Artificial wetland filter material and preparation method thereof

Abstract

The present invention provides an artificial wetland filter material and a preparation method thereof, specifically relating to the technical field of water environment treatment. The artificial wetland filter material comprises an inorganic matrix and a modified PLA coating located on the surface of the inorganic matrix; the modified PLA is a hydrophilic modified PLA; and the thickness of the modified PLA coating is less than 2 mm. The artificial wetland filter material provided by the present invention has significantly improved hydrophilicity, and the surface biofilm density is increased by more than 30%, thereby greatly improving the microbial attachment capacity. In terms of denitrification performance, the nitrate removal rate of the filter material is improved by 20% to 40%. Even under low temperature conditions of 5 to 15°C, the nitrate removal rate can still be stably maintained at more than 60%, which is significantly better than traditional filter materials. In addition, the filter material also has excellent mechanical properties, with compressive strength increased by more than 30%, and wear resistance and anti-scouring capabilities are also significantly enhanced, so that it exhibits higher stability and durability in complex environments and long-term operation.

Description

Technical Field

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

[0002] Constructed wetlands are an important ecological water treatment technology widely used in wastewater purification, offering high treatment efficiency, low operating costs, and eco-friendliness. Their core principle is to utilize microbial metabolic processes to degrade and transform pollutants. In particular, the denitrification process requires sufficient soluble organic carbon (a carbon source) as an electron donor for the denitrification reaction. However, under low carbon-to-nitrogen (C / N) ratios, insufficient soluble organic carbon in wastewater significantly reduces denitrification efficiency, thereby impacting overall water treatment effectiveness.

[0003] Constructed wetlands face numerous challenges when treating water bodies with low C / N ratios, including low denitrification efficiency, insufficient filter media carbon source supply, inflexible system adjustments, long treatment cycles, limited plant root activity, and the negative impact of low temperatures on denitrification. The root cause of these issues lies in the instability of traditional filter media and treatment methods, including unstable carbon source supply, slow system response, and diminished effectiveness over long-term operation.

[0004] At present, the main technical means to solve the problem of low C / N ratio water treatment in artificial wetlands include the following three:

[0005] Artificial addition of carbon sources: By adding methanol, sodium acetate and other external carbon sources to the system, denitrification efficiency can be rapidly improved. However, this method has significant disadvantages: high operating costs; complex operation; and environmental risks.

[0006] Modified filter media: By embedding natural materials such as biochar and sawdust into the filter media, 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 media stability, and limited application range.

[0007] Electron donor-enhanced materials: By using materials such as iron-carbon composite filter media or sulfur-based filter media (such as pyrite and calcium sulfide), denitrification efficiency can be improved under carbon-deficient conditions by utilizing non-organic carbon electron donors. However, these materials still have significant drawbacks in practical applications: the risk of byproduct formation, insufficient long-term performance, and limited adaptability.

[0008] While existing technologies can alleviate the challenges of treating low C / N ratio water to some extent, they all have significant limitations. Artificially adding carbon sources is costly and complex, modified filter media lack stability, and electron donor-enhanced materials present environmental risks and long-term performance issues. Therefore, developing a novel filter media technology that is efficient, stable, and economically viable is crucial for improving the performance of constructed wetlands in treating low C / N ratio water.

[0009] In view of this, the present invention is proposed. Summary of the Invention

[0010] One of the purposes of the present invention is to provide an artificial wetland filter material, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0011] A second object of the present invention is to provide a method for preparing artificial wetland filter material.

[0012] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0013] A first aspect of the present invention provides a constructed wetland filter material, 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; and the thickness of the modified PLA coating is less than 2 mm.

[0014] Furthermore, the pore diameter of the hydrophilically modified PLA is 1-10 μm.

[0015] And / or, the specific surface area of ​​the hydrophilic modified PLA is ≥50m 2 / g.

[0016] Furthermore, the hydrophilic functional groups introduced into the hydrophilically modified PLA include at least one of hydroxyl, carboxyl and amino groups.

[0017] Furthermore, the inorganic matrix includes ceramsite or quartz sand.

