A method for simultaneous nitrogen and phosphorus removal in slightly polluted water bodies

Abstract

This application relates to the technical field of environmental engineering and aquatic ecological restoration, specifically disclosing a method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies. The method includes the following steps: Preparation of composite packing material: Pyrite powder, organic solvent, and dispersant are pre-prepared into a pyrite suspension, which is then added to a polyurethane foaming system to obtain a mixture. The mixture is injected into a foaming, curing, shaping, perforating, and cutting process to obtain the composite packing material; Biofilm formation: The composite packing material is first subjected to nitrifying bacteria adsorption and biofilm formation; Deployment: The biofilm-formed packing material is deployed in the river water for nitrogen and phosphorus removal, completing the treatment of the slightly polluted water body.

Description

Technical Field

[0001] This application relates to the technical fields of environmental engineering and water ecological restoration, and in particular to a method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies. Background Technology

[0002] With the acceleration of urbanization, a large amount of domestic sewage and non-point source pollution flows into urban waterways, leading to excessive levels of nitrogen and phosphorus nutrients in the water, causing eutrophication problems such as algal blooms and black and smelly water, which seriously damages the aquatic ecological environment. The purification and treatment of slightly polluted water bodies such as rivers and lakes have the following characteristics: large water volume, relatively low pollutant concentration, water temperature varies with the seasons, and the purification and treatment facilities are required to be low-energy, easy to maintain, and eco-friendly.

[0003] Existing technologies for treating slightly polluted water bodies such as rivers and lakes, such as simple aeration and reoxygenation, chemical dosing, ecological floating beds, and constructed wetlands, often have drawbacks, including low nitrogen and phosphorus removal efficiency, the potential for secondary pollution from chemical dosing, high operating costs, and large land area requirements for treatment facilities. This is especially true for urban rivers and lakes, where land area is often the primary limiting factor.

[0004] For slightly polluted water bodies, traditional methods struggle to efficiently remove ammonia nitrogen and phosphorus in a single space, often requiring a combination of methods. Biological methods have long been considered the most effective for nitrogen removal. Compared to traditional biological methods, biofilm methods have gained widespread attention due to their higher resistance to ammonia nitrogen shock loads and lower sludge residue. However, biofilm methods are largely ineffective at phosphorus removal because polyphosphate-accumulating bacteria cannot proliferate in large quantities, and total phosphorus is difficult to remove from the system through sludge discharge.

[0005] The total phosphorus concentration in slightly polluted rivers and lakes is often only 0.4-0.8 mg / L, which is considered low. Chemical adsorption is a promising method for phosphorus removal due to its low cost and ease of operation. Pyrite is a common natural mineral with abundant reserves and a price far lower than traditional chemical phosphorus removal agents. The resulting iron phosphate precipitate has very low solubility and is a very stable solid product, not easily released back into the water, ensuring thorough and reliable phosphorus removal. Traditional aluminum or iron salt chemical phosphorus removal produces large amounts of inorganic chemical sludge. However, the sludge produced by pyrite phosphorus removal mainly consists of iron phosphate and a small amount of sulfide oxidation products, and its volume increase is theoretically lower than that produced by directly adding iron salts. Therefore, using pyrite as a packing material for phosphorus removal has broad application prospects. However, the dissolution of pyrite and the presence of Fe... 2+The release of phosphorus is strongly dependent on a low pH environment. Under neutral or alkaline conditions, its dissolution rate is very slow, resulting in a sharp decline in phosphorus removal efficiency. However, the pH of slightly polluted water bodies in rivers and lakes is usually neutral, making it difficult to achieve good phosphorus removal results by directly using pyrite. Therefore, developing a method that can adapt to the characteristics of rivers, does not require the addition of chemical agents, and can utilize the river's own conditions to achieve simultaneous removal of nitrogen and phosphorus has an urgent practical need and huge application potential. Summary of the Invention

[0006] In order to utilize the river's own conditions to achieve simultaneous nitrogen and phosphorus removal, this application provides a method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies.

