Electrically-mediated iron-carbon composite filler constructed wetland system for removing sulfonamide antibiotics and resistance genes and construction and use method of electrically-mediated iron-carbon composite filler constructed wetland system

Abstract

The invention discloses an electrically-mediated iron-carbon composite filler constructed wetland system for removing sulfonamide antibiotics and resistance genes as well as a construction method and a use method of the electrically-mediated iron-carbon composite filler constructed wetland system, and belongs to the technical field of water treatment. Coconut shell biochar is modified by hydrochloric acid and then compounded with pyrite to form a composite filler with targeted adsorption, efficient electron conduction and multi-mechanism catalysis functions, and the composite filler is used as a core matrix to construct a vertical flow constructed wetland system applying an external direct-current electric field. The system realizes efficient, synchronous and stable removal of sulfonamide antibiotics and resistance genes thereof in a water body by virtue of directional enrichment of the filler on pollutants, an electron transfer network formed by a composite material and an electrochemical-microorganism synergistic effect jointly excited by a direct-current electric field and the filler.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically, it relates to an electro-enhanced constructed wetland system coupled with hydrochloric acid-modified coconut shell biochar and pyrite, and its application in removing antibiotics and resistance genes from domestic sewage. Background Technology

[0002] With the rapid development of modern medicine, animal husbandry, and aquaculture, antibiotics are widely used for disease prevention and growth promotion. This results in a large amount of incompletely absorbed antibiotics entering the aquatic environment, either unchanged or as metabolites, through pharmaceutical wastewater, aquaculture wastewater, and urban sewage. Even at trace concentrations, these antibiotics pose a threat to aquatic ecosystems and may accumulate through the food chain, ultimately endangering human health. More seriously, the persistent residues of antibiotics in the environment create long-term selective pressure, inducing and accelerating the proliferation and spread of antibiotic resistance genes (ARGs), thus posing a profound threat to ecosystem stability and public health security.

[0003] Sulfonamide antibiotics, as one of the oldest and most widely used antibiotic classes globally, have become emerging pollutants frequently detected in water bodies due to their stable chemical structure and difficulty in degradation in the natural environment. Sulfamethoxazole (SMX) is a typical example, with concentrations in wastewater effluent from Chinese wastewater treatment plants reaching 0-18000 ng / L. 1 Sulfonamides are the antibiotics with the highest detected concentrations among sulfonamide antibiotics. Traditional wastewater treatment processes have limited removal efficiency for sulfonamides and struggle to effectively control the spread of ARGs. Therefore, the development of sustainable water treatment technologies that can simultaneously and efficiently remove antibiotics and their resistance genes is urgently needed.

[0004] Currently, technologies for removing antibiotics from water bodies mainly include physical adsorption, chemical oxidation, and biological treatment. Physical adsorption methods (such as activated carbon adsorption), while simple to operate, suffer from problems such as adsorption saturation, the need for regeneration, and potential secondary pollution. Advanced oxidation technologies (such as the Fenton process and photocatalysis), while effectively degrading antibiotics, generally face challenges such as high treatment costs, large reagent consumption, and the potential generation of toxic intermediates. Traditional biological treatment processes (such as activated sludge processes) have limited removal efficiency for antibiotics like SMX due to the antibacterial activity of antibiotics, and may even promote the proliferation and spread of ARGs. Constructed wetlands (CWs), as an eco-friendly, low-cost, and easy-to-manage wastewater treatment technology, are increasingly being applied to antibiotic removal while effectively removing conventional pollutants such as nitrogen and phosphorus. They achieve the conversion and removal of antibiotics through the synergistic effects of multiple mechanisms, including plant absorption, matrix adsorption, and microbial degradation. To improve their removal efficiency for sulfonamide pollutants, bioelectrochemical systems have been introduced to enhance wetland efficiency. Existing research indicates that coupling a DC electric field or a microbial fuel cell with constructed wetlands can significantly improve the removal rate of sulfamethoxazole by stimulating microbial activity and promoting electron transfer through electrochemical action.

