A method for treating agricultural drainage water using an aerated ecological filter

Abstract

This invention provides a method for treating farmland drainage using an aerated ecological filter, relating to the field of wastewater treatment technology. The aerated ecological filter comprises, from top to bottom, a coarse-particle packing layer, an aeration device, a filter screen, a Fe-BC@CS-MOF porous material layer, another filter screen, and a fine-particle packing layer. Pseudomonas taiwanensis and Pseudomonas chengduensis are introduced into the aerated ecological filter for cultivation and acclimatization, which converts nitrate nitrogen in farmland drainage into ammonia nitrogen and degrades organic pollutants, reducing COD in the water. The Fe-BC@CS-MOF porous material layer can adsorb ammonia nitrogen, phosphate, and heavy metals. Ammonia nitrogen and phosphate are desorbed through acid leaching, while heavy metals are retained in the porous material, allowing for the recovery and reuse of ammonia nitrogen and phosphate.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for treating farmland drainage using an aerated ecological filter. Background Technology

[0002] Agricultural drainage is eutrophic wastewater generated during agricultural production due to irrigation, rainfall, or rising groundwater levels. It contains pollutants such as nitrogen, phosphorus, pesticide residues, and suspended solids. Direct discharge into water bodies can easily lead to eutrophication and black, foul-smelling water. Modern agricultural technology relies on high fertilizer inputs (such as slow-release fertilizers and precision fertilization), but drainage systems have not been upgraded accordingly, resulting in significant nitrogen and phosphorus loss through drainage. While currently promoted smart irrigation technologies can improve water use efficiency, they do not solve the problem of pollutant interception at the end of drainage, allowing fertilizer residues to directly enter water bodies through underground pipes and ditches. Although drone spraying and slow-release pesticides reduce pesticide usage, they fail to prevent pesticide diffusion through drainage. Agricultural drainage is generally treated using methods such as constructed wetlands, sedimentation tanks, biofilters, and chemical treatment. Constructed wetlands rely on physical interception, chemical reactions, and biological metabolism to remove pollutants. However, this method requires a large area, takes a long time to establish a biological ecosystem, and the rate of biological metabolism is related to environmental temperature and greatly affected by seasons. Biofilters degrade pollutants using microorganisms, but existing biofilter treatment methods suffer from several drawbacks: high water quality requirements, complex operation and maintenance, and treatment efficiency significantly affected by environmental fluctuations. Chemical methods, while fast, require large quantities of chemical reagents, leading to high costs and the potential for secondary pollution. Furthermore, agricultural wastewater contains substantial amounts of nitrogen and phosphorus; how to recover and return this nitrogen and phosphorus to farmland to avoid waste is also a challenge for those skilled in the art.

[0003] Based on the above problems, those skilled in the art urgently need to develop a treatment method that is low-cost, highly efficient, less affected by the environment, and capable of recycling and reusing nutrients in farmland drainage. Summary of the Invention

[0004] The purpose of this invention is to provide a method for treating farmland drainage using an aerated ecological filter, in order to solve the problems of high cost, low efficiency, and easy loss of nitrogen and phosphorus resources in existing farmland drainage pretreatment methods.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for treating farmland drainage using an aerated ecological filter, comprising the following steps:

[0007] 1) Inoculate Pseudomonas aeruginosa inside the aerated ecological filter and use diluted farmland drainage to cultivate and acclimate the Pseudomonas aeruginosa.

[0008] 2) After preliminary filtration, farmland drainage is passed into an aerated ecological filter pond for further treatment;

[0009] The Pseudomonas species mentioned in step 1) are Pseudomonas taiwanensis and Pseudomonas chengduensis;

[0010] The aerated ecological filter described in step 2) consists of a coarse particle packing layer, an aeration device, a filter screen, a Fe-BC@CS-MOF porous material layer, a filter screen, and a fine particle packing layer from top to bottom. The aerated ecological filter has an outlet at the bottom.

[0011] The preparation method of the Fe-BC@CS-MOF porous material is as follows: agricultural waste is pyrolyzed at high temperature to obtain biochar material; the biochar material is then mixed with Fe... 2+ and Fe 3+ The solutions were mixed, and the pH of the system was adjusted to 10-11. A hydrothermal reaction was carried out to obtain biochar material loaded with magnetic Fe3O4. The biochar material loaded with magnetic Fe3O4 was immersed in chitosan solution, and then glutaraldehyde solution was added dropwise to carry out a cross-linking reaction to obtain biochar material with chitosan surface coating. The biochar material with chitosan surface coating, ferric chloride, terephthalic acid and N,N-dimethylformamide were mixed and carried out a solvothermal reaction. After the reaction was completed, the precipitate was mixed with deionized water, polyacrylic acid and ammonium persulfate, and a surface grafting reaction was carried out under an inert gas atmosphere to obtain Fe-BC@CS-MOF porous material.

