Constructed wetland filter material and preparation method thereof

Abstract

The invention provides a constructed wetland filter material and a preparation method thereof, and particularly relates to the technical field of water environment treatment. The constructed wetland filter material comprises an inorganic matrix and a modified PLA coating positioned on the surface of the inorganic matrix, the modified PLA is hydrophilic modified PLA; and the thickness of the modified PLA coating is less than 2mm. The constructed wetland filter material provided by the invention has significantly improved hydrophilicity, and the surface biofilm density is increased by 30% or more, so that the microbial adhesion ability is greatly improved. In the aspect of denitrification performance, the nitrate removal rate of the filter material is increased by 20-40%. Even under the low-temperature condition of 5-15 DEG C, the removal rate of nitrate can still be stably kept at 60% or above, and is remarkably superior to that of a traditional filter material. In addition, the filter material also has excellent mechanical properties, the compressive strength is improved by 30% or more, and the wear resistance and the anti-scouring capability are also remarkably enhanced, so that the filter material shows higher stability and durability in a complex environment and long-term operation.

Description

Technical Field

[0001] The present invention relates to the technical field of water environment treatment, and particularly to an artificial wetland filter material and a preparation method thereof. Background Art

[0002] An artificial wetland is an important ecological water treatment technology, widely used in the field of sewage purification, with the advantages of high treatment efficiency, low operation cost, and ecological friendliness. Its core principle is to utilize the microbial metabolic process to achieve the degradation and transformation of pollutants. Especially in the denitrification process, sufficient soluble organic carbon (carbon source) is required as the electron donor for the denitrification reaction. However, under the condition of a low carbon-nitrogen ratio (C / N), the soluble organic carbon in the sewage is insufficient, resulting in a significant reduction in the denitrification efficiency, and thus affecting the overall water treatment effect.

[0003] When treating water bodies with a low C / N ratio, artificial wetlands face many challenges, including low denitrification efficiency, insufficient carbon source supply of the filter material, inflexible system regulation, long treatment cycle, limited role of plant roots, and negative impact of low temperature on the denitrification effect. The root causes of these problems lie in the deficiencies of traditional filter materials and treatment methods, such as unstable carbon source supply, untimely system response, and attenuation of long-term operation effect.

[0004] Currently, the main technical means to solve the problem of artificial wetland treating water with a low C / N ratio include the following three: Artificial addition of carbon source: By adding external carbon sources such as methanol and sodium acetate to the system, the denitrification efficiency can be quickly improved. However, this method has significant disadvantages: high operation cost; complex operation; environmental risks.

[0005] Modified filter material: By embedding natural materials such as biochar and wood chips into the filter material, the controllability of carbon source release can be improved to a certain extent. However, this method still has problems such as uncontrollable release rate, insufficient filter material stability, and limited application range.

[0006] Electron donor-enhanced materials: By using materials such as iron-carbon composite filter materials or sulfur-based filter materials (such as pyrite and calcium sulfide), the denitrification efficiency can be improved by using non-organic carbon electron donors under carbon-deficient conditions. However, these materials still have significant defects in practical applications: risk of by-product generation; insufficient long-term performance; limited adaptability.

[0007] Although the existing technical means can alleviate the problems in the treatment of water with a low C / N ratio to a certain extent, they all have obvious limitations. The artificial addition of carbon source has a high cost and complex operation, the modified filter material has insufficient stability, and the electron donor-enhanced materials have environmental risks and long-term performance problems. Therefore, the development of a new filter material technology that is efficient, stable, and economically feasible is crucial for improving the performance of artificial wetlands in the treatment of water with a low C / N ratio.

[0008] In view of this, the present invention is specifically proposed. Summary of the Invention

[0009] One of the objectives of the present invention is to provide an artificial wetland filter material, aiming to solve at least one of the above technical problems in the prior art.

[0010] Another objective of the present invention is to provide a preparation method for the artificial wetland filter material.

[0011] In order to achieve the above objectives of the present invention, the following technical solutions are specifically adopted: The first aspect of the present invention provides an artificial wetland filter material, including an inorganic matrix and a modified PLA coating on the surface of the inorganic matrix; the modified PLA in the modified PLA coating is hydrophilic modified PLA; the thickness of the modified PLA coating is < 2 mm.

[0012] Furthermore, the pore diameter of the hydrophilic modified PLA is 1 - 10 μm.

[0013] And / or, the specific surface area of the hydrophilic modified PLA is ≥ 50 m 2 / g.

[0014] Furthermore, the hydrophilic functional groups introduced into the hydrophilic modified PLA include at least one of hydroxyl, carboxyl, and amino groups.

[0015] Furthermore, the inorganic matrix includes ceramsite or quartz sand.