[0005] However, the efficiency of such bioelectrochemical coupling systems is highly dependent on the performance of the packing material (matrix). On the one hand, the packing material needs to have excellent adsorption capacity to enrich pollutants; on the other hand, it also needs to have good conductivity to promote electron transfer between the electrodes and the microbial community. Currently used iron-based materials (such as pyrite) can promote the transformation and adsorption of pollutants through iron cycling, but their own conductivity is limited, restricting the full realization of the electrochemical effect. Biochar, especially after acid modification, has a significantly increased specific surface area and surface functional groups, enhancing its adsorption capacity for sulfonamide antibiotics. However, conventional biochar usually has insufficient conductivity and catalytic activity, making it difficult to independently support an efficient electrochemical-biological synergistic degradation process. Single-function packing materials cannot simultaneously meet the multiple requirements of efficient adsorption, efficient electron transfer, and multi-pathway synergistic degradation, resulting in significant bottlenecks in the overall removal efficiency, long-term operational stability, and resistance to load shocks of electro-enhanced constructed wetlands for sulfonamide antibiotics and resistance genes. Therefore, developing a composite filler that can integrate the synergistic effects of adsorption, electrochemical conversion and biological metabolism, and using it to construct an efficient and stable electro-enhanced constructed wetland system, has become the key to overcoming current technological limitations. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an electro-mediated iron-carbon composite filler constructed wetland system for removing sulfonamide antibiotics and their resistance genes, along with its construction and application methods. This invention involves modifying coconut shell biochar with hydrochloric acid and then compounding it with pyrite to form a composite filler with targeted adsorption, efficient electron conduction, and multi-mechanism catalysis. This composite filler serves as the core matrix in a vertical flow constructed wetland system under an applied external DC electric field. This system achieves efficient, simultaneous, and stable removal of sulfonamide antibiotics and their resistance genes from water bodies through the directional enrichment of pollutants by the filler, the electron transport network formed by the composite material, and the electrochemical-microbial synergistic effect stimulated by the DC electric field and the filler.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The technical solution of this invention covers three aspects: the preparation of hydrochloric acid modified coconut shell biochar, the construction and operation of wetland systems.

[0008] In a first aspect, the present invention provides a method for preparing hydrochloric acid-modified coconut shell biochar. The specific steps are as follows: S1: The coconut shell is cleaned, dried, crushed and sieved, then pyrolyzed in an inert gas atmosphere, cooled and ground and sieved to obtain basic biochar. S2: Mix the obtained basic biochar with hydrochloric acid solution, stir magnetically at room temperature, wash repeatedly with deionized water until the filtrate is neutral, dry, and sieve to obtain hydrochloric acid modified coconut shell biochar.

[0009] To further specify, the inert gas is nitrogen.

[0010] Further specified, the pyrolysis is carried out in a tubular furnace at 500°C, with a heating rate of 10°C / min and a pyrolysis time of 4 h.

[0011] Further specified, drying at 60°C for 24 hours.

[0012] Further specified, particles with a diameter of 4-8 mm are sieved.

[0013] Further specified, the hydrochloric acid concentration is 1 M, and it is mixed at a solid-liquid ratio of 1 g: 30 mL.

[0014] The hydrochloric acid-modified coconut shell biochar particles, natural pyrite particles, and gravel obtained in step S2 are layered according to a preset structure to construct the iron-carbon composite filler treatment layer. This method, used in the constructed wetland system, aims to combine the adsorption properties of coconut shell biochar with the electrical conductivity and chemical activity of pyrite, and further enhance the performance of the biochar through acid modification.

[0015] Secondly, this invention provides an electrically mediated constructed wetland system based on the aforementioned iron-carbon composite filler. The system is a vertical subsurface flow structure, with the main body being a cylindrical container. From bottom to top, the system includes: a coarse gravel support layer, a fine gravel support layer, a hydrochloric acid-modified coconut shell biochar layer, a gravel layer or a mixed gravel and pyrite layer, a hydrochloric acid-modified coconut shell biochar layer, and a fine sand layer planted with wetland vegetation. The anode and cathode are located within the hydrochloric acid-modified coconut shell biochar layer. The anode and cathode are externally connected to an adjustable DC power supply. A microporous aeration disc is installed at the bottom, and an aeration pump is externally connected to the aeration disc. A perforated pipe is installed at the top of the aeration disc, with evenly distributed air holes. The perforated pipe penetrates each layer from the bottom layer upwards, finally exiting from the top of the fine sand layer. The perforated pipe is covered with a mesh screen, and an outlet is provided at the bottom of the system.

[0016] Further specified, the coarse gravel has a particle size of 20 mm-50 mm and a laying thickness of 10 cm.

[0017] Further specified, the fine gravel has a particle size of 4 mm-8 mm and a thickness of 5 cm.

[0018] Further specified, the volume ratio of pyrite to gravel is 1:1, the particle size of pyrite is 4 mm-8 mm, and the particle size of gravel is 4 mm-8 mm.

[0019] Further specifying, the hydrochloric acid modified coconut shell biochar layer is 5 cm.