[0012] Preferably, the inoculation amount of each type of Pseudomonas is 10 based on the volume of the aerated ecological filter. 12 ~10 13 CFU / m 3 ;

[0013] The farmland drainage contains the following pollutants at the following concentrations: total nitrogen 10–200 mg / L, nitrate nitrogen 10–150 mg / L, soluble phosphate 0.5–20 mg / L, COD 50–500 mg / L, Cd 0.001–0.5 mg / L, and As 0.005–0.5 mg / L.

[0014] Preferably, the process of culturing and acclimatizing Pseudomonas involves gradient acclimatization of Pseudomonas using farmland drainage at different dilution ratios. Acclimatization is completed when the degradation rate of nitrate nitrogen and COD in undiluted farmland drainage by Pseudomonas is ≥90%.

[0015] Preferably, the preliminary filtration is performed using a filter screen with a pore size of 0.1 to 1 mm;

[0016] The rate at which farmland drainage is introduced into the aerated ecological filter is 10–30 L / min, the residence time of farmland drainage in the aerated ecological filter is 10–24 h, and the effluent rate of farmland drainage is 5–10 L / min.

[0017] Preferably, the agricultural waste in the preparation method of the Fe-BC@CS-MOF porous material includes one or more of straw, rice husks, fruit shells and wood;

[0018] The high-temperature pyrolysis temperature is 600-800℃, the high-temperature pyrolysis time is 2-5 hours, and the high-temperature pyrolysis atmosphere is an inert gas atmosphere.

[0019] Preferably, the preparation method of the Fe-BC@CS-MOF porous material contains Fe. 2+ and Fe 3+ Fe in solution 2+ The concentration was 0.1–0.4 mol / L, Fe 3+ The concentration is 0.05–0.2 mol / L;

[0020] The biochar material contains Fe 2+ and Fe 3+ The mixing ratio of the solution is 5g: 20-40mL;

[0021] The hydrothermal reaction is carried out at a temperature of 80–100°C for a duration of 6–12 hours.

[0022] Preferably, in the preparation method of the Fe-BC@CS-MOF porous material, the mass concentration of the chitosan solution is 1-2%, and the mass concentration of the glutaraldehyde solution is 2-5%.

[0023] The mixing ratio of the magnetic Fe3O4-loaded biochar to the chitosan solution is 1g: 10-20mL;

[0024] The volume ratio of the glutaraldehyde solution to the chitosan solution is 1:5 to 10;

[0025] The cross-linking reaction is carried out at a temperature of 20–30°C for 2–4 hours.

[0026] Preferably, in the preparation method of the Fe-BC@CS-MOF porous material, the mixing ratio of surface-coated chitosan biochar material, ferric chloride, terephthalic acid and N,N-dimethylformamide is 1g:0.1-0.2mol:0.1-0.4mol:5-10mL;

[0027] The solvothermal reaction is carried out at a temperature of 110–130°C for a duration of 12–24 hours.

[0028] The mixing ratio of the precipitate, deionized water, polyacrylic acid, and ammonium persulfate is 10g: 30-50mL: 0.5-1g: 0.01-0.05g;

[0029] The surface grafting reaction is carried out at a temperature of 60–80°C for 10–20 hours.

[0030] Preferably, the coarse particle filler includes one or more of quartz sand, anthracite, and ceramsite;

[0031] The particle size of the coarse-grained filler is 10–50 mm;

[0032] The filter screen has a pore size of 0.1–2 mm;

[0033] The fine-particle filler includes one or more of diatomaceous earth, ceramsite sand, and resin particles;

[0034] The particle size of the fine-particle filler is 0.01 to 0.5 mm.

[0035] The present invention has at least the following beneficial effects:

[0036] This invention utilizes an aerated ecological filter to treat farmland drainage. It leverages two Pseudomonas species, *Pseudomonas taiwanensis*, which decomposes large organic molecules in wastewater, reducing COD, and *Pseudomonas chengduensis*, which converts nitrate nitrogen in wastewater into ammonia nitrogen. The invention incorporates a filter layer and an adsorption layer at the bottom of the aeration tank. The coarse-particle packing layer serves as a habitat for microorganisms. The Fe-BC@CS-MOF porous material layer adsorbs ammonia nitrogen, phosphorus, and heavy metal ions. The Fe-OH groups on the surface of this porous material can react with PO42-. 3- The formation of Fe-OP bonds and the introduction of amino and hydroxyl groups in the chitosan coating layer can adsorb ammonia nitrogen. The magnetic Fe3O4 can enhance the adsorption of heavy metals Pd, As, or Cd. After a period of treatment, the porous material is taken out and soaked in an acidic aqueous solution to desorb ammonia nitrogen and phosphate ions, which can be recycled and reused. The desorbed porous material can be put back into the aerated ecological filter for recycling. Detailed Implementation

[0037] This invention provides a method for treating farmland drainage using an aerated ecological filter, comprising the following steps:

[0038] 1) Inoculate Pseudomonas aeruginosa inside the aerated ecological filter and use diluted farmland drainage to cultivate and acclimate the Pseudomonas aeruginosa.