[0016] And / or, the particle size of the inorganic matrix is 2 - 10 mm.

[0017] And / or, the specific gravity of the inorganic matrix is 1.5 - 2.5 g / cm 3 .

[0018] The second aspect of the present invention provides a preparation method for the artificial wetland filter material, where a solution of modified PLA is coated on the surface of the inorganic matrix, and the artificial wetland filter material is obtained after drying.

[0019] Furthermore, the solvents used in the solution of modified PLA include chloroform and / or dichloromethane.

[0020] And / or, the mass percentage concentration of the solution of modified PLA is 30 - 40%.

[0021] Furthermore, the coating method includes spray coating method.

[0022] And / or, during the spray coating process, the distance between the nozzle and the inorganic matrix is 10 - 15 cm, the spray pressure is 2 - 3 bar, and the spray flow rate is 10 - 20 mL / min.

[0023] Furthermore, the preparation method of the modified PLA includes: first subjecting PLA particles to physical foaming, then performing oxygen plasma treatment, and finally performing surface modification by compounding with a modifier to obtain the modified PLA.

[0024] And / or, the molecular weight of the PLA is 100,000 - 300,000.

[0025] Furthermore, in the physical foaming, the foaming gas used is carbon dioxide and / or nitrogen.

[0026] And / or, the pressure of the physical foaming is 2.5 - 3.5 MPa, the time is 10 - 20 min, and the temperature is 120 - 180 °C.

[0027] And / or, the power of the oxygen plasma treatment is 80 - 100 W, and the time is 2 - 4 min.

[0028] Furthermore, the modifier provides at least one functional group among hydroxyl, carboxyl, and amino groups.

[0029] And / or, the modifier includes at least one of chitosan, lignin, carboxymethyl cellulose, aminated chitosan, sodium lignosulfonate, and carboxylated lignin.

[0030] And / or, the modifier is made into a modifier solution and mixed with the PLA particles after oxygen plasma treatment to complete the surface modification, and the modified PLA is obtained after drying.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects: The artificial wetland filter material provided by the present invention has significantly improved hydrophilicity, and the surface biofilm density increases by more than 30%, thus greatly improving the microbial attachment ability. In terms of denitrification performance, the filter material shows excellent efficiency, and the nitrate removal rate increases by 20% to 40%. Even under low temperature conditions of 5 - 15 °C, the nitrate removal rate can still be stably maintained above 60%, which is significantly better than traditional filter materials. In addition, the filter material also has excellent mechanical properties, the compressive strength increases by more than 30%, and the wear resistance and erosion resistance are also significantly enhanced, making it show higher stability and durability in complex environments and long-term operations.

[0032] The preparation method provided by the present invention has a large batch processing capacity, is simple to operate, and is suitable for large-scale industrial production. Detailed Embodiments

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0034] As used hereinafter, the terms "comprising", "having" and their cognates that can be used in various embodiments of the present invention are only intended to denote specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be construed as precluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or as precluding the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0035] Through the analysis of the technical problems of the present invention, it is found that on the one hand, the prior art lacks efficient and economically feasible slow-release carbon source materials and it is difficult to dynamically match the treatment requirements under different pollution loads; on the other hand, the filter media modification technologies are mostly limited to single physical or chemical methods and fail to comprehensively consider the coordination relationship among carbon source supply, microorganism attachment and mechanical properties. In addition, the long-term performance research on composite filter media is insufficient and there is a lack of mechanical properties and environmental stability design suitable for long-term operation.

[0036] The first aspect of the present invention provides an artificial wetland filter media, comprising an inorganic matrix and a modified PLA coating located on the surface of the inorganic matrix; the modified PLA in the modified PLA coating is hydrophilic modified PLA; the thickness of the modified PLA coating < 2 mm.

[0037] The artificial wetland filter media provided by the present invention has significantly improved hydrophilicity, and the surface biofilm density increases by more than 30%, thus greatly improving the microorganism attachment ability. In terms of denitrification performance, the filter media shows excellent efficiency, and the nitrate removal rate increases by 20% to 40%. Even under low temperature conditions of 5 to 15 °C, the nitrate removal rate can still be stably maintained above 60%, which is significantly better than traditional filter media. In addition, the filter media also has excellent mechanical properties, the compressive strength increases by more than 30%, and the wear resistance and anti-scouring ability are also significantly enhanced, making it show higher stability and durability in complex environments and long-term operations.

[0038] The present invention selects inorganic materials as the matrix, and these materials have good mechanical properties in the wetland environment and can effectively withstand the impact of water flow and the collision and friction between particles. By compounding and processing inorganic materials with polylactic acid (PLA), the filter media has the function of slow-release carbon source while maintaining good mechanical strength.

