A polyamide fiber filter media for anaerobic biological filters and its preparation method

Abstract

This invention discloses a polyamide fiber filter media for anaerobic biofilters and its preparation method. The method involves surface plasma treatment of polyamide fibers at 90-110W, followed by cleaning of residual reactants. The fibers are then oxidized using a primary oxidant and an auxiliary oxidant. A chitosan coating and a sodium alginate coating are sequentially coated onto the oxidized polyamide fibers. The mass ratio of chitosan, sodium alginate, and plasma-treated polyamide fibers in S1 is (0.075-0.25):(0.075-0.25):1, resulting in the polyamide fiber filter media for anaerobic biofilters. This invention modifies the surface of polyamide fibers through hydrophilication and functional coatings, improving their hydrophilicity and biocompatibility, thereby accelerating the microbial biofilm formation process, enhancing biofilm stability and degradation efficiency, and solving the problem of low treatment efficiency in existing recalcitrant organic wastewater treatment methods.

Description

Technical Field

[0001] This invention belongs to the field of recalcitrant organic wastewater treatment, specifically a polyamide fiber filter media for anaerobic biological filters and its preparation method. Background Technology

[0002] With the advancement of industrialization, the treatment of recalcitrant organic wastewater has become a major challenge in environmental engineering. Anaerobic biological filters are a type of bioreactor commonly used for treating recalcitrant organic wastewater. They utilize anaerobic microorganisms to attach to solid packing materials to form a biofilm, thereby degrading the organic matter in the wastewater.

[0003] While traditional anaerobic biofilters offer certain advantages in treating organic wastewater, their widespread application is limited by issues such as slow microbial biofilm formation and unstable treatment effects. Therefore, improving the biofilm formation efficiency and treatment effectiveness of anaerobic biofilters has become a pressing technical challenge. In anaerobic biofilters, the filter media, as the carrier for microbial growth and biofilm formation, directly affects the removal efficiency of pollutants. Common anaerobic biofilter media often suffer from low strength and poor corrosion resistance, severely impacting their treatment performance. Therefore, preparing filter media with good biofilm formation performance and high stability is crucial for improving the treatment efficiency of anaerobic biofilters.

[0004] Currently, polyamide fibers are widely used in water treatment due to their excellent mechanical properties and chemical resistance. However, the poor hydrophilicity and biocompatibility of polyamide fiber surfaces result in slow biofilm formation in anaerobic biological filters, weak microbial adhesion, and negatively impact overall treatment efficiency. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a polyamide fiber filter media for anaerobic biological filters and its preparation method. The polyamide fiber is modified by surface hydrophilization and functional coating to improve its hydrophilicity and biocompatibility, thereby accelerating the microbial biofilm formation process, enhancing the stability and degradation efficiency of the biofilm, and solving the problem of low treatment efficiency of existing recalcitrant organic wastewater.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing polyamide fiber filter media for anaerobic biological filters includes the following steps:

[0008] S1, the polyamide fiber is subjected to surface plasma treatment at a power of 90-110W, and then the residual reactants are cleaned to obtain the plasma-treated polyamide fiber.

[0009] S2, the plasma-treated polyamide fibers are oxidized by a primary oxidant and an auxiliary oxidant. When the primary oxidant is ammonium persulfate, the auxiliary oxidant is ferric chloride; when the primary oxidant is potassium permanganate, the auxiliary oxidant is sulfuric acid; when the primary oxidant is ozone, the auxiliary oxidant is hydrogen peroxide; and when the primary oxidant is benzoyl peroxide, the auxiliary oxidant is silver nitrate, to obtain oxidized polyamide fibers.

[0010] S3, chitosan coating and sodium alginate coating are sequentially coated on the oxidized polyamide fiber. The mass ratio of chitosan, sodium alginate and plasma-treated polyamide fiber in S1 is (0.075-0.25):(0.075-0.25):1, to obtain polyamide fiber filter media for anaerobic biological filters.

[0011] Preferably, the polyamide fiber described in S1 is PA6.

[0012] Preferably, in S1, the polyamide fiber is treated at a power of 90-110W for 12-18 minutes, and the gas flow rate for generating plasma is 8-12L / min.

[0013] Preferably, when the main oxidant is ammonium persulfate and the auxiliary oxidant is ferric chloride, the oxidation treatment in S2 is carried out according to the following process:

[0014] The plasma-treated polyamide fibers obtained from S1 were immersed in a 0.1M ammonium persulfate solution at 45-55℃ for 25-35 minutes. After washing, the polyamide fibers were immersed in a 0.05M ferric chloride solution for 15-25 minutes. After washing and drying, oxidized polyamide fibers were obtained.

[0015] Preferably, when the primary oxidant is potassium permanganate and the secondary oxidant is sulfuric acid, the oxidation treatment in S2 is carried out according to the following process:

[0016] Add sulfuric acid with a concentration of 0.1-0.5M to a 0.01-0.05M KMnO4 solution to obtain a mixed solution. Then, immerse the plasma-treated polyamide fiber obtained in S1 in the mixed solution at 40-50℃ for 30-60 minutes. After washing and drying, oxidized polyamide fiber is obtained.

[0017] Preferably, when the primary oxidant is ozone and the secondary oxidant is hydrogen peroxide, the oxidation treatment in S2 is carried out as follows:

[0018] The plasma-treated polyamide fibers obtained in S1 were placed in an ozone environment with a concentration of 5-10 ppm for 15-30 min, and then immersed in a 0.1-0.5 M H2O2 solution at 30-40℃ for 20-40 min. After washing and drying, oxidized polyamide fibers were obtained.