[0018] And / or, the particle size of the inorganic matrix is ​​2-10 mm.

[0019] And / or, the specific gravity of the inorganic matrix is ​​1.5-2.5 g / cm 3 .

[0020] The second aspect of the present invention provides a method for preparing the artificial wetland filter material, which comprises coating a modified PLA solution on the surface of an inorganic substrate and drying the solution to obtain the artificial wetland filter material.

[0021] Furthermore, the solvent used in the modified PLA solution includes chloroform and / or dichloromethane.

[0022] And / or, the mass percentage concentration of the modified PLA solution is 30-40%.

[0023] Furthermore, the coating method includes a spray coating method.

[0024] 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.

[0025] Furthermore, the preparation method of the modified PLA includes: first physically foaming PLA particles, then subjecting them to oxygen plasma treatment, and finally compounding with a modifier for surface modification to obtain the modified PLA.

[0026] And / or, the molecular weight of the PLA is 100,000 to 300,000.

[0027] Furthermore, in the physical foaming, the foaming gas used is carbon dioxide and / or nitrogen.

[0028] And / or, the physical foaming is performed at a pressure of 2.5-3.5 MPa, a time of 10-20 min, and a temperature of 120-180°C.

[0029] And / or, the power of the oxygen plasma treatment is 80-100 W, and the time is 2-4 minutes.

[0030] Furthermore, the modifier provides at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, and an amino group.

[0031] And / or, the modifier includes at least one of chitosan, lignin, carboxymethyl cellulose, amino chitosan, sodium lignin sulfonate and carboxylated lignin.

[0032] And / or, the modifier is prepared into a modifier solution and mixed with the PLA particles treated with oxygen plasma to complete the surface modification, and then dried to obtain the modified PLA.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects:

[0034] The artificial wetland filter material provided by the present invention has significantly improved hydrophilicity, and the surface biofilm density is increased by more than 30%, thereby greatly improving the microbial attachment ability. In terms of denitrification performance, the filter material shows excellent efficiency, and the nitrate removal rate is increased by 20% to 40%. Even under low temperature conditions of 5~15℃, the nitrate removal rate can still be stably maintained at more than 60%, which is significantly better than traditional filter materials. In addition, the filter material also has excellent mechanical properties, the compressive strength is increased by more than 30%, and the wear resistance and anti-scouring ability are also significantly enhanced, so that it exhibits higher stability and durability in complex environments and long-term operation.

[0035] The preparation method provided by the present invention has large batch processing capacity, simple operation, and is suitable for large-scale industrial production. DETAILED DESCRIPTION

[0036] In order to make the purpose, 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 combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0037] Hereinafter, the terms "including", "having" and their cognates, which may be used in various embodiments of the present invention, are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0038] Analysis of the technical issues of this invention revealed that, on the one hand, existing technologies lack efficient and economically viable slow-release carbon source materials, making it difficult to dynamically adapt to treatment requirements under varying pollution loads. On the other hand, filter media modification technologies are often limited to single physical or chemical methods, failing to comprehensively consider the coordinated relationship between carbon source supply, microbial attachment, and mechanical properties. Furthermore, there is insufficient research on the long-term performance of composite filter media, lacking designs for mechanical properties and environmental stability suitable for long-term operation.

[0039] A first aspect of the present invention provides a constructed wetland filter material, 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; and the thickness of the modified PLA coating is less than 2 mm.

[0040] The artificial wetland filter material provided by the present invention has significantly improved hydrophilicity, and the surface biofilm density is increased by more than 30%, thereby greatly improving the microbial attachment ability. In terms of denitrification performance, the filter material shows excellent efficiency, and the nitrate removal rate is increased by 20% to 40%. Even under low temperature conditions of 5~15℃, the nitrate removal rate can still be stably maintained at more than 60%, which is significantly better than traditional filter materials. In addition, the filter material also has excellent mechanical properties, the compressive strength is increased by more than 30%, and the wear resistance and anti-scouring ability are also significantly enhanced, so that it exhibits higher stability and durability in complex environments and long-term operation.

