Iron-carbon micro-electrolysis coupling soil infiltration system, application and sewage treatment method

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to an iron-carbon micro-electrolysis coupling soil infiltration system, application and a sewage treatment method. According to the technical scheme, the iron-carbon micro-electrolysis coupling soil infiltration system sequentially comprises a soil covering layer, a gravel water cloth layer, a matrix filler layer and a gravel supporting layer from top to bottom. And the matrix filler layer is at least filled with iron-carbon filler. The invention further provides application of the iron-carbon micro-electrolysis coupled soil infiltration system in sewage treatment and a sewage treatment method. The main purpose of the invention is to provide a new choice for removal of pollutants in domestic sewage and emission reduction of greenhouse gases.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and in particular relates to an iron-carbon micro-electrolysis coupled soil infiltration system, its application and sewage treatment method. Background Art

[0002] my country's high-altitude cold regions, including Qinghai, Tibet, and parts of Sichuan, Yunnan, Gansu, and Xinjiang, are characterized by low temperatures, low oxygen levels, and strong ultraviolet radiation. As rural living standards improve, sewage discharge increases, but inadequate sewage systems and treatment facilities lead to low sewage treatment rates. The direct discharge of untreated domestic wastewater threatens the ecology and public health, and the greenhouse gases generated by existing treatment systems exacerbate environmental pressures. There is an urgent need to improve treatment efficiency and address technical challenges such as low-temperature operation and low carbon-to-nitrogen ratios.

[0003] Wastewater in high-altitude rural areas is divided into graywater (50-80% containing washing pollutants) and blackwater (30% including aquaculture toilet wastewater). Treatment methods primarily include biological processes (activated sludge, biofilm) and ecological processes (constructed wetlands, etc.). Biological processes are costly and difficult to popularize. While ecological processes are the mainstream, they are still subject to fluctuations in water quality, climatic conditions, large land requirements, and temperature sensitivity.

[0004] Alpine regions should adopt a dual model of meeting discharge standards and resource utilization. Dispersed agricultural areas should adopt resource utilization, while densely populated areas should meet pollution prevention standards. Direct discharge of pollutants leads to excessive nitrate levels in groundwater, eutrophication of surface water, and soil degradation. Despite national efforts to improve environmental performance, facilities generally face technical challenges, costly operations and maintenance, and poor management. There is an urgent need to develop low-cost, energy-efficient, and easy-to-maintain treatment technologies. Summary of the Invention

[0005] In response to the problems existing in the existing technology, the present invention provides an iron-carbon micro-electrolysis coupled soil infiltration system, application and sewage treatment method to solve the problem that the existing technology is not effective in removing pollutants from domestic sewage in high-altitude and cold areas and reducing greenhouse gas emissions. It can also solve the problem of insufficient adaptability of microorganisms to the environment.

[0006] The technical solution of the present invention is as follows: The present invention provides an iron-carbon micro-electrolysis coupled soil infiltration system, which includes, from top to bottom, a soil cover layer, a gravel water cloth layer, a matrix filler layer and a gravel support layer; the matrix filler layer is at least filled with iron-carbon filler. Through the careful design of the iron-carbon micro-electrolysis coupled soil infiltration system, the top soil cover layer can initially intercept some pollutants, the gravel water cloth layer plays a filtering and supporting role, and the iron-carbon filler added to the key matrix filler layer, on the one hand, utilizes the principle of iron-carbon micro-electrolysis, iron and carbon form countless tiny primary batteries in the sewage, producing a strong redox effect, causing the complex organic matter in the sewage to break and decompose, reducing toxicity and improving biodegradability; on the other hand, the iron-carbon filler provides a special environment for microorganisms, screens out microbial populations adapted to high redox potentials and specific matrices, promotes microbial metabolic activities, and synergistically degrades remaining organic pollutants. At the same time, it inhibits the activity of greenhouse gas-producing bacteria such as methanogens, reduces the emission of greenhouse gases such as methane, and ultimately achieves significant results in efficient removal of pollutants in sewage and reduction of greenhouse gas emissions. The addition of iron-carbon fillers has a screening effect on microorganisms, causing microorganisms to develop towards a favorable population that adapts to the system environment.

[0007] Preferably, the matrix filler layer also includes zeolite filler. The matrix filler layer is composed of filler and soil, with the filler to soil volume ratio being 1:2. The soil cover layer is composed of soil. The gravel water layer is composed of gravel filler, and the gravel support layer is composed of gravel filler, with a particle size of 4-6 mm. By carefully arranging the filler layers, the stability of the iron-carbon micro-electrolysis coupled soil infiltration system can be increased, reducing maintenance costs and workload. Preferably, the matrix filler layer is composed of iron-carbon filler, zeolite filler, and soil, with the zeolite filler layer located in the upper layer and the iron-carbon filler layer located in the lower layer. Both the zeolite filler layer and the iron-carbon filler layer are doped with soil. Water injection is used to promote natural soil settling and compaction within the iron-carbon filler and zeolite filler. This layered design leverages the zeolite's efficient adsorption properties to prioritize the interception of pollutants in the water. The iron-carbon filler's reduction action then further degrades and transforms the pollutants. Combined with the soil's biological purification capabilities, this achieves multi-stage pollutant treatment, significantly improving water purification efficiency and the system's overall ecological function. Preferably, the volume ratio of the zeolite filler layer to the iron-carbon filler layer is 1~3:1~3. The volume ratio of the zeolite filler layer to the iron-carbon filler layer is 3:1, 1:1 or 1:3. Preferably, the volume ratio of the zeolite filler layer to the iron-carbon filler layer is 1:1. Preferably, the mass ratio of Fe / C in the iron-carbon filler is 3~5:1. Preferably, the mass ratio of Fe / C in the iron-carbon filler is 3:1. Preferably, the soil is brown soil, the organic matter content of the soil is greater than 8%, the nitrogen content is greater than 0.4%, the phosphorus content is greater than 0.2%, the potassium content is greater than 17%, and the pH value is greater than 5%.