[0019] Preferably, when the primary oxidant is benzoyl peroxide and the secondary oxidant is silver nitrate, the oxidation treatment in S2 is carried out as follows:

[0020] The plasma-treated polyamide fibers obtained in S1 were immersed in a 0.05-0.2M benzoyl peroxide solution, and then the benzoyl peroxide was decomposed by ultraviolet light or heating to 60-80℃ for 20-30 minutes. The resulting polyamide fibers were then immersed in a 0.01-0.05M silver nitrate solution for 15-25 minutes, followed by washing and drying to obtain oxidized polyamide fibers.

[0021] Preferably, S3 involves sequentially coating the oxidized polyamide fiber with a chitosan coating and a sodium alginate coating via the following process:

[0022] The pH of chitosan solution and sodium alginate solution, each with a mass percentage of 1.5%-2.5%, was adjusted to 4.3-4.7 and 7.0, respectively, to obtain mixed solution a and mixed solution b. The oxidized polyamide fiber obtained in S2 was immersed in mixed solution a, then dried, then immersed in mixed solution b, and finally dried to obtain polyamide fiber filter media for anaerobic biological filters.

[0023] Preferably, the chitosan has a degree of deacetylation of 80% and a molecular weight range of 50,000-190,000 Da, the sodium alginate has a viscosity of 200-800 mPa·s, and the polyamide fiber is immersed in mixed solution a for 45-75 min, then immersed in mixed solution b for 45-75 min, and then dried.

[0024] A polyamide fiber filter media obtained by the preparation method of polyamide fiber filter media for anaerobic biological filters as described in any one of the above.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] This invention discloses a method for preparing polyamide fiber filter media for anaerobic biofilters. High-energy particles and active species generated at 90-110W introduce polar hydrophilic functional groups (hydroxyl, carbonyl, and carboxyl groups) onto the fiber surface, enhancing its hydrophilicity and surface energy, thereby strengthening microbial adhesion and biofilm stability. Ion bombardment etching increases the surface roughness of the fiber, increasing microbial attachment points and surface energy, making it easier for the fiber to interact with water molecules and microorganisms. Synergistic oxidation treatment with four primary and secondary oxidants introduces hydrophilic functional groups onto the polyamide fiber surface, improving its surface hydrophilicity, biocompatibility, and polarity. Increased chemical reactivity on the fiber surface further enhances microbial adhesion and biofilm stability. Further etching of the fiber surface significantly increases surface roughness and chemical activity, providing favorable conditions for microbial biofilm formation, making it more suitable as a biofilm packing material for biofilters. Biocompatible materials chitosan and sodium alginate coatings can form complementary coating structures. When coated on the surface of polyamide fibers, by controlling the amounts of both, a functionalized coating with a stable cross-linked network is formed, providing more attachment points and a favorable environment to promote microbial growth and fixation. Chitosan possesses excellent antibacterial and biocompatibility, promoting microbial attachment and growth; sodium alginate forms a stable gel network structure, improving the mechanical strength and stability of the coating. The combination of the two provides more attachment points and a favorable environment, significantly enhancing microbial fixation and biofilm stability. This invention combines surface hydrophilization and functionalized coating technologies to significantly improve the physicochemical properties of polyamide fibers, enhancing the treatment efficiency and stability of biofilters. Plasma treatment acts as a coarse sculpting agent, oxidation treatment as a fine sculpting agent, and the coating as a functionalization agent; this treatment sequence ensures maximum surface modification effects. Plasma treatment provides initial modification, dual oxidation further enhances it, and the chemical coating forms a stable coating on the optimized surface, providing the best microbial attachment environment and biofilm stability, significantly improving its biofilm formation rate and treatment efficiency in hydrolytic biofilters. The modified polyamide fiber has excellent hydrophilicity and biocompatibility, which enhances the adhesion of microorganisms and the stability of biofilm. Its treatment effect is significantly better than that of unmodified fiber and traditional fiber filter media, and it has significant technical advantages and market application prospects. Attached Figure Description

[0027] Figure 1 The thickness of the biofilm observed by laser confocal optical microscope 3D reconstruction two weeks after biofilm formation, as described in the embodiment of this invention.

[0028] Figure 2 The thickness of the biofilm observed by laser confocal optical microscope 3D reconstruction two weeks after biofilm formation, as described in Comparative Case 1 of this invention.

[0029] Figure 3The thickness of the biofilm observed by laser confocal optical microscope 3D reconstruction two weeks after biofilm formation, as described in Comparative Case 2 of this invention.

[0030] Figure 4 This is a scanning electron microscope image of the biofilm growth two weeks after the biofilm was attached, as described in an embodiment of the present invention.

[0031] Figure 5 This is a scanning electron microscope image of the biofilm growth two weeks after the biofilm was attached, as described in Comparative Case 1 of this invention.

[0032] Figure 6 This is a scanning electron microscope image of the biofilm growth two weeks after the biofilm was attached, as described in Comparative Case 2 of this invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0034] This invention discloses a method for preparing polyamide fiber filter media for anaerobic biological filters, which specifically includes the following steps:

[0035] Step 1. Surface Plasma Treatment

[0036] Polyamide fiber type: PA6 is selected, as PA6 has good toughness and fatigue resistance.

[0037] Equipment type: Low-temperature atmospheric pressure plasma discharge equipment.

