Biochar modified sulfur-based slow-release filter material, preparation method and application thereof

Abstract

The present application belongs to the technical field of preparation of sulfur-based filter material, and specifically discloses a biochar modified slow-release sulfur-based filter material, a preparation method and application thereof. The present application is used to solve the problems of loose structure and uncontrollable release of electron donors of traditional sulfur-based filter material. The biochar modified slow-release sulfur-based filter material is a composite filter material with biochar as a substrate, loaded with multifunctional active components, and coated with a high-molecular controlled-release film. The multifunctional active components are uniformly fixed in the pores of the biochar. The preparation method comprises the following steps: pretreatment of biochar raw materials, loading of functional components, initial embryo granulation and molding, coating of high-molecular controlled-release film, surface activation and microbial film formation. The present application can be used for the synergistic removal of nitrate nitrogen, phosphate and antibiotics in wastewater, can improve the overall structural stability of the filter material, and can achieve slow-release control of the active components, avoid rapid loss of the components, prolong the service life of the filter material, and maintain long-term stable supply of the electron donors.

Description

Technical Field

[0001] This invention belongs to the field of sulfur-based filter material preparation technology, and particularly relates to a biochar-modified slow-release sulfur-based filter material, its preparation method and application. Background Technology

[0002] In complex water bodies such as rural sewage, livestock wastewater, and medical wastewater, nitrate-type nitrogen pollution, phosphate-type nutrients, and trace antibiotic pollutants coexist. If these pollutants are not effectively controlled, they will lead to environmental problems such as eutrophication, the spread of antibiotic-resistant genes, and increased ecotoxicity. Therefore, developing a highly efficient, economical, and suitable synergistic removal technology for water bodies with low to medium concentrations of combined pollutants is one of the key directions in the current development of water treatment technology. In rural and dispersed areas, pollutant concentrations are generally low, carbon sources are scarce, and water quality fluctuates greatly. Traditional multi-stage treatment methods suffer from problems such as complex operation, high costs, and incompatibility. Compared with traditional multi-stage treatment processes, filter-driven integrated reaction systems have become the preferred solution due to their compact structure, ease of operation, and low maintenance costs.

[0003] Sulfur autotrophic denitrification is a highly efficient nitrogen removal pathway driven by sulfur-based filter media and requiring no external organic carbon source, making it particularly suitable for applications with insufficient carbon sources or significant water quality fluctuations. This process relies on sulfur autotrophic denitrifying bacteria to reduce nitrate nitrogen to nitrogen gas, resulting in a highly efficient, stable process with low operating costs. However, a byproduct of this pathway is sulfate, which easily accumulates in the system, increasing water salinity and inhibiting microbial activity. Under anaerobic conditions, sulfate is further reduced to hydrogen sulfide by sulfate-reducing bacteria. Hydrogen sulfide is highly corrosive and toxic, not only lowering system pH, corroding pipelines and facilities, and harming human health, but also causing black and odorous water and exceeding emission standards, seriously affecting system safety and operational stability. Furthermore, traditional sulfur-based filter media have a loose structure, uncontrollable electron donor release, and lack a stable carrier to support bacterial adhesion, further limiting the system's treatment efficiency and lifespan. Moreover, existing process filter media cannot achieve synergistic removal of antibiotics. Summary of the Invention

[0004] One objective of this invention is to provide a biochar-modified slow-release sulfur-based filter material that effectively solves the problems of loose structure and uncontrollable electron donor release in traditional sulfur-based filter materials.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: biochar modified slow-release sulfur-based filter material, which is a composite filter material with biochar as matrix, loaded with multifunctional active components, and coated with a polymer controlled-release membrane. The multifunctional active component loading is to uniformly fix sulfur, manganese oxide and calcium oxide in the pores of biochar.

[0006] Another objective of this invention is to provide a method for preparing biochar-modified slow-release sulfur-based filter media as described in the above embodiments, comprising the following steps: S1, pretreatment of biochar raw materials: using rice husks, straw or woody biomass as raw materials, crushing the raw materials and then pyrolyzing and activating them, cooling to room temperature, soaking in 0.1 mol / L hydrochloric acid to remove ash, then rinsing with deionized water until neutral, drying and then alkali-modifying to obtain biochar.

[0007] S2, Functional Component Loading: Sulfur was loaded onto biochar and sulfur powder at a mass ratio of 1:2 using a melt-adsorption method to obtain S... 0 @Biochar; Next, S was deposited using a chemical deposition method. 0 @Biochar and KMnO4 solution were used for manganese oxide loading at a molar ratio of manganese:biochar = 1:5 to obtain MnO2 / S 0 @Biochar; Finally, the MnO2 / S was processed using an impregnation-calcination method. 0 @Biochar was loaded with saturated Ca(OH)₂ solution at a solid-liquid ratio of 1:5 to obtain CaO / MnO₂ / S 0 @Biochar functionalized complex.

