Method for treating farmland drainage by using aeration ecological filter tank

Abstract

The invention provides a method for treating farmland drainage by using an aeration ecological filter tank, and relates to the technical field of sewage treatment. A coarse particle filler layer, an aeration device, a filter screen, a Fe-BC and CS-MOF porous material layer, a filter screen and a fine particle filler layer are sequentially arranged in the aeration ecological filter tank from top to bottom, Pseudomonas taiwanensis and Pseudomonas chengduensis are introduced into the aeration ecological filter tank for culture and domestication, nitrate nitrogen in farmland drainage can be converted into ammonia nitrogen, organic pollutants are degraded, and COD (Chemical Oxygen Demand) of a water body is reduced. The Fe-BC-CS-MOF porous material layer can adsorb ammonia nitrogen, phosphate and heavy metal, the ammonia nitrogen and the phosphate are desorbed through acid leaching, the heavy metal is reserved in the porous material, and the ammonia nitrogen and the phosphate can be recycled.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to a method for treating farmland drainage by using an aerated ecological filter tank. Background Art

[0002] Farmland drainage is eutrophic wastewater generated in agricultural production due to irrigation, rainfall or rising groundwater, containing pollutants such as nitrogen, phosphorus, pesticide residues and suspended solids. If directly discharged into water bodies, it is likely to cause problems such as eutrophication and black and odorous water bodies. Modern agricultural technologies rely on high fertilizer inputs (such as slow-release fertilizers and precision fertilization), but the drainage systems have not been upgraded synchronously, resulting in a large amount of nitrogen and phosphorus being lost with the drainage. Although the currently promoted intelligent irrigation technology can improve water use efficiency, it has not solved the problem of intercepting pollutants at the drainage end, resulting in fertilizer residues directly entering water bodies through buried pipes and ditches. Although pesticide application technologies such as drone spraying and slow-release pesticides have reduced the amount of pesticides used, they have not blocked the diffusion of pesticides with the drainage. Generally, artificial wetlands, sedimentation tanks, biological filter tanks and chemical treatment are used to treat farmland drainage. Among them, artificial wetlands rely on physical interception, chemical reactions and biological metabolism to remove pollutants. This method has a large floor area, a long time required to construct the biological ecosystem, and the speed of biological metabolism is related to the environmental temperature and is greatly affected by seasons. The biological filter tank method degrades pollutants through microorganisms, but the biological filter tank treatment methods disclosed in the prior art all have the following problems: high requirements for water quality, complex operation and maintenance, and the treatment efficiency is greatly affected by environmental fluctuations. Although the chemical method has a fast treatment speed, it requires a large amount of chemical reagents, which not only has a high cost but also easily introduces other pollutants, resulting in secondary pollution. In addition, there is a large amount of nitrogen and phosphorus in farmland drainage. How to recycle and return it to farmland to avoid waste of nitrogen and phosphorus resources is also a problem faced by those skilled in the art.

[0003] Based on the above problems, those skilled in the art urgently need to develop a treatment method with low cost, high efficiency, little environmental impact and capable of recycling nutrients in farmland drainage. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for treating farmland drainage by using an aerated ecological filter tank, so as to solve the problems of high cost, low efficiency and easy loss of nitrogen and phosphorus resources existing in the prior treatment methods of farmland drainage.

[0005] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

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

[0007] 1) Inoculate Pseudomonas in the aerated ecological filter tank, and use diluted farmland drainage to culture and domesticate Pseudomonas.

[0008] 2) The farmland drainage is preliminarily filtered and then introduced into an aerated ecological filter for treatment;

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

[0010] In the aerated ecological filter mentioned in step 2), a coarse particle packing layer, an aeration device, a filter screen, an Fe-BC@CS-MOF porous material layer, a filter screen, and a fine particle packing layer are successively arranged from top to bottom. An outlet is provided at the bottom of the aerated ecological filter;

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

[0012] Preferably, the inoculation amount of each Pseudomonas is 10 12 -10 13 CFU / m 3 ;

[0013] The farmland drainage contains the following pollutants in mass concentration: total nitrogen 10-200 m / 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 m / L.