[0020] Further specified, the fine sand particle size is 1 mm-2 mm, and the fine sand layer thickness is 5 cm.

[0021] Further specifying, the wetland plant is yellow iris. After the seedlings have their roots cleaned, they are pre-cultured in tap water for about a week. Plants with good growth and a height of about 25 cm are selected and transplanted into the wetland system at a rate of 5 plants per column.

[0022] Further specifying, the cathode and anode are titanium mesh electrodes.

[0023] Thirdly, this invention relates to a method for using the aforementioned constructed wetland system to remove sulfonamide antibiotics and resistance genes from water. The system operates in an intermittent flow mode: water enters from the top, submerging the system, and exits from the bottom; the hydraulic retention time is set to 72 hours. The aeration system performs intermittent aeration daily from 6:00-7:00 and 18:00-19:00, at a rate controlled at 0.6 L / min, to regulate the redox environment within the system. To reduce the photolytic effect of light on target pollutants and control algal proliferation, the outer surface of the column is wrapped with black tape to simulate the dark environment of an actual wetland. During operation, the temperature is controlled at 20-25°C, the humidity is maintained at 60-70%, and plant grow lights are used to simulate natural light conditions.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) Targeted enrichment: After wastewater containing target pollutants such as SMX enters the system, it flows through the core functional layer. Hydrochloric acid modified coconut shell biochar, with its huge specific surface area and abundant surface functional groups (such as -COOH, -OH), specifically adsorbs and enriches SMX molecules, rapidly fixing them from the aqueous phase to the surface of the packing material, increasing the local concentration and creating conditions for subsequent deep treatment. (2) Electron transfer and electrochemical activation: The externally applied DC electric field and pyrite with good conductivity work together to construct an efficient electron transfer network in the packing layer. On the one hand, the electric field drives the directional migration of electrons; on the other hand, pyrite (FeS2) can act as a micro-electrode and electron donor, and redox reactions (such as Fe) occur on its surface. 2+ / Fe 3+ (3) Multi-pathway synergistic degradation: SMX enriched on the surface of the packing material faces a triple attack: a) Electrochemical conversion: Active substances generated by electric field and iron cycle directly oxidize and decompose SMX molecules; b) Biometabolism: Electroactive bacteria and obligate degrading bacteria in the biofilm formed on the surface of the packing material use the electron and interface environment provided by the packing material to biooxidize or co-metabolize SMX; c) Adsorbed state conversion: The surface catalytic properties of the packing material itself may promote the non-biochemical conversion of adsorbed SMX. These three pathways work together to achieve synergistic degradation and deep mineralization of pollutants. (4) Resistance gene control: The system fundamentally weakens the selective pressure on the microbial community by efficiently removing the SMX parent. At the same time, the establishment of electrochemical processes and competitive microbial niches may inhibit the existing ARGs host bacteria and interfere with the horizontal transfer of ARGs, thereby achieving synergistic control of ARGs proliferation and diffusion.

[0025] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the electrically mediated iron-carbon composite filler constructed wetland system of the present invention. 1 - coarse gravel support layer, 2 - fine gravel support layer, 3 - biochar or acid-modified biochar layer, 4 - gravel layer or gravel and pyrite mixed layer, 5 - biochar or acid-modified biochar layer, 6 - fine sand layer, 7 - titanium mesh electrode (cathode), 8 - titanium mesh electrode (anode), 9 - DC power supply, 10 - wetland plants, 11 - perforated pipe, 12 - aeration disc, 13 - aeration pump, 14 - aeration hole, 15 - outlet. Figure 2These are SEM-EDS images of coconut shell biochar in the comparative example and hydrochloric acid modified coconut shell biochar in the examples of this invention. Figure 3 These are the FTIR spectra of coconut shell biochar in the comparative example and hydrochloric acid modified coconut shell biochar in the examples of this invention; Figure 4 The above are XPS spectra of coconut shell biochar in the comparative example and hydrochloric acid modified coconut shell biochar in the examples of this invention. Figure 5 The pH, conductivity, and zeta potential of coconut shell biochar in the comparative example and hydrochloric acid modified coconut shell biochar in the examples of this invention are shown. Figure 6 The removal efficiency of constructed wetland systems CW1, CW2, and EC-CW on basic water quality indicators; Figure 7 The removal efficiency of constructed wetland systems CW1, CW2, and EC-CW for SMX; Figure 8 The removal efficiency of constructed wetland systems CW1, CW2, and EC-CW on ARGs. Detailed Implementation