[0008] S3, Initial pelleting and molding: CaO / MnO2 / S 0 @The biochar functionalized composite is mixed with binder and pore-forming agent in a mass ratio of 20:3:2. Plasticizer is added, and the mixture is kneaded into a plastic lumps. Then, it is extruded and granulated, cut into segments, and pre-cured to remove the pore-forming agent and enhance its hardness.

[0009] S4. Polymer controlled-release membrane coating: First, prepare the coating solution, then place the preform in a fluidized bed coating machine, spray the coating solution, and control the membrane thickness to 50±5μm; after spraying, the particles are cross-linked and cured to form a dense sustained-release membrane layer, thus obtaining the coated filter material.

[0010] S5. Surface activation and microbial biofilm formation: First, surface activation is carried out by removing impurities from the surface of the coated filter media and rinsing with deionized water. Finally, microbial biofilm formation is carried out by immersing the surface-activated coated filter media in a solution containing sulfur autotrophic denitrifying bacteria and sulfate-reducing bacteria and culturing it under anaerobic conditions for 72 hours to form an initial biofilm, thus preparing biochar-modified slow-release sulfur-based filter media.

[0011] Furthermore, in step S1, the pyrolysis activation method is as follows: the raw material is placed in a tube furnace, nitrogen is introduced to remove oxygen, and then the temperature is raised to 600℃ and kept constant for 2 hours; the alkali modification method is as follows: biochar is immersed in a 2 mol / L potassium hydroxide solution with a solid-liquid ratio of 1:10, stirred at 80℃ for 4 hours, filtered, and repeatedly washed with water until pH=7, and dried at 120℃.

[0012] Furthermore, in step S2, the sulfur loading method is as follows: sulfur powder is heated to 120°C to melt, biochar at 80°C is immersed in the molten sulfur powder, vacuum shaken for 1 hour under a negative pressure of -0.08MPa and a rotation speed of 200rpm, and then rapidly cooled to 25°C to solidify, obtaining S 0 @Biochar

[0013] The manganese oxide loading method is as follows: Prepare a 0.5 mol / L KMnO4 solution, add S 0 @Biochar, and add 1 mol / L H2SO4 dropwise until pH=2, stir the reaction at 60℃, filter, wash with water until no sulfate is detected by BaCl2 test, and dry to obtain MnO2 / S 0 @Biochar

[0014] The calcium oxide loading method is as follows: MnO2 / S 0 @Biochar was immersed in a saturated Ca(OH)₂ solution and sonicated, then dried at 120°C and calcined at 400°C for 2 hours under nitrogen protection. After cooling, CaO / MnO₂ / S was obtained. 0 @Biochar functionalized complex.

[0015] Furthermore, in step S4, the coating solution is prepared as follows: ethyl cellulose and chitosan are dissolved in ethyl acetate at a mass ratio of 7:3, and then 5% triethyl citrate is added. The concentration of the coating solution is controlled at 8 wt%.

[0016] Furthermore, in step S4, the preform is placed in a fluidized bed coating machine with the inlet air temperature set to 40°C. The coating liquid is sprayed at a rate of 2 mL / min and the atomization pressure is 0.3 MPa. After spraying, the particles are fluidized and dried in hot air at 50°C for 1 hour, immersed in 5% glutaraldehyde solution for 10 seconds, and vacuum dried at 60°C for 6 hours to form a dense slow-release film layer.

[0017] Furthermore, in step S5, during surface activation, the coated filter material is rinsed with a 0.01 mol / L sodium hydroxide solution for 5 minutes to remove surface impurities.

[0018] Another object of the present invention is to provide the application of the biochar-modified slow-release sulfur-based filter media described in the above embodiments or the biochar-modified slow-release sulfur-based filter media prepared by the preparation method of the biochar-modified slow-release sulfur-based filter media described in the above embodiments, for the synergistic removal of nitrate nitrogen, phosphate and antibiotics in wastewater.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are:

[0020] (1) This invention improves the overall structural stability of the filter material by constructing a polymer controlled-release membrane to coat the outer layer of the filter material, and achieves slow-release control of active components (manganese oxide, calcium oxide and sulfur), avoiding rapid loss of components, extending the service life of the filter material, and maintaining a long-term stable supply of electron donors.

[0021] (2) By introducing the porous structure of biochar, this invention enhances the adhesion and mass transfer performance of microorganisms, assists in the synergistic colonization and symbiosis of sulfate-reducing bacteria and sulfur-autotrophic denitrifying bacteria, realizes the biological regulation of sulfate and the in-situ conversion of hydrogen sulfide, and reduces its accumulation and emission risks.

