Landfill leachate treatment system

Abstract

The invention relates to the technical field of sewage treatment, and provides a landfill leachate treatment system aiming at the problems that the existing landfill leachate treatment technology is large in occupied area and low in treatment efficiency. An integrated structure of an inner cylinder and a peripheral ring is adopted, the inner cylinder is an EEA anaerobic tower, the surface of the EEA anaerobic tower is coated with a resin-based composite coating containing a carbon-based filler, modified activated carbon in the coating adsorbs organic matters through hydroxyl and carboxyl and provides microorganism attachment sites, and a conductive network of modified graphene accelerates direct electron transfer among microorganisms; the composite organic acid maintains the stability of the coating through a hydrogen bond network and serves as a carbon source to start biofilm formation, and the three components synergistically strengthen anaerobic degradation; the peripheral annular device is sequentially provided with an anoxic bin, an aerobic bin, a sedimentation tank and other units, and coagulating sedimentation, biological nitrogen and phosphorus removal and membrane filtration processes are combined; the system shortens the water flow path through the cylindrical structure, cooperates with the coating and the multi-stage treatment unit to achieve efficient removal of pollutants, and has the advantages of being small in occupied area and high in efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of sewage treatment, and in particular to a landfill leachate treatment system. Background Art

[0002] With the increasing amount of municipal solid waste generated, the production of landfill leachate is generally on the rise. This leachate primarily originates from landfills, incineration plants, and transfer stations. Landfill leachate has a complex composition, characterized by high pollutant concentrations, nutrient imbalances, and a wide range of water quality fluctuations. Its levels of conventional pollutants, such as biochemical oxygen demand and chemical oxygen demand, are significantly higher than those in municipal sewage. Currently, commonly used leachate treatment technologies include biological treatment and physicochemical treatment. Biological treatment methods include activated sludge and membrane bioreactors. However, due to high shock loads, difficulty in microbial biofilm formation, and temperature fluctuations, conventional biological methods struggle to consistently meet discharge standards. Physicochemical treatment methods, such as coagulation and sedimentation and membrane separation, offer advantages in removing specific pollutants. Existing leachate treatment technologies typically utilize pretreatment followed by membrane filtration or pretreatment followed by multi-stage biological processes. Membrane filtration processes are subject to challenges such as membrane fouling, short lifespan, difficult operation and maintenance, and high costs. Multi-stage biological processes are limited by lengthy processes, large facility footprints, and treatment efficiency that is susceptible to fluctuations in water quality. Summary of the Invention

[0003] To address the shortcomings of the existing technology, the present application provides a landfill leachate treatment system that utilizes an integrated structure consisting of an inner cylinder and an outer ring. The inner cylinder is an EEA (Effluent Equalization Anaerobic) anaerobic tower, the surface of which is coated with a resin-based composite coating containing carbon-based fillers. The modified activated carbon in the coating adsorbs organic matter through hydroxyl and carboxyl polar groups and provides microbial attachment sites. The conductive network of the modified graphene accelerates direct electron transfer between microorganisms. The composite organic acid maintains the stability of the coating through a hydrogen bond network and acts as a carbon source to initiate biofilm formation. The three synergistically enhance anaerobic degradation. The outer ring device is sequentially equipped with an anoxic chamber, an aerobic chamber, a sedimentation tank, and other units, combining coagulation and sedimentation, biological denitrification and phosphorus removal, and membrane filtration processes. The system shortens the water flow path through a cylindrical structure, and the coating and multi-stage treatment units work together to achieve efficient pollutant removal, with the advantages of small footprint and high efficiency.

[0004] To achieve the above objectives, this application adopts the following technical solutions:

[0005] The present invention provides a landfill leachate treatment system, comprising an inner cylindrical device and an outer annular device, wherein the inner cylindrical device is an EEA anaerobic tower for degrading organic pollutants and generating methane; the inner surface of the EEA anaerobic tower is coated with a resin-based composite coating containing a carbon-based filler; the resin-based composite coating containing a carbon-based filler comprises a water-based epoxy resin, a curing agent, a composite carbon slurry, a composite organic acid, and a porogen; the outer annular device comprises: an anoxic bin for denitrification and denitrification; a first aerobic bin for nitrification; an anaerobic bin for phosphorus release; a second aerobic bin for nitrification and organic matter degradation; a sedimentation tank for solid-liquid separation; a denitrification filter for deep denitrification; and a clear water tank for storing and discharging effluent; a flocculant is added to the sedimentation tank to obtain sludge, which is refluxed to the EEA anaerobic tower according to a set sludge return ratio; after being treated in the EEA anaerobic tower, the landfill leachate to be treated enters the outer annular device in a balanced effluent manner for sequential treatment, and finally discharges from the clear water tank.

[0006] In a feasible implementation scenario, the curing agent is polyamide 651; the carbon-based filler is a composite carbon slurry of modified activated carbon and modified graphene in a mass ratio of (20-25):(1-2); the composite organic acid includes citric acid and tartaric acid in a mass ratio of (3-3.2):1; the porogen is one of ammonium bicarbonate and sodium bicarbonate; the mass ratio of the water-based epoxy resin, curing agent, composite carbon slurry, composite organic acid and porogen is (40-45):18:(20-25):(8-10):(5-8).

[0007] During the preparation of the composite carbon slurry, graphene sheets are embedded in the pores of the modified activated carbon, forming a composite interface that neither blocks the pores nor creates electron conduction pathways. The large π bonds of graphene form conjugated interactions with the aromatic rings on the modified activated carbon surface, enhancing the composite carbon slurry's conductivity and providing a medium for microbial direct electron transfer (DIET). Hydrogen bonds between the three carboxyl groups of citric acid and the two adjacent carboxyl groups of tartaric acid form a network structure in the composite organic acid. This network increases the solubility of the composite organic acid in water compared to single citric acid and ensures uniform dispersion in the resin matrix. Citric acid, as a metabolizable carbon source, initiates anaerobic biofilm formation in the anaerobic reactor. Tartaric acid, due to its vicinal diol structure, is difficult for microbial enzymes to recognize and acts as a structural support to maintain interface stability.