[0007] This application provides a method for simultaneous nitrogen and phosphorus removal in slightly polluted water bodies, employing the following technical solution: A method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies includes the following steps: Preparation of composite filler: Pyrite powder, organic solvent and dispersant are prepared into pyrite suspension in advance, and then added into polyurethane foaming system to obtain a mixture. The mixture is injected into foaming, curing and shaping, opening and cutting to obtain composite filler. Biofilm formation: The composite packing material is first subjected to nitrifying bacteria adsorption and biofilm formation. Deployment: The biofilm-coated packing material is deployed in the river water to remove nitrogen and phosphorus, thus completing the treatment of slightly polluted water bodies.

[0008] By adopting the above technical solution, pyrite powder, organic solvent, and dispersant are first prepared into a pyrite suspension, which is then added to a polyurethane foaming system for foaming and molding. This allows the pyrite to be simultaneously embedded in the pore walls and pore network of the polyurethane foam during the molding process. On the one hand, this improves the load-bearing stability of pyrite in the composite filler, reducing the problem of pyrite powder detachment and loss after being placed in the river. On the other hand, the pore structure of the foam provides an attachment space for nitrifying bacteria. After biofilm formation, the nitrifying bacteria produce H⁺ during the oxidation of ammonia nitrogen, creating a locally weakly acidic microenvironment on the surface of the filler and inside the pores, thereby promoting the release of Fe from the pyrite. 2+ Fe 2+ Further oxidation and reaction with phosphates to form iron phosphate precipitate achieves efficient phosphorus removal; thus, nitrification denitrification and iron release phosphorus removal are coupled, improving the simultaneous removal of nitrogen and phosphorus in slightly polluted water bodies. At the same time, the packing material can be directly deployed in river water bodies without introducing river water into sewage treatment plants or continuously adding chemical phosphorus removal agents such as iron salts and aluminum salts. It has the advantages of small engineering workload, low operating cost, and low risk of secondary pollution.

[0009] In one specific implementation, the dispersant comprises a mixture of a polyether-modified polycarboxylate ammonium salt dispersant, a phosphate ester wetting and dispersing agent, polyvinylpyrrolidone, and γ-glycidoxypropyltrimethoxysilane.

[0010] By adopting the above technical solutions, the polyether-modified polycarboxylate ammonium salt dispersant can reduce the agglomeration tendency between pyrite particles by providing steric hindrance through the polyether segments; the phosphate ester wetting and dispersing agent can improve the wettability of the pyrite powder surface, making pyrite easier to be wetted and dispersed by organic solvents and polyurethane foaming systems; polyvinylpyrrolidone improves the stability of the suspension and reduces pyrite sedimentation; γ-glycidyl etheroxypropyltrimethoxysilane can play an interfacial coupling role between pyrite particles and polyurethane system, improving the bonding strength between pyrite particles and polyurethane skeleton. Therefore, this compound dispersant not only plays a simple dispersing role, but also takes into account wetting, dispersion and interfacial bonding. It can improve the dispersion uniformity and load stability of pyrite inside the sponge, and reduce problems such as pyrite sedimentation, local accumulation, powder shedding and pore blockage.

[0011] In one specific implementation scheme, the weight ratio of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane in the dispersant is (55-75):(15-35):(5-15):(1-5).

[0012] In one specific implementation, the method for preparing the polyurethane foam system includes the following steps: Polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening agent are stirred at 20-30℃ and 500-900 r / min for 5-10 min to obtain a polyurethane foam system; wherein the weight ratio of polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening agent is 100: (2.8-3.6): (0.8-1.2): (0.2-0.4): (0.1-0.2): (4-7): (0.8-1.5).

[0013] By adopting the above technical solution, the addition of hydrophilic modifier can improve the water absorption and microbial adhesion of the filler, which facilitates the subsequent biofilm formation of the filler.

[0014] In one specific implementation, the method for preparing the pyrite powder includes the following steps: Pyrite is crushed to 300 mesh. Then, the pyrite powder is added to deionized water at a mass ratio of pyrite to deionized water of 1:4.5, and stirred for 10-30 minutes. After standing, the upper suspended impurities are removed. The washed pyrite is then added to a citric acid aqueous solution with a molar concentration of 0.05-0.20 mol / L at a mass ratio of pyrite to citric acid aqueous solution of 1:3.5, and stirred for 10-25 minutes. Subsequently, it is washed with deionized water until the pH of the washing solution reaches 6.5-7.5. Finally, the washed pyrite is dried at 50-70℃ for 4-8 hours to obtain pyrite powder.