[0038] Processing gas: a mixture of argon and oxygen (volume ratio: 80% argon, 20% oxygen).

[0039] Processing parameters: power 90-110W, processing time 12-18 minutes, gas flow rate 8-12L / min.

[0040] Specific process: Place the polyamide fiber sample in the reaction chamber; start the low-temperature atmospheric pressure plasma discharge equipment and adjust the power and gas flow rate; during the process, high-energy particles and active species in the plasma react with the fiber surface, introducing hydrophilic functional groups and increasing surface roughness; after the process is completed, take out the fiber sample, wash it with deionized water to remove residual reactants, and then dry it to remove deionized water.

[0041] Effects: The main function of low-temperature atmospheric pressure plasma treatment of polyamide fibers is to introduce polar hydrophilic functional groups hydroxyl (-OH), carbonyl (=O), and carboxyl (-COOH) groups onto the fiber surface through high-energy particles and active species in the plasma. This enhances the fiber's hydrophilicity and surface energy, thereby strengthening the adhesion of microorganisms and the stability of the biofilm. Etching also increases the surface roughness of the fiber, providing more attachment points for microorganisms. Furthermore, increasing the surface energy of the fiber makes it easier for it to interact with water molecules and microorganisms.

[0042] Plasma is a partially ionized gas containing a large number of high-energy electrons, ions, free radicals, and neutral atoms. The principle of low-temperature atmospheric pressure plasma treatment of polyamide fibers is as follows:

[0043] Plasma excitation: Argon and oxygen are excited by an electric field to form plasma. High-energy electrons collide with gas molecules, producing various reactive species (free radicals, ions, and ultraviolet photons). In argon plasma, high-energy electrons can excite argon molecules to produce reactive argon atoms and ions: Ar + e⁻. - →Ar*+e - (Excited argon atom) Ar* → Ar + hv (emits ultraviolet photons)

[0044] Surface reaction: High-energy electrons, ions, and free radicals react chemically with molecules on the surface of polyamide fibers, introducing polar functional groups. Oxygen free radicals (O·) and ozone (O3) in oxygen plasma can react with carbon-hydrogen bonds on the fiber surface to generate hydroxyl, carboxyl, and carbonyl groups: O· + RH → R· + HO; O3 + RH → ROH + O2

[0045] Etching: High-energy ions in the plasma bombard the fiber surface, physically removing some material and increasing surface roughness. This is based on the following reaction: Ar + +R-CH2-CH2-R'→R-CH2-CH-R'+H+Ar, Argon ion (Ar + A layer of molecules on the fiber surface can be removed by kinetic energy impact, forming a micro-rough structure:

[0046] Step 2. Chemical modification

[0047] Chemical reagents: A double oxidation treatment was performed using ammonium persulfate (APS) and ferric chloride (FeCl3).

[0048] Processing procedure:

[0049] Ammonium persulfate treatment: Immerse 10 grams of plasma-treated polyamide fibers in 500 ml of 0.1 M APS solution for 25-35 minutes at a temperature controlled at 45-55°C. After treatment, thoroughly rinse the fibers with deionized water to remove any residual APS solution.

[0050] Ferric chloride treatment: Transfer the cleaned fibers to 500 mL of 0.05 M FeCl3 solution and react for 15-25 minutes at room temperature. After treatment, thoroughly rinse the fibers with deionized water to remove residual FeCl3 solution, and then dry them.

[0051] Effect: The dual oxidation treatment introduces a large number of hydrophilic functional groups on the fiber surface, improving surface polarity and roughness.

[0052] The main function of dual oxidation treatment is to introduce hydrophilic functional groups onto the surface of polyamide fibers, thereby improving the surface hydrophilicity, biocompatibility, and polarity of the fibers. This increases the chemical reactivity of the fiber surface, thus enhancing the adhesion of microorganisms and the stability of the biofilm. This treatment significantly increases the surface roughness and chemical activity of the fibers, providing favorable conditions for microbial biofilm formation and making them more suitable as biofilm packing materials for biological filters.

[0053] Ammonium persulfate (APS) oxidation treatment: Ammonium persulfate decomposes under heating conditions to produce sulfate free radicals (SO4· ... - These free radicals possess strong oxidizing properties and can react with the chemical bonds on the surface of polyamide fibers to generate polar functional groups such as hydroxyl (-OH), carbonyl (=O), and carboxyl (-COOH). Reaction process: APS → 2SO4· - +H₂O₂ + H⁺; SO₄· - +R-CH2-CH2-R'→R-CH·-CH2-R'+SO4 2- R-CH·-CH2-R'+O2→R-CH(OH)-CH2-R' (generating hydroxyl groups); R-CH·-CH2-R'→R-CH=CH-R' (generating carbonyl and carboxyl groups).

[0054] Ferric chloride (FeCl3) oxidation treatment: Ferric chloride is a strong oxidizing agent that can react with organic molecules on the fiber surface, further introducing more polar functional groups. FeCl3 hydrolyzes in aqueous solution to produce Fe(OH)3, while releasing H2O. + It can react with alkaline sites on the fiber surface to generate oxygen-containing functional groups. The reaction process is: FeCl3 + 3H2O → Fe(OH)3 + 3HCl; Fe(OH)3 → Fe 3+ +3OH - Fe 3+ +R-CH2-CH2-R'→R-CH·-CH2-R'+Fe 2+ R-CH·-CH2-R'+H2O→R-CH(OH)-CH2-R' (generating a hydroxyl group).