[0022] (3) This invention achieves simultaneous nitrogen and phosphorus removal without relying on external chemical agents by driving the sulfur autotrophic denitrification process and manganese oxide precipitation reaction through the synergistic effect of elemental sulfur and manganese oxide in the filter material.

[0023] (4) This invention utilizes the adsorption and conductivity properties of biochar, combined with the slow-release calcium oxide and manganese oxide in the controlled-release membrane, to jointly construct an "adsorption-catalytic oxidation" composite mechanism, effectively achieving the synergistic removal of trace pollutants such as antibiotics, and meeting the current comprehensive treatment needs of complex polluted water bodies.

[0024] In summary, this invention can be widely applied to actual water bodies with scarce carbon sources, low pollutant concentrations, and diverse treatment targets, and has significant environmental adaptability and engineering promotion value. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of the biochar-modified slow-release sulfur-based filter material of the present invention.

[0026] Figure 2 This is a schematic diagram of the connection structure of the filter system for the synergistic removal of nitrogen, phosphorus and antibiotics provided in Example 2.

[0027] Explanation of reference numerals in the attached diagrams: Inlet tank - 1; Inlet pump - 2; Inlet pipe - 3; Filter body - 4; Inlet of filter body - 5; Buffer zone - 6; Load-bearing plate - 7; Reaction zone - 8; Filter plate - 9; Effluent zone - 10; Overflow weir - 11; Effluent outlet of filter body - 12; Dissolved oxygen monitoring probe - 13; Hydrogen sulfide monitoring probe - 14; Data monitoring system - 15; Aeration blower - 16; Gas flow meter - 17; Aeration pipe - 18; Microporous aeration disc - 19; Sedimentation tank - 20; Sludge return pump - 21; Sludge return pipe - 22; Effluent pipe - 23; Effluent tank - 24; Gravel - 25; Biochar modified slow-release sulfur-based filter media - 26. Detailed Implementation

[0028] Example 1: The biochar-modified slow-release sulfur-based filter media provided in this example is a composite filter media with biochar as the matrix, loaded with multifunctional active components (sulfur, manganese oxide, and calcium oxide), and coated with a polymer controlled-release membrane. The biochar-modified slow-release sulfur-based filter media uses elemental sulfur as an electron donor to drive autotrophic denitrification, achieving low-carbon nitrogen removal; manganese oxide achieves pH regulation and synergistic phosphorus removal; and biochar, in conjunction with calcium oxide and manganese oxide, catalytically oxidizes and degrades antibiotics, ultimately achieving synergistic removal of nitrogen, phosphorus, and antibiotics. By enhancing the specific surface area of ​​the filter media with biochar, the colonization of sulfate-reducing bacteria and sulfur-autotrophic denitrifying bacteria is increased, electron migration efficiency is enhanced, and the accumulation of sulfate and hydrogen sulfide is resolved. Furthermore, the release behavior of the multifunctional components is regulated by the polymer controlled-release membrane, achieving a stable structure, synergistic function, and sustained-release synergistic purification effect for nitrogen, phosphorus, and antibiotic pollution.

[0029] Preparation methods of biochar-modified slow-release sulfur-based filter media, such as... Figure 1 As shown, the process includes the following steps: (1) Pretreatment of biochar raw materials. After pretreatment, the biochar raw materials have a specific surface area ≥ 800 m². 2 The biochar has a pore size distribution of 2–50 nm and a surface oxygen-containing functional group density ≥1.2 mmol / g. Pretreatment of biochar raw materials can increase the specific surface area and enhance the activity of functional groups.

[0030] The specific method is as follows: Agricultural waste (rice husks / straw) or woody biomass (pine sawdust) is used as raw material, and the raw material is crushed to a particle size ≤0.5mm; then, pyrolysis activation is carried out, the raw material is placed in a tube furnace, nitrogen is introduced at a flow rate of 200mL / min to remove oxygen, the temperature is raised to 600℃ at 10℃ / min and held at a constant temperature for 2h; after cooling to room temperature, it is soaked in 0.1mol / L hydrochloric acid for 24h to remove ash, then rinsed with deionized water until neutral, and dried at 105℃ for 12h; then, alkali modification is carried out, the biochar is immersed in 2mol / L potassium hydroxide solution at a solid-liquid ratio of 1:10, stirred at 80℃ for 4h, filtered, and repeatedly washed with water until pH=7, and dried at 120℃ for later use to obtain modified biochar.