[0008] In a feasible implementation scenario, the modified activated carbon is obtained by mixing activated carbon and hydrogen peroxide solution in a solid-liquid mass ratio of 1:(4-5), reacting at 60-65° C. for 2 to 3 hours, and then filtering and drying; the modified graphene is obtained by mixing graphene and hydrogen peroxide solution in a solid-liquid mass ratio of 1:(4-5), reacting at 60-65° C. for 2 to 3 hours, and then filtering and drying.

[0009] Activated carbon undergoes an oxidation reaction with a 5% hydrogen peroxide solution at 60-65°C. The inert carbon atoms on its surface are oxidized to polar groups such as hydroxyl and carboxyl groups, providing reaction sites for subsequent hydrogen bonding with organic modifiers. The free radicals produced by the decomposition of hydrogen peroxide etch the activated carbon's micropore walls, increasing the average pore size and specific surface area, improving mass transfer resistance while retaining high adsorption capacity. Graphene undergoes edge oxidation in hydrogen peroxide, generating epoxy and hydroxyl groups, increasing surface defect sites, which become active centers for electron transfer and enhance the efficiency of electron transfer in microbial metabolism.

[0010] In a feasible implementation scenario, the modified graphene is mixed with water at a solid-liquid mass ratio of 1:(40-50) to prepare a graphene dispersion, which is then mixed with the modified activated carbon and stirred to obtain the composite carbon slurry. Citric acid and tartaric acid are mixed and dissolved in water at a solid-liquid mass ratio of 1:(3-3.5) to obtain a composite organic acid. The composite organic acid is added to a water-based epoxy resin and emulsified at 2000-2500 rpm for 15 to 20 minutes to obtain a pre-emulsion. The porogen is added to the pre-emulsion and stirred at 300-500 rpm for 15 to 20 minutes to obtain a coating emulsion. The composite carbon slurry and the coating emulsion are mixed and homogenized at 50-60 MPa to obtain a composite emulsion. A curing agent is added to the composite emulsion to obtain the resin-based composite coating containing a carbon-based filler, and the particle size of the resin-based composite coating containing a carbon-based filler is D50≤5μm and D90≤15μm.

[0011] Under high-speed shearing at a speed of 2000-2500 rpm, the resin droplets are broken up, and the hydroxyl / carboxyl groups of the composite organic acid are adsorbed at the droplet interface, reducing the oil-water interfacial tension and forming a stable oil-in-water (O / W) emulsion. The shock wave generated during the rupture further refines the droplets, ensuring full contact between the resin and the organic acid. Under low-speed stirring at 300-500 rpm, the bicarbonate (negatively charged) ions of the porogen and the resin microspheres (negatively charged) in the emulsion are evenly dispersed due to like-charge repulsion. The resin matrix in the emulsion forms a thin adsorption layer on the particle surface, preventing the porogen from agglomerating and providing a uniform dispersion medium for subsequent carbon paste compounding.

[0012] In a feasible implementation scenario, the treatment time of the to-be-treated landfill leachate in the EEA anaerobic tower is 24 to 30 hours, the residence time in the anoxic bin is 2.5 to 3 hours, the residence time in the first aerobic bin is 2.5 to 3 hours, the residence time in the anaerobic bin is 2 to 2.5 hours, the residence time in the second aerobic bin is 3 to 3.5 hours, the residence time in the sedimentation tank is 0.5 to 1 hour, the residence time in the denitrification filter is 2.5 to 3 hours, and the residence time in the clear water tank is 0.5 to 1 hour.

[0013] The present application regulates the residence time of landfill leachate in the system by adjusting the volume of each treatment unit during the construction phase of the device, and the inlet and outlet water of all devices are set to enter from the bottom and exit from the top.

[0014] In a feasible implementation, the EEA anaerobic tower uses a heat circulation system to maintain the temperature inside the tower at 28-35°C.

[0015] The EEA anaerobic tower is an inner cylindrical device with an inner surface coated with a resin-based composite coating containing carbon-based fillers. Among them: the modified activated carbon adsorbs organic matter through hydroxyl and carboxyl polar groups, and its porous structure provides attachment sites for microorganisms; the edge defect sites of the modified graphene provide a conductive network, accelerating direct electron transfer (DIET) between microorganisms and promoting the metabolism of methanogens (such as acetic acid decomposition to produce CH4); the composite organic acid acts as a metabolizable carbon source to initiate biofilm formation, while maintaining the stability of the coating interface through a hydrogen bond network. The organic matter (such as protein and fat) in the leachate is decomposed into small molecular fatty acids by hydrolytic bacteria, and the acid-producing bacteria convert them into volatile fatty acids (VFA). Finally, the methanogens convert VFA and H2 / CO2 into CH4 and CO2, achieving COD removal.

[0016] The anoxic chamber uses the organic matter (such as acetic acid) remaining in the effluent of the EEA anaerobic tower as a carbon source. Under anoxic conditions (dissolved oxygen DO is 0.2-0.5 mg / L), denitrifying bacteria (such as Pseudomonas) convert NO3 - The nitrogen is reduced to N2 and escapes to achieve total nitrogen removal; the first aerobic chamber maintains DO at 2-4 mg / L through aeration, and nitrite bacteria and nitrate bacteria oxidize ammonia nitrogen (NH3-N) into nitrite (NO2 - ) and nitrates, providing substrates for subsequent denitrification; in the anaerobic chamber, under anaerobic conditions (DO < 0.2 mg / L), polyphosphate bacteria decompose polyphosphates in cells to generate energy, absorb volatile fatty acids (VFA) in the water and synthesize poly-β-hydroxybutyric acid (PHB), while releasing phosphates into the water; the second aerobic chamber continues to aerate to a DO of 2-4 mg / L, on the one hand completing the nitrification of the remaining ammonia nitrogen, on the other hand aerobic microorganisms degrade residual organic matter (such as difficult-to-degrade COD) to ensure that the effluent COD is ≤100 mg / L.

