Bio-based composite phosphorus removal agent and application thereof in landfill leachate

Abstract

The invention discloses a bio-based composite phosphorus removal agent and application of the bio-based composite phosphorus removal agent in landfill leachate. The bio-based composite phosphorus removal agent is prepared from the following raw materials in parts by mass: 2-5 parts of phosphorus removal bacteria, 5-8 parts of a biomass carrier, 1-2 parts of bio-enzyme, 1.5-3 parts of metal salt, 4-8 parts of a carbon source and 1-3 parts of quaternized SiO2 coated Fe3O4, the quaternized SiO2 coated Fe3O4 is prepared by the following steps: taking Fe3O4 and orthosilicate in a mass ratio of 1: (0.5-2) as raw materials, preparing SiO2 coated Fe3O4 by a sol-gel method, and then reacting SiO2 coated Fe3O4 with an epoxy silane coupling agent and a quaternized modifier in sequence, thereby obtaining the quaternized SiO2 coated Fe3O4. According to the application, the nano plastic particles in the landfill leachate can be effectively adsorbed and removed, the negative influence of the nano plastic particles on the phosphorus removal performance of the phosphorus removal thalli is weakened, and the water treatment effect is guaranteed.

Description

Technical Field

[0001] This application relates to the field of water treatment technology, and in particular to a bio-based composite phosphorus removal agent and its application in landfill leachate. Background Technology

[0002] Bio-based composite phosphorus removal agents typically use porous biochar as a structural carrier, consisting of loaded metal salt active ingredients and specific phosphorus-removing bacteria. This multi-level composite structure fully leverages the synergistic advantages of each component: the biochar carrier not only possesses a well-developed porous structure to provide ample loading space and adsorption sites, but its abundant surface functional groups also effectively anchor metal ions; the loaded metal salts achieve rapid phosphorus removal through chemical precipitation, while the immobilized phosphorus-removing bacteria selectively absorb and transform phosphorus through their metabolic activities, thereby achieving deep and long-lasting phosphorus removal.

[0003] Landfill leachate is a typical high-concentration, recalcitrant organic wastewater. Applying bio-based composite phosphorus removal agents to this complex leachate often presents significant challenges to its actual effectiveness. Specifically, leachate contains a large number of nanoplastic particles generated from the degradation of plastic waste. These nanoscale plastic particles have a huge specific surface area, easily migrating in the aqueous phase and attaching to the surface of phosphorus-removing bacteria. This physical covering significantly hinders the normal metabolic activities of the bacteria, inhibiting their absorption efficiency of key nutrients such as carbon and phosphorus sources from the surrounding environment, thus impairing or even eliminating the biological phosphorus removal function of the immobilized bacterial agent. Summary of the Invention

[0004] To address the negative impact of nanoplastic particles in landfill leachate on bio-based composite phosphorus removal agents, this application provides a bio-based composite phosphorus removal agent and its application in landfill leachate.

[0005] In a first aspect, this application provides a bio-based composite phosphorus removal agent, comprising the following raw materials in parts by weight: The mixture comprises 2-5 parts of phosphorus-removing bacteria, 5-8 parts of biomass carrier, 1-2 parts of biological enzyme, 1.5-3 parts of metal salt, 4-8 parts of carbon source, and 1-3 parts of quaternized SiO2-coated Fe3O4. The quaternized SiO2-coated Fe3O4 is prepared by first using Fe3O4 and orthosilicate in a mass ratio of 1:0.5-2 as raw materials, and then reacting it sequentially with an epoxy silane coupling agent and a quaternization modifier.

[0006] The bio-based composite phosphorus removal agent of this application achieves efficient phosphorus removal through the synergistic effect of multiple components. Its biomass carrier, with its well-developed porous structure, adsorbs phosphorus and immobilizes phosphorus-removing bacteria; the metal salt rapidly removes some phosphorus through chemical precipitation; and the phosphorus-removing bacteria, through their metabolic activities, biologically absorb and transform dissolved phosphorus, achieving deep phosphorus removal. Regarding nanoplastics in landfill leachate, the biomass carrier in this phosphorus removal agent can capture some nanoplastics through physical adsorption, reducing their toxicity to the bacteria. More importantly, nanoplastics in leachate are mostly negatively charged due to ionization and other reasons. The quaternized SiO2-coated Fe3O4 introduced in this application, after quaternization modification, carries a positive charge on its surface, enabling efficient adsorption of negatively charged nanoplastics through strong electrostatic interaction, ensuring the normal functioning of its biological phosphorus removal capabilities.