[0039] Polylactic acid (PLA) has biodegradability, can release available organic carbon sources through hydrolysis and microbial metabolism, and the degradation products are non-toxic and friendly to the wetland environment. It degrades into harmless substances naturally after the life of the artificial wetland filter media ends. However, the single material of polylactic acid (PLA) has deficiencies such as too slow release rate and low microbial utilization efficiency, and it is necessary to modify the material properties.

[0040] By using modified PLA on the surface of the inorganic matrix to construct a uniform composite layer, the overall erosion resistance of the filter material is enhanced, and the rapid degradation of a single PLA material under the hydraulic erosion of the wetland is avoided.

[0041] Furthermore, the pore diameter of the hydrophilic modified PLA is 1 - 10 μm. In the specific implementation process, the PLA is foamed to construct a controllable porous structure to achieve precise regulation of the slow-release carbon source.

[0042] And / or, the specific surface area of the hydrophilic modified PLA ≥ 50 m 2 / g.

[0043] Furthermore, the hydrophilic functional groups introduced in the hydrophilic modified PLA include at least one of hydroxyl, carboxyl, and amino groups.

[0044] Furthermore, the inorganic matrix includes ceramsite or quartz sand.

[0045] And / or, the particle size of the inorganic matrix is 2 - 10 mm.

[0046] And / or, the specific gravity of the inorganic matrix is 1.5 - 2.5 g / cm 3 . Typically but not restrictively, the specific gravity of the inorganic matrix can be, for example, 1.5 g / cm 3 , 1.6 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 , 1.9 g / cm 3 , 2.0 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 or 2.5 g / cm 3 , and it can also be any value within the range of 1.5 g / cm 3 ~2.5 g / cm 3 .

[0047] The artificial wetland filter material provided by the present invention has the following technical effects: 1. Improve the utilization efficiency of the carbon source The present invention realizes the efficient slow release of carbon sources by modifying polylactic acid (PLA) and designing the porous structure of its composite materials. This design enables the carbon source to be released dynamically according to the actual needs of the denitrification reaction in the wetland system, significantly improving the denitrification efficiency and enhancing the treatment capacity of low carbon-nitrogen ratio (C / N) sewage. Compared with traditional artificial addition of carbon sources or extensive carbon sources, the controlled release technology of the present invention reduces the dosing frequency and cost of external carbon sources, thus greatly reducing the operating cost.

[0048] 2. Significantly improve the denitrification effect The present invention adopts surface functionalization technology, significantly enhancing the hydrophilicity and microbial adhesion of the filter material, thus rapidly promoting the growth of biofilms. Microorganisms can adapt to the filter material surface faster and improve the nitrate reduction ability. Under low C / N conditions, this design significantly increases the denitrification reaction rate, greatly improving the denitrification efficiency. Especially in low-temperature environments, the denitrification efficiency can be increased by more than 30%. This not only improves the sewage treatment efficiency but also enhances the adaptability of the wetland system in cold regions, having important environmental significance.

[0049] 3. Enhance mechanical stability and durability The present invention significantly improves the anti-scouring ability and wear resistance of the filter material by optimizing the composite material coating process. Coating the PLA-based composite material on the surface of high-strength substrates such as ceramsite and quartz sand not only enhances the mechanical strength of the filter material but also makes it show higher stability under complex water flow conditions and long-term operation. Compared with traditional filter materials, the filter material of the present invention has a longer service life, which can effectively reduce the maintenance frequency and replacement cost of equipment.

[0050] 4. Significantly improve low-temperature adaptability The present invention fully considers the denitrification requirements under low-temperature environments. By optimizing the biological activity and stability of the materials, the filter material can still maintain high denitrification ability under low-temperature conditions below 5°C. Compared with conventional filter materials, the filter material of the present invention can operate efficiently continuously in winter or cold regions, improving the seasonal stability of the wetland system, reducing the negative impacts brought by seasonal changes, and meeting the sewage treatment needs of more regions.

[0051] 5. Ecological friendliness and environmental sustainability The filter material of the present invention uses polylactic acid (PLA) as the main material and has good biodegradability. After its service life ends, it can be naturally degraded to reduce the environmental burden. At the same time, the optimized production process reduces energy consumption and pollution emissions during production. This ecologically friendly characteristic is more environmentally friendly than traditional plastic filter materials, meeting the requirements of sustainable development and green environmental protection, and providing strong support for the comprehensive promotion of wetland systems.

[0052] In summary, the artificial wetland filter media of the present invention have achieved significant improvements in aspects such as carbon source utilization efficiency, nitrogen removal effect, mechanical stability, low-temperature adaptability, and ecological friendliness. At the same time, this technology optimizes the operating cost and maintenance cycle of the wetland system, providing a brand-new technical solution for achieving more efficient, energy-saving, and environmentally friendly sewage treatment.