[0031] (2) Functional component loading: Sulfur, manganese oxide, and calcium oxide are uniformly fixed in the pores of biochar. Manganese oxide is a multivalent metal oxide. On the one hand, it can react with reduced sulfur substances such as hydrogen sulfide to form precipitates that stabilize their release and control the accumulation of sulfur pollution. On the other hand, it can form manganese phosphate precipitates with phosphates, achieving simultaneous phosphorus removal without the need for iron components. More importantly, manganese oxide has catalytic oxidation function, which can stimulate free radical degradation of trace antibiotics in water. Based on this, biochar is introduced. Its rich microporous structure and surface functional groups can significantly improve the specific surface area and adsorption capacity of the filter media, and enhance the retention capacity of antibiotic organic pollutants. Biochar also has good conductivity and biocompatibility, which is conducive to the co-attachment and stable synergy of sulfur autotrophic denitrifying bacteria and sulfate-reducing bacteria. At the same time, through the electron transfer synergistic mechanism, it accelerates the autotrophic reaction rate and improves the system treatment efficiency.

[0032] The specific method for loading functional components is as follows: First, sulfur element loading is carried out using a melt-adsorption method. Sulfur powder (purity greater than 99.5%) is heated to 120℃ to melt. Hot biochar at 80℃ is immersed in the molten sulfur powder at a mass ratio of biochar:sulfur powder = 1:2. Vacuum shaking is performed for 1 hour under a negative pressure of -0.08MPa and a rotation speed of 200rpm to ensure sulfur penetration into the micropores. The mixture is then rapidly cooled to 25℃ to solidify, yielding S. 0 @Biochar

[0033] Next, manganese oxide loading was performed using chemical deposition. A 0.5 mol / L KMnO4 solution was prepared, and S was added at a molar ratio of manganese:biochar = 1:5. 0 @Biochar, and add 1 mol / L H2SO4 dropwise until pH=2, stir at 60℃ for 3 h, the reaction formula is: 2KMnO4+3C+2H2SO4→2MnO2+K2SO4+2CO2+2H2O; filter, wash with water until no sulfate is detected by BaCl2, dry to obtain MnO2 / S 0 @Biochar

[0034] Finally, calcium oxide loading was performed using an impregnation-calcination method. MnO2 / S 0 @Biochar was immersed in a saturated Ca(OH)₂ solution with a solid-liquid ratio of 1:5, sonicated for 30 min, dried at 120℃, and then calcined at 400℃ for 2 h under nitrogen protection (Ca(OH)₂→CaO+H₂O). After cooling, CaO / MnO₂ / S was obtained. 0 @Biochar functionalized complex.

[0035] (3) Pre-embryo granulation. Pre-embryo granulation can enhance mechanical strength and optimize hydraulic mass transfer performance.

[0036] First, the binder is added, including CaO / MnO2 / S. 0The biochar functionalized composite was mixed with bentonite binder and NH4HCO3 pore-forming agent at a mass ratio of 20:3:2; 20% polyvinyl alcohol (PVA) solution was added as a plasticizer, and the mixture was kneaded until it formed a plastic agglomerate. Then, it was extruded and granulated into cylindrical granules using a screw extruder with a 3mm orifice; the granules were then cut into preforms with a length of 4±0.5mm. Finally, a pre-curing treatment was performed, placing the preforms in a 60℃ hot air drying oven for 12 hours; then transferring them to a muffle furnace and calcining at 300℃ for 2 hours under a nitrogen atmosphere to remove the pore-forming agent and enhance hardness.

[0037] (4) Polymer controlled-release membrane coating enables the slow release of active components and extends the filter media life.

[0038] First, prepare the coating solution by dissolving ethyl cellulose (EC) and chitosan (CS) in ethyl acetate at a mass ratio of 7:3, and then adding 5% triethyl citrate as a plasticizer to control the concentration of the coating solution to 8 wt%.

[0039] Next, fluidized bed coating is performed. The preform is placed in a fluidized bed coating machine with the inlet air temperature set to 40℃. The coating liquid is sprayed at a rate of 2mL / min, the atomization pressure is 0.3MPa, and the film thickness is controlled to be 50±5μm.

[0040] Finally, the cross-linking and curing process is completed. After spraying, the particles are fluidized and dried in hot air at 50°C for 1 hour, then immersed in 5% glutaraldehyde solution for 10 seconds to initiate chitosan cross-linking. The particles are then vacuum dried at 60°C for 6 hours to form a dense slow-release membrane layer, thus obtaining the coated filter material.

[0041] (5) Surface activation and microbial biofilm formation enhance biocompatibility and activate reaction sites.

[0042] First, surface activation was performed. The coated filter media was rinsed with 0.01 mol / L sodium hydroxide solution for 5 minutes to remove surface impurities; after rinsing with deionized water, it was sealed and stored at 4°C for later use.

[0043] Finally, microbial biofilm formation was carried out. The surface-activated coated filter media was immersed in a solution containing sulfur autotrophic denitrifying bacteria and sulfate-reducing bacteria, and cultured under anaerobic conditions (dissolved oxygen concentration less than 0.2 mg / L) for 72 h to form an initial biofilm, thus preparing biochar-modified slow-release sulfur-based filter media.