[0017] In a feasible implementation scenario, the landfill leachate to be treated enters the EEA anaerobic tower after passing through a water quality regulating tank, a dissolved air flotation tank and a pH regulating tank; the water quality regulating tank is used to uniformize the water quality, with a residence time of 6 to 12 hours; the dissolved air flotation tank is used to remove suspended matter and grease, and 30 to 70 mg / L of PAC (polyaluminum chloride) and 0.5 to 2 mg / L of anionic PAM (polyacrylamide) are added; sodium hydroxide is added to the pH regulating tank until the pH at the outlet of the pH regulating tank is 7±0.1.

[0018] The water conditioning tank balances water quality and volume through hydraulic mixing and a 6-12-hour retention period, buffering fluctuations in the influent load. High concentrations of organic matter, ammonia nitrogen, and other pollutants in the leachate are initially diluted at this stage, reducing the impact on the EEA anaerobic tower. The dissolved air flotation tank adds 30-70 mg / L of PAC, which hydrolyzes to generate positively charged hydroxyaluminum ions, neutralizing the negative surface charge of suspended solids (SS) and forming initial flocs. Subsequently, 0.5-2 mg / L of anionic PAM is added, aggregating small flocs into larger alum flocs through the bridging action of long-chain molecules. The dissolved air system dissolves air in water at 0.5 MPa. After decompression, microbubbles are generated. These bubbles adhere to the flocs, and their buoyancy pulls SS and oil to the surface, forming scum, which is removed by a scraper. Sodium hydroxide is added to the pH adjustment tank to create a neutral pH of 7±0.1, creating a neutral environment for the subsequent anaerobic tower. Anaerobic microorganisms, especially methanogens, are sensitive to pH, and neutral conditions prevent enzyme inhibition and ensure efficient anaerobic degradation.

[0019] In a feasible implementation scenario, 10-30 mg / L of PAC and 0.2-1 mg / L of anionic PAM are added to the sedimentation tank.

[0020] By adding 10-30 mg / L of PAC and 0.2-1 mg / L of PAM, sludge flocculation is enhanced through charge neutralization and bridging to form dense flocs; solid-liquid separation is achieved by gravity sedimentation, and part of the sludge is returned to the EEA anaerobic tower to maintain the microbial concentration, and the remaining sludge is dried.

[0021] In a feasible implementation scenario, part of the sludge in the sedimentation tank is returned to the EEA anaerobic tower, the sludge return ratio is set to 200% to 250%, and the aqueous phase is pumped to the membrane biological filter; the system also includes a sludge tank, the remaining sludge after returning from the sedimentation tank enters the sludge tank, the supernatant of the sludge tank is returned to the water quality regulating tank, and the bottom sludge is pumped to the screw press for drying treatment.

[0022] In a feasible implementation, the peripheral annular device further includes a membrane biofilter, which is used to filter the effluent from the denitrification filter. The outlet of the membrane biofilter is connected to the inlet of the clean water tank, and the residence time is 0.5 to 1.5 hours.

[0023] The denitrification filter is filled with quartz sand filter media. The denitrifying bacteria in the biofilm on the filter media use residual organic matter to reduce nitrate to N2. The filter media also intercepts suspended solids through physical filtration to reduce effluent turbidity. The membrane biofilter uses PVDF membrane for microfiltration to intercept SS and large molecular organic matter. The biofilm on the membrane surface further degrades residual COD and ammonia nitrogen to ensure that the effluent COD is ≤35mg / L and SS is ≤1mg / L, meeting drainage standards.

[0024] Beneficial technical effects:

[0025] The present invention designs a landfill leachate treatment system, comprising an inner cylinder and an outer ring. The inner cylinder is a high-efficiency anaerobic tower, and the outer ring is a ring-shaped treatment system. The EEA anaerobic tower is located in the center of the cylindrical treatment system. Surrounding the high-efficiency anaerobic tower are an anoxic chamber, a primary aerobic chamber, an anaerobic chamber, a secondary aerobic chamber, a sedimentation tank, a denitrification filter, and a clear water tank. This system integrates anaerobic pretreatment, multi-stage biochemical treatment, and advanced treatment processes, reducing the overall system footprint while minimizing heat loss from the anaerobic tower, facilitating thermal insulation, and improving anaerobic degradation efficiency. By coating the inner surface of a high-efficiency anaerobic tower with a carbon-doped (mixed carbon-based) resin coating, anaerobic decomposition efficiency is enhanced. The hydroxyl and carboxyl groups of the composite organic acid in the coating form a hydrogen-bonding network with oxygen-containing groups on the surface of the composite carbon slurry. Polar functional groups such as carboxyl and hydroxyl groups in the organic modifier hydrogen-bond with pollutant molecules, promoting their migration from the aqueous phase to the coating surface, thereby increasing pollutant concentration on the coating surface. Simultaneously, cross-linking occurs with the water-based epoxy resin matrix, creating a stable coating interface. The activated carbon and graphene composite interface forms molecular-level adhesion to the microbial cell surface through hydrogen bonding and electrostatic adsorption, providing a shelter for the microorganisms from fluid shear forces. The coating accelerates electron transfer through the conductive properties and edge defects of graphene, synergistically with the adsorption function of the activated carbon, providing a medium for electron transfer and promoting direct electron transfer (DIET) between microorganisms. This accelerates the decomposition of organic matter and the production of methane, thereby improving the efficiency of the anaerobic treatment system, reducing the impact load on subsequent multi-stage biochemical systems, and improving effluent quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the process flow of the landfill leachate treatment system of the present invention;

[0027] Figure 2 This is a schematic cross-sectional view of the EEA anaerobic tower and the peripheral annular device in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions, and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below with reference to the following examples. However, this should not be construed as limiting the scope of this application to the following examples. Without departing from the above-mentioned method concepts of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0029] In this application, the terms used in this application are for the purpose of describing specific embodiments only and are not intended to be limiting of the application.