[0014] Preferably, the process of culturing and domesticating the Pseudomonas is to carry out gradient domestication of the Pseudomonas with farmland drainage at different dilution multiples. The domestication is completed when the degradation rates of nitrate nitrogen and COD in the undiluted farmland drainage by the Pseudomonas are both ≥ 90%.

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

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

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

[0018] The temperature of the high-temperature pyrolysis is 600 - 800 °C, the time of the high-temperature pyrolysis is 2 - 5 h, and the atmosphere of the high-temperature pyrolysis is an inert gas atmosphere.

[0019] Preferably, the preparation method of the Fe-BC@CS-MOF porous material contains Fe 2+ and Fe 3+ In the solution containing Fe 2+ the concentration of Fe 3+ is 0.1 - 0.4 mol / L, and the concentration of Fe

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

[0021] The temperature of the hydrothermal reaction is 80 - 100 °C, and the time is 6 - 12 h.

[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 biochar loaded with magnetic Fe3O4 and the chitosan solution is 1 g : 10 - 20 mL;

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

[0025] The temperature of the crosslinking reaction is 20 - 30 °C, and the time is 2 - 4 h.

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

[0027] The temperature of the solvothermal reaction is 110 - 130 °C, and the time is 12 - 24 h;

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

[0029] The temperature of the surface grafting reaction is 60 - 80 °C, and the time is 10 - 20 h.

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

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

[0032] The pore size of the filter screen is 0.1 - 2 mm;

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

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

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

[0036] The present invention uses an aerated ecological filter to treat farmland drainage. Among the two types of Pseudomonas, Pseudomonas taiwanensis can decompose organic macromolecular compounds in wastewater, reducing the COD of the water body, and Pseudomonas chengduensis can convert nitrate nitrogen in wastewater into ammonia nitrogen; in the present invention, a filter layer and an adsorption layer are provided at the bottom of the aeration tank. The coarse particle filler layer can serve as a living place for microorganisms; the Fe-BC@CS-MOF porous material layer can adsorb ammonia nitrogen, phosphorus and heavy metal ions. The Fe-OH groups on the surface of the porous material can react with PO4 3- to form Fe-O-P bonds. The amino and hydroxyl groups introduced by the chitosan coating layer can adsorb ammonia nitrogen, and magnetic Fe3O4 can enhance the adsorption of heavy metals Pd, As or Cd by the material. After a period of treatment, the porous material is taken out and immersed in an acidic aqueous solution to desorb ammonia nitrogen and phosphate radicals for recycling. The desorbed porous material can be continuously put into the aerated ecological filter for recycling. Specific Embodiments

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

[0038] 1) Inoculate Pseudomonas in the aerated ecological filter and use diluted farmland drainage to culture and domesticate Pseudomonas;

[0039] 2) Pass the farmland drainage through preliminary filtration and then into the aerated ecological filter for treatment;

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

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

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

[0043] In the present invention, the inoculation amount of each Pseudomonas is 10 12 ~10 13 CFU / m 3 preferably 2×10 13 ~8×10 13 CFU / m 3 more preferably 3×10 13 ~6×10 13 CFU / m 3 even more preferably 4×10 13 ~5×10 13 CFU / m 3 .

[0044] In the present invention, the farmland drainage contains pollutants with 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, the total nitrogen is 30 - 150 mg / L, nitrate nitrogen is 20 - 120 mg / L, soluble phosphate is 1 - 18 mg / L, COD is 80 - 400 mg / L, Cd is 0.005 - 0.3 mg / L, and As is 0.01 - 0.4 mg / L. Further preferably, the total nitrogen is 50 - 100 mg / L, nitrate nitrogen is 30 - 80 mg / L, soluble phosphate is 2 - 15 mg / L, COD is 100 - 300 mg / L, Cd is 0.01 - 0.2 mg / L, and As is 0.05 - 0.3 mg / L. More preferably, the total nitrogen is 60 - 80 mg / L, nitrate nitrogen is 40 - 60 mg / L, soluble phosphate is 5 - 10 mg / L, COD is 150 - 200 mg / L, Cd is 0.05 - 0.1 mg / L, and As is 0.1 - 0.2 mg / L.