[0008] Preferably, the organic matter content of soil is 8.46%, nitrogen content is 0.469%, phosphorus content is 0.25%, potassium content is 17.4%, and pH value is 5.94%. By rationally matching the volume ratio of zeolite packing layer and iron-carbon packing layer, and using organic-rich brown soil as soil, the adsorption performance of zeolite and the reduction performance of iron-carbon can be fully utilized, while providing a good growth environment for microorganisms with the help of high organic matter brown soil, thereby significantly improving the water purification effect and the stability of the ecosystem, and achieving efficient and stable ecological restoration and water purification functions. Preferably, the volume ratio of soil cover layer, gravel water cloth layer, matrix filler layer and gravel support layer is 1:1:16:2. Preferably, the thickness of soil cover layer, gravel water cloth layer, matrix filler layer and gravel support layer is 5cm, 5cm, 80cm and 10cm respectively. By rationally allocating the volume ratio or thickness of each layer, the ecological function of the soil and the drainage and support functions of the gravel can be effectively exerted, while the purification capacity of the matrix filler layer can be fully utilized, achieving an optimal balance between ecological function and engineering performance, and improving the stability and operational efficiency of the system. Preferably, the iron-carbon micro-electrolysis coupled soil infiltration system has at least one of the following characteristics: the particle size of the iron-carbon filler is 8~12mm; the particle size of the zeolite filler is 4~8mm. By rationally selecting the particle size of the iron-carbon filler and the zeolite filler, the porosity and water flow permeability of the filler layer can be effectively improved, while ensuring sufficient contact between the filler and the pollutants, thereby enhancing the pollutant removal efficiency and operational stability of the system. Preferably, the iron-carbon micro-electrolysis coupled soil infiltration system also includes a water inlet and a water outlet; the water inlet is located in the gravel water cloth layer, 7cm from the upper surface of the soil cover layer; the water outlet is located in the gravel support layer, 3cm from the bottom of the gravel support layer. By strategically positioning the inlet and outlet, hydraulic load and dry-wet ratio can be more effectively adjusted, enabling the iron-carbon micro-electrolysis coupled soil infiltration system to achieve optimal removal of wastewater pollutants and greenhouse gas emissions reduction, effectively treating domestic sewage. By properly positioning the inlet and outlet, even water distribution and adequate filtration are ensured, improving the system's overall purification efficiency and stability.

[0009] The present invention also provides for the application of an iron-carbon micro-electrolysis coupled with soil infiltration system in sewage treatment. This system can fully leverage the efficient reduction and degradation effects of iron-carbon micro-electrolysis and the biological purification function of soil infiltration to achieve synergistic removal of multiple pollutants in sewage, significantly improving sewage treatment efficiency and effluent quality. It offers the advantages of low operating costs, simple operation, and environmental friendliness.

[0010] The present invention also provides a sewage treatment method, comprising the following steps: S1, inoculating and cultivating activated sludge in domestic sewage in a high-altitude cold region; S2, introducing the domestic sewage inoculated with the cultivated activated sludge in the high-altitude cold region into the iron-carbon micro-electrolysis coupled soil infiltration system of the present invention for treatment and then discharging the treated sewage from the water outlet after meeting the standards, wherein the hydraulic load of the iron-carbon micro-electrolysis coupled soil infiltration system is 0.001~0.01 m 3 / m 2 ·h, dry-wet ratio is 1~5:1; the pH value of domestic sewage in high-altitude cold areas is 6.5~8.0, SS is 100~200mg / L, COD is 200~450mg / L, BOD5 is 200~300mg / L, NH4 + -N is 20-90 mg / L, and TP is 2.0-6.5 mg / L. Aiming at the characteristics of domestic sewage in high-altitude cold regions, this system effectively solves the sewage treatment challenges in these regions by inoculating activated sludge and treating it using an iron-carbon micro-electrolysis coupled soil infiltration system, combined with appropriate hydraulic load, dry-wet ratio, and temperature conditions, ensuring that sewage discharge meets standards. It boasts the advantages of high efficiency, stability, strong adaptability, and environmental friendliness.