[0053] The second aspect of the present invention provides a method for preparing the artificial wetland filter media, wherein a solution of modified PLA is coated on the surface of an inorganic substrate, and the artificial wetland filter media are obtained after drying.

[0054] The preparation method provided by the present invention has a large batch processing capacity and is simple to operate, making it suitable for large-scale industrial production.

[0055] In the specific implementation process of the present invention, a multi-layer protective structure is formed on the surface of the substrate by using a layer-by-layer coating process, enabling the filter media to have high anti-peeling performance and improving its durability during operation. The layer-by-layer coating process controls the thickness of a single layer of coating to be 100 - 500 µm, and the number of layers is 4 - 20 layers, preferably 8 - 12 layers.

[0056] Furthermore, the solvents used in the solution of the modified PLA include chloroform and / or dichloromethane.

[0057] And / or, the mass percentage concentration of the solution of the modified PLA is 30 - 40%. Typically but not restrictively, the mass percentage concentration of the solution of the modified PLA can be, for example, 30%, 32%, 34%, 36%, 38%, or 40%, or any value within the range of 30% - 40%.

[0058] Furthermore, the coating method includes spray coating.

[0059] And / or, during the spray coating process, the distance between the nozzle and the inorganic substrate is 10 - 15 cm, the spray pressure is 2 - 3 bar, and the spray flow rate is 10 - 20 mL / min.

[0060] Typically but not restrictively, the distance between the nozzle and the inorganic substrate can be, for example, 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, or 15 cm, or any value within the range of 10 cm - 15 cm; the spray pressure can be, for example, 2 bar, 2.2 bar, 2.4 bar, or 3 bar, or any value within the range of 2 bar - 3 bar; the spray flow rate can be, for example, 10 mL / min, 12 mL / min, 14 mL / min, 16 mL / min, 18 mL / min, or 20 mL / min, or any value within the range of 10 mL / min - 20 mL / min.

[0061] Furthermore, the preparation method of the modified PLA includes: first subjecting PLA particles to physical foaming or chemical etching to construct a controllable porous structure on the polylactic acid (PLA) matrix; then performing oxygen plasma treatment, and finally performing surface modification by compounding with a modifier to obtain the modified PLA.

[0062] Constructing a porous structure in the PLA material by physical foaming and chemical etching can significantly increase the specific surface area, thereby enhancing the release rate of the carbon source. At the same time, by regulating the size and distribution of the pores, precise adjustment of the carbon release rate can be achieved to meet the denitrification requirements of the wetland system under different load conditions.

[0063] Chemical etching is to locally dissolve the PLA material with a suitable solvent, so that after partial regions in the material are dissolved, voids are left after the solvent volatilizes or is removed, thereby forming a microporous structure. The porous structure can be selected in one of two ways or both at the same time, and the purpose is to increase the specific surface area.

[0064] Hydrophilic modification of PLA is achieved by introducing hydrophilic functional groups (such as hydroxyl, carboxyl or amino groups) to enhance the hydrophilicity of the PLA material, making it more suitable for the attachment of microbial biofilms. An efficient microbial attachment matrix can be constructed on the surface of the filter media obtained from the modified PLA material, effectively promoting the rapid formation and stability of the biofilm. To address the problem of the decline in denitrification efficiency under low-temperature conditions, methods to promote hydrophilicity and microbial activity are adopted in the design of the filter media, significantly improving its adaptability in low-temperature environments. At the same time, hydrophilic modification treatment can improve the interfacial bonding performance between PLA and the inorganic matrix, preventing coating peeling caused by weak bonding force during long-term operation.

[0065] In one embodiment of the present invention, the PLA particles are placed in an oxygen plasma environment (for example, treated at a power of 90 W for 3 minutes). Under the bombardment of high-energy oxygen ions, a large number of hydrophilic functional groups (such as hydroxyl, carboxyl, etc.) will be generated on the surface of PLA, thereby significantly improving the hydrophilicity and biocompatibility of the material surface. This modification helps microorganisms attach to the surface of the filter media faster and more firmly, further improving the denitrification (nitrogen removal) efficiency.

[0066] And / or, the molecular weight of the PLA is 100,000 - 300,000.

[0067] Furthermore, in the physical foaming, the foaming gas used is carbon dioxide and / or nitrogen.

[0068] And / or, the pressure of the physical foaming is 2.5 - 3.5 MPa, the time is 10 - 20 min, and the temperature is 120 - 180 °C.