[0039] 2) After preliminary filtration, farmland drainage is passed into an aerated ecological filter pond for further treatment;

[0040] The Pseudomonas species mentioned in step 1) are Pseudomonas taiwanensis and Pseudomonas chengduensis;

[0041] The aerated ecological filter described in step 2) consists of a coarse particle packing layer, an aeration device, a filter screen, a Fe-BC@CS-MOF porous material layer, a filter screen, and a fine particle packing layer from top to bottom. The aerated ecological filter has an outlet at the bottom.

[0042] The preparation method of the Fe-BC@CS-MOF porous material is as follows: agricultural waste is pyrolyzed at high temperature to obtain biochar material; the biochar material is then mixed with Fe... 2+ and Fe 3+ The solutions were mixed, and the pH of the system was adjusted to 10-11. A hydrothermal reaction was carried out to obtain biochar material loaded with magnetic Fe3O4. The biochar material loaded with magnetic Fe3O4 was immersed in chitosan solution, and then glutaraldehyde solution was added dropwise to carry out a cross-linking reaction to obtain biochar material with chitosan surface coating. The biochar material with chitosan surface coating, ferric chloride, terephthalic acid and N,N-dimethylformamide were mixed and carried out a solvothermal reaction. After the reaction was completed, the precipitate was mixed with deionized water, polyacrylic acid and ammonium persulfate, and a surface grafting reaction was carried out under an inert gas atmosphere to obtain Fe-BC@CS-MOF porous material.

[0043] In this invention, the inoculation amount of each type of Pseudomonas is 10 based on the volume of the aerated ecological filter. 12 ~10 13 CFU / m 3 Preferably 2×10 13 ~8×10 13 CFU / m 3 Further preferred is 3×10 13 ~6×10 13 CFU / m 3 More preferably 4×10 13 ~5×10 13 CFU / m 3 .

[0044] In this invention, the farmland drainage contains the following pollutants at the following mass concentrations: total nitrogen 10-200 mg / L, nitrate nitrogen 10-150 mg / L, soluble phosphate 0.5-20 mg / L, COD 50-500 mg / L, Cd 0.001-0.5 mg / L, As 0.005-0.5 mg / L; preferably, total nitrogen 30-150 mg / L, nitrate nitrogen 20-120 mg / L, soluble phosphate 1-18 mg / L, COD 80-400 mg / L, Cd 0.005-0.3 mg / L, As 0.01-0.4 mg / L; more preferably, total nitrogen 50-100 mg / L, nitrate nitrogen 30-80 mg / L, soluble phosphate 2-15 mg / L, COD 100-300 mg / L, Cd 0.01–0.2 mg / L, As 0.05–0.3 mg / L, more preferably total nitrogen 60–80 mg / L, nitrate nitrogen 40–60 mg / L, soluble phosphate 5–10 mg / L, COD 150–200 mg / L, Cd 0.05–0.1 mg / L, As 0.1–0.2 mg / L.

[0045] In this invention, the process of culturing and acclimatizing Pseudomonas involves gradient acclimatization of Pseudomonas using farmland drainage at different dilution ratios. Acclimatization is completed when the degradation rate of nitrate nitrogen and COD in undiluted farmland drainage by Pseudomonas is ≥90%.

[0046] In this invention, the preliminary filtration is performed using a filter screen with a pore size of 0.1 to 1 mm, preferably 0.2 to 0.8 mm, more preferably 0.4 to 0.6 mm, and even more preferably 0.5 mm.

[0047] In this invention, the rate at which farmland drainage is introduced into the aerated ecological filter is 10–30 L / min, preferably 13–25 L / min, more preferably 15–20 L / min, and even more preferably 18 L / min; the residence time of farmland drainage in the aerated ecological filter is 10–24 h, preferably 13–22 h, more preferably 15–20 h, and even more preferably 16–18 h; and the effluent rate of farmland drainage is 5–10 L / min, preferably 6–9 L / min, and even more preferably 7–8 L / min.

[0048] In this invention, the agricultural waste used in the preparation method of the Fe-BC@CS-MOF porous material includes one or more of straw, rice husks, fruit shells, and wood. The particle size of the agricultural waste is preferably 0.5–3 cm, more preferably 1–2 cm, and even more preferably 1.2–1.5 cm.