[0055] The two-step treatment described above can significantly increase the hydrophilicity and polarity of the fiber surface, making it more suitable for the attachment and growth of microorganisms.

[0056] In addition to ammonium persulfate (APS) and ferric chloride (FeCl3), the present invention can also use the following reagents to perform similar dual oxidation treatments:

[0057] The combination of potassium permanganate (KMnO4) and sulfuric acid (H2SO4): Potassium permanganate is a strong oxidizing agent that can oxidize the chemical bonds on the fiber surface under acidic conditions to generate polar functional groups hydroxyl and carboxyl groups. Sulfuric acid provides an acidic environment, enhancing the oxidizing power of potassium permanganate.

[0058] Specific steps:

[0059] Prepare potassium permanganate solution: Prepare a 0.01-0.05M KMnO4 aqueous solution in the reaction vessel.

[0060] Add sulfuric acid: Slowly add concentrated sulfuric acid to the KMnO4 solution, controlling the sulfuric acid concentration to 0.1-0.5M to maintain an acidic environment.

[0061] Fiber soaking: Immerse the pretreated polyamide fiber sample in this mixed solution for 30-60 minutes at a temperature of 40-50℃.

[0062] Cleaning: After the treatment is completed, thoroughly clean the fibers with deionized water to remove residual KMnO4 and H2SO4 solution and ensure the surface is clean.

[0063] Drying: Dry the fibers at 60°C in preparation for the next step of processing.

[0064] result:

[0065] Under acidic conditions, KMnO4 oxidizes the fiber surface to form hydroxyl (-OH) and carboxyl (-COOH) groups, enhancing the fiber's hydrophilicity and biocompatibility.

[0066] The combination of ozone (O3) and hydrogen peroxide (H2O2): Ozone, with its strong oxidizing properties, can directly react with the fiber surface to generate peroxides, ⁵O, and ozone compounds. Hydrogen peroxide, as an auxiliary oxidant, works synergistically with ozone to further enhance the oxidation effect, producing a large number of hydroxyl groups and COOH, significantly increasing the hydrophilicity and biocompatibility of the fiber. The chemical reactivity of the fiber surface is improved, especially the introduction of functional groups, making the fiber more susceptible to reaction with microorganisms or other chemical substances, thus enhancing the stability and adhesion of the biofilm. The oxidation reaction of ozone and hydrogen peroxide removes or oxidizes some of the fiber surface material, making the surface rougher and increasing the number of microbial attachment points. The oxidation effect in this process lies in physically altering the surface morphology, providing favorable conditions for microbial biofilm formation. The oxidation reaction not only modifies the fiber surface but also removes existing hydrophobic contaminants (such as surface grease or organic compounds), making the fiber surface cleaner and more suitable for biofilm formation.

[0067] Specific steps:

[0068] Ozone treatment:

[0069] The fiber sample was placed in an ozone generator with an ozone concentration of 5-10 ppm. The reaction time was controlled at 15-30 minutes, and the temperature was maintained at 25℃ (room temperature).

[0070] Hydrogen peroxide treatment:

[0071] Remove the ozone-treated fibers and immediately immerse them in a 0.1-0.5M H2O2 solution. The reaction time is 20-40 minutes, and the temperature is controlled at 30-40℃.

[0072] Cleaning and drying:

[0073] Rinse the fibers with deionized water to remove residual hydrogen peroxide.

[0074] The fibers are dried at 60°C.

[0075] Peroxides: When ozone reacts with organic molecules on the fiber surface, peroxides (ROO-R') are generated. These peroxides have active oxygen and can further participate in the reaction.

[0076] Hydroxyl group (-OH, R-CH2-CH2-R'+O3→R-CH(OH)-CH2-R'): The reaction of ozone and hydrogen peroxide can break the CH bonds on the fiber surface, introducing the polar functional group hydroxyl, increasing the fiber's hydrophilicity. Carboxyl group (-COOH, R-CH2-CH2-R'+O3→R-COOH+O2): The action of ozone and hydrogen peroxide can oxidize the carbon chains on the surface of organic materials, generating carboxyl groups. These functional groups are highly polar, further enhancing the fiber's hydrophilicity and surface energy.

[0077] Carbonyl group (=O): The strong oxidizing properties of ozone can convert carbon-hydrogen bonds (CH) on the fiber surface into carbonyl functional groups (C=O), thereby increasing the chemical reactivity of the surface.

[0078] Ozone compounds: Ozone can react with unsaturated carbon chains (such as C=C) to form ozone compounds (such as ozone rings), which can further decompose into oxidation products.

[0079] The combination of benzoyl peroxide (BPO) and silver nitrate (AgNO3): Benzoyl peroxide is an organic peroxide that decomposes under heat or light to generate free radicals, which then oxidize organic molecules on the fiber surface. Silver nitrate, as an auxiliary oxidant, works synergistically with the free radicals to introduce hydroxyl and carboxyl groups onto the fiber surface, further enhancing the fiber's hydrophilicity and biocompatibility.

[0080] Specific steps:

[0081] Benzoyl peroxide treatment:

[0082] The fibers were immersed in a 0.05-0.2M BPO solution at room temperature (25°C).

[0083] BPO decomposition is activated by ultraviolet light or heating to 60-80℃ for 20-30 minutes.

[0084] Silver nitrate treatment:

[0085] The BPO-treated fibers were transferred to a 0.01-0.05M AgNO3 solution, and the reaction time was 15-25 minutes. During the reaction, silver ions (Ag...)... + It works synergistically with free radicals to further enhance the oxidation of the fiber surface.