[0015] By adopting the above technical solution, deionized water washing can remove muddy impurities, fine dust, and soluble impurities from the surface of pyrite, reducing the interference of impurities on the foaming system and water treatment process. Citric acid treatment can remove part of the oxide layer on the surface of pyrite, improving the surface activity of pyrite and making it easier for it to be wetted and dispersed by dispersants. Finally, drying at 50-70℃ reduces the moisture content of pyrite, avoiding excessive moisture from interfering with the polyurethane foaming reaction and reducing problems such as abnormal bubbles, local collapse, or uncontrolled pore size during the foaming process. Therefore, this pretreatment step can simultaneously improve the reactivity, dispersion stability, and foaming compatibility of pyrite.

[0016] In one specific implementation, the method for preparing the pyrite suspension includes the following steps: Add the organic solvent to the dispersion container, add the dispersant, and stir at 500-800 r / min for 5-10 min to fully dissolve or uniformly disperse the dispersant. Slowly add the pyrite powder while stirring. After all the pyrite powder has been added, increase the stirring speed to 1500-2500 r / min and continue dispersing for 20-40 min to obtain a primary pyrite suspension. Ball mill the primary pyrite suspension to make the pyrite particle size D90 ≤ 45 μm, thus obtaining a pyrite suspension.

[0017] In one specific implementation scheme, the weight ratio of the pyrite powder, organic solvent, and dispersant is (22-35):(8-14):(1.5-2.5).

[0018] In one specific implementation, the composite filler preparation step, the mixture injection foaming step is as follows: TDI is added to the mixture, and the mixture is stirred at high speed at 1500-2500 r / min for 8-20 s to obtain a foaming reaction material. The foaming reaction material is poured into a mold preheated to 25-35℃, and the mold filling amount is controlled to be 45-70% of the mold volume. Then, it is allowed to foam freely. During the foaming process, the milky white time of the system is controlled to be 8-20 s, the fiber drawing time is controlled to be 40-90 s, and the free rise time is controlled to be 2-6 min.

[0019] In one specific implementation, the curing and shaping process in the composite filler preparation step is as follows: the mold is placed in an environment of 30-50℃ for 1-3 hours to cure the polyurethane foam initially; then it is demolded and cured at 50-70℃ for 4-8 hours.

[0020] In one specific implementation, in the composite filler preparation step, the opening rate is 85-98%, the average pore size is 0.5-3.0 mm, and the porosity is 80-95%.

[0021] By adopting the above technical solution, the pore structure range can improve the biofilm formation performance, mass transfer performance and anti-clogging performance of the packing material, which is conducive to the long-term stable realization of simultaneous nitrogen and phosphorus removal in slightly polluted water bodies.

[0022] In summary, this application includes at least one of the following beneficial technical effects: The method described in this application involves first preparing a pyrite suspension from pyrite powder, organic solvent, and dispersant, and then adding it to a polyurethane foaming system for foaming and molding. This allows the pyrite to be simultaneously embedded into the pore walls and network of the polyurethane foam during the molding process. On one hand, this improves the load-bearing stability of the pyrite in the composite filler, reducing the problem of pyrite powder detachment and loss after being placed in waterways. On the other hand, the porous structure of the foam provides attachment space for nitrifying bacteria. After biofilm formation, the nitrifying bacteria produce H⁺ during the oxidation of ammonia nitrogen, creating a locally weakly acidic microenvironment on the surface and inside the pores of the filler, thereby promoting the release of Fe from the pyrite. 2+ Fe 2+ Further oxidation and reaction with phosphate to form iron phosphate precipitate, achieving efficient phosphorus removal; thus, nitrification denitrification and iron release phosphorus removal are coupled, improving the simultaneous removal of nitrogen and phosphorus in slightly polluted water bodies. At the same time, the packing material can be directly deployed in river water bodies, without the need to introduce river water into sewage treatment plants, and without the need for continuous addition of chemical phosphorus removal agents such as iron salts and aluminum salts. It has the advantages of small engineering workload, low operating cost, and low risk of secondary pollution. The method in this application utilizes a polyether-modified polycarboxylate ammonium salt dispersant that provides steric hindrance through polyether segments, reducing the tendency for pyrite particles to agglomerate; a phosphate ester-type wetting and dispersing agent that improves the wettability of the pyrite powder surface, making pyrite easier to wet and disperse by organic solvents and polyurethane foaming systems; polyvinylpyrrolidone that improves suspension stability and reduces pyrite sedimentation; and γ-glycidyl etheroxypropyltrimethoxysilane that acts as an interfacial coupling agent between pyrite particles and the polyurethane system, increasing the bonding strength between pyrite particles and the polyurethane skeleton. Therefore, this compound dispersant not only plays a simple dispersing role, but also takes into account wetting, dispersion and interfacial bonding. It can improve the dispersion uniformity and load stability of pyrite inside the sponge, and reduce the problems of pyrite settling, local accumulation, powder shedding and pore blockage. The method described in this application, by adding a hydrophilic modifier, can improve the water absorption and microbial adhesion of the filler, thus facilitating the subsequent biofilm formation on the filler. Detailed Implementation