[0069] Typically but not restrictively, the pressure of the physical foaming can be, for example, 2.5 MPa, 2.8 MPa, 3.0 MPa, 3.2 MPa or 3.5 MPa, or any value within the range of 2.5 MPa to 3.5 MPa; the foaming time can be, for example, 10 min, 12 min, 15 min, 18 min or 20 min, or any value within the range of 10 min to 20 min; the foaming temperature can be, for example, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C or 180 °C, or any value within the range of 120 °C to 180 °C.

[0070] And / or, the power of the oxygen plasma treatment is 80 - 100 W, and the time is 2 - 4 min.

[0071] Typically but not restrictively, the power of the oxygen plasma treatment can be, for example, 80 W, 85 W, 90 W, 95 W or 100 W, or any value within the range of 80 W to 100 W; the treatment time can be, for example, 2 min, 2.5 min, 3 min, 3.5 min or 4 min, or any value within the range of 2 min to 4 min.

[0072] Furthermore, the modifier provides at least one functional group among hydroxyl group, carboxyl group and amino group.

[0073] And / or, the modifier includes at least one of chitosan, lignin, carboxymethyl cellulose, aminated chitosan, sodium lignosulfonate and carboxylated lignin.

[0074] To ensure that the modifier can fully penetrate into the micropores on the surface of the PLA particles and improve the dispersion effect, mild ultrasonic treatment (such as low-power ultrasonic for several minutes) can be supplemented to further promote the interaction between the modifier and the PLA surface.

[0075] After the mixing reaction lasts for a certain time (such as 10 - 20 minutes), the modified PLA particles are separated from the solution by filtration or centrifugation, and then dried in a ventilated or low-temperature oven until the solvent completely volatilizes, obtaining a uniformly modified dry PLA powder.

[0076] And / or, the modifier is made into a modifier solution and mixed with the PLA particles after oxygen plasma treatment to complete the surface modification, and the modified PLA is obtained after drying.

[0077] The present invention will be further illustrated below through specific examples and comparative examples. However, it should be understood that these examples are only for more detailed illustration and should not be construed as limiting the present invention in any way. For the raw materials used in the examples and comparative examples of the present invention, unless otherwise specified, they are carried out under conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0078] Example 1 This example provides an artificial wetland filter material, and the preparation method is as follows: 1. 30 g of industrial-grade PLA particles (molecular weight 200,000) and 10 g of CO2 gas (a mixture of nitrogen and CO2) are placed in a high-pressure vessel, and foaming treatment is carried out at a pressure of 3 MPa and a temperature of 150 °C for 15 minutes. The specific surface area of the foamed PLA reaches about 100 m 2 / g.

[0079] 2. The foamed PLA particles are subjected to oxygen plasma treatment (power 90 W, treatment time 3 minutes).

[0080] 3. 15 g of chitosan is dissolved in a 2% acetic acid solution to form a solution. The PLA particles treated with oxygen plasma are slowly added to the pre-prepared chitosan solution, and at the same time, they are fully mixed under stirring conditions. During this process, the amino and hydroxyl groups in chitosan will form hydrogen bonds or electrostatic interactions with the polar functional groups on the surface of PLA, achieving uniform adsorption. The modified PLA particles are separated from the solution by centrifugation, and then dried in a well-ventilated or low-temperature oven until the solvent is completely volatilized to obtain a uniformly modified dry PLA powder.

[0081] 4. The modified PLA is redissolved in chloroform to prepare a 30% modified PLA solution. The modified PLA solution is poured into the liquid storage tank of the spraying device, and the distance between the nozzle and the surface of the ceramsite (particle size 2 - 10 mm, 500 g) is adjusted to 15 cm, the spraying pressure is 2.5 bar, and the spraying flow rate is 15 mL / min. The switch of the spraying device is turned on to uniformly coat the surface of the ceramsite.

[0082] 5. After the coating is completed, the ceramsite is placed in a well-ventilated area and dried naturally for 12 hours to ensure that the solvent is completely volatilized to obtain the artificial wetland filter material.

[0083] Example 2 This example provides an artificial wetland filter material, and the preparation method is as follows: 1. Use 25 g of PLA particles (molecular weight 150,000) and CO2 gas (pure CO2) to physically foam for 18 minutes at a pressure of 2.8 MPa and 140 °C to obtain foamed PLA with a specific surface area of approximately 80 m² / g.

[0084] 2. Perform oxygen plasma treatment on the foamed PLA particles (power 85 W, time 3.5 minutes).