[0086] Cleaning and drying:

[0087] After treatment, immediately rinse the fibers with deionized water to remove residual AgNO3 and BPO.

[0088] The fibers are dried at 60°C.

[0089] Ammonium persulfate (APS) and ferric chloride (FeCl3) have relatively good safety and environmental friendliness, so this option was selected in the following examples.

[0090] Step 3. Functionalized Coating

[0091] 3.1 Chitosan Coating

[0092] Type: Medium molecular weight chitosan with a degree of deacetylation of 80% and a molecular weight range of 50,000-190,000 Da.

[0093] Solution preparation: Prepare a chitosan solution with a mass percentage of 1.5-2.5%, and adjust the pH to 4.3-4.7 by adding acetic acid solution with a mass percentage of 0.5% to obtain mixed solution a.

[0094] Coating treatment: Immerse the chemically modified polyamide fibers in mixed solution a for 45-75 minutes. The weight ratio of chitosan solution to fiber is (5-10):1. Chitosan is coated on the polyamide fibers, and then dried in a hot air drying oven at 60°C for 30 minutes.

[0095] 3.2 Sodium alginate coating

[0096] Type: High purity (e.g., 99%) sodium alginate, viscosity 200-800 mPa.s.

[0097] Solution preparation: Prepare a sodium alginate solution with a mass percentage of 1.5-2.5%, and adjust the pH to 7.0 by adding an acetic acid solution with a mass percentage of 0.5%, to obtain mixed solution b.

[0098] Coating treatment: Immerse the chitosan-coated fibers in mixed solution b for 45-75 minutes. The weight ratio of sodium alginate solution to fibers is (5-10):1. Then dry in a hot air drying oven at 60°C for 30 minutes.

[0099] Synergistic effect of chitosan and sodium alginate coating

[0100] Synergistic Mechanism: Chitosan and sodium alginate coatings can form complementary coating structures. Chitosan possesses excellent antibacterial and biocompatibility, promoting microbial attachment and growth; sodium alginate forms a stable gel network structure, improving the mechanical strength and stability of the coating. The combination of the two provides more attachment points and a favorable environment, significantly enhancing microbial immobilization and biofilm stability.

[0101] Effect verification: In the experiment, the combination of chitosan and sodium alginate coating significantly improved the amount of microbial adhesion and biofilm stability compared to using chitosan or sodium alginate coating alone, resulting in better treatment effect.

[0102] Implementation Cases and Comparison Cases

[0103] Implementation Cases

[0104] Step 1. Surface Plasma Treatment

[0105] PA6 was selected, and the processing parameters of the low-temperature atmospheric pressure plasma discharge equipment were: power 100W, processing time 15 minutes, and gas flow rate 10L / min. After processing, the fiber sample was removed and washed with deionized water to remove residual reactants.

[0106] Step 2. Chemical modification

[0107] Ammonium persulfate treatment: Immerse 10 grams of plasma-treated polyamide fibers in 500 ml of 0.1 M APS solution for 30 minutes at a controlled temperature of 50°C. After treatment, thoroughly rinse the fibers with deionized water to remove any residual APS solution.

[0108] Ferric chloride treatment: Transfer the cleaned fibers to 500 mL of 0.05 M FeCl3 solution and react for 20 minutes at room temperature. After treatment, thoroughly rinse the fibers with deionized water to remove any residual FeCl3 solution.

[0109] Step 3. Functionalized Coating

[0110] 3.1 Chitosan Coating

[0111] The degree of deacetylation is 80%, and the molecular weight range is 50,000-190,000 Da. A 2% (w / w) chitosan solution was prepared, and the pH was adjusted to 4.5 by adding 0.5% (w / w) acetic acid solution to obtain mixed solution a. The chemically modified polyamide fibers were immersed in mixed solution a for 60 min, with a chitosan solution to fiber volume ratio of 8:1. The chitosan was coated onto the polyamide fibers, and then dried in a hot air drying oven at 60°C for 30 min.

[0112] 3.2 Sodium alginate coating

[0113] Sodium alginate with a purity of 99% and a viscosity of 200-800 mPa·s was prepared. A 2% (w / w) sodium alginate solution was prepared, and the pH was adjusted to 7.0 by adding 0.5% (w / w) acetic acid solution to obtain mixed solution b. Chitosan-coated fibers were immersed in mixed solution b for 60 min, with a sodium alginate solution to fiber weight ratio of 8:1, and then dried in a hot air drying oven at 60°C for 30 min.

[0114] In the experiment of treating recalcitrant organic wastewater, polyamide-based composite fibers modified as described above were used as biofilm packing material for the anaerobic biological filter. The operating conditions were: wastewater flow rate: 500 mL / h; biofilm formation time: 2 weeks; operating time: 8 weeks.

[0115] The treatment results are as follows: COD removal rate: over 85%; BOD (biochemical oxygen demand) removal rate: over 90%; ammonia nitrogen removal rate: 75%; total phosphorus removal rate: 70%; microbial adhesion rate: 1500 CFU / cm³ 2 Biofilm thickness: 600 μm.

[0116] The biofilm formation experiment and the construction and operation of the anaerobic biological filter were described, with detailed explanations of the relevant conditions.

[0117] Water sample preparation:

[0118] The water sample used for treatment was the pre-biochemical wastewater after distillation and phenol removal from coking wastewater.