[0027] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0028] Example 1 Combined with appendix Figure 1As can be seen, this embodiment provides an electrically mediated iron-carbon composite filler constructed wetland system (EC-CW) for removing sulfonamide antibiotics and resistance genes, including a constructed wetland reactor, filler layer, plant system, DC power supply system, and inlet and outlet water control system. The constructed wetland reactor is a vertical subsurface flow structure, made of PVC, with a height of 65 cm and a diameter of 20 cm. The filler layer of EC-CW, from bottom to top, includes a coarse gravel support layer 1 (thickness 10 cm, particle size 20-50 mm), a fine gravel support layer 2 (thickness 5 cm, particle size controlled at 4-8 mm), an acid-modified biochar layer 3 (thickness 5 cm, particle size controlled at 4-8 mm), a gravel and pyrite mixed layer 4 (thickness 20 cm, particle size controlled at 4-8 mm), an acid-modified biochar layer 5 (thickness 5 cm, particle size 4-8 mm), and a fine sand layer 6 (thickness 10 cm, particle size controlled at 1-2 mm). Within the acid-modified biochar layers 3 and 5, titanium mesh composite electrodes 7 and 8 are arranged in parallel, serving as the cathode and anode respectively, connected to an external adjustable DC power supply 9, applying a 0.3 V DC voltage. The wetland plant 10 is *Iris tectorum*, approximately 25 cm tall, planted at a density of 5 plants per column, embedded in the fine sand layer 6. To monitor dissolved oxygen and water temperature in situ and achieve uniform aeration, a PVC perforated pipe 11 (61 cm high, 4 cm in diameter) is vertically installed at the center of the device, its end connected to a microporous aeration disc 12. The perforated pipe 11 is covered with a mesh to prevent the packing material from clogging the holes. The aeration pump 13 is connected sequentially to the aeration holes 14 and the aeration disc 12 via a silicone hose, forming a complete aeration circuit.

[0029] The preparation method of the acid-modified biochar includes the following steps: The specific steps are as follows: Step S1: The coconut shell raw material was washed, dried, crushed, and sieved through a 100-mesh sieve. It was then placed in a tube furnace and pyrolyzed at a rate of 10℃ / min to 500℃ under a nitrogen atmosphere for 4 hours. After cooling, it was ground and sieved to obtain basic biochar. Step S2: The obtained basic biochar was mixed with 1 M hydrochloric acid solution at a solid-liquid ratio of 1:30 (g: mL). The mixture was magnetically stirred at room temperature for 24 hours. The product was repeatedly washed with deionized water until the filtrate was neutral. It was then dried at 60℃ for 24 hours. Finally, particles with a diameter of 4-8 mm were sieved to obtain hydrochloric acid-modified coconut shell biochar. Scanning electron microscopy (SEM) showed that the surface of the hydrochloric acid-modified coconut shell biochar was rougher, with a significantly increased and unevenly distributed pore structure, as shown in the attached figure. Figure 2Fourier transform infrared spectroscopy (FTIR) analysis showed that the modified biochar exhibited a stronger C≡C stretching vibration peak near 2340 nm, while the stretching peaks of C=O or C=C showed a redshift. The significantly increased intensity of the OH characteristic peak indicates a greater enrichment of oxygen-containing functional groups such as carboxyl groups on the surface, as shown in the attached figure. Figure 3 X-ray photoelectron spectroscopy (XPS) further confirmed the aforementioned trends in functional group changes. The C1s spectrum showed that the relative content of -COOH increased from 3.12% in BC to 5.85% in HBC; the O1s spectrum indicated that the relative content of C=O increased from 25.92% in BC to 32.43% in HBC. See attached figure for details. Figure 4 As shown in the attached figure. Furthermore, the pH value of the acid-modified biochar decreased significantly, its conductivity slightly decreased, and its Zeta potential shifted positively, indicating a reduction in ash content and a more positively charged surface. Figure 5 .

[0030] The system operates in an intermittent flow mode: water enters from the top, submerging the column, and exits from outlet 15 at the bottom, with an effective volume of 7 L; the hydraulic retention time is set to 72 h. Intermittent aeration is performed daily from 6:00-7:00 and 18:00-19:00 at a rate controlled at 0.6 L / min to regulate the redox environment within the system. To reduce the photolysis effect of light on target pollutants and control algal proliferation, the outside of the column is wrapped with black tape to simulate the dark environment of an actual wetland. During operation, the temperature is controlled at 20 ℃-25 ℃, the humidity is maintained at 60%-70%, and plant supplemental lighting is used to simulate natural light conditions.