[0049] In this invention, the temperature of the high-temperature pyrolysis is 600-800℃, preferably 620-780℃, more preferably 650-750℃, and even more preferably 680-720℃; the time of the high-temperature pyrolysis is 2-5h, preferably 2.5-4.5h, and even more preferably 3-4h; the atmosphere of the high-temperature pyrolysis is an inert gas atmosphere, which can be selected from nitrogen, argon, helium or neon.

[0050] In this invention, the preparation method of the Fe-BC@CS-MOF porous material contains Fe. 2+ and Fe 3+ Fe in solution 2+ The concentration is 0.1–0.4 mol / L, preferably 0.15–0.35 mol / L, more preferably 0.2–0.3 mol / L, and even more preferably 0.25 mol / L; Fe 3+ The concentration is 0.05–0.2 mol / L, preferably 0.07–0.18 mol / L, more preferably 0.1–0.15 mol / L, and even more preferably 0.12 mol / L.

[0051] In this invention, the biochar material contains Fe 2+ and Fe 3+ The mixing ratio of the solution is 5g:20-40mL, preferably 5g:23-38mL, more preferably 5g:25-35mL, and even more preferably 5g:28-32mL.

[0052] In this invention, the temperature of the hydrothermal reaction is 80-100°C, preferably 85-90°C, more preferably 88-92°C, and even more preferably 90°C; the time is 6-12 hours, preferably 7-11 hours, more preferably 8-10 hours, and even more preferably 9 hours.

[0053] In this invention, the mass concentration of the chitosan solution in the preparation method of the Fe-BC@CS-MOF porous material is 1-2%, preferably 1.2-1.8%, more preferably 1.4-1.6%, and more preferably 1.5%; the mass concentration of the glutaraldehyde solution is 2-5%, preferably 2.5-4.5%, more preferably 3-4%, and more preferably 3.5%.

[0054] In this invention, the mixing ratio of the biochar loaded with magnetic Fe3O4 to the chitosan solution is 1g:10-20mL, preferably 1g:12-18mL, more preferably 1g:14-16mL, and even more preferably 1g:15mL.

[0055] In this invention, the volume ratio of the glutaraldehyde solution to the chitosan solution is 1:5 to 10, preferably 1:6 to 9, and more preferably 1:7 to 8.

[0056] In this invention, the temperature of the crosslinking reaction is 20-30°C, preferably 23-28°C, and more preferably 25°C; the time is 2-4 hours, preferably 2.5-3.5 hours, and more preferably 3 hours.

[0057] In this invention, the mixing ratio of surface-coated chitosan biochar material, ferric chloride, terephthalic acid, and N,N-dimethylformamide in the preparation method of the Fe-BC@CS-MOF porous material is 1g:0.1-0.2mol:0.1-0.4mol:5-10mL, preferably 1g:0.12-0.18mol:0.15-0.35mol:6-9mL, and more preferably 1g:0.14-0.16mol:0.2-0.3mol:7-8mL.

[0058] In this invention, the temperature of the solvothermal reaction is 110-130°C, preferably 112-128°C, more preferably 115-125°C, and even more preferably 120°C; the time is 12-24h, preferably 14-22h, more preferably 16-20h, and even more preferably 18h.

[0059] In this invention, the mixing ratio of the precipitate, deionized water, polyacrylic acid and ammonium persulfate is 10g:30-50mL:0.5-1g:0.01-0.05g, preferably 10g:35-45mL:0.6-0.9g:0.02-0.04g, and more preferably 10g:38-42mL:0.7-0.8g:0.03g.

[0060] In this invention, the temperature of the surface grafting reaction is 60-80°C, preferably 63-78°C, more preferably 65-75°C, and even more preferably 68-72°C; the time is 10-20h, preferably 12-18h, more preferably 14-16h, and even more preferably 15h.

[0061] In this invention, the coarse particle filler includes one or more of quartz sand, anthracite, and ceramsite.

[0062] In this invention, the particle size of the coarse filler is 10-50 mm, preferably 13-40 mm, more preferably 15-30 mm, and even more preferably 18-20 mm.

[0063] In this invention, the pore size of the filter screen is 0.1-2 mm, preferably 0.3-1.8 mm, more preferably 0.5-1.5 mm, and even more preferably 0.8-1 mm.

[0064] In this invention, the fine particle filler includes one or more of diatomaceous earth, ceramsite sand, and resin particles.

[0065] In this invention, the particle size of the fine particle filler is 0.01-0.5 mm, preferably 0.03-0.3 mm, more preferably 0.05-0.2 mm, and even more preferably 0.08-0.1 mm.