[0085] 3. Dissolve 12 g of lignin in an alkaline solution and continuously stir at 40 - 50 °C until the lignin is completely dissolved to form a homogeneous lignin solution. Mix and modify it with the treated PLA particles, and continuously stir for 10 - 20 minutes under magnetic stirring conditions to allow the lignin molecules to fully adsorb on the surface of the PLA particles. Use filtration or centrifugation to separate the PLA particles after the modification reaction from the solution; wash the separated particles several times with deionized water to fully remove the residual alkaline solution and unreacted lignin. Place the washed modified PLA particles in a well-ventilated area or in an oven with a temperature controlled at 40 - 60 °C, and obtain modified PLA after drying.

[0086] 4. Dissolve the modified PLA in chloroform to prepare a 35% solution, and coat it on quartz sand (particle size 5 mm, 500 g) by spray coating (nozzle distance 12 cm, pressure 2.8 bar, flow rate 12 mL / min).

[0087] 5. After coating, place the quartz sand in a well-ventilated area and dry it naturally for 12 hours to ensure that the solvent is completely volatilized, and obtain the artificial wetland filter material.

[0088] Example 3 This example provides an artificial wetland filter material, and the preparation method is as follows: 1. Place 35 g of PLA particles (molecular weight 250,000) and 10 g of CO2 gas (a mixture of nitrogen and CO2) in a high-pressure container, and foam at 3.2 MPa and 160 °C for 12 minutes, with a specific surface area reaching 120 m² / g.

[0089] 2. Perform oxygen plasma treatment on the foamed PLA particles (power 95 W, time 2.5 minutes).

[0090] 3. Weigh 15 g of chitosan and 15 g of carboxymethyl cellulose separately, and dissolve them together in a 2% acetic acid solution to prepare a composite solution. Subsequently, slowly add the PLA particles treated with oxygen plasma into the above composite solution, and mix well under magnetic stirring conditions to ensure that chitosan and carboxymethyl cellulose are evenly adsorbed on the surface of the PLA particles, forming a modified layer. After mixing, filter or centrifuge to separate, then wash with deionized water to remove the residual solution, and finally dry at low temperature under well-ventilated conditions to obtain modified PLA powder.

[0091] 4. The same steps as in Example 1.

[0092] 5. The same steps as in Example 1.

[0093] Example 4 This example provides an artificial wetland filter material. Different from Example 1, the modifier is aminated chitosan, and the remaining raw materials and preparation methods are the same as those in Example 1, which will not be elaborated here.

[0094] Example 5 This example provides an artificial wetland filter material. Different from Example 1, the modifier is sodium lignin sulfonate, and the remaining raw materials and preparation methods are the same as those in Example 1, which will not be elaborated here.

[0095] Example 6 This example provides an artificial wetland filter material, and the preparation method is as follows: 1. Place 40 g of industrial-grade PLA particles (molecular weight 280,000) and CO2 gas (a mixture of nitrogen and CO2) in a high-pressure vessel, and foam for 10 minutes at 3.5 MPa and 180°C, with a specific surface area of 130 m² / g.

[0096] 2. Perform oxygen plasma treatment on the foamed PLA particles (power 100 W, time 2.0 minutes).

[0097] 3. Prepare a solution of 15 g of carboxylated lignin. Add the PLA particles treated with oxygen plasma into the solution, mix well, and dry after surface modification to obtain modified PLA.

[0098] 4. Prepare a modified PLA solution with a concentration of 40%. Pour the modified PLA solution into the liquid storage tank of the spraying device, adjust the distance between the nozzle and the surface of quartz sand (particle size 2 mm, 500 g) to 10 cm, the spraying pressure to 3.0 bar, and the spraying flow rate to 20 mL / min. Turn on the switch of the spraying device and uniformly coat the surface of the ceramsite.

[0099] 5. Obtain the filter material after drying.

[0100] Comparative Example 1 This comparative example provides an artificial wetland filter material. Different from Example 1, the foaming treatment in Step 1 is not carried out, and it directly enters Step 2. The remaining steps are the same as those in Example 1 and will not be elaborated here.

[0101] Comparative Example 2 This comparative example provides an artificial wetland filter material. The oxygen plasma treatment in Step 2 is not carried out, and the remaining steps are the same as those in Example 1 and will not be elaborated here.

[0102] Comparative Example 3 This comparative example provides an artificial wetland filter material. Polybutylene succinate (PBS) is used to replace PLA in Example 1, and the remaining raw materials and steps are the same as those in Example 1 and will not be elaborated here.

[0103] Comparative Example 4 This comparative example provides an artificial wetland filter material, which is the ceramsite used in Example 1.

[0104] Comparative Example 5 This comparative example provides an artificial wetland filter material, which is the quartz sand used in Example 2.

[0105] Test Example 1 The present invention uses a contact angle tester to measure the surface water contact angle of the artificial wetland filter materials obtained in the examples and comparative examples. The test steps are as follows: 1. Fix the prepared filter material sample on a horizontal platform to ensure that the surface of the sample is flat and has no obvious defects.