[0031] To ensure stable influent water quality and good repeatability and comparability of the experiment, this invention uses artificially prepared synthetic wastewater as the influent source. The synthetic wastewater uses glucose as the organic carbon source, urea, ammonium sulfate, and potassium nitrate as the nitrogen source, and potassium dihydrogen phosphate as the phosphorus source. In addition, to maintain the normal growth of plants and microorganisms in the system, calcium and magnesium ions, as well as trace elements including iron, zinc, molybdenum, and copper, are supplemented into the influent. Specific components and proportions are shown in Table 1. The influent loads (mean ± standard deviation) were: NH4+-N: 20.09 mg / L ± 0.42 mg / L, NO3--N: 6.02 mg / L ± 0.10 mg / L, NO2--N: 0.00 mg / L ± 0.00 mg / L, TN: 30.19 mg / L ± 0.76 mg / L, TP: 3.01 mg / L ± 0.07 mg / L, COD: 210.28 mg / L ± 4.97 mg / L.

[0032] Table 1. Composition ratio of synthetic wastewater from constructed wetlands

[0033] After system startup, a 30-day microbial acclimatization period was implemented. Once the removal rates of COD, TN, NH4+-N, NO3--N, and TP in each system stabilized, formal testing commenced. During formal operation, SMX (theoretical concentration: 100 μg / L) was theoretically added to the influent, with an actual influent SMX load of 98.69 μg / L ± 5.35 μg / L, and an operating cycle of 30 days.

[0034] Comparative Example 1: Constructed wetland, denoted as CW1. The filler layers of CW1, from bottom to top, include: a coarse gravel support layer 1 (10 cm thick, 20-50 mm particle size); a fine gravel support layer 2 (5 cm thick, 4-8 mm particle size); an unmodified biochar layer 3 (5 cm thick, 4-8 mm particle size); a gravel layer 4 (20 cm thick, 4-8 mm particle size); an unmodified biochar layer 5 (5 cm thick, 4-8 mm particle size); and a fine sand layer 6 (10 cm thick, 1-2 mm particle size). The wetland plant 10 is *Iris tectorum*, approximately 25 cm tall, planted at a density of 5 plants per column in the fine sand layer 6. To monitor dissolved oxygen and water temperature in situ and achieve uniform aeration, a PVC perforated pipe 11 (61 cm high, 4 cm in diameter) is vertically installed at the center of the device, with its end connected to a microporous aeration disc 12. The perforated pipe 11 is covered with a mesh to prevent the packing material from clogging the holes. The aeration pump 13 is connected to the aeration holes 14 and the aeration disc 12 in sequence via silicone hoses to form a complete aeration circuit. Except for the absence of acid-modified biochar and DC power supply, the structure, operation mode and experimental conditions of CW1 are consistent with the aforementioned embodiments.

[0035] Comparative Example 2 The constructed wetland, designated CW2, comprises the following layers from bottom to top: a coarse gravel support layer 1 (10 cm thick, 20-50 mm particle size), a fine gravel support layer 2 (5 cm thick, 4-8 mm particle size), an acid-modified biochar layer 3 (5 cm thick, 4-8 mm particle size), a gravel and pyrite mixed layer 4 (20 cm thick, 4-8 mm particle size), an acid-modified biochar layer 5 (5 cm thick, 4-8 mm particle size), and a fine sand layer 6 (10 cm thick, 1-2 mm particle size). The wetland plant 10 is *Iris tectorum*, approximately 25 cm tall, planted at a density of 5 plants per column in the fine sand layer 6. To monitor dissolved oxygen and water temperature within the system in situ and ensure uniform aeration, a PVC perforated pipe 11 (61 cm high, 4 cm in diameter) is vertically installed at the center of the device, with its end connected to a microporous aeration disc 12. The perforated pipe 11 is covered with a mesh to prevent the packing material from clogging the holes. The aeration pump 13 is connected to the aeration holes 14 and the aeration disc 12 in sequence via silicone hoses to form a complete aeration circuit. Except for the absence of a DC power supply, the structure, operation mode, and experimental conditions of CW2 are consistent with those of the aforementioned embodiment.

[0036] Comparative experiments between the examples and the comparative examples I. Advantages of Electro-mediated Iron-Carbon Composite Filler Constructed Wetland Systems in Removing Basic Water Quality Indicators Based on continuous monitoring results of influent and effluent water samples from each system during the experiment, the removal efficiencies of CW1, CW2, and EC-CW systems for conventional water quality indicators such as COD, TP, TN, NH4+-N, NO3--N, and NO2--N are shown in the attached figure. Figure 6 As shown, all systems maintained stable processing performance during the 30-day operational period.