[0041] This invention uses inorganic materials as the matrix. These materials possess excellent mechanical properties in wetland environments, effectively withstanding the impact of water flow and the friction between particles. By combining these inorganic materials with polylactic acid (PLA), the filter media maintains excellent mechanical strength while also providing a slow-release carbon source.

[0042] Polylactic acid (PLA) is biodegradable, releasing a usable organic carbon source through hydrolysis and microbial metabolism. Its degradation products are non-toxic and environmentally friendly to wetlands. At the end of its lifespan, PLA naturally degrades into harmless substances. However, PLA alone has limitations, such as a slow release rate and low microbial utilization efficiency, necessitating modifications to its properties.

[0043] By using modified PLA to construct a uniform composite layer on the surface of the inorganic matrix, the overall scour resistance of the filter material is enhanced, avoiding the rapid degradation of the single PLA material under the action of wetland hydraulic scouring.

[0044] 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.

[0045] And / or, the specific surface area of ​​the hydrophilic modified PLA is ≥50m 2 / g.

[0046] Furthermore, the hydrophilic functional groups introduced into the hydrophilically modified PLA include at least one of hydroxyl, carboxyl and amino groups.

[0047] Furthermore, the inorganic matrix includes ceramsite or quartz sand.

[0048] And / or, the particle size of the inorganic matrix is ​​2-10 mm.

[0049] And / or, the specific gravity of the inorganic matrix is ​​1.5-2.5 g / cm 3 Typically, but not limiting, the specific gravity of the inorganic matrix may be, for example, 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 or 2.5g / cm 3 , or 1.5g / cm 3 ~2.5g / cm 3 Any value in the range.

[0050] The artificial wetland filter material provided by the present invention has the following technical effects:

[0051] 1. Improve carbon source utilization efficiency

[0052] This invention achieves efficient, controlled-release carbon source by modifying polylactic acid (PLA) and engineering the porous structure of its composite material. This design allows for dynamic release of the carbon source based on the actual needs of the denitrification reaction within the wetland system, significantly improving denitrification efficiency and enhancing the treatment capacity for wastewater with a low carbon-to-nitrogen ratio (C / N). Compared to traditional artificially added or extensive carbon sources, this controlled-release technology reduces the frequency and expense of external carbon source addition, thereby significantly reducing operating costs.

[0053] 2. Significantly improve denitrification effect

[0054] The present invention uses surface functionalization technology to significantly enhance the hydrophilicity and microbial adhesion of the filter material, thereby rapidly promoting the growth of biofilms. Microorganisms can adapt to the filter material surface more quickly and improve their ability to reduce nitrates. Under low C / N conditions, this design significantly increases the denitrification reaction rate, significantly improving denitrification efficiency, especially in low-temperature environments, where denitrification efficiency can be increased by more than 30%. This not only improves sewage treatment efficiency but also enhances the adaptability of wetland systems in cold regions, which has important environmental significance.

[0055] 3. Enhance mechanical stability and durability

[0056] This invention significantly enhances the filter media's erosion resistance and wear resistance by optimizing the composite coating process. Coating a PLA-based composite material onto a high-strength substrate such as ceramsite or quartz sand not only enhances the filter media's mechanical strength but also improves its stability in complex flow conditions and during long-term operation. Compared to traditional filter media, this invention offers a longer service life, effectively reducing equipment maintenance frequency and replacement costs.

[0057] 4. Significantly improve low temperature adaptability

[0058] This invention fully considers the need for denitrification in low-temperature environments. By optimizing the biological activity and stability of the material, the filter material can maintain efficient denitrification capabilities even at temperatures below 5°C. Compared with conventional filter media, the filter material of this invention can continue to operate efficiently in winter or cold regions, improving the seasonal stability of wetland systems, reducing the negative impact of seasonal changes, and meeting the sewage treatment needs of more regions.

[0059] 5. Eco-friendliness and environmental sustainability

[0060] The filter material of this invention, primarily made of polylactic acid (PLA), exhibits excellent biodegradability. After its service life, it degrades naturally, reducing environmental impact. Furthermore, the optimized production process reduces energy consumption and pollutant emissions during production. This eco-friendly feature is more environmentally friendly than traditional plastic filter materials, meeting the requirements of sustainable development and environmental protection, and providing strong support for the widespread promotion of wetland systems.