[0011] The main function of inoculated sludge is to cultivate denitrifying bacteria, which work in the matrix filler layer. The functions of denitrifying bacteria in sewage treatment include: 1) Ammonification. Many organic nitrogen compounds such as proteins and amino acids cannot be directly absorbed and utilized by microorganisms. Denitrifying bacteria can decompose these complex organic nitrogen into ammonia nitrogen (NH4 + For example, during the decomposition of proteins, denitrifying bacteria secrete a variety of enzymes to hydrolyze proteins into peptides and amino acids, ultimately releasing ammonia. 2) Nitrification, converting ammonia nitrogen into nitrate nitrogen (NO3 - This process is usually divided into two stages: Nitrification: ammonia oxidizing bacteria (such as nitrite bacteria) convert ammonia (NH3) or ammonium ions (NH4 + ) is oxidized to nitrite (NO2 - For example, under suitable temperature, pH and dissolved oxygen conditions, nitrite bacteria use enzymes such as ammonia monooxygenase in their cells to oxidize ammonia into nitrite. Nitrification: Nitrite bacteria further oxidize nitrite into nitrate (NO3 -Nitrate bacteria convert nitrite to nitrate through the action of enzymes such as nitrite oxidase. 3) Denitrification reduces nitrate nitrogen to gaseous nitrogen (such as N2, NO, and NO), thereby removing nitrogen from water. Under anoxic conditions, denitrifying bacteria use nitrate as an electron acceptor to reduce nitrate to nitrite, and then further to gaseous nitrogen. For example, during the denitrification process, denitrifying bacteria use organic matter as an electron donor and, through a series of enzymatic reactions, ultimately convert nitrate to nitrogen gas, which is released into the atmosphere. Through these actions, denitrifying bacteria can effectively reduce the nitrogen content in wastewater, reduce nitrogen pollution in water bodies, prevent eutrophication, and thus improve water quality. Furthermore, denitrifying bacteria work synergistically with other microorganisms in wastewater treatment systems to form complex microbial communities that collectively remove pollutants such as organic matter, nitrogen, and phosphorus from wastewater, improving wastewater treatment efficiency. The activated sludge was obtained from a mixed sludge of anaerobic and aerobic tanks at a mass ratio of 1:1 from a sewage treatment plant in Danma Town, Huzhu County, Haidong City, Qinghai Province. The activated sludge contained a mixture of bacteria from both anaerobic and aerobic tanks.

[0012] Furthermore, the iron-carbon micro-electrolysis coupled soil infiltration system is operated to control the hydraulic load to 0.001m 3 / m 2 h, 0.003m 3 / m 2 h, 0.006m 3 / m 2 h or 0.01 m 3 / m 2 ·h; the dry-wet ratio is 5:1, 3:1 or 1:1. Preferably, the hydraulic load is 0.003m 3 / m 2 h, with a dry-wet ratio of 5:1. By precisely controlling the hydraulic load and dry-wet ratio during system operation, efficient pollutant removal and stable system operation can be achieved, while reducing energy consumption and operating costs.

[0013] The beneficial effects of the present invention are as follows: the iron-carbon micro-electrolysis coupled soil infiltration system of the present invention can very effectively treat domestic sewage, can efficiently remove pollutants in sewage, and reduce greenhouse gas emissions; the iron-carbon micro-electrolysis coupled soil infiltration system of the present invention also has good denitrification capacity; the filler type and soil depth significantly affect the structure of the microbial community, and the addition of iron-carbon filler has a screening effect on microorganisms, allowing the microorganisms to develop towards a population adapted to the environment. In the field of sewage treatment technology, it has promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1Schematic diagram of the experimental soil and filler shapes: (a) gravel, (b) soil, (c) iron-carbon, and (d) zeolite; Figure 2 This is a schematic diagram of the structure of the iron-carbon micro-electrolysis coupled soil infiltration system; Figure 3 The COD concentration change diagram at different HL stages; Figure 4 The COD concentration change diagram at different D / W stages; Figure 5 The graph of COD concentration and removal rate changes in experimental columns with different fillers is shown in Figure 2. The bar graph represents the concentration, and the scatter plot represents the removal rate. Figure 6 NH4 in different HL stages + -N concentration change diagram; Figure 7 NH4 at different D / W stages + -N concentration change diagram; Figure 8 NH4 for different filler experimental columns + -N concentration and removal rate change diagram, where the bar graph represents the concentration and the scatter plot represents the removal rate; Figure 9 NO3 for different HL stages - -N concentration change diagram; Figure 10 NO3 for different D / W stages - -N concentration change diagram; Figure 11 For different filler experimental columns NO3 - -N concentration change diagram; Figure 12 NO2 in different HL stages - -N concentration change diagram; Figure 13 NO2 for different D / W stages - -N concentration change diagram; Figure 14 NO2 for different filler experimental columns - -N concentration change diagram; Figure 15 This is the graph showing the change of TN concentration at different HL stages; Figure 16 The graph of TN concentration changes at different D / W stages; Figure 17 This is a graph showing the changes in TN concentration and removal rate of experimental columns with different fillers. The bar graph represents the concentration, and the scatter plot represents the removal rate. Figure 18 This is a graph showing the changes in TP concentration at different HL stages; Figure 19 is the graph showing the change of TP concentration at different D / W stages; Figure 20 This is a graph showing the changes in TP concentration and removal rate of experimental columns with different fillers. The bar graph represents the concentration, and the scatter plot represents the removal rate. Figure 21 The CH4 emission flux changes in different HL stages; Figure 22 The CH4 emission flux change diagram at different D / W stages; Figure 23 This is the CH4 emission flux change diagram of the experimental column with different fillers; Figure 24 The N2O emission flux changes in different HL stages; Figure 25 The N2O emission flux change diagram at different D / W stages; Figure 26This is the N2O emission flux change diagram of the experimental columns with different fillers; Figure 27 The left picture is the SEM analysis picture of the original zeolite packing after magnification of 20,000 times, and the right picture is the SEM picture of the zeolite packing in column 5 after magnification of 5,000 times; Figure 28 The left picture is the SEM analysis picture of the iron-carbon filler. The left picture is the SEM picture of the original iron-carbon filler after magnification of 20,000 times. The left picture is the SEM picture of the iron-carbon filler in column 5 after magnification of 5,000 times. Figure 29 The XPS spectrum of the original iron-carbon filler; Intensity: strength; Binding energy: binding energy; Figure 30 This is the XPS spectrum of the iron-carbon filler in the lower layer of the experimental column; Intensity: strength; Binding energy: binding energy; Figure 31 Dilution curve graph; Sobs index: observed species index; Number of Reads Sampled: number of sampled reads; Rarefaction curves: dilution curve; Figure 32 It is the Venn diagram between samples at different depths; Figure 33 This is the principal component analysis diagram of the sample genus components; PCA on Genus level: principal component analysis at the genus level; Figure 34 Clustering tree on genus level (>1%); Hierarchical clustering tree on Genus level: hierarchical clustering tree on genus level; Tree Plot: dendrogram; Group: group; Taxa: classification unit; Figure 35 Relative abundance on Phylum level: relative abundance of major microbial communities in different samples (>1%). Figure 36 Relative abundance on Class level: relative abundance of the main microbial communities in different samples at the class level (>1%); Figure 37 Relative abundance on Genus level: Relative abundance on Genus level of the main microbial communities in different samples (>1%). Figure 38 Redundancy analysis diagram of microbial community structure and environmental factors; RDA on Genus level: genus level redundancy analysis; COD Concentration: COD concentration; COD Removed efficiency: COD removal efficiency; Time (days): time (days); stage: stage; NH4 +-N Concentration: NH4 + -N concentration; NH4 + -NRemoved efficiency: NH4 + -N removal efficiency; TN Concentration: TN concentration; TN Removed efficiency: TN removal efficiency; TP Concentration: TP concentration; TP Removed efficiency: TP removal efficiency. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below by way of examples, but the present invention is not limited thereto in any way.