[0119] Filter media preparation:

[0120] Modified polyamide fiber (PA6) and traditional fiber filter media were selected as control groups.

[0121] The modified polyamide fibers are subjected to plasma treatment and dual oxidation treatment, and then coated with chitosan and sodium alginate.

[0122] Film application steps:

[0123] Cut the treated fiber samples into small segments (approximately 5-10 cm) suitable for the size of the biofilter. Distribute the fiber samples evenly within the biofilter, ensuring sufficient space between the fiber samples to facilitate water flow and microbial attachment.

[0124] reactor design

[0125] Reactor dimensions: Taking a treatment capacity of 500 mL / h and a hydraulic retention time (HRT) of 12 hours as an example, the total volume is calculated as follows: Total volume = Treatment capacity × Hydraulic retention time = 500 mL / h × 12 h = 6000 mL = 6 L. Length: 20 cm; Width: 10 cm; Height: 30 cm; Total volume: 20 cm × 10 cm × 30 cm = 6000 cm³ 3 =6L

[0126] Use corrosion-resistant stainless steel or high-density polyethylene (HDPE) as reactor materials to ensure the reactor's durability and corrosion resistance.

[0127] Inlet and outlet water system

[0128] Inlet: Installed at the bottom of the reactor to ensure that water flows from bottom to top through the filter media.

[0129] Outlet: Installed at the top of the reactor to prevent excessive biofilm accumulation from affecting the treatment effect.

[0130] Water inlet pipe: Install flow meters and regulating valves to control the water sample flow.

[0131] Water outlet pipe: Equipped with an overflow outlet to ensure a constant water level.

[0132] Filter media filling: Modified polyamide fibers are selected and evenly distributed within the reactor. The filter media layer thickness is approximately 20 cm. A support mesh is placed above the filter media layer to prevent media loss.

[0133] Operating conditions

[0134] Water sample flow rate:

[0135] The treatment capacity is 500 mL / h, and the influent flow rate is stable.

[0136] Hydraulic retention time (HRT): HRT = Total volume / Treatment capacity = 6L / 0.5L / h = 12 hours. Maintain temperature at 25-30℃ (or room temperature). Maintain pH value within the range of 5.5-7.0, adjusted by adding common acids or alkalis according to relevant standards.

[0137] The total running time is 8 weeks.

[0138] Start-up phase: Conduct a clean water trial run to ensure the system is leak-free and free of blockages. Gradually introduce pre-biochemical wastewater from the distillation and phenol removal process of coking wastewater, gradually increasing the water flow rate to avoid excessive microbial shock load.

[0139] Normal operation phase:

[0140] Water flow rate: maintained at 500 mL / h. Temperature: 25-30℃ (or room temperature). pH value maintained at 5.5-7.0. HRT: 12 hours.

[0141] Monitoring and Maintenance: Samples were taken every 3 days, and the microbial adhesion on the fiber surface was observed using a scanning electron microscope (SEM). The colony forming units (CFU / cm²) were used to measure the microbial adhesion. 2 Counting method for quantitative analysis of microbial attachment. Record biofilm thickness. Regularly monitor effluent water quality indicators, including COD, BOD, ammonia nitrogen, and total phosphorus concentrations. Inspect the influent and effluent systems weekly to ensure normal operation.

[0142] Compare with Case 1

[0143] Unmodified PA6 polyamide fibers were used as the biofilm packing material in the biological filter under identical operating conditions. The treatment results are as follows: COD removal rate: approximately 60%; BOD removal rate: 65%; ammonia nitrogen removal rate: 50%; total phosphorus removal rate: 45%; microbial attachment rate: 800 CFU / cm³. 2 Biofilm thickness: 300 μm.

[0144] Compare with Case 2:

[0145] Traditional polypropylene fiber filter media was used as the biofilm packing material in the biological filter, and the operating conditions were the same as in the case study. The treatment results are as follows: COD removal rate: approximately 55%; BOD removal rate: 60%; ammonia nitrogen removal rate: 45%; total phosphorus removal rate: 40%; microbial attachment rate: 700 CFU / cm³. 2 Biofilm thickness: 250 μm.

[0146] Figure 4 The image shows the biofilm growth observed using a scanning electron microscope two weeks after biofilm formation, as described in the implementation case. The image illustrates the biofilm growth of the modified polyamide fibers two weeks after biofilm formation. The biofilm is uniformly distributed on the fiber surface, forming a continuous and dense layer with obvious microbial communities attached. The fiber structure is thoroughly covered by the biofilm, and no obvious peeling or damage is observed. The surface modification treatment of the fiber effectively promotes microbial attachment, forming a stable, dense, and thick biofilm. Figure 1 As can be seen from the 3D reconstruction images based on laser confocal optical microscopy, the biofilm thickness in this case is significantly thicker than in other cases.

[0147] Figure 5 The image shows the biofilm growth observed under a scanning electron microscope two weeks after biofilm formation, as described in Case 1. The image reveals an uneven distribution of the biofilm on the fiber surface, with incomplete adhesion in some areas, a loose biofilm structure, and sparse microbial attachment in localized regions, resulting in poor membrane integrity. Unmodified polyamide fibers, due to their low hydrophilicity, exhibit weak microbial adhesion, leading to unstable and thin biofilm formation. Figure 2 It can be seen that the film thickness is significantly lower than that in the implementation case, and the film attachment effect is significantly worse than that of the modified fiber.