[0007] It is worth noting that the quaternized SiO2-coated Fe3O4 has a core-shell structure. The core Fe3O4 endows the material with excellent magnetism, enabling it to be rapidly separated and recovered from adsorbed pollutants under an external magnetic field, greatly improving the material's recyclability. The shell SiO2 coating layer plays a protective role, effectively isolating the Fe3O4 from the corrosion and oxidation of acidic substances and dissolved oxygen in the leachate, preventing it from losing its magnetism due to conversion into non-magnetic Fe2O3, thus ensuring the stability of the material's magnetic recovery performance during multiple cycles.

[0008] In any of the above technical solutions, the quaternization modifier is N,N-dimethylethanolamine and long-chain alkyl tertiary amine in a mass ratio of 2 to 3:1.

[0009] In the modification process of quaternizing SiO2 to coat Fe3O4, an epoxy silane coupling agent introduces epoxy groups by hydrolyzing its siloxane ends and bonding to the SiO2 surface. Subsequently, the tertiary amine compound in the quaternizing modifier acts as a nucleophile to attack the epoxy groups, causing them to open and achieving surface quaternization. This application uses a complex of N,N-dimethylethanolamine and long-chain alkyl tertiary amines as the modifier, which exhibits a significant synergistic effect. N,N-dimethylethanolamine has high reactivity and can react with epoxy groups to generate a large number of cationic quaternary ammonium salts, increasing the positive charge density on the product surface and thus enhancing the electrostatic adsorption capacity and efficiency for nanoplastics. In contrast, long-chain alkyl tertiary amines have lower direct reactivity but can generate permanent quaternary ammonium salts with long-chain alkyl groups. These long-chain alkyl groups can enhance the affinity for nanoplastics, which also have hydrophobic properties, thereby increasing the adsorption capacity for nanoplastics.

[0010] In any of the above technical solutions, the mass ratio of SiO2-coated Fe3O4, epoxy silane coupling agent, and quaternization modifier is 1:0.3-0.5:0.8-1.2.

[0011] In any of the above technical solutions, the carbon chain length of the long-chain alkyl tertiary amine is ≥10, preferably 14 to 18.

[0012] For example, the long-chain alkyl tertiary amine is hexadecyl dimethyl tertiary amine or N,N-dimethyl octadecylamine.

[0013] In any of the above technical solutions, the epoxy silane coupling agent is selected from any one or more of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, γ-glycidoxypropyltriisopropoxysilane, and γ-glycidoxypropylmethyldiethoxysilane.

[0014] In any of the above technical solutions, the orthosilicate is selected from any one or more of ethyl orthosilicate, butyl orthosilicate, and isobutyl orthosilicate.

[0015] In any of the above technical solutions, the average particle size of Fe3O4 is 10nm to 200nm, preferably 20nm to 100nm.

[0016] In any of the above technical solutions, the preparation method of quaternized SiO2 coated Fe3O4 is as follows: Fe3O4 was uniformly dispersed in ethanol to prepare a magnetic particle dispersion. Under nitrogen protection and constant temperature of 25-35℃, orthosilicate was added dropwise to the magnetic particle dispersion while stirring. After the addition was complete, alkali solution was added dropwise until the pH was 9-10. After the addition was complete, the temperature was raised to 40-50℃ and the reaction was stirred for 4-6 hours. After the reaction was completed, SiO2-coated Fe3O4 was obtained. SiO2-coated Fe3O4 was dispersed in a solvent to prepare a suspension. An epoxy silane coupling agent was added, the temperature was raised to 75-85℃, and the reaction was stirred for 3-5 hours. After maintaining the temperature, a quaternization modifier was added dropwise, the temperature was raised to 80-95℃, and the reaction was stirred for 6-8 hours to obtain quaternized SiO2-coated Fe3O4.

[0017] In any of the above technical solutions, the biomass carrier is any one or more of activated carbon, straw, rice husk, sawdust, starch, cellulose, pectin, sodium alginate, and lignin.

[0018] In any of the above technical solutions, the biological enzyme is a phosphatase.

[0019] In any of the above technical solutions, the metal salt is selected from one or more of calcium salts, iron salts, aluminum salts, and magnesium salts. It should be noted that all the metal salts are water-soluble metal salts.

[0020] In any of the above technical solutions, the carbon source is glucose or white sugar.

[0021] In any of the above technical solutions, the SiO2-coated Fe3O4 first reacts with a mercaptosilane coupling agent, and then reacts sequentially with an epoxysilane coupling agent and a quaternization modifier.

[0022] In any of the above technical solutions, the mercaptosilane coupling agent is selected from mercaptotrimethoxysilane and / or mercaptotriethoxysilane.