[0016] The following experimental materials and water quality were used: Experimental Materials: Soil: air-dried and then passed through a 2mm sieve. Its cross-section color changes slightly, with the surface layer showing gray-brown and the lower layer mainly transitioning from brown to light brown. Soil properties: brown soil; organic matter content 8.46%; nitrogen content 0.469%; phosphorus content 0.25%; potassium content 17.4%; pH value 5.94. Soil shape see Figure 1 (b). Use gravel filler with specifications of 4-6mm, zeolite filler with specifications of 4-8mm, and iron-carbon filler with specifications of 8-12mm. The shapes are shown in Figure 1 (a), 1 (d) and 1 (c). The mass ratio of Fe / C in the iron-carbon filler is 3-5:1. Water quality of rural domestic sewage in high-altitude cold areas: pH: 6.5-8.0; SS: 100-200 mg / L; COD: 200-450 mg / L; BOD5: 200-300 mg / L; NH4 + -N: 20~90 mg / L; TP: 2.0~6.5 mg / L.

[0017] Example 1 like Figure 2As shown, an iron-carbon micro-electrolysis coupled soil infiltration system includes a soil column device with a diameter of 20 cm and a height of 100 cm, and is made of organic glass. A 5 cm space is reserved at the top of the soil column to prevent soil leakage, the water inlet is located 7 cm from the upper surface of the soil cover, and the water outlet is 3 cm from the bottom. Five matrix sampling points are set, and the sampling points are 10 cm from the soil surface at point a, 30 cm from point b, 50 cm from point c, 70 cm from point d, and 90 cm from point e. In this embodiment, a total of 6 soil columns are set, respectively named 1# column, 2# column, 3# column, 4# column, 5# column, and 6# column, wherein 1# column, 4# column, 5# column, and 6# column are used as examples, and 2# column and 3# column are used as control examples. From top to bottom, the soil column device is composed of a 5 cm soil cover layer, a 5 cm gravel water distribution layer, an 80 cm matrix filler layer, and a 10 cm gravel support layer. The matrix packing layer of column 3 was filled with 80 cm of gravel, the matrix packing layer of column 1 was filled with 80 cm of iron-carbon packing, and the matrix packing layer of column 2 was filled with 80 cm of zeolite packing. The matrix packing layers of columns 4, 5, and 6 were filled with zeolite:iron-carbon packing in a volume ratio of 3:1, 1:1, and 1:3, respectively. Both the zeolite and iron-carbon packings in the matrix packing layers were doped with soil, with the volume ratio of zeolite to soil being 1:2 for each. To prevent short-circuit effects from affecting the reliability of the experimental data, petroleum jelly was evenly applied to the inner walls of the columns before filling to enhance sealing. After filling, water was injected to promote natural soil settlement and compaction. To simulate a dark environment, the soil columns were wrapped in aluminum foil to prevent light from entering the soil before the actual experiment.