[0045] In the present invention, the process of culturing and domesticating Pseudomonas is to perform gradient domestication on Pseudomonas using farmland drainage with different dilution multiples. The domestication is completed when the degradation rates of nitrate nitrogen and COD in the undiluted farmland drainage by Pseudomonas are both ≥ 90%.

[0046] In the present invention, the preliminary filtration is carried out using a filter screen with a pore size of 0.1 - 1 mm, preferably 0.2 - 0.8 mm, further preferably 0.4 - 0.6 mm, and more preferably 0.5 mm.

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

[0048] In the preparation method of the Fe - BC@CS - MOF porous material in the present invention, the agricultural waste includes one or several of straw, rice husk, fruit shell, and wood. The particle size of the agricultural waste is preferably 0.5 - 3 cm, further preferably 1 - 2 cm, and more preferably 1.2 - 1.5 cm.

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

[0050] In the present invention, the preparation method of the Fe-BC@CS-MOF porous material contains Fe 2+ and Fe 3+ In the solution containing Fe 2+ the concentration of Fe 3+ 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; the concentration of Fe

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

[0052] In the present 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 h, preferably 7 - 11 h, more preferably 8 - 10 h, and even more preferably 9 h.

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

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

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

[0056] In the present invention, the temperature of the cross-linking reaction is 20 to 30 °C, preferably 23 to 28 °C, and more preferably 25 °C; the time is 2 to 4 h, preferably 2.5 to 3.5 h, and more preferably 3 h.

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

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

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

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

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

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

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

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

[0065] In the present 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 in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0067] Example 1

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

[0069] Wheat straw with a length between 1 - 2 cm is pyrolyzed at high temperature for 3 h under a nitrogen atmosphere at 700 °C to obtain a biochar material. The biochar material is acid-leached and activated in a 5 mol / L hydrochloric acid solution for 1 h, washed 3 times with deionized water, and then placed in a vacuum drying oven at 80 °C for 5 h. Take 10 g of the activated biochar and soak it in 40 mL of a mixed solution of FeSO4 and FeCl3. The concentration of Fe 2+ in the mixed solution is 0.3 mol / L, and the concentration of Fe 3+ is 0.15 mol / L. The pH value of the system is adjusted to 10 using ammonia water (2 mol / L), and then the temperature is quickly raised to 80 °C for hydrothermal reaction. After 8 h, heating is stopped, and it is allowed to stand and cool to room temperature (28 °C). It is filtered, washed 3 times with water, and vacuum-dried at 80 °C for 10 h to obtain a biochar material loaded with magnetic Fe3O4. Soak 5 g of the biochar material loaded with magnetic Fe3O4 in 50 mL of a 2 wt% chitosan solution (the solvent contains 5 wt% acetic acid), and then add 5 mL of a 5 wt% glutaraldehyde solution dropwise into the system at a rate of 1 mL / min, and stir at 25 °C for 4 h to complete the cross-linking reaction. After the cross-linking reaction, it is filtered, washed, and dried to obtain a biochar material with a chitosan coating on the surface.

[0070] Mix the biochar material with a chitosan coating on the surface, ferric chloride, terephthalic acid, and N,N-dimethylformamide in a ratio of 1 g:0.12 mol:0.4 mol:10 mL, and react at 120 °C for 20 h to in-situ synthesize MIL-101(Fe) on the material surface; then mix the precipitate with deionized water, polyacrylic acid, and ammonium persulfate in a ratio of 10 g:35 mL:0.6 g:0.02 g, and react at 80 °C under a nitrogen atmosphere for 10 h to graft PAA on the material surface to obtain the Fe-BC@CS-MOF porous material.