[0023] This application adds a surface pretreatment step of using a mercaptosilane coupling agent to coat Fe3O4 with SiO2 before epoxidation and quaternization modification. The main purpose of this step is to protect the Fe3O4 core layer. Although SiO2 grown via the sol-gel method can cover most of the Fe3O4 surface, during the formation and drying of the SiO2 network, factors such as gel shrinkage may result in extremely small defects or incomplete coating sites in certain areas. These sites, in the acidic leachate environment, become weak points for Fe3O4 oxidation and erosion, leading to a gradual weakening of magnetism and affecting long-term recycling rates. After hydrolysis, the siloxane end can bond with the hydroxyl groups at the defect sites of SiO2, and the mercapto end coordinates with the iron atoms on the Fe3O4 surface to form an anchoring structure, preventing the loss of small molecule protective agents in acidic landfill leachate. At the same time, the hydrophobic carbon chain of mercaptosilane can form a dense layer on the surface, isolating the acid solution from eroding Fe3O4, and working together with the SiO2 layer to form a dense barrier, significantly enhancing the chemical stability of the material in harsh environments and ensuring that its magnetic recovery rate remains at a high level.

[0024] In any of the above technical solutions, the self-assembly reaction is prepared by placing SiO2-coated Fe3O4 in a 5-10 wt% mercaptosilane coupling agent solution and reacting for 1-2 hours.

[0025] In any of the above technical solutions, the phosphorus removal agent contains 0.3 to 1 part of chitosan with a degree of deacetylation ≥ 85%.

[0026] Chitosan molecules carry a positive charge under acidic to neutral conditions, enabling them to adsorb some negatively charged nanoplastics through electrostatic interactions, forming a synergistic adsorption with the quaternized SiO2-coated Fe3O4 component. Furthermore, as a natural polymeric flocculant, chitosan promotes the aggregation of quaternized particles, bacteria, and other suspended solids already adsorbed with nanoplastics in water through bridging and trapping effects, forming larger flocs. This not only improves the overall pollutant removal efficiency but also makes these flocculated complexes easier to capture during subsequent magnetic separation, thereby indirectly improving the recovery rate of the entire phosphorus removal system, especially the magnetic components.

[0027] Secondly, this application provides an application of a bio-based composite phosphorus removal agent, wherein the bio-based composite phosphorus removal agent described in the first aspect is added to landfill leachate for phosphorus removal treatment at a dosage of 0.5 to 3 g / L.

[0028] In summary, this application has the following beneficial effects: This application provides a bio-based composite phosphorus removal agent for landfill leachate, effectively overcoming the problem of nanoplastics in leachate inhibiting biological phosphorus-removing bacteria. The phosphorus removal agent integrates multiple phosphorus removal mechanisms, including physical adsorption, chemical precipitation (metal salts), and bioconversion. By introducing quaternized SiO2 to coat Fe3O4 material, it achieves efficient adsorption and removal of negatively charged nanoplastics, ensuring the effective functioning of the bacterial agent. The unique core-shell structure and surface modification scheme of this magnetic material ensure its stability and excellent magnetic recovery performance in harsh leachate environments. Ultimately, this application combines highly efficient deep phosphorus removal, resistance to complex water quality interference, and ease of recycling. Detailed Implementation Preparation Example

[0029] Preparation Example 1: Quaternized SiO2 coated with Fe3O4 was prepared by the following steps: Step 1: Under nitrogen protection, 100g of Fe3O4 powder with an average particle size of 50nm was uniformly dispersed in 500mL of anhydrous ethanol to form a stable magnetic particle dispersion, and continuously mechanically stirred in a 30℃ constant temperature water bath. Then, 100g of tetraethyl orthosilicate was slowly added dropwise using a constant pressure dropping funnel, controlling the dropping rate to approximately 1 drop / second. After the addition was complete, a 10% (w / w) ammonia solution was slowly added dropwise to adjust the pH of the system to 9.5. After the addition was complete, the reaction system was heated to 45℃ and stirred continuously at this temperature for 5 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field. The obtained solid product was washed three times each with anhydrous ethanol and deionized water, and finally dried in a 60℃ vacuum drying oven for 6 hours to obtain SiO2-coated Fe3O4 powder.

[0030] Step 2: 100g of SiO2-coated Fe3O4 powder obtained in Step 1 was dispersed in 1.5L of a 7.5wt% mercaptotriethoxysilane solution (ethanol-water (95:5, V / V)) and stirred at 200rpm for 2.5 hours at 40℃. After the reaction was completed, the solid product was collected by applying an external magnetic field and thoroughly washed with deionized water until the washing solution was neutral. Then, it was vacuum dried at 60℃ for 2 hours to obtain SiO2-coated Fe3O4 with mercaptosilane coupling agent surface treatment.