[0023] The present application will be further described in detail below with reference to the embodiments.

[0024] All raw materials used in the examples are commercially available. The polyether-modified polycarboxylate ammonium salt dispersant is NOPCALL 5200; the phosphate ester wetting and dispersing agent is DISPERBYK-103; the polyether polyol is VORANOL 3010; the foaming water is deionized water; the silicone foam stabilizer is Niax Silicone L-580; the tertiary amine catalyst is DABCO 33-LV; the hydrophilic modifier is a mixture of PEG-400 and dodecyl dimethyl betaine in a mass ratio of 5:1; the cell-opening aid is an ORTEGOL series polyurethane cell-opening aid; and the organic solvent is ethyl acetate. Preparation Example

[0025] Preparation Example 1 Preparation Example 1 provides a method for preparing pyrite powder, comprising the following steps: Pyrite was crushed to 300 mesh, and then the pyrite powder was added to deionized water at a mass ratio of pyrite to deionized water of 1:4.5. The mixture was stirred and washed for 20 minutes, and after standing, the upper suspended impurities were removed. The washed pyrite was then added to a 0.10 mol / L citric acid aqueous solution at a mass ratio of pyrite to citric acid aqueous solution of 1:3.5. The mixture was stirred and treated for 20 minutes, and then washed with deionized water until the pH of the washing solution reached 7. Finally, the washed pyrite was dried at 60℃ for 6 hours to obtain pyrite powder. Example

[0026] Example 1 Example 1 provides a method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies, comprising the following steps: Preparation of composite filler: Polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening aid were stirred at 700 r / min for 8 min at 25℃ to obtain a polyurethane foam system; wherein the weight ratio of polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening aid was 100:2.8:0.8:0.2:0.1:4:0.8 respectively. Organic solvent was added to a dispersion container, followed by the dispersant. The mixture was stirred at 650 rpm for 8 minutes to ensure the dispersant was fully dissolved or uniformly dispersed. Pyrite powder from Preparation Example 1 was slowly added while stirring. After all the pyrite powder was added, the stirring speed was increased to 2000 rpm, and dispersion continued for 30 minutes to obtain a primary pyrite suspension. The primary pyrite suspension was ball-milled to ensure that the pyrite particle size (D90) was ≤45 μm, resulting in a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 22:8:1.5. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane, with a weight ratio of 55:15:5:1. The weight ratio of pyrite powder to polyether polyol was 22:100. A pyrite suspension was added to a polyurethane foaming system and stirred at 1000 rpm for 12 minutes to obtain a mixture. The mixture was then injected into the foaming system, cured and shaped, pore-opened, and cut to a size of 3cm × 3cm × 3cm. After cutting, the mixture was rinsed twice with deionized water to remove free powder and cutting debris from the filler surface. It was then dried at 40℃ for 4 hours, and finally, the edge burrs were removed to obtain the composite filler. The foaming step involved adding TDI to the mixture at a weight ratio of 45:100 (TDI to polyether polyol) and stirring at 2000 rpm. Stir rapidly for 14 seconds to obtain a foaming reactant. Pour the foaming reactant into a mold preheated to 30°C, filling the mold to 60% of its volume, and then allow it to foam freely. During the foaming process, the milky white time is controlled at 14 seconds, the fiber-drawing time at 65 seconds, and the free-rise time at 4 minutes. The curing and shaping steps are as follows: place the mold in a 40°C environment for 2 hours to allow the polyurethane foam to initially shape; then demold and further cure at 60°C for 6 hours. The opening rate is 85-98%, the average pore size is 0.5-3.0 mm, and the porosity is 80-95%. Biofilm formation: The composite packing material is first subjected to nitrifying bacteria adsorption and biofilm formation. The composite packing material is then put into the nitrifying sludge to form a biofilm. During the immobilization process, the concentration of nitrifying sludge is 10 g / L, the ammonia nitrogen is 200 mg / L, the temperature is 28℃, the dissolved oxygen is greater than 3.0 mg / L, the pH is 8, and biofilm formation is completed in seven days. Deployment: The packing material after biofilm formation is wrapped in polyethylene spherical shells to prepare suspended ball packing material, which is then deployed in the river water at a ratio of 10% of the volume of the river to be treated, to remove nitrogen and phosphorus and complete the treatment of slightly polluted water bodies.