[0018] Example 2 A sewage treatment method, comprising the following steps: S1, inoculating and cultivating activated sludge in domestic sewage in high-cold areas; S2, introducing the domestic sewage in high-cold areas inoculated with activated sludge into the water inlets of columns 1#, 2#, 3#, 4#, 5# and 6# in the iron-carbon micro-electrolysis coupled soil infiltration system in Example 1, so as to treat domestic sewage in high-cold areas; wherein, the cultivated activated sludge is taken from the anaerobic tank and aerobic tank of the sewage treatment station in Danma Town, Danma Town, Huzhu County, Qinghai Province, Haidong City, with a mass ratio of 1:1; the inoculated sludge is mainly used to cultivate denitrifying bacteria. Water quality of domestic sewage in high-cold areas: C / N=5 in the influent water sample, COD is 250 mg / L, TN is 50 mg / L, NH4 + -N is 50mg / L, BOD5 is 250mg / L, TP is 4.5mg / L, pH is 7.5, and SS is 150mg / L. During the treatment of domestic sewage in high-altitude areas, the NH4 + -N, TN, TP, COD, NO3 - -N, NO2 --N was tested, and the system was considered stable after the effluent quality remained stable for one week. The operating parameters of the iron-carbon micro-electrolysis coupled soil infiltration system are shown in Table 1.

[0019] Table 1 Operating parameters of the iron-carbon micro-electrolysis coupled soil infiltration system Pollutant removal effect analysis: The water quality of the inlet and outlet of the domestic sewage in the high-altitude cold region after treatment with different hydraulic loads and dry-wet ratios in Example 2 was measured. 0.5L of water samples were collected from the inlet and outlet every two days using 200mL polyethylene plastic bottles. All samples were tested on the day of sampling. Monitoring indicators include chemical oxygen demand (COD), ammonia nitrogen (NH4 + -N), nitrate nitrogen (NO3 - -N), nitrite nitrogen (NO2 - -N), total nitrogen (TN), total phosphorus (TP) and pH value, the determination method is the method specified in the "Water and Wastewater Monitoring and Analysis Methods (Fourth Edition)". pH is determined by PHS-3C using the electrode method, COD is determined by the Hach digestion instrument using the rapid digestion spectrophotometry method, NH4 + -N, NO2 - -N, NO3 - -N and TN were determined by UV-visible spectrophotometry using Nash reagent spectrophotometry (HJ665-2013), naphthylethylenediamine hydrochloride spectrophotometry (HJ668-2013), UV spectrophotometry (HJ / T346─2007), and alkaline potassium persulfate spectrophotometry (HJ636-2012), respectively. TP was determined by TOC-LCPH using ammonium molybdate spectrophotometry (HJ670-2013).

[0020] 1. Analysis of COD removal effect: 1) The influence of hydraulic load (HL) on COD removal effect. The changes of COD influent concentration and effluent concentration under different HL are as follows: Figure 3 As shown in the figure, the COD effluent concentration decreases significantly with the decrease of water HL. The decrease of HL significantly increases the contact time between COD and filler matrix. This change not only promotes the adsorption of COD by filler, but also creates more favorable conditions for microbial degradation of COD. Then, the removal rate of COD at different HL stages increases with the decrease of HL from 0.01m 3 / m 2 h(Ia) reduced to 0.001m 3 / m 2h (Id), COD removal efficiency showed an overall upward trend. This shows that as HL decreases, COD removal efficiency gradually improves and maintains a high removal efficiency throughout the experimental period. 2) Effect of dry-wet ratio on COD removal efficiency. COD influent concentration and effluent concentration under different D / W are shown in Figure 2. Figure 4 As shown, as the D / W ratio decreases from 5:1 (IIa) to 1:1 (IIc), the COD effluent concentration in the six experimental columns gradually increases over time under steady-state conditions. This indicates that the decrease in D / W ratio leads to a decrease in the system's DO content, which is detrimental to the oxidative decomposition of COD. Furthermore, as the influent time increases, the duration of hydraulic scouring on the filler matrix also increases. This change in hydraulic conditions reduces the matrix's COD adsorption efficiency. Furthermore, the COD removal rates at different D / W levels show that, under steady-state conditions, the COD removal rates of the six experimental columns decrease with decreasing dry-wet ratios. This indicates that while the decrease in D / W ratio prolongs the influent time and leads to a decrease in COD removal, the overall removal rate is not significantly affected and remains high. 3) Influence of filler on COD removal. Figure 5 The COD effluent concentration and removal efficiency change trends of different filler experimental columns in each HL stage and D / W stage are shown. - When -N and organic matter coexist in the reaction system, two chemical reactions can occur: 10Fe 2+ +6H2O+2NO3 - =10Fe 3+ +12OH - +N2 (I)8Fe 3+ + organic matter + 4H2O = 8Fe 2+ +2HCO3 - +9H + (II) Once the above reaction reaches a steady state, the system not only effectively controls the accumulation of specific Fe ions but also significantly improves the removal efficiency of organic pollutants. Consequently, the effluent concentration of the control group was higher than that of the experimental columns loaded with iron-carbon fillers. The abnormally high effluent concentration of column 1 may be due to the iron-carbon fillers providing fewer microbial growth sites, resulting in a much lower microbial population than in the other experimental columns.