[0066] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] (1) Preparation of Fe-BC@CS-MOF porous materials:

[0069] Wheat straw with a length of 1-2 cm was pyrolyzed at 700℃ for 3 hours under a nitrogen atmosphere to obtain biochar material. The biochar material was then activated by acid leaching in a 5 mol / L hydrochloric acid solution for 1 hour, washed three times with deionized water, and dried in a vacuum drying oven at 80℃ for 5 hours. 10 g of the activated biochar was then soaked in a 40 mL mixed solution of FeSO4 and FeCl3. The Fe in the mixed solution... 2+ The concentration was 0.3 mol / L, Fe 3+ The concentration of the active ingredient was 0.15 mol / L. The pH of the system was adjusted to 10 using ammonia (2 mol / L). The temperature was then rapidly increased to 80℃ for a hydrothermal reaction. After 8 hours, heating was stopped, and the mixture was allowed to cool to room temperature (28℃). The mixture was then filtered, washed three times with water, and vacuum dried at 80℃ for 10 hours to obtain biochar material loaded with magnetic Fe3O4. 5 g of the magnetic Fe3O4-loaded biochar material was immersed in 50 mL of a 2 wt% chitosan solution (containing 5 wt% acetic acid in the solvent). Then, 5 mL of a 5 wt% glutaraldehyde solution was added dropwise to the system at a rate of 1 mL / min. The mixture was stirred at 25℃ for 4 hours to complete the cross-linking reaction. After the cross-linking reaction, the mixture was filtered, washed, and dried to obtain biochar material coated with chitosan.

[0070] Chitosan-coated biochar material, ferric chloride, terephthalic acid, and N,N-dimethylformamide were mixed in a ratio of 1 g: 0.12 mol: 0.4 mol: 10 mL and reacted at 120 °C for 20 h to synthesize MIL-101(Fe) in situ on the material surface. Then, the precipitate was mixed with deionized water, polyacrylic acid, and ammonium persulfate in a ratio of 10 g: 35 mL: 0.6 g: 0.02 g and reacted at 80 °C under a nitrogen atmosphere for 10 h to graft PAA onto the material surface, thus obtaining Fe-BC@CS-MOF porous material.

[0071] (2) Lay filter cotton at the bottom of the aerated ecological filter and above the outlet, then lay a 10cm thick layer of fine particle filler (diatomaceous earth) with a particle size of 0.1 to 0.5mm, and then lay a plastic filter screen with a pore size of 0.1mm; lay Fe-BC@CS-MOF porous material on the plastic filter screen with a thickness of 3 to 5cm, lay a layer of filter screen with a pore size of 1mm, lay aeration pipes on the top of the filter screen, and finally lay coarse particle filler (quartz sand) with a particle size of 10 to 20mm.

[0072] (3) Inject farmland drainage diluted 10 times into the aerated ecological filter. The content of each pollutant in the farmland drainage is shown in Table 1. Then, inoculate with Pseudomonas taiwanensis (inoculation amount of 10). 13 CFU / m 3 ) and Pseudomonas chengduensis (inoculation dose of 10) 13 CFU / m 3 Air is introduced through the aeration pipe at a rate of 100 L / m³. 2 After 10 hours of treatment, samples were taken from the top of the tank for testing. The removal rate of nitrate nitrogen was 95%, and the removal rate of COD was 90%. The water was discharged from the bottom outlet at a rate of 10 L / min.

[0073] The microorganisms were acclimatized by using farmland drainage diluted at 8 times, 5 times, 2 times, and undiluted in sequence. Acclimatization was completed when the system achieved a removal rate of more than 90% for COD and nitrate nitrogen in the undiluted farmland drainage.

[0074] (4) Inject farmland drainage into the aerated ecological filter at a rate of 30 L / min, and introduce air through the aeration pipe at a rate of 100 L / m. 2 After a 15-hour retention period, water is discharged from the lower drain outlet at a rate of 5 L / min.

[0075] The pollutant content in the farmland drainage collected at the outlet is shown in Table 1.

[0076] Table 1. Content of various pollutants in farmland drainage before and after treatment.

[0077]

[0078] The heavy metals include Cd, Pd, As, etc.

[0079] (5) After repeating step (4) 8 times, take out the Fe-BC@CS-MOF porous material, take 10g of sample and soak it in 1L of hydrochloric acid solution with pH value 5 to desorb ammonia nitrogen and phosphate. No heavy metal ions were detected in the desorption solution. The concentration of ammonia nitrogen in the solution was 48.7mg / L and the concentration of phosphate was 8.33mg / L.

[0080] After soaking all Fe-BC@CS-MOF porous materials in hydrochloric acid solution with a pH of 5 for 3 hours, they were refilled into the aerated ecological filter. Step (4) was repeated to continue treating the farmland drainage. The concentrations of nitrate nitrogen, ammonia nitrogen, COD, and PO4 in the treated farmland drainage were 0.0032 mg / L, 0.03 mg / L, and 0.0001 mg / L, respectively. 3- The concentration was 0.087 mg / L, indicating that the material still has good adsorption effect after acid washing and desorption.