[0027] Example 2 The difference between Example 2 and Example 1 is that the organic solvent was added to the dispersion container, followed by the dispersant. The mixture was stirred at 650 r / min for 8 min to ensure the dispersant was fully dissolved or uniformly dispersed. The pyrite powder from Example 1 was slowly added while stirring. After all the pyrite powder was added, the stirring speed was increased to 2000 r / min, and dispersion continued for 30 min to obtain a primary pyrite suspension. The primary pyrite suspension was ball-milled to ensure that the pyrite particle size D90 was ≤45 μm, thus obtaining a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 22:8:1.5. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane, with a weight ratio of 65:25:10:3. The weight ratio of pyrite powder to polyether polyol was 22:100. The remaining steps were the same as in Example 1.

[0028] Example 3 The difference between Example 3 and Example 1 is that the organic solvent was added to the dispersion container, followed by the dispersant. The mixture was stirred at 650 r / min for 8 min to ensure the dispersant was fully dissolved or uniformly dispersed. The pyrite powder from Preparation Example 1 was slowly added while stirring. After all the pyrite powder was added, the stirring speed was increased to 2000 r / min, and dispersion continued for 30 min to obtain a primary pyrite suspension. The primary pyrite suspension was ball-milled to ensure that the pyrite particle size D90 was ≤45 μm, thus obtaining a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 22:8:1.5. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane, with a weight ratio of 75:35:15:5. The weight ratio of pyrite powder to polyether polyol was 22:100. The remaining steps were the same as in Example 1.

[0029] Example 4 The difference between Example 4 and Example 2 is that the organic solvent was added to the dispersion container, followed by the dispersant. The mixture was stirred at 650 r / min for 8 min to ensure the dispersant was fully dissolved or uniformly dispersed. The pyrite powder from Preparation Example 1 was slowly added while stirring. After all the pyrite powder was added, the stirring speed was increased to 2000 r / min, and dispersion continued for 30 min to obtain a primary pyrite suspension. The primary pyrite suspension was ball-milled to ensure that the pyrite particle size D90 was ≤45 μm, thus obtaining a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 22:8:1.5. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant and phosphate ester wetting dispersant, with a weight ratio of 65:25. The weight ratio of pyrite powder to polyether polyol was 22:100. The remaining steps were the same as in Example 2.

[0030] Example 5 The difference between Example 5 and Example 2 is that the organic solvent was added to the dispersion container, followed by the dispersant. The mixture was stirred at 650 r / min for 8 min to ensure the dispersant was fully dissolved or uniformly dispersed. The pyrite powder from Preparation Example 1 was slowly added while stirring. After all the pyrite powder was added, the stirring speed was increased to 2000 r / min, and dispersion continued for 30 min to obtain a primary pyrite suspension. The primary pyrite suspension was ball-milled to ensure that the pyrite particle size D90 was ≤45 μm, resulting in a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 22:8:1.5. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, and γ-glycidyl etheroxypropyltrimethoxysilane, with a weight ratio of 65:25:3. The weight ratio of pyrite powder to polyether polyol was 22:100. The remaining steps were the same as in Example 2.

[0031] Example 6 The difference between Example 6 and Example 2 is that the organic solvent was added to the dispersion container, followed by the dispersant. The mixture was stirred at 650 r / min for 8 min to ensure the dispersant was fully dissolved or uniformly dispersed. The pyrite powder from Preparation Example 1 was slowly added while stirring. After all the pyrite powder was added, the stirring speed was increased to 2000 r / min, and dispersion continued for 30 min to obtain a primary pyrite suspension. The primary pyrite suspension was ball-milled to ensure that the pyrite particle size D90 was ≤45 μm, resulting in a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 22:8:1.5. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, and polyvinylpyrrolidone, with a weight ratio of 65:25:10. The weight ratio of pyrite powder to polyether polyol was 22:100. The remaining steps were the same as in Example 2.