[0071] (2) Lay filter cotton at the bottom of the aerated ecological filter and above the water outlet, then lay fine particle fillers (diatomite) with a thickness of 10 cm and a particle size within 0.1 - 0.5 mm, and then lay a plastic filter screen with a pore size of 0.1 mm; lay the Fe-BC@CS-MOF porous material on the plastic filter screen with a laying thickness of 3 - 5 cm, lay a layer of filter screen with a pore size of 1 mm, lay an aeration pipe above the filter screen, and finally lay coarse particle fillers (quartz sand) with a particle size between 10 - 20 mm.

[0072] (3) Inject farmland drainage with a dilution factor of 10 times into the aerated ecological filter. The contents of various pollutants in the farmland drainage are shown in Table 1. Then inoculate Pseudomonas taiwanensis (inoculation amount is 10 13 CFU / m 3 ) and Pseudomonas chengduensis (inoculation amount is 10 13 CFU / m 3 ), and introduce air through the aeration pipe with an introduction amount of 100 L / m 2 / h. After treatment for 10 h, take samples from the upper part of the pool for testing. The removal rate of nitrate nitrogen is 95%, and the removal rate of COD is 90%. The water flows out from the lower water outlet with a water outlet rate of 10 L / min.

[0073] Domesticate the microorganisms successively with farmland drainage with dilution factors of 8 times, 5 times, 2 times, and undiluted. The domestication is completed when the removal rates of COD and nitrate nitrogen in the undiluted farmland drainage by the system reach over 90%.

[0074] (4) Inject the farmland drainage into the aerated ecological filter at a rate of 30 L / min, introduce air through the aeration pipe with an introduction amount of 100 L / m 2 / h. After a residence time of 15 h, the water flows out from the lower drain with a water outlet rate of 5 L / min.

[0075] The contents of pollutants in the farmland drainage collected at the water outlet are shown in Table 1.

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

[0077]

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

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

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

[0081] Example 2

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

[0083] Wheat straw with a length between 1 and 2 cm was pyrolyzed at high temperature for 3 h under a nitrogen atmosphere at 750 °C to obtain a biochar material. The biochar material was acid-leached and activated in 5 mol / L hydrochloric acid solution for 1 h, washed 3 times with deionized water, and then placed in a vacuum drying oven at 80 °C for drying for 5 h. 10 g of the activated biochar was immersed in 40 mL of a mixed solution of FeSO4 and FeCl3. The concentration of Fe 2+ in the mixed solution was 0.4 mol / L, and the concentration of Fe 3+ was 0.2 mol / L. The pH value of the system was adjusted to 10 with ammonia water (2 mol / L), and then the temperature was quickly raised to 90 °C for hydrothermal reaction. After 10 h, the heating was stopped, and it was allowed to stand and cool to room temperature (28 °C). After filtration, washing 3 times, and vacuum drying at 80 °C for 10 h, a biochar material loaded with magnetic Fe3O4 was obtained. 5 g of the biochar material loaded with magnetic Fe3O4 was immersed in 50 mL of a chitosan solution with a concentration of 2 wt% (the solvent contained 5 wt% acetic acid), and then 5 mL of a glutaraldehyde solution with a concentration of 5 wt% was added dropwise into the system at a rate of 1 mL / min. The cross-linking reaction was completed by stirring at 25 °C for 4 h. After the cross-linking reaction, filtration, washing, and drying were carried out to obtain a biochar material with chitosan coated on the surface.

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

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

[0086] (3) Inject farmland drainage diluted 10 times into the aerated ecological filter. The contents of various pollutants in the farmland drainage are shown in Table 2. Then inoculate Pseudomonas taiwanensis (inoculation amount is 10 12 CFU / m 3 ) and Pseudomonas chengduensis (inoculation amount is 10 12 CFU / m 3 ), pass air through the aeration pipe with an inlet volume of 100 L / m 2 / h. After treatment for 8 h, take samples from the upper part of the pool for testing. The removal rate of nitrate nitrogen is 92%, and the removal rate of COD is 90%. The water flows out from the lower water outlet with an outlet rate of 10 L / min.

[0087] Domesticate the microorganisms successively with farmland drainage diluted 8 times, 5 times, 2 times, and undiluted. The domestication is completed when the removal rates of COD and nitrate nitrogen in the undiluted farmland drainage by the system reach over 90%.