[0030] As used in this application, the singular forms "for," "or," "an," "any," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0031] In addition, the terms “first” and “second”, if used, are only used for descriptive purposes and should not be understood as indicating or implying relative importance.

[0032] The present invention provides a landfill leachate treatment system, which comprises an inner cylindrical device and a peripheral annular device, wherein the inner cylindrical device is an EEA anaerobic tower; the inner surface of the EEA anaerobic tower is coated with a resin-based composite coating containing a carbon-based filler; the resin-based composite coating containing a carbon-based filler comprises a water-based epoxy resin, a curing agent, a carbon-based filler, a composite organic acid and a porogen; the peripheral annular device comprises: an anoxic bin, a first aerobic bin, an anaerobic bin, a second aerobic bin, a sedimentation tank, a denitrification filter and a clear water tank; a flocculant is added to the sedimentation tank to obtain sludge, and the sludge is returned to the EEA anaerobic tower according to a set sludge return ratio; after the landfill leachate to be treated is treated in the EEA anaerobic tower, it enters the peripheral annular device for sequential treatment and finally discharges from the clear water tank.

[0033] The following will describe in detail a landfill leachate treatment system provided by the present application in combination with different embodiments.

[0034] Example 1

[0035] like Figure 1 、 Figure 2 As shown, a landfill leachate treatment system:

[0036] 1. Add activated carbon to a 5% hydrogen peroxide solution at a solid-liquid mass ratio of 1:4, react at 60°C for 3 hours, filter, wash, and dry to obtain modified activated carbon; add graphene to a 5% hydrogen peroxide solution at a solid-liquid mass ratio of 1:4, react at 60°C for 3 hours, filter, wash, and dry to obtain modified graphene; mix the modified graphene with water at a solid-liquid mass ratio of 1:40, and the mass ratio of modified activated carbon to modified graphene is 20:1.5. Add 0.5% Span-80 dispersant and ultrasonicate for 30 minutes to obtain a graphene dispersion; mix the modified activated carbon and the graphene dispersion, and stir at 800 rpm for 1 hour to obtain a composite carbon slurry;

[0037] 2. Mix citric acid and tartaric acid in a mass ratio of 3:1, mix with water in a solid-liquid mass ratio of 1:3, and stir and dissolve at 40°C to obtain a composite organic acid; add the composite organic acid to the water-based epoxy resin, emulsify at 2000 rpm for 20 minutes to obtain a pre-emulsion; add ammonium bicarbonate to the pre-emulsion, and stir at 300 rpm for 20 minutes to obtain a coating emulsion; add the composite carbon slurry to the coating emulsion in three times, with an interval of 5 minutes each time, maintain stirring at 800 rpm, and use a high-pressure homogenizer at a pressure of 50 MPa to obtain a composite emulsion with a particle size of D50≤5μm and D90≤15μm; add polyamide 651 to the composite emulsion, stir for 15 minutes to obtain a resin-based composite coating containing a carbon-based filler; the mass ratio of water-based epoxy resin, polyamide 651, composite carbon slurry, composite organic acid and ammonium bicarbonate is 40:18:25:8:8;

[0038] 3. The inner surface of the EEA anaerobic tower was sandblasted, and a resin-based composite coating containing a carbon-based filler was sprayed by air spraying with a nozzle diameter of 1.5 mm, a pressure of 0.3 MPa, and a spraying distance of 30 cm. The second spraying was performed 2 hours later. After spraying, the tower was allowed to stand at room temperature for 1 hour, and then cured at 35°C for 48 hours to obtain an EEA anaerobic tower with an inner surface coated with a resin-based composite coating containing a carbon-based filler;

[0039] 4. Pump the untreated landfill leachate into the water quality regulating tank, start paddle stirring to homogenize the water quality, and keep it there for 6 hours. Then, pump the leachate into the dissolved air flotation tank, start stirring, add 30 mg / L of PAC, and then add 0.5 mg / L of anionic PAM. At the same time, start the dissolved air system to prepare supersaturated dissolved air water by mixing air and water from the clean water tank at 0.5 MPa. After the water is decompressed to normal pressure by the releaser, it is released at the bottom of the dissolved air flotation tank. Use a scraper to scrape off the scum on the water surface, and the scum is transported to the spiral stacker for drying. The lower clear liquid enters the pH regulating tank. Add sodium hydroxide to the pH regulating tank until the pH at the outlet of the pH regulating tank is 7±0.1.

[0040] 5. Pump the leachate from the pH adjustment tank to an EEA anaerobic tower coated with a resin-based composite coating containing carbon-based fillers on its inner surface. Start stirring to allow anaerobic decomposition and methane production. The temperature of the EEA anaerobic tower is controlled at 28°C by a thermal circulation system, and the residence time is 30 hours.

[0041] 6. Pump the evenly stirred leachate after EEA anaerobic treatment into the anoxic bin for denitrification and denitrification. The DO of the anoxic bin is controlled within an appropriate range (e.g., 0.2-0.5 mg / L) by adjusting the aeration rate, the sludge return ratio is 200%, and the residence time is 3 hours. Then pump it into the first aerobic bin. The DO of the first aerobic bin is controlled within an appropriate range (e.g., 2-4 mg / L) by adjusting the aeration rate, and the residence time is 2.5 hours. Then pump it into the anaerobic bin. The residence time is 2.5 hours. Then pump it into the second aerobic bin. The DO of the second aerobic bin is controlled within an appropriate range (e.g., 2-4 mg / L) by adjusting the aeration rate, and the residence time is 3 hours.