[0037] Comparative Example 1 (CW1) showed a certain removal effect on various basic water quality indicators in synthetic wastewater. Its average removal efficiencies for COD, TP, TN, NH4+-N and NO3--N were 85.63%±2.91%, 43.39%±5.99%, 74.81%±6.21%, 85.63%±5.90% and 85.72%±5.49%, respectively, and the concentration of NO2--N in the effluent was 0.69 mg / L±0.23 mg / L.

[0038] Compared to CW1, the system using acid-modified biochar and pyrite composite matrix (CW2) showed improved removal rates for most indicators. Results indicated that CW2 significantly improved the removal efficiency of COD, TP, TN, and NH4+-N compared to CW1. p<0.05), with average removal efficiencies increasing by 9.33%, 34.91%, 8.30%, and 9.17%, respectively, and the average NO₂⁻⁴ ... 2+ / Fe 3+ Pyrite reacts directly with PO3- to form insoluble iron phosphate precipitates such as FePO4; on the other hand, pyrite and its oxidation products (such as amorphous FeOOH) provide a large number of adsorption sites, forming a highly efficient phosphorus removal interface together with acid-modified biochar. It is noteworthy that NO3-N removal was actually reduced by 20.21%. This is mainly because pyrite, as an electron donor, strongly drives the adsorption of Fe3- and Fe4-. 2+ / S 2 The nitrification-denitrification process is based on autotrophic denitrification. However, in this process, due to electron competition in the sulfur / iron cycle, the apparent removal rate of NO3-N in the traditional nitrification-denitrification sequence decreases, and the actual total amount of nitrogen removed does not decrease.

[0039] The electrically conductive iron-carbon composite filler constructed wetland system (EC-CW) described in this embodiment of the invention exhibits superior comprehensive wastewater treatment efficiency. The system's average removal efficiencies for COD, TP, TN, NH4+-N, and NO3--N are 97.18%±0.65%, 76.81%±3.51%, 91.72%±3.12%, 98.72%±0.39%, and 75.45%±9.34%, respectively, with an average NO2--N concentration in the effluent of only 0.11 mg / L±0.07 mg / L. The introduction of a DC electric field comprehensively enhances system performance: In terms of carbon and nitrogen removal, the electric field improves electron transfer efficiency, further stimulates microbial activity, and promotes simultaneous nitrification and denitrification, thus significantly improving the removal rates of COD, TN, and NH4+-N; in terms of phosphorus removal, the electric field accelerates the dissolution of pyrite to release iron ions and regulates the local pH environment, enhancing the chemical precipitation and adsorption processes, thereby further improving the TP removal rate; in the nitrogen conversion pathway, the electric field optimizes the denitrification process, reduces the accumulation of NO2-N, and at the same time, by promoting the coupling of iron / sulfur cycling and denitrification, the NO3-N removal rate recovers compared to CW2, making the overall nitrogen removal capacity of the system more balanced and efficient.

[0040] II. Advantages of Electrolytically Conducted Iron-Carbon Composite Filler Constructed Wetland Systems for SMX Removal Based on the continuous monitoring results of SMX concentration in the influent and effluent water in this experiment, and combined with the analysis of SMX content in the matrix, plant roots and plant leaves in the system, the removal efficiency and migration distribution characteristics of different treatment systems for the target antibiotic can be systematically evaluated.

[0041] During the 30-day SMX addition and operation phase, the SMX removal effects of each system were as follows: Figure 7 As shown in Figure a. Specific effluent concentrations and removal rates were as follows: CW1 effluent concentration was 18.39 μg / L ± 2.89 μg / L, with an average removal rate of 80.27% ± 3.10%; CW2 effluent concentration was 9.23 μg / L ± 1.46 μg / L, with an average removal rate of 90.10% ± 1.57%; and EC-CW effluent concentration was 0.85 μg / L ± 0.45 μg / L, with an average removal rate of 99.09% ± 0.48%. The results indicate that CW2 significantly improved removal efficiency compared to CW1, while EC-CW showed the best removal effect. The effluent SMX concentration was far below the common surface water environmental risk threshold, demonstrating good ecological safety.