[0031] Step 3: Redisperse 100g of the material obtained in Step 2 in 800mL of toluene solvent to form a suspension. Add 40g of γ-glycidyl etheroxypropyltrimethoxysilane to the suspension. Heat the mixture to 80℃ and reflux and stir at this temperature for 4 hours to complete the epoxy modification. Subsequently, continue to add a quaternizing agent mixture consisting of 70g of N,N-dimethylethanolamine and 30g of hexadecyl dimethyl tertiary amine dropwise to the reaction system at 80℃. After the addition is complete, raise the reaction temperature to 90℃ and continue to reflux and stir for 7 hours. After the reaction is completed, allow the system to cool to room temperature, separate the product by applying an external magnetic field, and wash three times each with toluene and anhydrous ethanol to remove unreacted reagents. The final product is dried overnight in a vacuum drying oven at 60℃ to obtain quaternized SiO2-coated Fe3O4.

[0032] Preparation Example 2: Quaternized SiO2 coated with Fe3O4 was prepared by the following steps: Step 1: Under nitrogen protection, 100g of Fe3O4 powder with an average particle size of 20nm was uniformly dispersed in 600mL of anhydrous ethanol to form a stable magnetic particle dispersion, and continuously mechanically stirred in a 30℃ constant temperature water bath. Then, 50g of tetrabutyl orthosilicate was slowly added dropwise using a constant pressure dropping funnel, controlling the dropping rate to approximately 1 drop / second. After the addition was complete, a 10% (w / w) ammonia solution was slowly added dropwise to adjust the pH of the system to 9.0. After the addition was complete, the reaction system was heated to 40℃ and stirred continuously at this temperature for 6 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field. The obtained solid product was washed three times each with anhydrous ethanol and deionized water, and finally dried in a 55℃ vacuum drying oven for 8 hours to obtain SiO2-coated Fe3O4 powder.

[0033] Step 2: 100g of SiO2-coated Fe3O4 powder obtained in Step 1 was dispersed in 2L of a 5wt% mercaptotrimethoxysilane solution (ethanol-water (95:5, V / V)) and stirred at 200rpm for 2 hours at 40℃. After the reaction was completed, the solid product was collected by applying an external magnetic field and thoroughly washed with deionized water until the washing solution was neutral. Then, it was vacuum dried at 55℃ for 3 hours to obtain SiO2-coated Fe3O4 surface-treated with mercaptosilane coupling agent.

[0034] Step 3: Redisperse 100g of the material obtained in Step 2 in 1000mL of toluene solvent to form a suspension. Add 30g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to the suspension. Heat the mixture to 75℃ and reflux and stir at this temperature for 5 hours to complete the epoxy modification. Subsequently, continue to add a quaternizing agent mixture consisting of 60g of N,N-dimethylethanolamine and 20g of hexadecyldimethyl tertiary amine dropwise to the reaction system at 75℃. After the addition is complete, raise the reaction temperature to 80℃ and continue to reflux and stir for 8 hours. After the reaction is completed, allow the system to cool to room temperature, separate the product by applying an external magnetic field, and wash three times each with toluene and anhydrous ethanol to remove unreacted reagents. The final product is dried overnight in a vacuum drying oven at 60℃ to obtain quaternized SiO2-coated Fe3O4.

[0035] Preparation Example 3: Quaternized SiO2 coated with Fe3O4 was prepared by the following steps: Step 1: Under nitrogen protection, 100g of Fe3O4 powder with an average particle size of 100nm was uniformly dispersed in 500mL of anhydrous ethanol to form a stable magnetic particle dispersion, and continuously mechanically stirred in a 30℃ constant temperature water bath. Then, 180g of tetraethyl orthosilicate was slowly added dropwise using a constant pressure dropping funnel, controlling the dropping rate to approximately 1 drop / second. After the addition was complete, a 10% (w / w) ammonia solution was slowly added dropwise to adjust the pH of the system to 10. After the addition was complete, the reaction system was heated to 50℃ and stirred continuously at this temperature for 4 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field. The obtained solid product was washed three times each with anhydrous ethanol and deionized water, and finally dried in a 60℃ vacuum drying oven for 6 hours to obtain SiO2-coated Fe3O4 powder.