[0032] Example 7 The difference between Example 7 and Example 2 is that the polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening aid are stirred at 25°C and 700 r / min for 8 min to obtain a polyurethane foam system; wherein the weight ratio of polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening aid is 100:3.2:1.0:0.3:0.15:5.5:1.2 respectively; the remaining steps are the same as in Example 2.

[0033] Example 8 The difference between Example 8 and Example 2 is that the polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening agent are stirred at 25°C and 700 r / min for 8 min to obtain a polyurethane foam system; wherein the weight ratio of polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening agent is 100:3.6:1.2:0.4:0.2:7:1.5 respectively; the remaining steps are the same as in Example 2.

[0034] Example 9 The difference between Example 9 and Example 7 is that the organic solvent was added to the dispersion container, a dispersant was added, and the mixture was stirred at 650 r / min for 8 min to ensure that the dispersant was fully dissolved or uniformly dispersed. The pyrite powder from Preparation Example 1 was slowly added while stirring. After all the pyrite powder was added, the stirring speed was increased to 2000 r / min, and dispersion continued for 30 min to obtain a primary pyrite suspension. The primary pyrite suspension was ball-milled to ensure that the pyrite particle size D90 was ≤45 μm, thus obtaining a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 28:11:2. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane, with a weight ratio of 65:25:10:3. The weight ratio of pyrite powder to polyether polyol was 28:100. The remaining steps were the same as in Example 7.

[0035] Example 10 The difference between Example 10 and Example 7 is that, in Example 10, an organic solvent was added to a dispersion container, a dispersant was added, and the mixture was stirred at 650 rpm for 8 minutes to ensure the dispersant was fully dissolved or uniformly dispersed; while stirring, the pyrite powder from Preparation Example 1 was slowly added. After all the pyrite powder was added, the stirring speed was increased to 2000 rpm, and dispersion continued for 30 minutes to obtain a primary pyrite suspension; the primary pyrite suspension was then ball-milled to further disperse the pyrite in the suspension. Particles with a diameter D90 ≤ 45 μm were used to obtain a pyrite suspension. The weight ratio of pyrite powder, organic solvent, and dispersant was 35:14:2.5. The dispersant was a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting and dispersing agent, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane, with a weight ratio of 65:25:10:3. The weight ratio of pyrite powder to polyether polyol was 35:100. The remaining steps were consistent with those in Example 7. Comparative Example

[0036] Comparative Example 1 The difference between Comparative Example 1 and Example 1 lies in the filler preparation: polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening aid are stirred at 25°C and 700 r / min for 8 min to obtain a polyurethane foam system; wherein the weight ratio of polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening aid is 100:2.8:0.8:0.2:0.1:4:0.8 respectively. The polyurethane foam system was injected, foamed, cured and shaped, opened and cut to a size of 3cm×3cm×3cm. After cutting, it was rinsed twice with deionized water to remove free powder and cutting debris from the surface of the filler. Then it was dried at 40℃ for 4 hours. Finally, the edge burrs were removed to obtain the filler. Biofilm formation: The composite packing material is first subjected to nitrifying bacteria adsorption and biofilm formation. The composite packing material is then added to the nitrifying sludge for biofilm formation. During the immobilization process, the concentration of nitrifying sludge is 10 g / L, the ammonia nitrogen is 200 mg / L, the temperature is 28℃, the dissolved oxygen is greater than 3.0 mg / L, and the pH is 8. Biofilm formation is completed in seven days. The remaining steps are the same as in Example 1.