[0106] 2. Slowly drop a drop of deionized water (generally with a volume of about 5 μL) on the surface of the sample using a micro syringe to ensure that the water droplet expands naturally without being disturbed by the outside.

[0107] 3. Wait for the water droplet to reach a stable state (within about 10 seconds), and use a contact angle measuring instrument (such as the OCA series) to take a side image of the interface between the water droplet and the surface of the filter material.

[0108] 4. Automatically or manually calibrate the contour of the water droplet using image analysis software, and measure the contact angle formed between the water droplet and the surface of the sample. After multiple measurements, take the average value as the final result, and record the data in Table 1.

[0109] The artificial wetland filter materials obtained in the examples and comparative examples are subjected to a wear resistance test. The wear resistance test is carried out under a flow rate of 0.5 m / s for 24 hours of continuous scouring test. The obtained data are shown in Table 1 below.

[0110] Table 1

[0111] From the data analysis in Table 1, the following conclusions can be drawn to highlight the technical effects of the present invention: 1. Significantly improve hydrophilicity In the examples, through foaming, oxygen plasma treatment, and the use of chitosan, lignin, and their composite modifiers, the surface of PLA was effectively modified, and the water contact angle was significantly reduced. For example, the contact angle of Example 6 was only 25°, much lower than that of the samples without modification in the comparative examples (such as 75% in Comparative Example 2 or as high as 90° in Comparative Example 5). This shows that the surface of the modified filter material has higher hydrophilicity, which is beneficial to the attachment of microorganisms and the formation of biofilms, thus improving the denitrification reaction efficiency.

[0112] 2. Improve wear resistance The data shows that the wear rates of the examples are generally lower than those of some comparative examples. Although the wear rates of Comparative Example 4 and Comparative Example 5 are relatively low due to the good wear resistance of the matrix material itself, considering the functionality of the filter material comprehensively, the coated modified PLA layer in the examples not only provides excellent hydrophilicity but also ensures a low wear rate (such as only 0.6% in Example 6), proving that the modification process has obvious advantages in ensuring the durability of the material.

[0113] 3. Synergistic effect brought by process optimization Each example uses different modifiers (chitosan, lignin, carboxymethyl cellulose, aminated chitosan, sodium lignosulfonate, carboxylated lignin, etc.) and different process parameters (foaming temperature, pressure, oxygen plasma treatment conditions, etc.) to achieve the best synergy between the coating structure and the matrix. The data shows that the filter materials after composite modification are superior to the comparative examples without modification or with some process deficiencies in terms of hydrophilicity and wear resistance, which further verifies the effectiveness and superiority of the technical solution of this application.

[0114] 4. Comprehensive performance improvement, facilitating practical applications The modified filter material not only has a low contact angle and excellent wear resistance but also can exhibit high and stable performance in subsequent microorganism cultivation and denitrification reactions, proving its practical application potential in artificial wetland water treatment systems. Compared with traditional filter materials, the technology of the present invention significantly improves the surface functionalization level of the filter material and effectively improves the denitrification efficiency and system stability.

[0115] Test Example 2 The artificial wetland filter materials obtained from the examples and comparative examples were tested for microorganism cultivation and denitrification reaction performance.

[0116] To ensure the efficient progress of the denitrification reaction, a standard denitrifying bacterial community (50 g) was inoculated. The experimental group wetland system was started with 20 L of sewage with a low C / N ratio (C / N ratio = 3:1), and the nitrogen content in the sewage was monitored at any time, and the data was tabulated in Table 2.

[0117] Table 2

[0118] As can be seen from Table 2, as the usage time prolongs, the denitrification reaction gradually enters the stable stage, and a relatively stable microbial population is formed on the surface of the PLA-coated ceramsite. Compared with the comparative examples, the examples all adopt the foaming, oxygen plasma treatment and modification processes, enabling microorganisms to form a stable biofilm on the surface of the filter material and significantly improving the denitrification reaction rate.

[0119] The nitrate removal rates of Comparative Examples 1 to 5 are all lower than those of the examples, proving that the technical solution of the present invention has obvious advantages in improving the nitrogen removal efficiency.

[0120] As the reaction time prolongs, the nitrate removal rates all show a gradually increasing trend and tend to be stable, reflecting that the system gradually establishes a stable microbial community, thereby achieving long-term efficient denitrification.

[0121] By detecting the nitrate content of the influent and effluent, the results show that within 24 hours, the nitrate removal rate can reach 75%, and there is no obvious load decline.

[0122] Test Example 3 The constructed wetland filter materials obtained in the examples and comparative examples were tested under low-temperature environments, and the long-term stability of the filter materials was concerned.