[0042] 7. The leachate treated in the second aerobic chamber is pumped into the sedimentation tank, and 10 mg / L PAC and 0.2 mg / L anionic PAM are added. The residence time is 1 hour. Part of the sludge produced is returned to the EEA anaerobic tower through a 200% sludge return ratio. The remaining sludge enters the sludge pool. The supernatant of the sludge pool is returned to the water quality regulating tank, and the bottom sludge is pumped to the spiral press for drying treatment;

[0043] 8. Pump the water phase from the sedimentation tank into the denitrification filter with a residence time of 2.5 hours. Use a fixed bed filter structure, fill it with quartz sand as the filter material, and the filtration rate is 6 m / s. The effluent from the denitrification filter enters the membrane biofilter with a residence time of 0.5 hours. The membrane material is PVDF with a pore size of 0.4 μm. The effluent from the membrane biofilter enters the clear water tank. After adding disinfectant to the clear water tank, test the water quality. After meeting the standards, discharge the water with a residence time of 0.5 hours.

[0044] Example 2

[0045] like Figure 1 As shown, a landfill leachate treatment system:

[0046] 1. Add activated carbon to a 5% hydrogen peroxide solution at a solid-liquid mass ratio of 1:4.5, react at 65°C for 2.5 hours, filter, wash, and dry to obtain modified activated carbon; add graphene to a 5% hydrogen peroxide solution at a solid-liquid mass ratio of 1:4.5, react at 65°C for 2.5 hours, filter, wash, and dry to obtain modified graphene; mix the modified graphene with water at a solid-liquid mass ratio of 1:45, and the mass ratio of modified activated carbon to modified graphene is 22:1, add 0.5% Span-80 dispersant, and ultrasonicate for 30 minutes to obtain a graphene dispersion; mix the modified activated carbon and the graphene dispersion, and stir at 800 rpm for 1 hour to obtain a composite carbon slurry;

[0047] 2. Mix citric acid and tartaric acid in a mass ratio of 3.1:1, mix with water in a solid-liquid mass ratio of 1:3.2, and stir and dissolve at 40°C to obtain a composite organic acid; add the composite organic acid to the water-based epoxy resin, emulsify at 2200 rpm for 18 minutes to obtain a pre-emulsion; add ammonium bicarbonate to the pre-emulsion, and stir at 400 rpm for 18 minutes to obtain a coating emulsion; add the composite carbon slurry to the coating emulsion in three times, with an interval of 5 minutes each time, maintain stirring at 800 rpm, and use a high-pressure homogenizer to treat at a pressure of 55 MPa to obtain a composite emulsion with a particle size of D50≤5μm and D90≤15μm; add polyamide 651 to the composite emulsion, stir for 18 minutes to obtain a resin-based composite coating containing a carbon-based filler; the mass ratio of water-based epoxy resin, polyamide 651, composite carbon slurry, composite organic acid and ammonium bicarbonate is 42:18:23:9:6;

[0048] 3. The inner surface of the EEA anaerobic tower was sandblasted, and a resin-based composite coating containing a carbon-based filler was sprayed by air spraying with a nozzle diameter of 1.5 mm, a pressure of 0.3 MPa, and a spraying distance of 30 cm. The second spraying was performed 2 hours later. After spraying, the tower was allowed to stand at room temperature for 1 hour, and then cured at 35°C for 48 hours to obtain an EEA anaerobic tower with an inner surface coated with a resin-based composite coating containing a carbon-based filler;

[0049] 4. Pump the leachate to be treated into the water quality regulating tank, start the paddle stirring to homogenize the water quality, and keep it for 9 hours; then pump the leachate into the dissolved air flotation tank, start the stirring, add 50mg / L of PAC, and then add 1mg / L of anionic PAM. At the same time, start the dissolved air system to prepare supersaturated dissolved air water at 0.5MPa by mixing air and water from the clean water tank. After the pressure is reduced to normal pressure by the releaser, it is released at the bottom of the dissolved air flotation tank. Use a scraper to scrape off the scum on the water surface, and the scum is transported to the spiral stacker for drying. The lower clear liquid enters the pH regulating tank; add sodium hydroxide to the pH regulating tank until the pH at the outlet of the pH regulating tank is 7±0.1;

[0050] 5. Pump the leachate from the pH adjustment tank to an EEA anaerobic tower coated with a resin-based composite coating containing carbon-based fillers on its inner surface. Start stirring to allow anaerobic decomposition and methane production. The temperature of the EEA anaerobic tower is controlled at 30°C by a thermal circulation system, and the residence time is 27 hours.

[0051] 6. Pump the evenly stirred leachate after EEA anaerobic treatment into the anoxic bin for denitrification and denitrification. The DO in the anoxic bin is controlled within an appropriate range (e.g., 0.2-0.5 mg / L) by adjusting the aeration rate, the sludge return ratio is 220%, and the residence time is 3 hours. Then pump it into the first aerobic bin, and the DO in the first aerobic bin is controlled within an appropriate range (e.g., 2-4 mg / L) by adjusting the aeration rate. The residence time is 2.5 hours. Then pump it into the anaerobic bin, and the residence time is 2 hours. Then pump it into the second aerobic bin, and the DO in the second aerobic bin is controlled within an appropriate range (e.g., 2-4 mg / L) by adjusting the aeration rate. The residence time is 3.5 hours.

[0052] 7. The leachate treated in the second aerobic chamber is pumped into the sedimentation tank, and 20 mg / L PAC and 0.5 mg / L anionic PAM are added. The residence time is 1 hour. Part of the sludge produced is returned to the EEA anaerobic tower through a 250% sludge return ratio. The remaining sludge enters the sludge pool. The supernatant of the sludge pool is returned to the water quality regulating tank, and the bottom sludge is pumped to the spiral press for drying treatment;

[0053] 8. Pump the water phase from the sedimentation tank into the denitrification filter with a residence time of 3 hours. Use a fixed bed filter structure, fill it with quartz sand as the filter material, and the filtration rate is 5m / s. The effluent from the denitrification filter enters the membrane biofilter with a residence time of 1 hour. The membrane material is PVDF with a pore size of 0.4μm. The effluent from the membrane biofilter enters the clear water tank. After adding disinfectant to the clear water tank, test the water quality. After meeting the standards, discharge the water with a residence time of 1 hour.