[0036] Step 2: 100g of SiO2-coated Fe3O4 powder obtained in Step 1 was dispersed in 1L of a 10wt% mercaptotriethoxysilane solution (ethanol-water (95:5, V / V)) and stirred at 200rpm for 2 hours at 45℃. After the reaction was completed, the solid product was collected by applying an external magnetic field and washed thoroughly with deionized water until the washing solution was neutral. Then, it was vacuum dried at 65℃ for 1.5 hours to obtain SiO2-coated Fe3O4 surface-treated with mercaptosilane coupling agent.

[0037] Step 3: Redisperse 100g of the material obtained in Step 2 in 600mL of toluene solvent to form a suspension. Add 50g of γ-glycidyl etheroxypropyltriethoxysilane to the suspension. Heat the mixture to 85℃ and reflux and stir at this temperature for 3 hours to complete the epoxy modification. Subsequently, continue to add a quaternizing agent mixture consisting of 80g of N,N-dimethylethanolamine and 40g of N,N-dimethyloctadecylamine to the reaction system at 85℃. After the addition is complete, raise the reaction temperature to 95℃ and continue to reflux and stir for 6 hours. After the reaction is completed, allow the system to cool to room temperature, separate the product by applying an external magnetic field, and wash three times each with toluene and anhydrous ethanol to remove unreacted reagents. The final product is dried overnight in a vacuum drying oven at 60℃ to obtain quaternized SiO2-coated Fe3O4.

[0038] Preparation Example 4, Fe3O4 coated with quaternized SiO2, differs from Preparation Example 1 in that, in step 3, hexadecyl dimethyl tertiary amine is replaced with an equal mass of N,N-dimethylethanolamine.

[0039] Preparation Example 5: Quaternized SiO2 coated Fe3O4. The difference from Preparation Example 1 is that in step 3, N,N-dimethylethanolamine is replaced with an equal mass of hexadecyl dimethyl tertiary amine.

[0040] Preparation Example 6: Quaternized SiO2 coated Fe3O4. The difference from Preparation Example 1 is that in step 3, hexadecyl dimethyl tertiary amine is replaced with an equal mass of octyl dimethyl tertiary amine.

[0041] Preparation Example 7, quaternized SiO2 coated Fe3O4, differs from Preparation Example 1 in that step 2 (i.e., surface treatment with mercaptosilane coupling agent) was not performed, and in step 3, the SiO2 obtained in step 1 was used to directly coat Fe3O4 for quaternization reaction. Example

[0042] Example 1: A bio-based composite phosphorus removal agent was prepared according to the following method: Weigh 70g of rice husk biochar with a particle size of 200 mesh and add it to a solution containing 40g of glucose and 15g of magnesium chloride (dissolved in 200mL of deionized water). Stir at 100 rpm for 2 hours at room temperature to ensure sufficient adsorption. Then add 20g of quaternized SiO2-coated Fe3O4 powder from Preparation Example 1 and 5g of chitosan powder with a degree of deacetylation of 90% (MW=100000), and continue stirring for 1 hour to form a homogeneous slurry. Weigh 30g of phosphorus-removing bacteria (Yineng Bio SCA-P, viable count ≥1×10⁻⁶). 9Add 15g of acid phosphatase (enzyme activity ≥5000 U / g) to the slurry and mix thoroughly. The uniformly mixed wet material is then extruded into cylindrical particles with a diameter of approximately 2-3mm using a granulator. The particles are then dried in a constant-temperature forced-air drying oven at 35℃ until constant weight is achieved.

[0043] Example 2: A bio-based composite phosphorus removal agent was prepared according to the following method: Weigh 50g of activated carbon with a particle size of 200 mesh and add it to a solution containing 20g of white sugar, 15g of ferric chloride, and 10g of aluminum sulfate (dissolved in 200mL of deionized water). Stir at 100 rpm for 2 hours at room temperature to ensure sufficient adsorption. Then add 10g of the quaternized SiO2-coated Fe3O4 powder from Preparation Example 2 and 3g of chitosan powder with a degree of deacetylation of 85% (MW=150000), and continue stirring for 1.5 hours to form a homogeneous slurry. Weigh 20g of phosphorus-removing bacteria (Yineng Bio SCA-P, viable count ≥1×10⁻⁶). 9 Add 10g of acid phosphatase (enzyme activity ≥5000 U / g) to the slurry and mix thoroughly. The uniformly mixed wet material is then extruded into cylindrical particles with a diameter of approximately 2-3 mm using a granulator. The particles are then dried in a constant-temperature forced-air drying oven at 35℃ until constant weight is achieved.