[0148] Figure 6 The image shows the biofilm growth observed under a scanning electron microscope two weeks after biofilm formation, as described in Case 2. The image reveals that the biofilm on the fiber surface is relatively thin, with a loose and unevenly distributed structure, low microbial attachment density, and some areas showing almost no effective biofilm formation. Traditional polypropylene fiber filter media suffers from poor mechanical strength and hydrophilicity, resulting in low biofilm formation efficiency and poor microbial adhesion. Figure 3 As can be seen, the biofilm thickness is significantly smaller than that of the standard biofilm. Figure 2 and Figure 3 However, its effect is not as good as that of polyamide fibers.

[0149] Detailed product performance test comparison data

[0150]

[0151] The methods for determining the required parameters are as follows:

[0152] Methods for determining biofilm stability:

[0153] After biofilm formation, the filter media was placed in a nutrient solution containing microorganisms. The filter media was weighed every 48 hours, and the biofilm growth morphology was observed using a laser confocal microscope to determine the biofilm stability. Biofilm stability is a key characteristic for evaluating whether filter media can form a durable, strongly adherent, and non-detachable biofilm during use. The following are specific results illustrating the improvement in biofilm stability in comparison cases 1 and 2 and the implementation case:

[0154] Implementation Case (Modified Polyamide Fiber):

[0155] Biomembrane stability: High

[0156] reason:

[0157] The modified polyamide fibers, through plasma treatment, chemical oxidation treatment, and a double-layer coating of chitosan and sodium alginate, have significantly enhanced hydrophilicity and surface energy. A large number of polar functional groups (such as hydroxyl and carboxyl groups) have been introduced onto the fiber surface, making it easier for microorganisms to attach and form stable biofilms.

[0158] After modification, the amount of microbial adhesion reached 1500 CFU / cm³. 2 The biofilm thickness is 600 μm, which indicates that the microorganisms formed a thick and dense membrane layer on the surface of the filter media, which can resist external conditions such as water flow impact.

[0159] The biofilm exhibited high stability throughout its entire operating cycle, with no membrane peeling or separation. The biofilm was able to maintain its degradation capacity and structural integrity for an extended period of time.

[0160] Compare with Case 1 (unmodified polyamide fiber, PA6):

[0161] Biomembrane stability: low

[0162] reason:

[0163] Unmodified PA6 fibers have poor hydrophilicity and lack polar functional groups, resulting in weak adhesion of microorganisms. Therefore, although biofilms can form to some extent, the membrane layer is thin, has weak adhesion, and is easily detached by water flow or external disturbances.

[0164] The amount of microorganisms attached was 800 CFU / cm³. 2 The biofilm thickness was 300 μm, indicating that the growth of microorganisms on the fiber surface was limited, the resulting membrane layer was relatively sparse, and the structure was not stable enough.

[0165] In actual operation, biofilm often peels off, has poor stability, and leads to unstable treatment efficiency.

[0166] Compare with Case 2 (traditional polypropylene fiber filter media):

[0167] Biomembrane stability: low

[0168] reason:

[0169] Traditional polypropylene fiber filter media has low mechanical strength and insufficient hydrophilicity and surface energy, resulting in very limited adhesion of microorganisms to its surface. Although a certain amount of biofilm can be formed, the membrane layer is very thin and easily detaches during operation.

[0170] The amount of microorganisms attached was only 700 CFU / cm³ 2 The biofilm thickness was 250 μm, indicating that the microbial activity on the fiber surface was low and the biofilm structure was loose and unstable.

[0171] The biofilm of this type of filter media is easily affected by water flow and operating conditions, and the membrane layer is easily damaged, resulting in unstable performance of the filter media in long-term use.

[0172] In the implementation case, the biofilm stability was significantly improved. This is because the modified polyamide fiber, through surface modification treatment, significantly improved the hydrophilicity and biocompatibility of the fiber surface, enabling microorganisms to quickly attach and form a thicker and more stable biofilm, resulting in a higher microbial attachment rate (1500 CFU / cm³). 2 The modified polyamide fiber significantly improved biofilm stability, allowing microorganisms to adhere firmly to the fiber surface and form a stable, dense, and thick biofilm. This is crucial for the long-term stable operation of the anaerobic biological filter. The filter media in Control Cases 1 and 2, lacking modification, exhibited poor biofilm stability, with the biofilm easily detaching or breaking down, thus affecting the overall treatment efficiency of the filter. In Control Cases 1 and 2, the unmodified filter media showed poor biofilm stability, with the biofilm easily detaching or breaking down, impacting the overall treatment efficiency of the filter.

[0173] COD value determination method:

[0174] COD values ​​were determined according to the national standard GB11914-89 using the potassium dichromate oxidation microwave digestion titration method. 5.00 mL of 0.0250 mol / L potassium dichromate solution was added to the water sample. Under strong acid conditions (hydrochloric acid), silver salt was used as a catalyst. After boiling and reflux, 3 drops of ferroin indicator were added. The unreduced potassium dichromate in the water sample was titrated with 0.005 mol / L ferrous ammonium sulfate. The mass concentration of oxygen consumed was calculated from the amount of potassium dichromate consumed, thus obtaining the COD determination result.

[0175] Methods for determining BOD values:

[0176] The water sample was filled into a completely sealed dissolved oxygen bottle and cultured in the dark at (20±1)℃ for 5 days±4 hours. The dissolved oxygen concentration in the water sample before and after culture was measured using a dissolved oxygen meter. The amount of dissolved oxygen consumed per liter of sample was calculated from the difference in dissolved oxygen concentration before and after culture, thus obtaining the BOD measurement result.