[0054] Example 3

[0055] like Figure 1 As shown, a landfill leachate treatment system:

[0056] 1. Add activated carbon to a 5% hydrogen peroxide solution at a solid-liquid mass ratio of 1:5, react at 65°C for 2h, filter, wash, and dry to obtain modified activated carbon; add graphene to a 5% hydrogen peroxide solution at a solid-liquid mass ratio of 1:5, react at 65°C for 2h, filter, wash, and dry to obtain modified graphene; mix the modified graphene with water at a solid-liquid mass ratio of 1:50, and the mass ratio of modified activated carbon to modified graphene is 25:2, add 0.5% Span-80 dispersant, and ultrasonicate for 30min to obtain a graphene dispersion; mix the modified activated carbon and the graphene dispersion, and stir at 800rpm for 1h to obtain a composite carbon slurry;

[0057] 2. Mix citric acid and tartaric acid in a mass ratio of 3.2:1, mix with water in a solid-liquid mass ratio of 1:3.5, and stir and dissolve at 40°C to obtain a composite organic acid; add the composite organic acid to the water-based epoxy resin, emulsify at 2500 rpm for 15 minutes to obtain a pre-emulsion; add sodium bicarbonate to the pre-emulsion, and stir at 500 rpm for 15 minutes to obtain a coating emulsion; add the composite carbon slurry to the coating emulsion in three times, with an interval of 5 minutes each time, maintain stirring at 800 rpm, and use a high-pressure homogenizer to treat at a pressure of 60 MPa to obtain a composite emulsion with a particle size of D50≤5μm and D90≤15μm; add polyamide 651 to the composite emulsion, stir for 20 minutes to obtain a resin-based composite coating containing a carbon-based filler; the mass ratio of water-based epoxy resin, polyamide 651, composite carbon slurry, composite organic acid and sodium bicarbonate is 45:18:20:10:5;

[0058] 3. The inner surface of the EEA anaerobic tower was sandblasted, and a resin-based composite coating containing a carbon-based filler was sprayed by air spraying with a nozzle diameter of 1.5 mm, a pressure of 0.3 MPa, and a spraying distance of 30 cm. The second spraying was performed 2 hours later. After spraying, the tower was allowed to stand at room temperature for 1 hour, and then cured at 35°C for 48 hours to obtain an EEA anaerobic tower with an inner surface coated with a resin-based composite coating containing a carbon-based filler;

[0059] 4. Pump the leachate to be treated into the water quality regulating tank, start the paddle stirring to homogenize the water quality, and keep it for 12 hours; then pump the leachate into the dissolved air flotation tank, start stirring, add 70 mg / L of PAC, and then add 2 mg / L of anionic PAM. At the same time, start the dissolved air system to prepare supersaturated dissolved air water by mixing air and water from the clean water tank at 0.5 MPa. After the pressure is reduced to normal pressure by the releaser, it is released at the bottom of the dissolved air flotation tank. The scum on the water surface is scraped off with a scraper, and the scum is transported to the spiral press for drying treatment. The lower clear liquid enters the pH regulating tank; sodium hydroxide is added to the pH regulating tank until the pH at the outlet of the pH regulating tank is 7±0.1;

[0060] 5. Pump the leachate from the pH adjustment tank to an EEA anaerobic tower coated with a resin-based composite coating containing carbon-based fillers on its inner surface. Start stirring to allow anaerobic decomposition and methane production. The temperature of the EEA anaerobic tower is controlled at 35°C by a thermal circulation system, and the residence time is 24 hours.

[0061] 6. Pump the evenly stirred leachate after EEA anaerobic treatment into the anoxic bin for denitrification and denitrification. The DO in the anoxic bin is controlled within an appropriate range (e.g., 0.2-0.5 mg / L) by adjusting the aeration rate, the sludge return ratio is 250%, and the residence time is 2.5 hours. Then pump it into the first aerobic bin, and control the DO in the first aerobic bin within an appropriate range (e.g., 2-4 mg / L) by adjusting the aeration rate. The residence time is 3 hours. Then pump it into the anaerobic bin, and control the DO in the second aerobic bin within an appropriate range (e.g., 2-4 mg / L) by adjusting the aeration rate. The residence time is 3.5 hours.

[0062] 7. The leachate treated in the second aerobic chamber is pumped into the sedimentation tank, and 30 mg / L PAC and 1 mg / L anionic PAM are added. The residence time is 0.5 h. Part of the sludge produced is returned to the EEA anaerobic tower through a sludge return ratio of 220%. The remaining sludge enters the sludge pool. The supernatant of the sludge pool is returned to the water quality regulating tank, and the bottom sludge is pumped to the spiral press for drying treatment;

[0063] 8. Pump the water phase from the sedimentation tank into the denitrification filter with a residence time of 3 hours. Use a fixed bed filter structure and fill it with quartz sand as the filter material with a filtration rate of 4 m / s. The effluent from the denitrification filter enters the clear water tank. Add disinfectant to the clear water tank and test the water quality. After meeting the standards, discharge the water with a residence time of 1 hour.

[0064] Comparative Example 1

[0065] A landfill leachate treatment system is different from Example 1 in that the inner surface of the EEA anaerobic tower is only coated with water-based epoxy resin.

[0066] Comparative Example 2

[0067] A landfill leachate treatment system is different from Example 1 in that the coating applied on the inner surface of the EEA anaerobic tower does not contain composite carbon slurry.