[0061] In summary, the constructed wetland filter material of this invention significantly improves carbon source utilization efficiency, nitrogen removal effectiveness, mechanical stability, low-temperature adaptability, and eco-friendliness. Furthermore, this technology optimizes the operating costs and maintenance cycles of wetland systems, providing a novel technical solution for more efficient, energy-efficient, and environmentally friendly wastewater treatment.

[0062] The second aspect of the present invention provides a method for preparing the artificial wetland filter material, which comprises coating a modified PLA solution on the surface of an inorganic substrate and drying the solution to obtain the artificial wetland filter material.

[0063] The preparation method provided by the present invention has large batch processing capacity, simple operation, and is suitable for large-scale industrial production.

[0064] In the specific implementation of the present invention, a layered coating process is used to form a multi-layer protective structure on the substrate surface, which gives the filter media high resistance to peeling and improves its durability during operation. The layered coating process controls the thickness of a single layer to 100-500µm, and the number of layers is 4-20, preferably 8-12.

[0065] Furthermore, the solvent used in the modified PLA solution includes chloroform and / or dichloromethane.

[0066] And / or, the mass percent concentration of the modified PLA solution is 30% to 40%. Typically, but not limiting, the mass percent concentration of the modified PLA solution can be 30%, 32%, 34%, 36%, 38%, or 40%, or any value within the range of 30% to 40%.

[0067] Furthermore, the coating method includes a spray coating method.

[0068] 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.

[0069] Typically but not limitatively, 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 to 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 to 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 to 20 mL / min.

[0070] 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 a polylactic acid (PLA) matrix; then subjecting the particles to oxygen plasma treatment, and finally subjecting the particles to surface modification by compounding with a modifier to obtain the modified PLA.

[0071] By creating a porous structure in PLA using physical foaming and chemical etching, the specific surface area can be significantly increased, thereby increasing the release rate of the carbon source. Furthermore, by regulating the size and distribution of the pores, the carbon release rate can be precisely adjusted to meet the denitrification needs of the wetland system under different load conditions.

[0072] Chemical etching involves locally dissolving the PLA material using a suitable solvent. This dissolves a portion of the material, leaving gaps after the solvent evaporates or is removed, thus forming a microporous structure. Porous structures can be created using either or both of these methods to increase the specific surface area.

[0073] Hydrophilic modification of PLA involves the introduction of hydrophilic functional groups (such as hydroxyl, carboxyl, or amino groups) to enhance the material's hydrophilicity, making it more suitable for microbial biofilm attachment. The resulting filter media surface can form an efficient microbial attachment matrix, effectively promoting the rapid formation and stability of biofilms. To address the issue of decreased denitrification efficiency under low-temperature conditions, the filter media design incorporates methods that promote hydrophilicity and microbial activity, significantly enhancing its adaptability to low-temperature environments. Furthermore, hydrophilic modification improves the interfacial bonding between PLA and the inorganic matrix, preventing coating peeling due to weak bonding during long-term operation.

[0074] In one embodiment of the present invention, PLA particles are exposed to an oxygen plasma environment (e.g., at 90W for 3 minutes). Under the bombardment of high-energy oxygen ions, a large number of hydrophilic functional groups (such as hydroxyl and carboxyl groups) are generated on the PLA surface, significantly improving the hydrophilicity and biocompatibility of the material. This modification helps microorganisms attach more quickly and firmly to the filter media surface, further enhancing denitrification efficiency.

[0075] And / or, the molecular weight of the PLA is 100,000 to 300,000.

[0076] Furthermore, in the physical foaming, the foaming gas used is carbon dioxide and / or nitrogen.

[0077] And / or, the physical foaming is performed at a pressure of 2.5-3.5 MPa, a time of 10-20 min, and a temperature of 120-180°C.

[0078] Typically but not limitatively, 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.

[0079] And / or, the power of the oxygen plasma treatment is 80-100 W, and the time is 2-4 minutes.