[0042] The distribution of SMX in various media of the system further revealed its migration and fixation patterns. The enrichment capacity of plant roots for SMX was as follows: EC-CW (616.07 μg / g ± 14.06 μg / g) > CW2 (410.43 μg / g ± 29.29 μg / g) > CW1 (295.09 μg / g ± 7.19 μg / g). The SMX content in leaves was as follows: EC-CW (28.46 μg / g ± 0.41 μg / g) > CW2 (15.19 μg / g ± 1.50 μg / g) > CW1 (7.99 μg / g ± 0.80 μg / g). This trend indicates that SMX can be absorbed by plant roots and migrate to the aboveground parts, but it is mainly enriched in the roots. Furthermore, electro-enhancing and iron-carbon composite significantly enhanced the root fixation capacity for SMX. The SMX contents in the matrix were CW1 (488.23 μg / kg ± 20.92 μg / kg), CW2 (684.44 μg / kg ± 26.66 μg / kg), and EC-CW (957.26 μg / kg ± 32.61 μg / kg), respectively. The composite of pyrite and acid-modified biochar effectively improved the adsorption capacity of the packing material, while the introduction of a DC electric field further promoted the electroadsorption and surface complexation of SMX on the packing surface, thereby enhancing its enrichment in the solid phase.

[0043] The improved performance of the CW2 system is mainly attributed to the multiple synergistic mechanisms introduced by pyrite: its surface active sites and oxidation products can strongly adsorb SMX; simultaneously, Fe... 2+ / S2 As an electron donor, pyrite can drive the reduction transformation of SMX or indirectly promote the free radical oxidation process; in addition, pyrite can also regulate the microbial community and enrich degrading bacteria. The further enhancement of the EC-CW system stems from the comprehensive synergistic effect of the DC electric field: the electric field greatly promotes the Fe... 2+ / Fe 3+ The redox cycle with S species not only continuously provides electrons and accelerates the chemical reduction of SMX, but also maintains a highly efficient Fenton-like reaction, generating more active free radicals (such as ·OH) to attack SMX molecules; the electric field also stimulates the metabolism of electroactive microorganisms, realizing the efficient coupling of electrochemical conversion and biodegradation, and enhancing the adsorption and fixation of pollutants on the surface of the packing material, creating a favorable micro-interface environment for deep degradation.

[0044] In summary, the electrically mediated iron-carbon composite filler constructed wetland exhibits multiple advantages in the removal of SMX: First, it achieves near-complete (99%) high-efficiency removal and deep purification; second, through multiphase distribution, SMX is mainly immobilized in the filler and plant roots, reducing the risk of environmental migration; finally, the system integrates multiple mechanisms such as adsorption, chemical redox, free radical attack, and biodegradation, forming a strong synergistic effect under the mediation of an electric field. These results fully validate the effectiveness, stability, and promising application prospects of this technical approach in enhancing the removal of novel organic pollutants by constructed wetlands.

[0045] III. Advantages of Electrodielectrically Conducted Iron-Carbon Composite Filler Constructed Wetland Systems in Removing ARGs This system not only efficiently removes SMX, but also shows significant removal and inhibition effects on its corresponding antibiotic resistance genes (ARGs). This invention selects two typical sulfonamide resistance genes (...). sul1 and sul2 ) and a key mobile genetic element ( intI1 Using this as an indicator, the synergistic advantages of electrically mediated iron-carbon composite matrix in controlling gene contamination were clarified by monitoring the absolute abundance of ARGs in the system matrix.

[0046] Within the system substrate, the retention and removal efficiencies of various constructed wetland systems for ARGs showed significant differences. In the CW1 substrate... intI1 , sul1 and sul2 The absolute abundances were (0.74±0.06)×10⁻⁶. 6 copies / g, (3.60±0.41)×10 6 copies / g and (0.94±0.18)×10 6copies / g; the abundance of the corresponding gene in the CW2 matrix decreased to (0.60±0.07)×10. 6 copies / g, (3.01±0.13)×10 6 copies / g and (0.75±0.09)×10 6 copies / g; while in the EC-CW system, all three decreased further to (0.52±0.09)×10 6 copies / g, (2.42±0.16)×10 6 copies / g and (0.59±0.12)×10 6 copies / g. The results showed that the introduction of iron-carbon composite filler enhanced the adsorption and fixation capacity of the matrix for ARGs, while the application of DC electric field enhanced the removal effect through multiple mechanisms: on the one hand, the micro-electrolysis effect driven by the electric field promoted the removal of Fe²⁺. + / Fe³ + Cyclic and reactive oxygen species (such as ·OH) are generated, directly oxidizing and degrading adsorbed ARG fragments; on the other hand, the electric field can change the microbial membrane potential and community structure, inhibiting the attachment of host bacteria carrying ARGs and biofilm formation, and interfering with... intI1 The mediated horizontal gene transfer process. In addition, changes in the organic load of the system influent affect the abundance of ARGs host bacteria and the competition for adsorption sites on the packing material, but the EC-CW system shows stronger resistance to load shocks.

