h, the filter bed thickness is 1.5-2.0 m, and the iodine value is greater than or equal to 950.

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