[0080] Typically but not limitatively, 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.

[0081] Furthermore, the modifier provides at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, and an amino group.

[0082] And / or, the modifier includes at least one of chitosan, lignin, carboxymethyl cellulose, amino chitosan, sodium lignin sulfonate and carboxylated lignin.

[0083] 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 (e.g., low-power ultrasonication for several minutes) can be used to further promote the interaction between the modifier and the PLA surface.

[0084] After the mixing reaction continues for a certain period of time (e.g., 10 to 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 is completely evaporated to obtain uniformly modified dry PLA powder.

[0085] And / or, the modifier is prepared into a modifier solution and mixed with the PLA particles treated with oxygen plasma to complete the surface modification, and then dried to obtain the modified PLA.

[0086] The present invention is further illustrated below by specific examples and comparative examples. However, it should be understood that these examples are merely for the purpose of further explanation and should not be construed as limiting the present invention in any form. The raw materials used in the examples and comparative examples of the present invention, unless otherwise specified, were prepared under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0087] Example 1

[0088] This embodiment provides a constructed wetland filter material, and the preparation method is as follows:

[0089] 1. 30 g of industrial-grade PLA pellets (molecular weight 200,000) and 10 g of CO2 gas (a mixture of nitrogen and CO2) were placed in a high-pressure container and foamed at a pressure of 3 MPa and a temperature of 150°C for 15 minutes. The specific surface area of ​​the foamed PLA reached approximately 100 m 2 / g.

[0090] 2. The foamed PLA particles were treated with oxygen plasma (power 90 W, treatment time 3 minutes).

[0091] 3. Dissolve 15 g of chitosan in 2% acetic acid to prepare a solution. Slowly add the oxygen plasma-treated PLA particles to the pre-prepared chitosan solution while stirring thoroughly. During this process, the amino and hydroxyl groups in the chitosan interact with the polar functional groups on the PLA surface through hydrogen bonding or electrostatic interactions, achieving uniform adsorption. Separate the modified PLA particles from the solution by centrifugation and then dry them in a ventilated or low-temperature oven until the solvent is completely evaporated, resulting in a uniformly modified, dry PLA powder.

[0092] 4. Redissolve the modified PLA in chloroform to prepare a 30% modified PLA solution. Pour the modified PLA solution into the reservoir of a spray device. Adjust the distance between the nozzle and the surface of the ceramsite (particle size 2-10 mm, 500 g) to 15 cm, the spray pressure to 2.5 bar, and the spray flow rate to 15 mL / min. Turn on the spray device and evenly coat the surface of the ceramsite.

[0093] 5. After coating, place the ceramsite in a well-ventilated area to dry naturally for 12 hours to ensure that the solvent is completely evaporated to obtain artificial wetland filter material.

[0094] Example 2

[0095] This embodiment provides a constructed wetland filter material, and the preparation method is as follows:

[0096] 1. Use 25 g of PLA pellets (molecular weight 150,000) and CO2 gas (pure CO2) for physical foaming at 2.8 MPa pressure and 140°C for 18 minutes to obtain foamed PLA with a specific surface area of ​​approximately 80 m² / g.

[0097] 2. The foamed PLA particles were treated with oxygen plasma (power 85 W, time 3.5 minutes).

[0098] 3. Dissolve 12 g of lignin in an alkaline solution and stir continuously at 40-50°C until the lignin is completely dissolved, forming a uniform lignin solution. Mix the solution with the treated PLA particles for modification and continue stirring under magnetic stirring for 10-20 minutes to allow the lignin molecules to fully adsorb onto the PLA particle surface. Separate the PLA particles from the solution by filtration or centrifugation. Wash the separated particles several times with deionized water to remove any residual alkaline solution and unreacted lignin. Place the washed modified PLA particles in a well-ventilated area or in an oven controlled at 40-60°C and dry to obtain the modified PLA.

[0099] 4. Dissolve the modified PLA in chloroform to make a 35% solution, and apply it to quartz sand (particle size 5 mm, 500 g) by spray coating (nozzle distance 12 cm, pressure 2.8 bar, flow rate 12 mL / min).