[0047] In summary, the electromediated iron-carbon composite filler system demonstrates the following core advantages in controlling ARGs: First, synergistic matrix adsorption and electrochemical degradation: the iron-carbon filler provides a high-capacity adsorption site, enabling rapid immobilization of ARGs; the DC electric field promotes the degradation and inactivation of immobilized ARGs through multiple pathways, including oxidation by reactive oxygen species and regulation of microbial communities. Second, microenvironment regulation and gene transfer inhibition: the system alters the local microenvironment through redox reactions and utilizes the electric field effect to directly inhibit the attachment of host bacteria and the horizontal transfer of moving genetic elements, thus curbing the spread of ARGs from the propagation pathway. These results confirm that this composite matrix system not only efficiently removes antibiotic pollutants but also achieves multi-stage control over the generation, storage, and transfer of ARGs through the synergistic effect of materials and the electric field, providing an efficient and stable technical solution for the treatment of combined antibiotic and resistance gene pollution in water bodies.

[0048] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A method for preparing hydrochloric acid-modified coconut shell biochar, characterized in that, Includes the following steps: S1: The coconut shell is cleaned, dried, crushed and sieved, then pyrolyzed in an inert gas atmosphere, cooled and ground and sieved to obtain basic biochar. S2: Mix the obtained basic biochar with hydrochloric acid solution, stir magnetically at room temperature, wash repeatedly with deionized water until the filtrate is neutral, dry, and sieve to obtain hydrochloric acid modified coconut shell biochar.

2. The method according to claim 1, characterized in that, The inert gas is nitrogen, which is pyrolyzed at 500℃ with a heating rate of 10℃ / min.

3. The method according to claim 1, characterized in that, The hydrochloric acid concentration is 1 M, and it is mixed at a solid-liquid ratio of 1 g: 30 mL; the particles with a diameter of 4-8 mm are sieved.

4. An iron-carbon composite filler for constructed wetland systems, characterized in that, The hydrochloric acid-modified coconut shell biochar particles, natural pyrite particles, and gravel described in any one of claims 1-3 are laid in layers.

5. An electrically mediated iron-carbon composite filler constructed wetland system for removing sulfonamide antibiotics and resistance genes, characterized in that, The system is a vertical subsurface flow structure. The main body of the system is a cylindrical container. From bottom to top, the system includes: a coarse gravel support layer, a fine gravel support layer, a biochar layer, a gravel layer or a mixed gravel and pyrite layer, a biochar layer, and a fine sand layer planted with wetland plants. The anode and cathode are located in the biochar layer. The anode and cathode are connected to an adjustable DC power supply. A microporous aeration disc is set at the bottom, and an aeration pump is connected to the aeration disc. A perforated pipe is set at the top of the aeration disc. The perforated pipe has evenly distributed air holes and runs through each layer from the bottom to the top, finally exiting from the top of the fine sand layer. The perforated pipe is covered with a mesh. An outlet is set at the bottom of the system. The biochar layer is made of hydrochloric acid modified coconut shell biochar particles as described in any one of claims 1-3.

6. The system according to claim 5, characterized in that, Coarse gravel with a particle size of 20 mm-50 mm and a laying thickness of 10 cm; fine gravel with a particle size of 4 mm-8 mm and a laying thickness of 5 cm.

7. The system according to claim 5, characterized in that, The volume ratio of pyrite to gravel is 1:1, with pyrite particles ranging from 4 mm to 8 mm in diameter and gravel particles ranging from 4 mm to 8 mm in diameter.

8. The system according to claim 5, characterized in that, The hydrochloric acid-modified coconut shell biochar layer is 5 cm thick, the fine sand particle size is 1 mm-2 mm, the fine sand layer thickness is 5 cm, and the wetland plant is yellow iris.

9. The system according to claim 5, characterized in that, The cathode and anode are titanium mesh electrodes.

10. A method for using the constructed wetland system according to any one of claims 5-8 to remove sulfonamide antibiotics and resistance genes from water, characterized in that... The system operates in an intermittent flow mode: water is introduced from the top to submerge the system, the hydraulic retention time is set to 72 hours, and intermittent aeration is carried out daily from 6:00 to 7:00 and from 18:00 to 19:00, with the rate controlled at 0.6 L / min. During operation, the temperature is controlled at 20℃-25℃, the humidity is maintained at 60%-70%, and plant grow lights are used to simulate natural light conditions, with a DC voltage of 0.3 V applied.

Images