[0177] Methods for determining ammonia nitrogen levels:

[0178] Ammonia nitrogen levels are measured using Nessler's reagent spectrophotometry. Ammonia in the air is absorbed by a dilute sulfuric acid solution. The resulting ammonium ions react with Nessler's reagent to form a yellow-brown complex. The absorbance of this complex is directly proportional to the ammonia concentration. The absorbance is measured at a wavelength of 420 nm, and the concentration in the air is calculated based on the absorbance.

[0179] Total phosphorus determination method:

[0180] Total phosphorus value was determined using the potassium persulfate digestion method—molybdenum-antimony anti-chromic reagent spectrophotometric method. Under high temperature conditions, the sample was fused with sodium hydroxide, causing all phosphorus-containing minerals and organic phosphorus compounds to be converted into soluble orthophosphates. Under acidic conditions, these orthophosphates reacted with a molybdenum-antimony anti-chromic reagent to form phosphomolybdic blue, and the absorbance was measured at a wavelength of 700 nm. Within a certain concentration range, the total phosphorus content and absorbance value conformed to the Lambert-Beer law.

[0181] Methods for determining the amount of microbial adhesion:

[0182] The amount of microorganisms attached to the filter media was measured using the plate count method, and the value was expressed as CFU / cm³. 2 .

[0183] Methods for measuring biofilm thickness:

[0184] The thickness of the biofilm on the filter media was measured using a laser confocal microscope and expressed in μm.

[0185] Methods for determining the mechanical strength of filter media:

[0186] The mechanical strength of the filter media was measured using a Roell Z 010 universal testing machine, and the strength was divided into three levels: high, medium, and low.

Claims

1. A method for producing a polyamide-based fiber filter material for an anaerobic biofilter, characterized by, The method comprises the following steps: S1, surface plasma treatment of the polyamide fiber for 12-18 min under the condition of 90-110 W power, the gas flow rate for generating plasma is 8-12 L / min, and then residual reactants are cleaned to obtain the plasma-treated polyamide fiber; S2, the plasma-treated polyamide fiber is subjected to oxidation treatment by a primary oxidizing agent and an auxiliary oxidizing agent, wherein when the primary oxidizing agent is ammonium persulfate and the auxiliary oxidizing agent is ferric chloride, the plasma-treated polyamide fiber obtained in S1 is soaked in a 0.1 M ammonium persulfate solution at 45-55 ℃ for 25-35 min, and then the obtained polyamide fiber is cleaned, and then soaked in a 0.05 M ferric chloride solution for 15-25 min, and then cleaned and dried to obtain the oxidized polyamide fiber; when the primary oxidizing agent is potassium permanganate and the auxiliary oxidizing agent is sulfuric acid, a 0.1-0.5 M sulfuric acid solution is added to a 0.01-0.05 M potassium permanganate solution to obtain a mixed solution, and then the plasma-treated polyamide fiber obtained in S1 is soaked in the mixed solution at 40-50 ℃ for 30-60 min, and then cleaned and dried to obtain the oxidized polyamide fiber; when the primary oxidizing agent is ozone and the auxiliary oxidizing agent is hydrogen peroxide, the plasma-treated polyamide fiber obtained in S1 is placed in an ozone environment with a concentration of 5-10 ppm for 15-30 min, and then soaked in a 0.1-0.5 M hydrogen peroxide solution at 30-40 ℃ for 20-40 min, and then cleaned and dried to obtain the oxidized polyamide fiber; when the primary oxidizing agent is benzoyl peroxide and the auxiliary oxidizing agent is silver nitrate, the plasma-treated polyamide fiber obtained in S1 is soaked in a 0.05-0.2 M benzoyl peroxide solution, and then the benzoyl peroxide is excited to decompose by using ultraviolet light or heating to 60-80 ℃, and the duration is 20-30 min, and then the obtained polyamide fiber is soaked in a 0.01-0.05 M silver nitrate solution for 15-25 min, and then cleaned and dried to obtain the oxidized polyamide fiber; S3, a chitosan coating and a sodium alginate coating are sequentially coated on the oxidized polyamide fiber by the following process, a chitosan solution and a sodium alginate solution with a mass percentage of 1.5%-2.5% are adjusted to pH 4.3-4.7 and 7.0 respectively to obtain a mixed solution a and a mixed solution b, the oxidized polyamide fiber obtained in S2 is immersed in the mixed solution a, and then dried, and then immersed in the mixed solution b, and finally dried, and the mass ratio of chitosan, sodium alginate and the plasma-treated polyamide fiber in S1 is (0.075-0.25):(0.075-0.25):1, to obtain the polyamide fiber filter material for an anaerobic biofilter.

2. The method for preparing the polyamide-based fiber filter media for an anaerobic biofilter according to claim 1, characterized by, The polyamide fiber in S1 is PA6.

3. The method for preparing the polyamide-based fiber filter media for an anaerobic biofilter according to claim 1, characterized by, The chitosan has a degree of deacetylation of 80% and a molecular weight ranging from 50,000 to 190,000 Da, the sodium alginate has a viscosity of 200-800 mPa.s, the polyamide fibres are immersed in the mixed solution a for 45-75 min, then in the mixed solution b for 45-75 min, and then dried.

4. A polyamide fibrous filter material obtained by the production method of the polyamide fibrous filter material for an anaerobic biofilter according to any one of claims 1 to 3.

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