[0081] Example 2

[0082] (1) Preparation of Fe-BC@CS-MOF porous materials:

[0083] Wheat straw with a length of 1-2 cm was pyrolyzed at 750℃ for 3 hours under a nitrogen atmosphere to obtain biochar material. The biochar material was then activated by acid leaching in a 5 mol / L hydrochloric acid solution for 1 hour, washed three times with deionized water, and dried in a vacuum drying oven at 80℃ for 5 hours. 10 g of the activated biochar was then soaked in a 40 mL mixed solution of FeSO4 and FeCl3. The Fe in the mixed solution... 2+ The concentration was 0.4 mol / L, Fe 3+ The concentration of the active ingredient was 0.2 mol / L. The pH of the system was adjusted to 10 using ammonia (2 mol / L). The mixture was then rapidly heated to 90℃ for a hydrothermal reaction. After 10 hours, heating was stopped, and the mixture was allowed to cool to room temperature (28℃). After filtration, washing three times with water, and vacuum drying at 80℃ for 10 hours, the resulting biochar material was loaded with magnetic Fe3O4. 5 g of the magnetic Fe3O4-loaded biochar material was immersed in 50 mL of a 2 wt% chitosan solution (containing 5 wt% acetic acid). Then, 5 mL of a 5 wt% glutaraldehyde solution was added dropwise at a rate of 1 mL / min. The mixture was stirred at 25℃ for 4 hours to complete the cross-linking reaction. After the cross-linking reaction, the mixture was filtered, washed, and dried to obtain biochar material coated with chitosan.

[0084] Chitosan-coated biochar material, ferric chloride, terephthalic acid, and N,N-dimethylformamide were mixed in a ratio of 1 g: 0.2 mol: 0.1 mol: 5 mL and reacted at 130 °C for 24 h to synthesize MIL-101(Fe) in situ on the material surface. Then, the precipitate was mixed with deionized water, polyacrylic acid, and ammonium persulfate in a ratio of 10 g: 40 mL: 1 g: 0.05 g and reacted at 80 °C under a nitrogen atmosphere for 10 h to graft PAA onto the material surface, thus obtaining Fe-BC@CS-MOF porous material.

[0085] (2) Lay filter cotton at the bottom of the aerated ecological filter and above the outlet, then lay a 10cm thick layer of fine particle filler (diatomaceous earth) with a particle size of 0.1 to 0.5mm, and then lay a plastic filter screen with a pore size of 0.1mm; lay Fe-BC@CS-MOF porous material on the plastic filter screen with a thickness of 3 to 5cm, lay a layer of filter screen with a pore size of 1mm, lay aeration pipes on the top of the filter screen, and finally lay coarse particle filler (quartz sand) with a particle size of 10 to 20mm.

[0086] (3) Inject farmland drainage diluted 10 times into the aerated ecological filter. The content of each pollutant in the farmland drainage is shown in Table 2. Then, inoculate with Pseudomonas taiwanensis (inoculation amount of 10). 12 CFU / m 3 ) and Pseudomonas chengduensis (inoculation dose of 10) 12 CFU / m 3 Air is introduced through the aeration pipe at a rate of 100 L / m³. 2 After 8 hours of treatment, samples were taken from the top of the tank for testing. The removal rate of nitrate nitrogen was 92%, and the removal rate of COD was 90%. The water was discharged from the bottom outlet at a rate of 10 L / min.

[0087] The microorganisms were acclimatized by using farmland drainage diluted at 8 times, 5 times, 2 times, and undiluted in sequence. Acclimatization was completed when the system achieved a removal rate of more than 90% for COD and nitrate nitrogen in the undiluted farmland drainage.

[0088] (4) Inject farmland drainage into the aerated ecological filter at a rate of 30 L / min, and introduce air through the aeration pipe at a rate of 100 L / m. 2 After a 13-hour retention period, water is discharged from the lower drain outlet at a rate of 5 L / min.

[0089] The pollutant content in the farmland drainage collected at the outlet is shown in Table 2.

[0090] Table 2. Content of various pollutants in farmland drainage before and after treatment.

[0091]

[0092] The heavy metals include Cd, Pd, As, etc.