[0123] Low-temperature environment test: Under a low-temperature environment (4°C), the denitrification reaction test of the constructed wetland filter material was carried out, and a total of 6 weeks of monitoring was carried out.

[0124] The data obtained are shown in Table 3 below.

[0125] Table 3

[0126] As can be seen from Table 3, during the 6-week monitoring process, the nitrate removal rate of the examples still remained in the high-efficiency range (>70%), and the system operated stably without freeze cracking or increased operation difficulty.

[0127] 1. The examples show stability: All examples can maintain a high nitrate removal rate under low-temperature conditions, and overall show a stable or slightly increasing trend within 6 weeks. For example, the nitrate removal rate of Example 6 increased from 78% in the first week to 87% in the sixth week, indicating that the modified filter material can still stably perform the denitrification function in the long-term low-temperature environment.

[0128] 2. The advantages of composite modification are obvious: Compared with the comparative examples (without foaming, oxygen plasma treatment, and surface modification), the nitrate removal rates of each example are about 15% - 40% higher. This further proves that the foaming, oxygen plasma treatment, and composite modification process with various modifiers adopted in the invention significantly enhances the microbial attachment ability and denitrification efficiency of the filter media.

[0129] 3. The system stability is better than that of the comparative example: The comparative example samples showed relatively stable performance during the low-temperature test, but the overall nitrate removal rate was always lower than 70%, indicating that the filter media without modification treatment has poor performance in a low-temperature environment, while the filter media of the examples can effectively alleviate the problem of the decline in denitrification efficiency caused by low temperature.

[0130] Finally, it should be noted that the above-described embodiments are only specific embodiments of the present invention, used to illustrate the technical solutions of the present invention, rather than limiting them. The protection scope of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: any person skilled in the art within the technical scope disclosed by the present invention can still modify the technical solutions recorded in the foregoing embodiments, or can easily think of changes, or make equivalent replacements for some of the technical features; and these modifications, changes, or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An artificial wetland filter material, characterized in that, It includes an inorganic matrix and a modified PLA coating located on the surface of the inorganic matrix; The modified PLA in the modified PLA coating is hydrophilic modified PLA; The thickness of the modified PLA coating < 2 mm.

2. The artificial wetland filter media according to claim 1, characterized in that, The pore diameter of the hydrophilic modified PLA is 1 - 10 μm; and / or, the specific surface area of the hydrophilically modified PLA ≥ 50 m 2 / g.

3. The artificial wetland filter media according to claim 1, characterized in that, The hydrophilic functional groups introduced in the hydrophilic modified PLA include at least one of hydroxyl group, carboxyl group and amino group.

4. The artificial wetland filter material according to any one of claims 1 to 3, characterized in that The inorganic matrix includes ceramsite or quartz sand; And / or, the particle size of the inorganic matrix is 2 - 10 mm; and / or, the specific gravity of the inorganic substrate is 1.5 to 2.5 g / cm 3 .

5. A preparation method of the artificial wetland filter material according to claim 1, characterized in that, Coat the solution of modified PLA on the surface of the inorganic matrix, and obtain the artificial wetland filter material after drying.

6. The preparation method according to claim 5, characterized in that, The solvents used in the solution of modified PLA include chloroform and / or dichloromethane; And / or, the mass percentage concentration of the solution of modified PLA is 30 - 40%.

7. The preparation method according to claim 5, characterized in that, The coating method includes spray coating method; And / or, during the spray coating process, the distance between the nozzle and the inorganic matrix is 10 - 15 cm, the spray pressure is 2 - 3 bar, and the spray flow rate is 10 - 20 mL / min.

8. The preparation method according to claim 5, characterized in that, The preparation method of the modified PLA includes: First, perform physical foaming on the PLA particles, then perform oxygen plasma treatment, and finally perform surface modification by compounding with a modifier to obtain the modified PLA; And / or, the molecular weight of the PLA is 100,000 - 300,000.

9. The preparation method according to claim 8, wherein, In the physical foaming, the foaming gas used is carbon dioxide and / or nitrogen; And / or, the pressure of the physical foaming is 2.5 - 3.5 MPa, the time is 10 - 20 min, and the temperature is 120 - 180 °C; And / or, the power of the oxygen plasma treatment is 80 - 100 W, and the time is 2 - 4 min.

10. The preparation method according to claim 8, characterized in that, The modifier provides at least one of the functional groups of hydroxyl group, carboxyl group and amino group; And / or, the modifier includes at least one of chitosan, lignin, carboxymethyl cellulose, amino chitosan, sodium lignosulfonate and carboxylated lignin; And / or, make the modifier into a modifier solution and mix it with the PLA particles after oxygen plasma treatment to complete the surface modification, and obtain the modified PLA after drying.

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