[0021] 2. NH4 + -N removal effect analysis: 1) HL to NH4 + -N removal effect. NH4 + -N inlet and outlet concentrations at different HL stages are as follows Figure 6 As shown, with the decrease of HL, the NH4 + -N effluent concentration decreases accordingly. The contact time between sewage and filler matrix increases with the decrease of HL, which is beneficial to NH4 +-N is better adsorbed by the filler. At the same time, it is beneficial to the reoxygenation of the system, promoting the nitrification process of nitrifying bacteria, and achieving the goal of NH4 + -N is better removed. It can be seen that NH4 + -N removal rate at different HL stages, with the decrease of HL, NH4 + -N removal rate gradually increases. 2) Dry-wet ratio of NH4 + -N removal effect. NH4 + -N inlet and outlet concentrations at different D / W stages are as follows Figure 7 As shown, the NH4 + -N effluent concentration increases with the decrease of D / W. Because the water inlet time of the system is prolonged with the decrease of D / W, it is not conducive to the reoxygenation of the system, which in turn inhibits the metabolic activity of nitrifying bacteria, and ultimately leads to the obstruction of nitrification reaction and the increase of effluent pollutant concentration. It can be seen that NH4 + -N removal rate at different D / W stages, with the decrease of D / W, NH4 + -N removal rate also gradually decreased. + The removal rate of -N showed a certain downward trend, but even the removal rate of the iron-carbon group (1#) with the lowest removal effect was above 80%, indicating that NH4 + -N removal will be affected by D / W, but the overall removal rate is within an acceptable range. 3) Filler removal of NH4 + -N removal effect. NH4 at each stage of the experimental column with different fillers + -N effluent concentration and removal rate are as follows Figure 8 As shown, the stability period of NH4 + The average effluent concentration of -N is: 1#>6#>5#>4#>2#>3#. It can be seen that the experimental column with iron-carbon filler and zeolite filler has NH4 + -N effluent concentration is higher than that of column 3#. NH4 + -N removal is mainly through the nitrification of microorganisms, and the iron-carbon filler and zeolite filler can provide a huge living space and a good living environment for nitrifying bacteria to meet the activities of nitrifying bacteria; in addition, the Fe 3+ It can also act as an electron acceptor to promote NH4 + -N oxidation, zeolite can better adsorb NH4 through the exchange of cations + -N. Therefore, the combination of iron carbon filler and zeolite filler helps NH4 + -N removal, where the lowest effluent concentration is 1.73 mg / L. Fe can remove part of NO3 - -N and NO2 - -N is reduced to NH4 + -N, NO3- -N and NO2 - -N is reduced to NH4 + -N reaction formula: 4Fe+7H2O+NO3 - =4Fe 2+ +10OH - +NH4 + (III) 3Fe+8H + +NO2 - =3Fe 2+ +2H2+NH4 + (IV). Therefore, the experimental column NH4 + -N effluent concentration is higher than that of column 3#.

[0022] 3. NO3 - -N removal effect analysis: 1) Hydraulic load on NO3 - -N removal effect. Different HL stages NO3 - -N effluent concentration as Figure 9 As shown, six groups of experimental columns NO3 - The effluent concentration of -N decreases with the decrease of HL. Since the soil is negatively charged, it is difficult to adsorb the negatively charged NO3 - -N, and the reduction of HL is beneficial to strengthening the soil's resistance to NO3 - -N adsorption. Therefore, when HL decreases, NO3 - -N concentration in the effluent also decreases. 2) Effect of dry-wet ratio on NO3 - -N removal effect. NO3 at different D / W stages - -N effluent concentration is as follows Figure 10 As shown, with the decrease of D / W, the NO3 - The effluent concentration of -N gradually increases. As the D / W value decreases, the water inflow duration is correspondingly prolonged, and the continuous water flow has a scouring effect on the filler, causing the NO3 originally attached to the filler surface to - -N is stripped and discharged with the effluent. 3) Filler to NO3 - -N removal effect. NO3 at each stage of the experimental column with different fillers - -N effluent concentration is as follows Figure 11 As shown in the figure, due to the low carbon-nitrogen ratio (C / N) of sewage, the denitrification process lacks sufficient carbon source supply, resulting in NO3 - -N continues to accumulate in the system and is discharged with the effluent. - The order of NO3 effluent concentration is: 3#>2#>4#>5#>6#>1#. Among them, the NO3 --N concentration is always higher than that of other experimental groups and remains at a high level for a long time. This shows that the addition of iron-carbon filler can significantly improve the denitrification efficiency, thereby reducing NO3 - -N residual. Iron (Fe) in the iron-carbon filler acts as an anode to release electrons in the reduction reaction, providing sufficient electron source for the denitrification process, promoting NO3 - It is reduced as an electron acceptor and removed. At the same time, the micro-electrolysis system will generate a large amount of reduced hydrogen atoms [H] and Fe 2+ / Fe 3+ The autotrophic microorganisms in the system can use these substances as electron donors to carry out autotrophic denitrification, converting NO3 - -N is eventually reduced to N2. In addition, Fe 2+ / Fe 3+ It can enhance the metabolic activity of microorganisms and further improve the denitrification efficiency of the system. The activated carbon component in the iron-carbon filler can also serve as a supplementary carbon source, providing the necessary organic matter support for the metabolic activities of the denitrifying bacteria. This characteristic enables activated carbon to play a dual role in the process of enhancing biological denitrification: as both an electron transfer medium and a carbon source supplier that can be used by microorganisms. Therefore, the addition of iron-carbon filler has a great effect on NO3 - -N removal has an excellent effect.