[0093] Example 3

[0094] (1) Preparation of Fe-BC@CS-MOF porous materials:

[0095] Wheat straw with a length of 1-2 cm was pyrolyzed at 800℃ for 3 hours under a nitrogen atmosphere to obtain biochar material. The biochar material was then activated by acid leaching in a 5 mol / L hydrochloric acid solution for 1 hour, washed three times with deionized water, and dried in a vacuum drying oven at 80℃ for 5 hours. 10 g of the activated biochar was then soaked in a 40 mL mixed solution of FeSO4 and FeCl3. The Fe in the mixed solution... 2+ The concentration was 0.4 mol / L, Fe 3+ The concentration of the active ingredient was 0.1 mol / L. The pH of the system was adjusted to 10 using ammonia (2 mol / L). The temperature was then rapidly increased to 80℃ for a hydrothermal reaction. After 8 hours, heating was stopped, and the mixture was allowed to cool to room temperature (28℃). The mixture was then filtered, washed three times with water, and vacuum dried at 80℃ for 10 hours to obtain biochar material loaded with magnetic Fe3O4. 5 g of the magnetic Fe3O4-loaded biochar material was immersed in 70 mL of a 2 wt% chitosan solution (containing 5 wt% acetic acid in the solvent). Then, 10 mL of a 5 wt% glutaraldehyde solution was added dropwise to the system at a rate of 2 mL / min. The mixture was stirred at 25℃ for 4 hours to complete the cross-linking reaction. After the cross-linking reaction, the mixture was filtered, washed, and dried to obtain biochar material coated with chitosan.

[0096] Chitosan-coated biochar material, ferric chloride, terephthalic acid, and N,N-dimethylformamide were mixed in a ratio of 1 g: 0.15 mol: 0.2 mol: 8 mL and reacted at 120 °C for 20 h to synthesize MIL-101(Fe) in situ on the material surface. Then, the precipitate was mixed with deionized water, polyacrylic acid, and ammonium persulfate in a ratio of 10 g: 50 mL: 1 g: 0.05 g and reacted at 80 °C under a nitrogen atmosphere for 10 h to graft PAA onto the material surface, thus obtaining Fe-BC@CS-MOF porous material.

[0097] (2) Lay filter cotton at the bottom of the aerated ecological filter and above the outlet, then lay a 10cm thick layer of fine particle filler (diatomaceous earth) with a particle size of 0.1 to 0.5mm, and then lay a plastic filter screen with a pore size of 0.1mm; lay Fe-BC@CS-MOF porous material on the plastic filter screen with a thickness of 3 to 5cm, lay a layer of filter screen with a pore size of 1mm, lay aeration pipes on the top of the filter screen, and finally lay coarse particle filler (quartz sand) with a particle size of 10 to 20mm.

[0098] (3) Inject farmland drainage diluted 10 times into the aerated ecological filter. The content of each pollutant in the farmland drainage is shown in Table 3. Then, inoculate with Pseudomonas taiwanensis (inoculation amount of 10). 13 CFU / m 3 ) and Pseudomonas chengduensis (inoculation dose of 10) 13 CFU / m 3 Air is introduced through the aeration pipe at a rate of 100 L / m³. 2 After 10 hours of treatment, samples were taken from the top of the tank for testing. The removal rate of nitrate nitrogen was 95%, and the removal rate of COD was 90%. The water was discharged from the bottom outlet at a rate of 10 L / min.

[0099] The microorganisms were acclimatized by using farmland drainage diluted at 8 times, 5 times, 2 times, and undiluted in sequence. Acclimatization was completed when the system achieved a removal rate of more than 90% for COD and nitrate nitrogen in the undiluted farmland drainage.

[0100] (4) Inject farmland drainage into the aerated ecological filter at a rate of 30 L / min, and introduce air through the aeration pipe at a rate of 100 L / m. 2 After a 15-hour retention period, water is discharged from the lower drain outlet at a rate of 5 L / min.

[0101] The pollutant content in the farmland drainage collected at the outlet is shown in Table 3.

[0102] Table 3. Content of various pollutants in farmland drainage before and after treatment.

[0103]

[0104] The heavy metals include Cd, Pd, As, etc.

[0105] As can be seen from the above embodiments, the method provided by the present invention has a good removal effect on nitrate nitrogen, ammonia nitrogen, organic pollutants, heavy metal ions and phosphates in farmland drainage, and the adsorption material can be recycled, which greatly reduces the treatment cost.

[0106] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating agricultural drainage water using an aerated ecological filter, characterized in that, Includes the following steps: 1) Inoculate Pseudomonas aeruginosa inside the aerated ecological filter and use diluted farmland drainage to cultivate and acclimate the Pseudomonas aeruginosa. 2) After preliminary filtration, farmland drainage is passed into an aerated ecological filter pond for further treatment; The Pseudomonas species mentioned in step 1) are Pseudomonas taiwanensis and Pseudomonas chengduensis; The aerated ecological filter described in step 2) consists of a coarse particle packing layer, an aeration device, a filter screen, a Fe-BC@CS-MOF porous material layer, a filter screen, and a fine particle packing layer from top to bottom. The aerated ecological filter has an outlet at the bottom. The preparation method of the Fe-BC@CS-MOF porous material is as follows: agricultural waste is pyrolyzed at high temperature to obtain biochar material; the biochar material is then mixed with Fe... 2+ and Fe 3+ The solutions were mixed, and the pH of the system was adjusted to 10-11. A hydrothermal reaction was carried out to obtain biochar material loaded with magnetic Fe3O4. The biochar material loaded with magnetic Fe3O4 was immersed in chitosan solution, and then glutaraldehyde solution was added dropwise to carry out a cross-linking reaction to obtain biochar material with chitosan surface coating. The biochar material with chitosan surface coating, ferric chloride, terephthalic acid and N,N-dimethylformamide were mixed and carried out a solvothermal reaction. After the reaction was completed, the precipitate was mixed with deionized water, polyacrylic acid and ammonium persulfate, and a surface grafting reaction was carried out under an inert gas atmosphere to obtain Fe-BC@CS-MOF porous material.