[0068] Comparative Example 3

[0069] A landfill leachate treatment system is different from Example 1 in that no composite organic acid is added to the coating coated on the inner surface of the EEA anaerobic tower.

[0070] Performance testing:

[0071] The COD concentrations at the water inlet and outlet of the EEA anaerobic tower in the landfill leachate treatment systems of Examples 1 to 3 and Comparative Examples 1 to 3 of the present application were tested, and the COD removal rate was calculated to illustrate the removal effect of the resin-based composite coating containing carbon-based fillers on organic matter; the methane yield of the EEA anaerobic tower was measured, and the volatile fatty acid concentration (VFA) at the water outlet of the EEA anaerobic tower was tested to illustrate the microbial activity of the EEA anaerobic tower. The test results are shown in Table 1.

[0072] Table 1 Test results

[0073]

[0074] As can be seen from Table 1, the COD at the water inlet of the EEA anaerobic tower in Examples 1 to 3 of the present application is 6790-9377 mg / L, the COD at the outlet is reduced to 893-1392 mg / L, the COD removal rate is 85.2%-86.8%, the VFA concentration is 145-172 mg / L, and the methane yield is 0.30-0.35 L / gCOD; while in Comparative Examples 1-3, due to the lack of composite carbon slurry or composite organic acid and other components in the coating, the COD removal rate is reduced to 69.6%-75.3%, the VFA concentration is increased to 284-367 mg / L, and the methane yield is only 0.13-0.19 L / gCOD, indicating that the resin-based composite coating containing carbon-based fillers in the present application can significantly improve the organic matter degradation efficiency and methane yield of the anaerobic tower.

[0075] Comparative Example 1, coated solely with water-based epoxy resin without composite carbon slurry or composite organic acid, achieved a COD removal rate of 69.6%, a VFA concentration of 367 mg / L, and a methane yield of 0.13 L / gCOD. Without the addition of modified activated carbon and modified graphene, the composite carbon slurry failed to form electron conduction channels on the inner surface of the EEA anaerobic tower, hindering direct electron transfer (DIET) between microorganisms. This resulted in a decreased organic matter decomposition rate and COD removal rate. The smooth surface of the pure epoxy resin coating lacks the porous structure and interfacial adsorption sites provided by the activated carbon / graphene, making it difficult for microorganisms to form a stable biofilm. Furthermore, the coating is susceptible to fluid shear forces, reducing its activity. Without the hydrogen bonding network formed by the hydroxyl and carboxyl groups of the composite organic acid, pollutant migration from the aqueous phase to the coating surface is hindered, resulting in low pollutant concentrations on the coating surface and reduced degradation efficiency. The absence of citric acid as a metabolizable carbon source slowed biofilm initiation within the anaerobic tower, insufficient microbial abundance, and the accumulation of VFAs, significantly reducing methane yield.

[0076] The coating in Comparative Example 2, without the addition of composite carbon slurry, achieved a COD removal rate of 75.3%, a VFA concentration of 284 mg / L, and a methane yield of 0.18 L / gCOD. The lack of modified activated carbon / graphene reduced the coating's conductivity, rendering it unable to act as an electron transfer medium to accelerate DIET. This blocked the electron transfer pathways involved in microbial metabolism, leading to incomplete organic matter decomposition and VFA accumulation. Furthermore, the high adsorption capacity of the modified activated carbon was lost, preventing pollutants from being concentrated on the coating surface, weakening the "adsorption-degradation" synergistic effect and reducing COD removal. The lack of edge defects in the graphene prevented the provision of electron acceptor binding sites for methanogens, reducing the efficiency of methane production pathways (such as acetic acid cracking and H2 / CO2 reduction) and yield.

[0077] The coating in Comparative Example 3, devoid of composite organic acids, achieved a COD removal rate of 72.1%, a VFA concentration of 306 mg / L, and a methane yield of 0.19 L / gCOD. The lack of hydroxyl and carboxyl groups in citric and tartaric acid prevents them from forming hydrogen-bonding networks with oxygen-containing groups on the surface of the carbon-based filler. This reduces coating interface stability, facilitates carbon-based filler agglomeration, and results in a reduced specific surface area and fewer microbial attachment sites. Furthermore, the lack of polar functional groups in the organic acids prevents pollutant migration to the coating surface through hydrogen bonding. High pollutant concentrations in the aqueous phase and low concentrations on the coating surface create mass transfer resistance and a decrease in COD removal. Furthermore, the absence of citric acid as a metabolizable carbon source hinders the initial colonization and biofilm formation of anaerobic microorganisms (especially acid-producing bacteria), resulting in a delayed VFA metabolic pathway and an accumulation of 306 mg / L. The lack of vicinal diol structures in tartaric acid prevents electrochemical stability at the coating interface, increasing electron transfer impedance between the microorganisms and the coating and significantly reducing methane yield.

[0078] The pH, COD, ammonia nitrogen (NH3-N), total nitrogen (TN), total phosphorus (TP) and suspended solids (SS) at the outlet of the clear water tank in the landfill leachate treatment system of Examples 1 to 3 of the present application were tested, and the results are shown in Table 2.

[0079] Table 2 Test results of the clear water tank outlet

[0080]

[0081] As can be seen from Table 2, the effluent quality of the clear water tank of Examples 1 to 3 of the present application meets the "Standard for Pollution Control of Municipal Waste Landfills" (GB16889-2008). The standard requires COD≤100mg / L, and Examples 1 to 3 are 32, 35, and 75mg / L respectively; NH3-N≤25mg / L is required, and Examples 1 to 3 are all ≤8.5mg / L; TN≤40mg / L is required, and Examples 1 to 3 are all ≤14mg / L; TP≤3.0mg / L is required, and Examples 1 to 3 are all ≤0.8mg / L; SS≤30mg / L is required, and Example 3 is 15mg / L, and Examples 1 to 2 are ≤0.9mg / L. Because Example 3 was not filtered using a membrane biofilter, the SS retention effect was reduced, but the emission standards were still met.