[0088] (4) Inject the farmland drainage into the aerated ecological filter at a rate of 30 L / min, pass air through the aeration pipe with an inlet volume of 100 L / m 2 / h. After a residence time of 13 h, the water flows out from the lower drain with an outlet rate of 5 L / min.

[0089] The contents of pollutants in the farmland drainage collected at the water outlet are shown in Table 2.

[0090] Table 2 Contents 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 material:

[0095] The wheat straw with a length between 1 and 2 cm is pyrolyzed at high temperature for 3 h under a nitrogen atmosphere at 800 °C to obtain a biochar material. The biochar material is acid-leached and activated in a 5 mol / L hydrochloric acid solution for 1 h, washed 3 times with deionized water, and then placed in a vacuum drying oven at 80 °C for drying for 5 h. Take 10 g of the activated biochar and soak it in a mixed solution of 40 mL of FeSO4 and FeCl3. The concentration of Fe 2+ in the mixed solution is 0.4 mol / L, and the concentration of Fe 3+ is 0.1 mol / L. The pH value of the system is adjusted to 10 with ammonia water (2 mol / L), and then the temperature is quickly raised to 80 °C for hydrothermal reaction. After 8 h, the heating is stopped, and it is left to stand and cool to room temperature (28 °C). It is filtered, washed 3 times with water, and vacuum-dried at 80 °C for 10 h to obtain a biochar material loaded with magnetic Fe3O4. Soak 5 g of the biochar material loaded with magnetic Fe3O4 in 70 mL of a 2 wt% chitosan solution (the solvent contains 5 wt% acetic acid), and then dropwise add 10 mL of a 5 wt% glutaraldehyde solution into the system at a rate of 2 mL / min, and stir at 25 °C for 4 h to complete the cross-linking reaction. After the cross-linking reaction is completed, it is filtered, washed, and dried to obtain a biochar material with a chitosan coating on the surface.

[0096] Mix the biochar material with a chitosan coating on the surface, ferric chloride, terephthalic acid, and N,N-dimethylformamide in a ratio of 1 g:0.15 mol:0.2 mol:8 mL, and react at 120 °C for 20 h to in-situ synthesize MIL-101(Fe) on the material surface; then mix the precipitate with deionized water, polyacrylic acid, and ammonium persulfate in a ratio of 10 g:50 mL:1 g:0.05 g, and react at 80 °C under a nitrogen atmosphere for 10 h to graft PAA on the material surface to obtain the Fe-BC@CS-MOF porous material.

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

[0098] (3) Inject farmland drainage with a dilution factor of 10 times into the aerated ecological filter. The contents of various pollutants in the farmland drainage are shown in Table 3. Then inoculate Pseudomonas taiwanensis (inoculation amount is 10 13 CFU / m 3 ) and Pseudomonas chengduensis (inoculation amount is 10 13 CFU / m 3 ). Pass air through the aeration pipe with an inlet volume of 100 L / m 2 / h. After treatment for 10 h, take samples from the upper part of the pool for testing. The removal rate of nitrate nitrogen is 95%, and the removal rate of COD is 90%. The water flows out from the lower water outlet with an outlet rate of 10 L / min.

[0099] Domesticate the microorganisms successively with farmland drainage with dilution factors of 8 times, 5 times, 2 times, and undiluted. The domestication is completed when the removal rates of COD and nitrate nitrogen in the undiluted farmland drainage by the system reach over 90%.

[0100] (4) Inject the farmland drainage into the aerated ecological filter at a rate of 30 L / min, pass air through the aeration pipe with an inlet volume of 100 L / m 2 / h. After a residence time of 15 h, the water flows out from the lower drain outlet with an outlet rate of 5 L / min.

[0101] The contents of pollutants in the farmland drainage collected at the water outlet are shown in Table 3.