[0044] The controlled-release membrane of biochar-modified slow-release sulfur-based filter media enables the slow release of manganese oxide, calcium oxide, and sulfur, regulating the mass transfer rate and extending the filter media's lifespan. This not only helps maintain a stable reaction environment in low-concentration pollutant conditions but also effectively avoids the inhibition of microbial systems by sudden high concentrations, further enhancing the filter media's continuous operation and shock resistance in engineering environments.

[0045] This embodiment constructs a biochar-modified slow-release sulfur-based filter material based on a polymer controlled-release membrane, achieving the synergistic removal of pollutants such as nitrate nitrogen, phosphate, and antibiotics. This significantly improves the problems of structural instability, byproduct accumulation, and limited treatment function of traditional sulfur-based filter materials.

[0046] Example 2: This example provides a filter system for the synergistic removal of nitrogen, phosphorus and antibiotics. The system consists of an influent unit, a filter unit, a sedimentation unit and an effluent unit.

[0047] like Figure 2 As shown, the inlet unit includes an inlet tank 1, an inlet pump 2, and an inlet pipe 3. The sedimentation unit includes a sedimentation tank 20, a sludge return pump 21, and a sludge return pipe 22. The inlet of the sedimentation tank 20 is located at the top of the sedimentation tank 20, the outlet of the sedimentation tank 20 is located at the upper part of the sedimentation tank 20, and the sludge outlet of the sedimentation tank 20 is located at the bottom of the sedimentation tank 20. The effluent unit includes an effluent pipe 23 and an effluent tank 24. The filter unit includes a filter body 4, a monitoring section, and an aeration section. The inlet 5 and sludge inlet of the filter body are both located at the bottom of the filter body 4, and the outlet 12 of the filter body is located at the top of the filter body 4. The inlet tank 1 of the inlet unit is connected to the inlet 5 of the filter body through the inlet pipe 3. The inlet of the sedimentation tank 20 of the sedimentation unit is connected to the outlet 12 of the filter body. The sludge outlet of the sedimentation tank 20 is connected to the sludge inlet of the filter body 4 through the sludge return pipe 22. The outlet of the sedimentation tank 20 is connected to the outlet tank 24 of the outlet unit through the outlet pipe 23.

[0048] The filter body 4 has a square structure and adopts an upflow design. The interior of the filter body 4 is divided into, from bottom to top, a buffer zone 6, a load-bearing plate 7, a reaction zone 8, a filter plate 9, and an effluent zone 10. An overflow weir 11 is provided in the effluent zone 10, which is connected to the effluent outlet 12 of the filter body. The reaction zone 8 has a lower support layer and an upper filter media layer. The support layer is filled with gravel 25 with a particle size of 4–8 mm, and the filter media layer is filled with biochar-modified slow-release sulfur-based filter media 26 as described in Example 1 with a particle size of 3–5 mm. The porosity of both the support layer and the filter media layer is 35%.

[0049] The monitoring section includes a dissolved oxygen monitoring probe 13, a hydrogen sulfide monitoring probe 14, and a data monitoring system 15. Both the dissolved oxygen monitoring probe 13 and the hydrogen sulfide monitoring probe 14 are connected to the data monitoring system 15. Both the dissolved oxygen monitoring probe 13 and the hydrogen sulfide monitoring probe 14 are located on the upper part of the filter media layer in the reaction zone 8 of the filter body 4. Since this is the end of the reaction zone 8, the hydrogen sulfide concentration monitored by the hydrogen sulfide monitoring probe 14 can represent the hydrogen sulfide concentration in the effluent.

[0050] The aeration section includes an aeration blower 16, a gas flow meter 17, an aeration pipe 18, and a microporous aeration disc 19. The gas flow meter 17 is connected to the data monitoring system 15. The microporous aeration disc 19 is placed in the buffer zone 6. In the buffer zone 6, dissolved oxygen first degrades the ammonia nitrogen in the wastewater and buffers the dissolved oxygen content. Then the wastewater enters the reaction zone 8.

[0051] Based on the above-described filter system, this embodiment also provides a method for controlling the synergistic removal of nitrogen, phosphorus, and antibiotics, with the following steps.

[0052] First, residual sludge from the secondary sedimentation tank of a municipal wastewater treatment plant is inoculated into the reaction zone 8 of the filter body 4 to start the process, achieving a MLSS of 2500–3000 mg / L. The influent contains ammonia nitrogen (5.1–15.2 mg / L), nitrate nitrogen (10.1–25.3 mg / L), total phosphorus (2.5–5.3 mg / L), and tetracycline antibiotics (300–600 μg / L). Wastewater from the influent tank 1 enters the buffer zone 6 of the filter body 4 through the influent inlet 5. The influent flow rate is adjusted by the influent pump 2 to ensure a hydraulic retention time of 3 hours. At this time, the aeration blower 16 is turned on, and the air intake is adjusted by the gas flow meter 17. Micro-aeration is achieved through the microporous aeration discs 19 in the buffer zone 6, where ammonia nitrogen in the influent is oxidized to nitrate nitrogen under the action of dissolved oxygen.