[0023] 4. NO2 - -N removal effect analysis: 1) Hydraulic load on NO2 - -N removal effect: NO2 at different HL stages - -N effluent concentration as Figure 12 As shown, with the decrease of HL, NO2 - -N effluent concentration showed a downward trend. This shows that HL has a great influence on NO2 - -N concentration in the effluent was significantly affected, possibly due to the reduction of HL, which led to a more complete denitrification process and NO2 - -N conversion is more thorough, NO2 - -N accumulation is less. 2) Effect of dry-wet ratio on NO2 - -N removal effect: NO2 under different D / W - -N effluent concentration is as follows Figure 13 As shown, as D / W decreases from 5:1 (IIa) to 1:1 (IIc), NO2 - -N concentration in the effluent gradually increases. This shows that D / W has a great influence on NO2 - -N effluent concentration has a significant impact. This is because the reduction of dry-wet ratio increases water inlet time, and the system forms a better anaerobic environment, which is conducive to denitrification. However, continuous water inflow leads to the accumulation of NO2 - -N has not yet completely reacted and flows out with water. --N effluent concentration is kept at a low level. Figure 13 In the NO2 - -N concentration in the effluent is higher than that in the inlet water because a small amount of NO3 - -N is converted to NO2 - -N. 3) Filler to NO2 - -N removal effect: NO2 at each stage of the experimental column with different fillers - -N effluent concentration is as follows Figure 14 As shown, all reaction columns effluent NO2 - -N concentration was maintained at a low level below 0.08 mg / L. - -N concentration was relatively high (p < 0.05), which was attributed to the effective enhancement of denitrification process by iron-carbon media through micro-electrolysis. - -N effluent concentration is significantly higher than that of pure iron-carbon reaction column. The main reasons are: First, the proportion of iron-carbon components in the mixed system is reduced, resulting in insufficient electron donors, which leads to the denitrification intermediate NO2 - -N failed to be completely reduced; secondly, the uneven distribution of fillers may form a local mass transfer barrier, affecting the electron transfer efficiency of the reaction system.

[0024] 5. Analysis of TN removal effect: 1) The effect of hydraulic load on TN removal effect. The changes of TN inlet and outlet concentrations under different HL conditions are as follows: Figure 15 As shown in the figure, the TN effluent concentration of the six experimental columns decreases with the decrease of HL. This is because the decrease of HL causes NO3 - -N and NH4 + -N concentration in the effluent decreases, and the concentration of TN in the effluent also decreases accordingly. It can be further seen that the removal rate of TN changes under different HL conditions, and the TN removal rate increases with the decrease of HL. It can be seen that the removal rate of TN is related to the addition ratio of iron-carbon fillers. The more iron-carbon fillers are added, the higher the TN removal rate. This is mainly because the electrons provided by the iron-carbon fillers as electron donors make up for the problem of insufficient carbon source in sewage with low C / N ratio. In addition, changes in hydraulic load (HL) have an important impact on the denitrification efficiency of the soil infiltration system. The mechanism of this phenomenon may involve two factors: first, the proliferation rate of autotrophic nitrite oxidizing bacteria (NOB) is relatively slow; second, the low carbon-nitrogen ratio (C / N) of the influent leads to the inhibition of the denitrification process. 2) The effect of dry-wet ratio on TN removal effect. The changes in TN inlet and outlet concentrations under different D / W conditions are shown in Figure 2. Figure 16 As shown in the figure, the TN effluent concentration of the six experimental columns increases with the decrease of D / W. This is mainly due to the increase of water inlet time, which causes NO3 --N effluent concentration increases, which in turn leads to an increase in TN effluent concentration. It can be seen that the TN removal rate changes under different D / W conditions. The TN removal rate of the six groups of experimental columns decreases with the decrease of D / W. It can be seen that D / W has a significant effect on the removal of TN in the soil infiltration system. 3) The effect of fillers on TN removal efficiency. The TN effluent concentration and removal rate of the experimental columns with different fillers at each stage are shown in Figure 2. Figure 17 As shown in the figure, the effluent concentration and removal rate of TN are similar to those of NO3 - -N follows the same pattern. The TN effluent concentration of different experimental columns during the stable period is from large to small: 3#>2#>4#>5#>6#>1#. It can be seen that the denitrification effect of the experimental column with iron-carbon filler is better than that of the control group. Column 1# filled with iron-carbon filler has the best TN removal effect, with the best effluent concentration (removal rate) of 5.92 mg / L (88.07%). This is because column 1# has the largest proportion of iron-carbon filler, which can provide more inorganic electrons to autotrophic denitrification and has a greater effect on NO3 - -N has the best removal effect, although increasing NH4 + -N concentration in the effluent, but the overall nitrogen removal was better. In addition, the experimental columns filled with iron-carbon fillers and zeolite fillers also had good TN removal effects, indicating that the combined addition of zeolite and iron-carbon has an excellent TN removal effect.