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

[0103]

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

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

[0106] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for treating farmland drainage using an aerated ecological filter, characterized in that, It includes the following steps: 1) Inoculate Pseudomonas in the aeration ecological filter, and use diluted farmland drainage to culture and domesticate Pseudomonas; 2) Pass the farmland drainage through a preliminary filter and then into the aeration ecological filter for treatment; The Pseudomonas described in step 1) are Pseudomonas taiwanensis and Pseudomonas chengduensis; In the aeration ecological filter described in step 2), 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 are successively arranged from top to bottom. An outlet is provided at the bottom of the aeration ecological filter; The preparation method of the Fe-BC@CS-MOF porous material is as follows: agricultural waste is pyrolyzed at high temperature to obtain a biochar material; the biochar material is mixed with a solution containing Fe 2+ and Fe 3+ , the pH value of the system is adjusted to 10-11, and a hydrothermal reaction is carried out to obtain a biochar material loaded with magnetic Fe3O4; the biochar material loaded with magnetic Fe3O4 is soaked in a chitosan solution, and then a glutaraldehyde solution is added dropwise for a cross-linking reaction to obtain a biochar material with chitosan coated on the surface; the biochar material with chitosan coated on the surface, ferric chloride, terephthalic acid and N,N-dimethylformamide are mixed for a solvothermal reaction. After the reaction is completed, the precipitate is mixed with deionized water, polyacrylic acid and ammonium persulfate, and a surface grafting reaction is carried out under an inert gas atmosphere to obtain the Fe-BC@CS-MOF porous material.

2. The method for treating farmland drainage by using an aerated ecological filter tank according to claim 1, characterized in that, The inoculation amount of each type of Pseudomonas is 10 12 ~10 13 CFU / m 3 ; The pollutants contained in the farmland drainage have the following mass concentrations: total nitrogen 10 - 200 m / 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 m / L.

3. The method for treating farmland drainage by using an aerated ecological filter according to claim 2, characterized in that, The process of culturing and domesticating Pseudomonas is to perform gradient domestication on Pseudomonas with farmland drainage at different dilution multiples. Domestication is completed when the degradation rates of nitrate nitrogen and COD in the undiluted farmland drainage by Pseudomonas are both ≥ 90%; 4. A method for treating farmland drainage using an aerated ecological filter tank according to claim 3, characterized in that, The preliminary filtration is performed using a filter screen with a pore size of 0.1 - 1 mm; The rate of the farmland drainage flowing into the aeration ecological filter is 10 - 30 L / min, the residence time of the farmland drainage in the aeration ecological filter is 10 - 24 h, and the effluent rate of the 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 In the preparation method of the Fe-BC@CS-MOF porous material, the agricultural waste includes one or several of straw, rice husk, fruit shell, and wood; The temperature of the high-temperature pyrolysis is 600 - 800 °C, the time of the high-temperature pyrolysis is 2 - 5 h, and the atmosphere of the high-temperature pyrolysis is an inert gas atmosphere.

6. A method for treating farmland drainage using an aerated ecological filter, as claimed in claim 5, wherein The preparation method of the Fe-BC@CS-MOF porous material contains Fe 2+ and Fe 3+ In the solution of Fe 2+ The concentration of Fe 3+ is 0.1 - 0.4 mol / L, and the concentration of Fe The biochar material and the solution containing Fe 2+ and Fe 3+ are mixed at a ratio of 5 g: 20 - 40 mL; The temperature of the hydrothermal reaction is 80 - 100 °C, and the time is 6 - 12 h.

7. A method for treating farmland drainage using an aerated ecological filter tank according to claim 6, characterized in that, 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%; The mixing ratio of the biochar loaded with magnetic Fe3O4 and the chitosan solution is 1 g: 10 - 20 mL; The volume ratio of the glutaraldehyde solution to the chitosan solution is 1: 5 - 10; The temperature of the cross-linking reaction is 20 - 30 °C, and the time is 2 - 4 h.

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

9. A method for treating farmland drainage using an aerated ecological filter, as claimed in claim 8, wherein The coarse particle filler includes one or several of quartz sand, anthracite and ceramsite; The particle size of the coarse particle filler is 10-50 mm; The aperture of the filter screen is 0.1-2 mm; The fine particle filler includes one or several of diatomite, ceramsite sand and resin particles; The particle size of the fine particle filler is 0.01-0.5 mm.

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