[0044] Example 3: A bio-based composite phosphorus removal agent was prepared according to the following method: Weigh 40g of straw biochar with a particle size of 200 mesh and 40g of lignin, and add them to a solution containing 60g of glucose, 10g of ferric chloride, and 5g of magnesium sulfate (dissolved in 300mL of deionized water). Stir at 150 rpm for 2 hours at room temperature to ensure complete adsorption. Then add 30g of the quaternized SiO2-coated Fe3O4 powder from Preparation Example 3 and 8g of chitosan powder with a degree of deacetylation of 90% (MW=100000), and continue stirring for 0.5 hours to form a homogeneous slurry. Weigh 40g of phosphorus-removing bacteria (Yineng Bio SCA-P, viable count ≥1×10⁻⁶). 9 Add 18g of acid phosphatase (enzyme activity ≥5000 U / g) to the slurry and mix thoroughly. The uniformly mixed wet material is then extruded into cylindrical particles with a diameter of approximately 2-3 mm using a granulator. The particles are then dried in a constant-temperature forced-air drying oven at 35℃ until constant weight is achieved.

[0045] Example 4, a bio-based composite phosphorus removal agent, differs from Example 1 in that the quaternized SiO2-coated Fe3O4 of Example 1 is replaced with the quaternized SiO2-coated Fe3O4 of Example 4 in equal mass.

[0046] Example 5, a bio-based composite phosphorus removal agent, differs from Example 1 in that the quaternized SiO2-coated Fe3O4 of Example 1 is replaced with the quaternized SiO2-coated Fe3O4 of Example 5 in equal mass.

[0047] Example 6, a bio-based composite phosphorus removal agent, differs from Example 1 in that the quaternized SiO2-coated Fe3O4 of Example 1 is replaced with the quaternized SiO2-coated Fe3O4 of Example 6 in equal mass.

[0048] Example 7, a bio-based composite phosphorus removal agent, differs from Example 1 in that the quaternized SiO2-coated Fe3O4 of Example 1 is replaced with the quaternized SiO2-coated Fe3O4 of Example 7 by means of the same mass of the preparation of Example 7.

[0049] Example 8, a bio-based composite phosphorus removal agent, differs from Example 1 in that chitosan powder is not added. Comparative Example

[0050] Comparative Example 1, a bio-based composite phosphorus removal agent, differs from Example 1 in that the quaternized SiO2-coated Fe3O4 prepared in step 1 of Example 1 is replaced with SiO2-coated Fe3O4 prepared in step 1 of Example 1 by an equal mass.

[0051] Comparative Example 2, a bio-based composite phosphorus removal agent, differs from Example 1 in that Fe3O4 coated with quaternized SiO2 in Preparation Example 1 is replaced with Fe3O4 of equal mass with an average particle size of 50 nm. Performance testing

[0052] Experiment 1: Phosphorus Removal Rate Test Add 5 mg / L potassium dihydrogen phosphate (calculated as P) and 50 mg / L polystyrene nanoplastic suspension (average particle size 100 nm) to 1 L of actual landfill leachate stock solution (total phosphorus concentration 12 mg / L, pH=5), and stir until homogeneous to prepare simulated landfill leachate. Weigh 1.0 g (accurate to 0.1 mg) each of the bio-based composite phosphorus removal agent prepared in the examples and comparative examples, and place them in 500 mL Erlenmeyer flasks. Add 400 mL of simulated landfill leachate to each Erlenmeyer flask to make the phosphorus removal agent concentration 2.5 g / L. Place the Erlenmeyer flasks in a constant temperature shaker and react for 24 h at 25 ± 1 °C and 150 rpm.

[0053] After the reaction was completed, the solution was immediately filtered through a 0.45 μm aqueous microporous membrane, and the filtrate was collected. An appropriate amount of the filtrate was digested and determined according to the standard method of GB11893-89 "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method": 25.00 mL of filtrate was placed in a digestion tube, and 4 mL of potassium persulfate solution (50 g / L) was added. The solution was then digested in an autoclave at 120 °C for 30 min. After cooling, 1 mL of ascorbic acid solution (100 g / L) and 2 mL of molybdate solution were added, mixed well, and allowed to stand for 15 min. The absorbance was measured at 700 nm using a spectrophotometer with a 30 mm cuvette, and the total phosphorus concentration (mg / L) was calculated based on the calibration curve.

[0054] The phosphorus removal rate (η) is calculated using the following formula: η(%)=(C0-C1) / C0×100%, where C0 is the total phosphorus concentration of the raw water and C1 is the total phosphorus concentration of the treated water sample.