[0037] Comparative Example 2 The difference between Comparative Example 2 and Comparative Example 1 is that the packing material after the film is attached is wrapped with a polyethylene spherical shell to prepare a suspended ball packing material, which is then placed in the river water at a ratio of 10% of the volume of the river to be treated. Then, pyrite powder from Preparation Example 1 is added, with a weight ratio of pyrite powder to polyether polyol of 22:100, to remove nitrogen and phosphorus, thus completing the treatment of the slightly polluted water body; the remaining steps are the same as those in Comparative Example 1. Performance testing experiment

[0038] Wastewater treatment effect: Slightly polluted water bodies from the examples and comparative examples were used as samples for treatment. The total nitrogen and total phosphorus contents in the water before treatment were measured. After 30 minutes of treatment, the total nitrogen and total phosphorus contents in the treated water were measured. The total nitrogen content was determined according to HJ 636-2012 "Determination of Total Nitrogen in Water - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometric Method", and the total phosphorus content was determined according to GB 11893-89 "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method". The total nitrogen removal rate and total phosphorus removal rate were calculated using the following formula: Removal rate / % = (Content before treatment - Content after treatment) / Content before treatment × 100%.

[0039] Table 1. Test results of river water treatment

[0040] Combining Example 1 and Comparative Examples 1-2, Comparative Example 1, without the addition of pyrite, only used polyurethane packing to treat the water, and its total nitrogen removal rate still reached 85.14%. This indicates that the porous polyurethane packing itself can provide a carrier for the attachment and growth of nitrifying bacteria, thus having a certain nitrogen removal effect. However, the total phosphorus removal rate of Comparative Example 1 was only 2.38%, almost no phosphorus removal capacity. This shows that it is difficult to effectively remove phosphorus from water by relying solely on biofilm packing, and further proves that the pyrite component in this application plays a key role in the phosphorus removal effect. Comparative Example 2 added pyrite powder after the ordinary polyurethane packing was laid out, and its total phosphorus removal rate was only 13.64%. This shows that pyrite cannot achieve efficient phosphorus removal simply by adding it. If pyrite exists in the form of free powder, on the one hand, it is easy to settle, agglomerate or be lost, and cannot be stably distributed near the biofilm; on the other hand, it is difficult for it to form an effective coupling with the local acidic microenvironment produced by nitrifying bacteria, resulting in insufficient iron ion release efficiency, which in turn affects the formation of iron phosphate precipitate. Therefore, the combination of "pre-dispersion of pyrite suspension - polyurethane foam embedding - nitrifying bacteria biofilm" in this application is the key to improving the simultaneous denitrification and phosphorus removal effect.

[0041] Referring to Examples 1-3, it can be seen that after changing the ratio of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting dispersant, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane in the compound dispersant, Examples 1-3 all maintained high total nitrogen and total phosphorus removal rates. Specifically, Example 2 achieved a total nitrogen removal rate of 90.79%, and Example 3 achieved a total phosphorus removal rate of 60.34%. This indicates that the compound dispersant system can improve the dispersion state of pyrite powder in organic solvents and polyurethane foaming systems, making pyrite less prone to local sedimentation or agglomeration, thereby facilitating the formation of stable and uniform iron release and phosphorus removal sites.

[0042] Combining Examples 2 and 4-6, it is evident that the overall treatment effect fluctuates when the compound dispersant lacks polyvinylpyrrolidone or silane coupling components. In particular, in Example 6, without the addition of γ-glycidoxypropyltrimethoxysilane, the total phosphorus removal rate decreased to 48.21%. This indicates that the silane coupling component can improve the bonding strength between pyrite particles and the polyurethane framework, allowing the pyrite to be more stably loaded in the pore wall structure, reducing powder shedding or localized loss; while polyvinylpyrrolidone helps improve suspension stability and reduces pyrite sedimentation. The dispersing components are not simply interchangeable, but rather each plays a role in wetting, dispersing, suspension stabilization, and interfacial bonding, respectively.

[0043] Combining Examples 2, 7, and 8, Example 8 achieved a total phosphorus removal rate of 61.11%, indicating that appropriately increasing hydrophilicity and porosity facilitates water entry into the pores of the packing material, enhancing the contact between phosphate and the active sites of pyrite. However, the total nitrogen removal rate of Example 8 was slightly lower than that of Example 7, suggesting that higher pore structure and hydrophilicity are not always better. If the pore structure is too open or the system is too hydrophilic, it may affect the biofilm attachment stability. Therefore, a balance needs to be struck between biofilm attachment performance, mass transfer performance, and structural stability.