[0053] Then, the wastewater enters the reaction zone 8 through the load-bearing plate 7. First, dissolved oxygen is consumed in the support layer, reducing the dissolved oxygen content to below 0.2 mg / L, providing the necessary dissolved oxygen content for the filter media layer. When the wastewater flows through the filter media layer, the polymer controlled-release membrane of the biochar-modified slow-release sulfur-based filter media 26 continuously releases elemental sulfur from the biochar-modified slow-release sulfur-based filter media 26 at a rate of 0.1–0.15 mg / (g·d). This provides electron donors for the sulfur-autotrophic denitrifying bacteria attached to the biochar pores. Utilizing nitrate nitrogen as an electron acceptor, the bacteria reduce nitrate nitrogen to nitrogen gas through metabolic reactions. This process reduces the nitrate nitrogen concentration in the effluent to below 0.5 mg / L, while the concentration of by-product sulfate increases to 80–120 mg / L.

[0054] The generated sulfate is captured by sulfate-reducing bacteria in an anaerobic microenvironment and converted into hydrogen sulfide through a reduction reaction. The biochar-modified slow-release sulfur-based filter media 26 simultaneously releases manganese oxide, which immediately reacts with hydrogen sulfide, releasing free Mn. 2+ It combines with residual hydrogen sulfide to form a stable precipitate, strictly controlling the hydrogen sulfide concentration to 0.05–0.1 mg / L. Simultaneously, the generated manganese sulfide can serve as a secondary sulfur source for subsequent denitrification, achieving sulfur recycling. Furthermore, the released Mn... 2+It reacts with phosphates in wastewater to form insoluble manganese phosphate, which is retained in the filter bed. The abundant carboxyl groups (-COOH) and hydroxyl groups (-OH) on the surface of biochar further complex phosphates through electrostatic adsorption. This dual action results in a total phosphorus removal rate of over 94%, with a stable total phosphorus concentration in the effluent ≤0.3 mg / L.

[0055] In the biochar-modified slow-release sulfur-based filter media 26, the high specific surface area of ​​biochar first adsorbs tetracycline antibiotic molecules through π-π stacking and hydrogen bonding. The pollutants enriched in the micropores are then removed by the Mn released from the biochar-modified slow-release sulfur-based filter media 26. 2+ / Ca 2+ Activate the catalytic oxidation system, Mn 2+ Disproportionation under near-neutral conditions produces hydroxyl radicals, while Ca... 2+ This promotes the generation of superoxide radicals. The two types of free radicals work together to attack the phenolic hydroxyl and dimethylamino groups in the tetracycline molecule, achieving ring-opening mineralization, and ultimately reducing the antibiotic residue concentration to below 50 μg / L, with a mineralization rate of over 70%.

[0056] The hydrogen sulfide concentration in reaction zone 8 is monitored by hydrogen sulfide monitoring probe 14 and then transmitted to the data monitoring system. When the hydrogen sulfide concentration in the effluent is greater than 0.1 mg / L, the data monitoring system 15 will increase the gas flow rate of the gas flow meter, thereby increasing the dissolved oxygen content and using the dissolved oxygen to further reduce the hydrogen sulfide content. When the hydrogen sulfide concentration in the effluent is less than or equal to 0.1 mg / L, the data monitoring system 15 will reduce the gas flow rate of the gas flow meter 17, thereby reducing the dissolved oxygen content, until the dissolved oxygen concentration monitored by dissolved oxygen monitoring probe 13 is less than 0.2 mg / L and then stops.

[0057] Subsequently, the wastewater flows upward in reaction zone 8, passes through filter plate 9 and enters effluent zone 10. Under the action of overflow weir 11, it flows into sedimentation tank 20 through outlet 12 of the filter body. The wastewater is left to stand in sedimentation tank 20 for 1 hour, and manganese phosphate sludge is separated by density difference (density ρ of manganese phosphate sludge > 2.5 g / cm³). 3 The density of the remaining mixed sludge is ρ≈1.03g / cm³. 3 The process removes phosphorus. The remaining sludge (the mixed activated sludge from the manganese phosphate removal sludge) is returned to the filter body 4 via sludge return pipe 22, with a return ratio set at 50%. The final treated wastewater is discharged into the effluent tank 24 through the outlet of sedimentation tank 20.