[0055] Experiment 2: Adsorption Performance Test of Nanoplastics Add 5 mg / L potassium dihydrogen phosphate (calculated as P) and 50 mg / L polystyrene nanoplastic suspension (average particle size 100 nm) to 1 L of actual landfill leachate stock solution (total phosphorus concentration 12 mg / L, pH=5), and stir until homogeneous to prepare simulated landfill leachate. Weigh 1.0 g (accurate to 0.1 mg) each of the bio-based composite phosphorus removal agent prepared in the examples and comparative examples, and place them in 500 mL Erlenmeyer flasks. Add 400 mL of simulated landfill leachate to each Erlenmeyer flask to make the phosphorus removal agent concentration 2.5 g / L. Place the Erlenmeyer flasks in a constant temperature shaker and react for 24 h at 25 ± 1 °C and 150 rpm.

[0056] Take 1 mL of supernatant directly from the reaction mixture (absorbed 2 cm below the surface after standing for 30 s), and dilute appropriately with ultrapure water. Measure the particle concentration (kcps) of the nanoplastics using a dynamic light scattering nanoparticle size analyzer at 25℃ and a scattering angle of 90°. Calculate the nanoplastic removal rate: Removal rate (%) = (N0 - N1) / N0 × 100%, where N0 is the particle concentration of the raw water and N1 is the particle concentration after treatment.

[0057] Experiment 3: Recovery Rate Test Add 5 mg / L potassium dihydrogen phosphate (calculated as P) and 50 mg / L polystyrene nanoplastic suspension (average particle size 100 nm) to 10 L of actual landfill leachate stock solution (total phosphorus concentration 12 mg / L, pH=5), and stir until homogeneous to prepare simulated landfill leachate. Weigh 10.0 g (accurate to 0.1 mg) each of the bio-based composite phosphorus removal agent prepared in the examples and comparative examples, and place them in 500 mL Erlenmeyer flasks. Add 400 mL of simulated landfill leachate to each Erlenmeyer flask to make the phosphorus removal agent concentration 2.5 g / L. Place the Erlenmeyer flasks in a constant temperature shaker and react for 24 h at 25 ± 1 °C and 150 rpm.

[0058] Pour the entire mixture after the reaction into a glass beaker, place the beaker next to a NdFeB permanent magnet with a strength of 0.4T, and allow it to stand for magnetic separation for 15 minutes. Carefully discard the supernatant. Then, using a pipette, slowly rinse the magnetic material clumps three times along the beaker wall with a dilute hydrochloric acid solution with a pH of ≈3 to dissolve the adsorbed phosphate precipitate and some metal hydroxides. Next, rinse twice with anhydrous ethanol to desorb and remove some hydrophobic nanoplastics and organic contaminants. Finally, transfer all the recovered magnetic material to a pre-weighed (m0) weighing bottle with a small amount of deionized water. Place the weighing bottle in a vacuum drying oven at 60℃ to dry to constant weight, cool, and then weigh (m1). The recovery rate (R) of the magnetic component is calculated by the following formula: R(%)=(m1-m0) / mᵢ×100%, where mᵢ is the theoretical mass of the quaternized SiO2-coated Fe3O4 component in the added phosphorus removal agent (calculated by the mass ratio of this component in the bio-based composite phosphorus removal agent).

[0059] Table 1. Performance Test Results

[0060] Analysis of experimental results: Compared to Example 1, Examples 4 (replacing long-chain alkyl tertiary amines with pure N,N-dimethylethanolamine) and 5 (replacing N,N-dimethylethanolamine with pure long-chain alkyl tertiary amines) showed poorer performance in phosphorus removal rate and nanoplastic removal rate, indicating that the lack of long-chain alkyl tertiary amines has a significant negative impact on the adsorption performance of nanoplastics, thereby weakening the phosphorus removal performance. This may be because, although N,N-dimethylethanolamine provides a positive charge and some hydrophilicity, it lacks the hydrophobic effect of long-chain alkyl groups, reducing its affinity for nanoplastics and decreasing its adsorption capacity. The hydrophilic groups provided by N,N-dimethylethanolamine help stabilize the dispersion of particles in the aqueous phase, and its higher reactivity provides a higher positive charge density, both of which contribute to promoting the adsorption of nanoplastics.

[0061] Example 6 (replacing the long-chain tertiary amine with a short-chain octyl tertiary amine) showed a significant decrease in the removal rate of nanoplastics, indicating that carbon chain length is crucial to the adsorption performance of nanoplastics. This may be because the hydrophobic effect of shorter carbon chains (C8) is much weaker than that of longer carbon chains (C16), thus weakening their affinity for nanoplastics.

[0062] Example 7 (without mercaptosilane coupling agent surface treatment) showed a significant decrease in magnetic recovery rate, indicating that mercaptosilane coupling agent treatment has a significant impact on magnetic stability. This may be because, without the protective layer of mercaptosilane coupling agent, the Fe3O4 core is more easily penetrated and oxidized from defect sites in an acidic environment, leading to weakened magnetism.