[0044] Based on Examples 7, 9, and 10, it is evident that appropriately increasing the pyrite loading can increase the number of sites for iron release and phosphorus removal, thereby improving phosphorus removal efficiency. However, excessively high pyrite loading may cause localized agglomeration, pore blockage, or deterioration of the sponge pore wall structure, which in turn affects water mass transfer and effective contact area. Therefore, the pyrite loading needs to be controlled within a reasonable range and is not necessarily better the higher it is.

[0045] 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 method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies, characterized in that: Includes the following steps: Preparation of composite filler: Pyrite powder, organic solvent and dispersant are prepared into pyrite suspension in advance, and then added into polyurethane foaming system to obtain a mixture. The mixture is injected into foaming, curing and shaping, opening and cutting to obtain composite filler. Biofilm formation: The composite packing material is first subjected to nitrifying bacteria adsorption and biofilm formation. Deployment: The biofilm-coated packing material is deployed in the river water to remove nitrogen and phosphorus, thus completing the treatment of slightly polluted water bodies.

2. The method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 1, characterized in that: The dispersant comprises a mixture of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting and dispersing agent, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane.

3. The method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 2, characterized in that: The weight ratio of polyether-modified polycarboxylate ammonium salt dispersant, phosphate ester wetting and dispersing agent, polyvinylpyrrolidone, and γ-glycidyl etheroxypropyltrimethoxysilane in the dispersant is (55-75):(15-35):(5-15):(1-5).

4. The method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 3, characterized in that: The preparation method of the polyurethane foam system includes the following steps: Polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening agent are stirred at 20-30℃ and 500-900 r / min for 5-10 min to obtain a polyurethane foam system; wherein the weight ratio of polyether polyol, foaming water, silicone foam stabilizer, tertiary amine catalyst, stannous octoate, hydrophilic modifier, and cell opening agent is 100: (2.8-3.6): (0.8-1.2): (0.2-0.4): (0.1-0.2): (4-7): (0.8-1.5).

5. The method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 1, characterized in that: The method for preparing the pyrite powder includes the following steps: Pyrite is crushed to 300 mesh. Then, the pyrite powder is added to deionized water at a mass ratio of pyrite to deionized water of 1:4.5, and stirred for 10-30 minutes. After standing, the upper suspended impurities are removed. The washed pyrite is then added to a citric acid aqueous solution with a molar concentration of 0.05-0.20 mol / L at a mass ratio of pyrite to citric acid aqueous solution of 1:3.5, and stirred for 10-25 minutes. Subsequently, it is washed with deionized water until the pH of the washing solution reaches 6.5-7.

5. Finally, the washed pyrite is dried at 50-70℃ for 4-8 hours to obtain pyrite powder.

6. The method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 5, characterized in that: The method for preparing the pyrite suspension includes the following steps: Add the organic solvent to the dispersion container, add the dispersant, and stir at 500-800 r / min for 5-10 min to fully dissolve or uniformly disperse the dispersant. Slowly add the pyrite powder while stirring. After all the pyrite powder has been added, increase the stirring speed to 1500-2500 r / min and continue dispersing for 20-40 min to obtain a primary pyrite suspension. Ball mill the primary pyrite suspension to make the pyrite particle size D90 ≤ 45 μm, thus obtaining a pyrite suspension.

7. A method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 6, characterized in that: The weight ratio of the pyrite powder, organic solvent, and dispersant is (22-35):(8-14):(1.5-2.5).

8. The method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 1, characterized in that: In the composite filler preparation step, the mixture injection foaming step is as follows: TDI is added to the mixture, and the mixture is stirred at high speed at 1500-2500 r / min for 8-20s to obtain a foaming reaction material. The foaming reaction material is poured into a mold preheated to 25-35℃, and the mold filling amount is controlled to be 45-70% of the mold volume. Then, it is allowed to foam freely. During the foaming process, the milky white time of the system is controlled to be 8-20s, the fiber drawing time is controlled to be 40-90s, and the free rise time is controlled to be 2-6min.

9. A method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 8, characterized in that: In the preparation steps of the composite filler, the curing and shaping process is as follows: the mold is placed in an environment of 30-50℃ for 1-3 hours to cure the polyurethane foam initially; then it is demolded and cured at 50-70℃ for 4-8 hours.

10. A method for simultaneous nitrogen and phosphorus removal suitable for slightly polluted water bodies according to claim 1, characterized in that: In the composite filler preparation step, the opening rate is 85-98%, the average pore size is 0.5-3.0 mm, and the porosity is 80-95%.

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