[0100] 5. After coating, place the quartz sand in a well-ventilated area to dry naturally for 12 hours to ensure that the solvent is completely evaporated to obtain artificial wetland filter material.

[0101] Example 3

[0102] This embodiment provides a constructed wetland filter material, and the preparation method is as follows:

[0103] 1. 35 g of PLA particles (molecular weight 250,000) and 10 g of CO2 gas (a mixture of nitrogen and CO2) were placed in a high-pressure container and foamed at 3.2 MPa and 160°C for 12 minutes, with a specific surface area of ​​120 m² / g.

[0104] 2. The foamed PLA particles were treated with oxygen plasma (power 95 W, time 2.5 minutes).

[0105] 3. Weigh 15 g of chitosan and 15 g of carboxymethyl cellulose separately and dissolve them together in 2% acetic acid solution to prepare a composite solution; then, slowly add the PLA particles treated with oxygen plasma to the composite solution and mix them thoroughly under magnetic stirring to allow chitosan and carboxymethyl cellulose to be uniformly adsorbed on the surface of the PLA particles to form a modified layer; after mixing, filter or centrifuge, 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.

[0106] 4. Same as the step in Example 1.

[0107] 5. Same as the step in Example 1.

[0108] Example 4

[0109] This embodiment provides a constructed wetland filter material. The difference from Example 1 is that the modifier is amino chitosan. The remaining raw materials and preparation methods are the same as those in Example 1 and are not described again here.

[0110] Example 5

[0111] This embodiment provides a constructed wetland filter material. The difference from Example 1 is that the modifier is sodium lignin sulfonate. The remaining raw materials and preparation methods are the same as those in Example 1 and are not described again here.

[0112] Example 6

[0113] This embodiment provides a constructed wetland filter material, and the preparation method is as follows:

[0114] 1. 40 g of industrial-grade PLA pellets (molecular weight 280,000) were placed in a high-pressure container with CO2 gas (a mixture of nitrogen and CO2) and foamed at 3.5 MPa and 180°C for 10 minutes. The specific surface area was 130 m² / g.

[0115] 2. The foamed PLA particles were treated with oxygen plasma (power 100 W, time 2.0 min).

[0116] 3. Prepare a solution of 15 g of carboxylated lignin. Add the oxygen plasma-treated PLA particles to the solution and mix well. Perform surface modification and dry to obtain modified PLA.

[0117] 4. Prepare a 40% modified PLA solution. Pour the modified PLA solution into the reservoir of a spray device. Adjust the distance between the nozzle and the surface of quartz sand (2 mm particle size, 500 g) to 10 cm, the spray pressure to 3.0 bar, and the spray flow rate to 20 mL / min. Turn on the spray device and evenly coat the surface of the ceramsite.

[0118] 5. After drying, the filter material is obtained.

[0119] Comparative Example 1

[0120] This comparative example provides a constructed wetland filter material. Unlike Example 1, the foaming treatment in step 1 is not performed, and the process directly proceeds to step 2. The remaining steps are the same as those in Example 1 and will not be repeated here.

[0121] Comparative Example 2

[0122] This comparative example provides a constructed wetland filter material, without performing the oxygen plasma treatment in step 2. The remaining steps are the same as those in Example 1 and will not be described again.

[0123] Comparative Example 3

[0124] This comparative example provides a constructed wetland filter material, using polybutylene succinate (PBS) to replace the PLA in Example 1. The remaining raw materials and steps are the same as those in Example 1 and will not be repeated here.

[0125] Comparative Example 4

[0126] This comparative example provides a constructed wetland filter material, which is the ceramsite used in Example 1.

[0127] Comparative Example 5

[0128] This comparative example provides a constructed wetland filter material, which is the quartz sand used in Example 2.

[0129] Test Example 1

[0130] The present invention uses a contact angle tester to measure the water contact angle of the surface of the artificial wetland filter material obtained in the embodiment and the comparative example. The test steps are as follows:

[0131] 1. Fix the prepared filter material sample on a horizontal platform to ensure that the sample surface is flat and has no obvious defects.