[0058] The biochar-modified slow-release sulfur-based filter media prepared in this invention has a stable structure and significantly improved hydrolysis resistance after being coated with a polymer controlled-release membrane. The dissolution rate of elemental sulfur in the filter media is maintained at 0.08-0.12 mg / (g·d), and the release of electron donors is stable and controllable. Under the condition that the influent nitrate nitrogen concentration is 10.1-25.3 mg / L, the effluent nitrate nitrogen concentration can be stably controlled at less than 0.5 mg / L. The denitrification efficiency is stable, and the operation cycle can reach more than 90 days without replacing the filter media.

[0059] The sulfate produced during denitrification is partially reduced to hydrogen sulfide in an anaerobic environment. The porous structure of biochar promotes the co-colonization of sulfate-reducing bacteria and sulfur-autotrophic denitrifying bacteria. Meanwhile, manganese oxide can react with hydrogen sulfide to form stable manganese sulfide precipitate, thus controlling the hydrogen sulfide concentration in the effluent to within 0.05–0.1 mg / L, which is significantly lower than the maximum allowable discharge standard (1 mg / L) stipulated in the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). This reduces the risk of black odor, acid corrosion, and gaseous toxicity at the source.

[0060] The sulfur element in the manganese sulfur compound formed by desulfurization exists stably in the form of sulfide, which can be released again in subsequent reactions and participate in the denitrification process. The average service life of the sulfur source can be extended to more than 120 days, reducing the frequency of filter media replenishment and resource waste, and is suitable for medium and long-term continuous operation systems.

[0061] Under the condition that the total phosphorus concentration in the influent is 2.5 to 5.3 mg / L, manganese oxide can react with phosphate to form manganese phosphate precipitate, so that the total phosphorus concentration in the effluent can be stably controlled at ≤0.3 mg / L, without the need for the addition of phosphorus removal agents such as iron salts or aluminum salts, thus achieving simultaneous and efficient phosphorus removal.

[0062] Biochar-modified slow-release sulfur-based filter media synergistically constructs an "adsorption-oxidation" composite system. Under conditions where tetracycline antibiotics (initial concentration 300–600 μg / L) are added to typical aquaculture wastewater, the residual antibiotic concentration in the effluent is below 50 μg / L. Furthermore, the system operates stably without the addition of additional carbon sources and advanced oxidants. The cost per ton of water treated is reduced by 0.82–0.89 yuan compared to traditional processes, and sludge production is reduced by 0.21–0.32 kg / m³. 3 It possesses both good economic and environmental friendliness.

[0063] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing biochar-modified slow-release sulfur-based filter media, characterized in that, Includes the following steps: S1. Biochar raw material pretreatment: Rice husks, straw or wood biomass are used as raw materials. After the raw materials are crushed, they are pyrolyzed and activated. After cooling to room temperature, they are soaked in 0.1 mol / L hydrochloric acid to remove ash. Then they are rinsed with deionized water until neutral. After drying, they are modified with alkali to obtain biochar. S2, Functional Component Loading: Sulfur was loaded onto biochar and sulfur powder at a mass ratio of 1:2 using a melt-adsorption method to obtain S... 0 @Biochar; Next, S was deposited using a chemical deposition method. 0 @Biochar and KMnO4 solution were used for manganese oxide loading at a molar ratio of manganese:biochar = 1:5 to obtain MnO2 / S 0 @Biochar; Finally, the MnO2 / S was processed using an impregnation-calcination method. 0 @Biochar was loaded with saturated Ca(OH)₂ solution at a solid-liquid ratio of 1:5 to obtain CaO / MnO₂ / S 0 @Biochar functionalized complex; S3, Initial pelleting and molding: CaO / MnO2 / S 0 @The biochar functionalized composite is mixed with binder and pore-forming agent in a mass ratio of 20:3:

2. Plasticizer is added and kneaded into a plastic lumps. Then it is extruded and granulated, cut into sections and pre-cured to remove the pore-forming agent and enhance hardness. S4. Polymer controlled-release membrane coating: First, prepare the coating solution, then place the preform in a fluidized bed coating machine, spray the coating solution, and control the membrane thickness to 50±5μm; after spraying, the particles are cross-linked and cured to form a dense slow-release membrane layer, thus obtaining the coated filter material. S5. Surface activation and microbial biofilm formation: First, surface activation is carried out by removing surface impurities from the coated filter media and rinsing with deionized water. Finally, microbial biofilm formation is carried out by immersing the surface-activated coated filter media in a solution containing sulfur autotrophic denitrifying bacteria and sulfate-reducing bacteria and culturing it under anaerobic conditions for 72 hours to form an initial biofilm and prepare biochar-modified slow-release sulfur-based filter media. The biochar-modified slow-release sulfur-based filter material is a composite filter material with biochar as the matrix, loaded with multifunctional active components, and coated with a polymer controlled-release membrane. The multifunctional active component loading involves uniformly fixing sulfur, manganese oxide, and calcium oxide in the pores of the biochar. The biochar-modified slow-release sulfur-based filter media is used for the synergistic removal of nitrate nitrogen, phosphate, and antibiotics from wastewater. When wastewater flows through the filter media layer, the polymer-controlled-release membrane of the biochar-modified slow-release sulfur-based filter media continuously releases elemental sulfur at a rate of 0.1–0.15 mg / (g·d), providing electron donors for sulfur-autotrophic denitrifying bacteria attached to the biochar pores. Utilizing nitrate nitrogen as an electron acceptor, the bacteria reduce nitrate nitrogen to nitrogen gas through metabolic reactions. The generated sulfate is captured by sulfate-reducing bacteria in an anaerobic microenvironment and converted into hydrogen sulfide through a reduction reaction. Simultaneously, the biochar-modified slow-release sulfur-based filter media releases manganese oxide, which immediately reacts with hydrogen sulfide, releasing free Mn. 2+ It combines with residual hydrogen sulfide to form a stable precipitate, suppressing the hydrogen sulfide concentration to 0.05–0.1 mg / L. Simultaneously, the generated manganese sulfide serves as a secondary sulfur source for subsequent denitrification, achieving sulfur recycling. Furthermore, the released Mn... 2+ The biochar reacts with phosphates in the wastewater to form insoluble manganese phosphate, which is retained in the filter bed. The carboxyl and hydroxyl groups on the surface of the biochar further complex the phosphates through electrostatic adsorption. In the biochar-modified slow-release sulfur-based filter media, the high specific surface area of ​​the biochar first adsorbs tetracycline antibiotic molecules through π-π stacking and hydrogen bonding. The pollutants enriched in the micropores are then removed by the manganese phosphate released by the biochar-modified slow-release sulfur-based filter media. 2+ / Ca 2+ Activate the catalytic oxidation system, Mn 2+ Disproportionation under near-neutral conditions produces hydroxyl radicals, while Ca... 2+ This promotes the generation of superoxide radicals. The two types of free radicals work together to attack the phenolic hydroxyl and dimethylamino groups in tetracycline antibiotic molecules, achieving ring-opening mineralization and ultimately reducing the residual concentration of antibiotics to below 50 μg / L, with a mineralization rate of over 70%.

2. The method for preparing biochar-modified slow-release sulfur-based filter media according to claim 1, characterized in that, In step S1, the pyrolysis activation method is as follows: the raw material is placed in a tube furnace, nitrogen is introduced to remove oxygen, and then the temperature is raised to 600℃ and kept constant for 2 hours. The alkali modification method is as follows: biochar is immersed in a 2 mol / L potassium hydroxide solution with a solid-liquid ratio of 1:10, stirred at 80℃ for 4 hours, filtered, and repeatedly washed with water until pH=7, and then dried at 120℃.

3. The method for preparing biochar-modified slow-release sulfur-based filter media according to claim 1, characterized in that, In step S2, the sulfur loading method is as follows: sulfur powder is heated to 120℃ to melt, biochar at 80℃ is immersed in the molten sulfur powder, vacuum shaken for 1 hour under a negative pressure of -0.08MPa and a rotation speed of 200rpm, and then rapidly cooled to 25℃ to solidify, obtaining S 0 @Biochar; The manganese oxide loading method is as follows: Prepare a 0.5 mol / L KMnO4 solution, add S 0 @Biochar, and add 1 mol / L H2SO4 dropwise until pH=2, stir the reaction at 60℃, filter, wash with water until no sulfate is detected by BaCl2 test, and dry to obtain MnO2 / S 0 @Biochar; The calcium oxide loading method is as follows: MnO2 / S 0 @Biochar was immersed in a saturated Ca(OH)₂ solution and sonicated, then dried at 120°C and calcined at 400°C for 2 hours under nitrogen protection. After cooling, CaO / MnO₂ / S was obtained. 0 @Biochar functionalized complex.

4. The method for preparing biochar-modified slow-release sulfur-based filter media according to claim 1, characterized in that, In step S4, the coating solution is prepared by dissolving ethyl cellulose and chitosan in ethyl acetate at a mass ratio of 7:3, and then adding 5% triethyl citrate.

5. The method for preparing biochar-modified slow-release sulfur-based filter media according to claim 1, characterized in that, In step S4, the preform is placed in a fluidized bed coating machine with the inlet air temperature set to 40°C. The coating liquid is sprayed at a rate of 2 mL / min and the atomization pressure is 0.3 MPa. After spraying, the particles are fluidized and dried in hot air at 50°C for 1 hour, immersed in 5% glutaraldehyde solution for 10 seconds, and vacuum dried at 60°C for 6 hours to form a dense slow-release film.

6. The method for preparing biochar-modified slow-release sulfur-based filter media according to claim 1, characterized in that, In step S5, during surface activation, the coated filter material is rinsed with 0.01 mol / L sodium hydroxide solution for 5 minutes to remove surface impurities.

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