[0063] Example 8 (without chitosan) showed a decrease in both nanoplastic removal rate and magnetic recovery rate, indicating that the synergistic adsorption and flocculation effects of chitosan contributed to the overall performance. This may be because chitosan both enhanced the adsorption of nanoplastics and promoted the recovery of magnetic components through flocculation.

[0064] Comparative Example 1 (Fe3O4 coated with unquaternized SiO2) showed a significant decrease in both phosphorus removal rate and nanoplastic removal rate, indicating that quaternization modification is key to achieving efficient phosphorus removal and nanoplastic adsorption. This may be because the lack of a positive surface charge prevents the effective adsorption of negatively charged nanoplastics and phosphate ions through electrostatic interactions.

[0065] Comparative Example 2 (using pure Fe3O4) performed the worst across all metrics, particularly showing a significant drop in magnetic recovery, indicating that the SiO2 coating layer is indispensable for protecting the magnetic core. This may be because pure Fe3O4 rapidly oxidizes and fails in acidic environments and lacks surface functionalization sites.

[0066] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A bio-based composite phosphorus removal agent, characterized in that, The raw materials include the following parts by weight: The mixture comprises 2-5 parts of phosphorus-removing bacteria, 5-8 parts of biomass carrier, 1-2 parts of biological enzyme, 1.5-3 parts of metal salt, 4-8 parts of carbon source, and 1-3 parts of quaternized SiO2-coated Fe3O4. The quaternized SiO2-coated Fe3O4 is prepared by first using Fe3O4 and orthosilicate in a mass ratio of 1:0.5-2 as raw materials, and then reacting it sequentially with an epoxy silane coupling agent and a quaternization modifier.

2. The bio-based composite phosphorus removal agent according to claim 1, characterized in that, The quaternization modifier is N,N-dimethylethanolamine and long-chain alkyl tertiary amine in a mass ratio of 2 to 3:

1.

3. The bio-based composite phosphorus removal agent according to claim 1, characterized in that, The mass ratio of SiO2-coated Fe3O4, epoxy silane coupling agent, and quaternization modifier is 1:0.3-0.5:0.8-1.

2.

4. The bio-based composite phosphorus removal agent according to claim 2, characterized in that, The carbon chain length of the long-chain alkyl tertiary amine is ≥10.

5. The bio-based composite phosphorus removal agent according to claim 1, characterized in that, The method for preparing quaternized SiO2-coated Fe3O4 is as follows: Fe3O4 was uniformly dispersed in ethanol to prepare a magnetic particle dispersion. Under nitrogen protection and constant temperature of 25-35℃, orthosilicate was added dropwise to the magnetic particle dispersion while stirring. After the addition was complete, alkali solution was added dropwise until the pH was 9-10. After the addition was complete, the temperature was raised to 40-50℃ and the reaction was stirred for 4-6 hours. After the reaction was completed, SiO2-coated Fe3O4 was obtained. SiO2-coated Fe3O4 was dispersed in a solvent to prepare a suspension. An epoxy silane coupling agent was added, the temperature was raised to 75-85℃, and the reaction was stirred for 3-5 hours. After maintaining the temperature, a quaternization modifier was added dropwise, the temperature was raised to 80-95℃, and the reaction was stirred for 6-8 hours to obtain quaternized SiO2-coated Fe3O4.

6. The bio-based composite phosphorus removal agent according to claim 1, characterized in that, The SiO2-coated Fe3O4 first reacts with a mercaptosilane coupling agent, and then reacts sequentially with an epoxysilane coupling agent and a quaternization modifier.

7. The bio-based composite phosphorus removal agent according to claim 6, characterized in that, The self-assembly reaction is prepared by placing SiO2-coated Fe3O4 in a 5-10 wt% mercaptosilane coupling agent solution and reacting for 1-2 hours.

8. The bio-based composite phosphorus removal agent according to claim 1, characterized in that, The phosphorus removal agent contains 0.3 to 1 part of chitosan with a degree of deacetylation ≥85%.

9. The bio-based composite phosphorus removal agent according to claim 1, characterized in that, The metal salt is selected from any one or more of calcium salts, iron salts, aluminum salts, and magnesium salts.

10. The application of a bio-based composite phosphorus removal agent, characterized in that, The bio-based composite phosphorus removal agent described in any one of claims 1 to 9 is added to landfill leachate for phosphorus removal treatment at a dosage of 0.5 to 3 g / L.

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