[0132] 2. Use a micro syringe to slowly add a drop of deionized water (usually about 5 μL) to the sample surface, ensuring that the water droplet expands naturally without being disturbed by the outside world.

[0133] 3. When the shape of the water droplet stabilizes (within about 10 seconds), use a contact angle meter (such as the OCA series) to capture a side image of the interface between the water droplet and the filter surface.

[0134] 4. Use image analysis software to automatically or manually calibrate the water droplet profile and measure the contact angle between the water droplet and the sample surface. Take the average of multiple measurements and record the data in Table 1.

[0135] The artificial wetland filter materials obtained in the examples and comparative examples were subjected to a wear resistance test. The wear resistance test was conducted under a flow rate of 0.5 m / s and was continuously flushed for 24 hours. The obtained data are shown in Table 1 below.

[0136] Table 1

[0137]

[0138] From the data analysis of Table 1, the following conclusions can be drawn, highlighting the technical effects of the present invention:

[0139] 1. Significantly improve hydrophilicity

[0140] In the examples, the PLA surface was effectively modified through foaming, oxygen plasma treatment, and the use of chitosan, lignin, and their composite modifiers, significantly reducing the water contact angle. For example, the contact angle of Example 6 was only 25°, significantly lower than that of the unmodified samples in the comparative examples (e.g., 75% in Comparative Example 2 and 90° in Comparative Example 5). This indicates that the modified filter media surface has a higher hydrophilicity, which facilitates microbial attachment and biofilm formation, thereby improving the efficiency of the denitrification reaction.

[0141] 2. Improve wear resistance

[0142] The data shows that the wear rates of the examples are generally lower than those of some of the comparative examples. While comparative examples 4 and 5 exhibit lower wear rates due to the inherently good wear resistance of the base material, considering the functionality of the filter material, the modified PLA layer applied in the examples not only provides excellent hydrophilicity but also ensures a low wear rate (for example, only 0.6% in Example 6), demonstrating the significant advantages of the modification process in ensuring material durability.

[0143] 3. Synergistic effects brought by process optimization

[0144] Each example employed different modifiers (chitosan, lignin, carboxymethyl cellulose, amino-modified chitosan, sodium lignin sulfonate, carboxylated lignin, etc.) and process parameters (foaming temperature, pressure, oxygen plasma treatment conditions, etc.) to achieve optimal synergy between the coating structure and the substrate. Data showed that the filter media after composite modification exhibited superior hydrophilicity and wear resistance compared to unmodified or partially omitted control samples, further validating the effectiveness and superiority of the technical solutions presented herein.

[0145] 4. Comprehensive performance improvement to facilitate practical applications

[0146] The modified filter media not only exhibits a low contact angle and excellent abrasion resistance, but also demonstrates efficient and stable performance in subsequent microbial cultivation and denitrification reactions, demonstrating its practical application potential in constructed wetland water treatment systems. Compared to traditional filter media, this technology significantly enhances the surface functionalization of the filter media, effectively improving denitrification efficiency and system stability.

[0147] Test Example 2

[0148] The artificial wetland filter materials obtained in the examples and comparative examples were subjected to microbial culture and denitrification reaction performance tests.

[0149] To ensure efficient denitrification, a standard denitrifying bacterial colony (50 g) was inoculated. The experimental wetland system was initiated with 20 L of wastewater containing a low C / N ratio (C / N ratio = 3:1). Nitrogen content in the wastewater was monitored over time, and the data are summarized in Table 2.

[0150] Table 2

[0151]

[0152] As can be seen in Table 2, the denitrification reaction gradually entered a stable phase with extended use, forming a relatively stable microbial population on the surface of the PLA-coated ceramsite. Compared to the comparative example, the examples all employed foaming, oxygen plasma treatment, and modification processes, allowing microorganisms to form a stable biofilm on the filter media surface, significantly increasing the denitrification reaction rate.

[0153] The nitrate removal rates of Comparative Examples 1 to 5 are all lower than those of the embodiment, which proves that the technical solution of the present invention has obvious advantages in improving the denitrification efficiency.