[0082] The above results show and describe the basic principles and main features of this application as well as the advantages of this application.

[0083] Those skilled in the art should understand that the present application is not limited to the above-described embodiments. The above-described embodiments and descriptions are merely illustrative of the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. Such changes and improvements are intended to fall within the scope of the present application. The scope of protection claimed in the present application is defined by the equivalents of the appended claims.

Claims

1. A landfill leachate treatment system, characterized in that: The system includes an inner cylindrical device and an outer annular device. The inner cylindrical device is an EEA anaerobic tower for degrading organic pollutants and producing methane. The inner surface of the EEA anaerobic tower is coated with a resin-based composite coating containing a carbon-based filler. The resin-based composite coating containing a carbon-based filler includes a water-based epoxy resin, a curing agent, a composite carbon slurry, a composite organic acid and a porogen. The outer annular device includes: an anoxic bin for denitrification and denitrification; a first aerobic bin for nitrification; an anaerobic bin for phosphorus release; a second aerobic bin for nitrification and organic matter degradation; a sedimentation tank for solid-liquid separation; a denitrification filter for deep denitrification; and a clear water tank for storing and discharging effluent. Flocculant is added to the sedimentation tank to obtain sludge, which is returned to the EEA anaerobic tower according to a set sludge return ratio. After the untreated landfill leachate is treated in the EEA anaerobic tower, it enters the outer annular device in a balanced effluent manner for sequential treatment and finally discharges from the clear water tank.

2. A landfill leachate treatment system according to claim 1, characterized in that: The curing agent is polyamide 651; the carbon-based filler is a composite carbon slurry of modified activated carbon and modified graphene in a mass ratio of (20-25):(1-2); the composite organic acid includes citric acid and tartaric acid in a mass ratio of (3-3.2):1; the porogen is one of ammonium bicarbonate and sodium bicarbonate; the mass ratio of the water-based epoxy resin, curing agent, composite carbon slurry, composite organic acid and porogen is (40-45):18:(20-25):(8-10):(5-8).

3. A landfill leachate treatment system according to claim 2, characterized in that: The modified activated carbon is obtained by mixing activated carbon and hydrogen peroxide solution at a solid-liquid mass ratio of 1:(4-5), reacting at 60-65°C for 2-3 hours, and then filtering and drying; the modified graphene is obtained by mixing graphene and hydrogen peroxide solution at a solid-liquid mass ratio of 1:(4-5), reacting at 60-65°C for 2-3 hours, and then filtering and drying.

4. A landfill leachate treatment system according to claim 2, characterized in that: The modified graphene is mixed with water at a solid-liquid mass ratio of 1:(40-50) to obtain a graphene dispersion, which is then mixed with the modified activated carbon and stirred to obtain the composite carbon slurry. Citric acid and tartaric acid are mixed and dissolved in water at a solid-liquid mass ratio of 1:(3-3.5) to obtain a composite organic acid. The composite organic acid is added to a water-based epoxy resin and emulsified at 2000-2500 rpm for 15-20 minutes to obtain a pre-emulsion. The porogen is added to the pre-emulsion and stirred at 300-500 rpm for 15-20 minutes to obtain a coating emulsion. The composite carbon slurry and the coating emulsion are mixed and homogenized at 50-60 MPa to obtain a composite emulsion. A curing agent is added to the composite emulsion to obtain the resin-based composite coating containing a carbon-based filler, and the particle size of the resin-based composite coating containing a carbon-based filler is D50≤5μm and D90≤15μm.

5. The landfill leachate treatment system according to claim 1, characterized in that: The treatment time of the to-be-treated landfill leachate in the EEA anaerobic tower is 24 to 30 hours, the residence time in the anoxic bin is 2.5 to 3 hours, the residence time in the first aerobic bin is 2.5 to 3 hours, the residence time in the anaerobic bin is 2 to 2.5 hours, the residence time in the second aerobic bin is 3 to 3.5 hours, the residence time in the sedimentation tank is 0.5 to 1 hour, the residence time in the denitrification filter is 2.5 to 3 hours, and the residence time in the clear water tank is 0.5 to 1 hour.

6. The landfill leachate treatment system according to claim 1, characterized in that: The EEA anaerobic tower uses a heat circulation system to maintain the temperature inside the tower at 28-35°C.

7. The landfill leachate treatment system according to claim 1, characterized in that: The landfill leachate to be treated enters the EEA anaerobic tower after passing through a water quality regulating tank, a dissolved air flotation tank and a pH regulating tank; the water quality regulating tank is used to uniformize the water quality, and the residence time is 6 to 12 hours; the dissolved air flotation tank is used to remove suspended matter and grease, and 30 to 70 mg / L of PAC and 0.5 to 2 mg / L of anionic PAM are added; sodium hydroxide is added to the pH regulating tank until the pH at the water outlet of the pH regulating tank is 7±0.

1.

8. The landfill leachate treatment system according to claim 1, characterized in that: 10-30 mg / L of PAC and 0.2-1 mg / L of anionic PAM are added to the sedimentation tank.

9. The landfill leachate treatment system according to claim 7, characterized in that: Part of the sludge in the sedimentation tank is returned to the EEA anaerobic tower, and the sludge return ratio is set to 200% to 250%, and the aqueous phase is pumped to the membrane biological filter; the system also includes a sludge tank, and the remaining sludge after returning from the sedimentation tank enters the sludge tank, the supernatant of the sludge tank is returned to the water quality regulating tank, and the bottom sludge is pumped to the screw press for drying treatment.

10. The landfill leachate treatment system according to claim 1, characterized in that: The peripheral annular device also includes a membrane biofilter, which is used to filter the effluent from the denitrification filter. The outlet of the membrane biofilter is connected to the inlet of the clean water tank, and the residence time is 0.5 to 1.5 hours.

Images