2. The method for treating agricultural drainage water using an aerated ecological filter according to claim 1, characterized in that, The inoculation amount of each of the Pseudomonas was 1 x 10 12 1 x 10 13 CFU / m 3 ; The farmland drainage contains the following pollutants at the following concentrations: total nitrogen 10-200 mg / L, nitrate nitrogen 10-150 mg / L, soluble phosphate 0.5-20 mg / L, COD 50-500 mg / L, Cd 0.001-0.5 mg / L, and As 0.005-0.5 mg / L.

3. The method for treating agricultural drainage water using an aerated ecological filter according to claim 2, characterized in that, The process of culturing and acclimatizing Pseudomonas involves gradient acclimatization of Pseudomonas using farmland drainage at different dilution ratios. Acclimatization is completed when Pseudomonas achieves a degradation rate of ≥90% for both nitrate nitrogen and COD in undiluted farmland drainage.

4. The method for treating agricultural drainage water using an aerated ecological filter according to claim 3, characterized in that, The preliminary filtration is performed using a filter screen with a pore size of 0.1~1mm; The rate at which farmland drainage is introduced into the aerated ecological filter is 10-30 L / min, the retention time of farmland drainage in the aerated ecological filter is 10-24 h, and the effluent rate of farmland drainage is 5-10 L / min.

5. A method for treating farmland drainage using an aerated ecological filter according to any one of claims 1 to 4, characterized in that, The agricultural waste in the preparation method of the Fe-BC@CS-MOF porous material includes one or more of straw, rice husks, fruit shells and wood; The high-temperature pyrolysis temperature is 600~800℃, the high-temperature pyrolysis time is 2~5h, and the high-temperature pyrolysis atmosphere is an inert gas atmosphere.

6. The method for treating agricultural drainage water using an aerated ecological filter according to claim 5, wherein The preparation method of the Fe-BC@CS-MOF porous material contains Fe 2+ and Fe 3+ ; the concentration of Fe 2+ in the solution is 0.1-0.4 mol / L, and the concentration of Fe 3+ is 0.05-0.2 mol / L; The biochar material contains Fe 2+ and Fe 3+ The mixing ratio of the solution is 5g: 20~40mL; The hydrothermal reaction is carried out at a temperature of 80~100℃ for 6~12 hours.

7. The method for treating agricultural drainage water using an aerated ecological filter according to claim 6, characterized in that, In the preparation method of the Fe-BC@CS-MOF porous material, the mass concentration of chitosan solution is 1~2%, and the mass concentration of glutaraldehyde solution is 2~5%. The mixing ratio of the magnetic Fe3O4-loaded biochar to the chitosan solution is 1g: 10~20mL; The volume ratio of the glutaraldehyde solution to the chitosan solution is 1:5~10; The cross-linking reaction is carried out at a temperature of 20-30°C for 2-4 hours.

8. The method for treating agricultural drainage water using an aerated ecological filter according to claim 7, characterized in that, In the preparation method of the Fe-BC@CS-MOF porous material, the mixing ratio of surface-coated chitosan biochar material, ferric chloride, terephthalic acid and N,N-dimethylformamide is 1g:0.1~0.2mol:0.1~0.4mol:5~10mL; The solvothermal reaction is carried out at a temperature of 110~130℃ for a time of 12~24h. The mixing ratio of the precipitate, deionized water, polyacrylic acid, and ammonium persulfate is 10g: 30~50mL: 0.5~1g: 0.01~0.05g; The surface grafting reaction is carried out at a temperature of 60-80°C for 10-20 hours.

9. A method for treating farmland drainage using an aerated ecological filter according to claim 8, characterized in that, The coarse granular filler includes one or more of quartz sand, anthracite and ceramsite; The coarse granular filler has a particle size of 10-50 mm; The filter screen has a pore size of 0.1-2 mm; The fine granular filler includes one or more of diatomite, ceramsite sand and resin particles; The fine granular filler has a particle size of 0.01-0.5 mm.

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