[0154] As the reaction time increased, the nitrate removal rate showed a gradual upward trend and tended to be stable, reflecting that the system gradually established a stable microbial community, thus achieving long-term and efficient denitrification.

[0155] By testing the nitrate content of the inlet and outlet water, the results showed that the nitrate removal rate could reach 75% within 24 hours, and there was no obvious load decline.

[0156] Test Example 3

[0157] The artificial wetland filter materials obtained in the examples and comparative examples were subjected to low-temperature environment tests, and attention was paid to the long-term stability of the filter materials.

[0158] Low temperature environment test: The denitrification reaction of the constructed wetland filter media was tested in a low temperature environment (4°C) and monitored for a total of 6 weeks.

[0159] The obtained data are shown in Table 3 below.

[0160] Table 3

[0161]

[0162] As can be seen from Table 3, during the 6-week monitoring process, the nitrate removal rate of the embodiment remained in the high efficiency range (>70%), and the system operated stably without freezing cracks or increased operational difficulty.

[0163] 1. The embodiment performs stably:

[0164] All examples maintained high nitrate removal rates under low-temperature conditions, with an overall trend of stable or slightly increasing performance over the six weeks. For example, Example 6 saw a significant improvement from 78% in week 1 to 87% in week 6, demonstrating that the modified filter media can maintain its denitrification function even in long-term low-temperature environments.

[0165] 2. The advantages of composite modification are obvious:

[0166] Compared to the control examples (without foaming, oxygen plasma treatment, and surface modification), the nitrate removal rates of each example were approximately 15% to 40% higher. This further demonstrates that the foaming, oxygen plasma treatment, and multi-modifier composite modification process employed in the present invention significantly enhances the microbial attachment capacity and denitrification efficiency of the filter media.

[0167] 3. System stability is better than the control example:

[0168] The comparative samples performed relatively steadily during the low-temperature test, but the overall nitrate removal rate was always below 70%, indicating that the filter material without modification had poor performance in a low-temperature environment, while the filter material of the embodiment can effectively alleviate the problem of decreased denitrification efficiency caused by low temperature.

[0169] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above-described embodiments within the technical scope disclosed by the present invention, or replace some of the technical features therein with equivalents. Such modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing artificial wetland filter material, characterized in that: PLA particles are first subjected to physical foaming and then to oxygen plasma treatment, a modifier solution is mixed with the oxygen plasma-treated PLA particles to complete surface modification, and the modified PLA is obtained after drying; the modified PLA solution is then coated on the surface of an inorganic substrate, and the constructed wetland filter material is obtained after drying; The molecular weight of the PLA is 100,000 to 300,000; In the physical foaming, the foaming gas used is carbon dioxide and / or nitrogen; 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; The power of the oxygen plasma treatment is 80-100W, and the time is 2-4 minutes; The modifier provides at least one functional group selected from the group consisting of hydroxyl, carboxyl, and amino groups; The modifier comprises at least one of chitosan, lignin, carboxymethyl cellulose, amino chitosan, sodium lignin sulfonate and carboxylated lignin; The solvent used in the modified PLA solution includes chloroform and / or dichloromethane; The coating method includes a spray coating method; 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.

2. The preparation method according to claim 1, characterized in that The mass percentage concentration of the modified PLA solution is 30-40%.

3. The preparation method according to claim 1, characterized in that The artificial wetland filter material 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 is less than 2 mm.

4. The preparation method according to claim 3, characterized in that The pore diameter of the hydrophilic modified PLA is 1-10 μm; The specific surface area of ​​the hydrophilic modified PLA is ≥50m 2 / g.

5. The preparation method according to claim 3, characterized in that The hydrophilic functional groups introduced into the hydrophilically modified PLA include at least one of hydroxyl, carboxyl and amino groups.

6. The preparation method according to any one of claims 1 to 5, characterized in that The inorganic matrix includes ceramsite or quartz sand; The particle size of the inorganic matrix is ​​2 to 10 mm; The specific gravity of the inorganic matrix is ​​1.5-2.5 g / cm 3 .

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