[0025] 6. Analysis of TP removal effect: 1) Effect of hydraulic load on TP removal effect. The effluent concentration of TP under different HL conditions is as follows: Figure 18 As shown, when HL is 0.01 m 3 / m 2 h(Ia) reduced to 0.006 m 3 / m 2 h (Ib), the TP effluent concentration of the six experimental columns showed a decreasing trend. Because the decrease in HL reduces the scouring intensity of the water flow on the filler matrix, it is beneficial to the adsorption of TP by the filler matrix. It can be seen that the TP removal rate under different HLs shows an upward trend as the HL decreases. The results show that the TP removal rate of each group remains at a high level, which is consistent with the results of other experiments. 2) The effect of dry-wet ratio on TP removal effect. The inlet and outlet concentrations of TP at different D / W stages are as follows: Figure 19As shown, when the dry-wet ratio decreases from 5:1 (IIa) to 1:1 (IIc), the effluent concentrations of the six experimental columns increase significantly. This shows that with the accumulation of running time, the adsorption capacity of the filler matrix for TP shows a downward trend. First, the hydraulic flushing effect causes the adsorbed TP to gradually desorb from the filler surface; second, some TP that is not completely fixed will be lost with the effluent, causing the effluent TP concentration to increase. Furthermore, it can be seen that the TP removal rate under different D / W, when D / W decreases from 5:1 (IIa) to 1:1 (IIc), the TP removal rate of the six experimental columns decreases significantly. This shows that with the extension of running time, the system's removal efficiency for TP shows a downward trend. However, even under long-term operating conditions, the TP removal rate can still be maintained at a relatively ideal level, indicating that the TP removal performance of each experimental column is relatively superior. 3) The effect of filler on TP removal effect. The effluent concentration and removal rate of TP at each stage of the experimental columns with different fillers are shown as follows Figure 20 As shown in the figure, the addition of iron and carbon has a better effect on the removal of TP, and the ratio of iron and carbon added also has a significant effect on the removal of TP. 2+ / Fe 3+ The TP removal rate increases with the increase of the iron-carbon filler ratio. The above analysis of the effect of adding iron-carbon micro-electrolysis fillers and zeolite on the removal of pollutants in the soil infiltration system can be concluded as follows: 1) The results of HL on pollutant removal show that when HL increases from 0.010 m 3 / m 2 h is reduced to 0.001 m 3 / m 2 ·h, COD, NH4 + -N, NO3 - -N, NO2 - The effluent concentration of pollutants such as -N, TN, and TP showed a downward trend, and the removal rate of various pollutants showed an upward trend. 2) The results of D / W on pollutant removal showed that when D / W was reduced from 5:1 to 1:1, COD, NH4 + -N, NO3 - -N, NO2 - The effluent concentration of pollutants such as -N, TN, and TP showed an upward trend, while the removal rate of various pollutants showed a downward trend. 3) The results of the filler's removal of pollutants showed that the optimal operating parameters were HL=0.003 m³ / ㎡·h, D / W=5:1, and the iron-carbon / zeolite volume ratio was 1:1. At this time, the best removal effect was achieved. COD, NH4 + The removal rates of -N, TN and TP were 94.94%, 94.79%, 81.06% and 99.25% respectively.

[0026] Analysis of Greenhouse Gas Emission Reduction Efficiency: The greenhouse gas reduction efficiency of an iron-carbon micro-electrolysis coupled soil infiltration system was investigated by analyzing the effects of different hydraulic loads (HL), dry-to-wet ratios (D / W), and filler ratios on CH4 and N2O emissions. Greenhouse gas monitoring was conducted simultaneously during the parameter experiments. Greenhouse gas analysis primarily focused on CH4 and N2O, using a static darkroom method. The gas sampling chamber consisted of a 100 cm high, 20 cm diameter organic plastic column. To ensure uniform gas mixing, a simple gas mixing fan was installed within the column. Before greenhouse gas collection began, the column was placed over the soil column and sealed with water to prevent gas leakage. Greenhouse gas measurements were taken every two days during each parameter stabilization phase, with three measurements taken during each phase. To minimize environmental interference during sampling, gas sampling was conducted every hour between 11:00 AM and 2:00 PM, for a total of four times. Gas samples were drawn into 100 mL aluminum bags using syringes. The bags collected the greenhouse gases, and their composition was analyzed by gas chromatography. The greenhouse gas flux calculation formula is as follows (V): (V); In formula (V): F is the gas emission flux (CH4 unit is mg·m -2 h -1 The unit of N2O is μg·m -2 h -1 H is the height of the organic plastic column (m); T is the temperature during the sampling period (K); P is the atmospheric pressure during sampling (Pa); P0 is the atmospheric pressure under standard conditions (Pa); ρ is the density of a certain gas to be measured (molar mass / molar volume of gas under standard conditions, g·L -1 ); dc / dt is the rate of change of concentration of a certain gas under test in the sampling box during the sampling period (the unit of CH4 is cm 3 ·m -3 h -1 and N2O in mm 3 ·m -3 h -1 This study used SPSS 20 statistical software to process and analyze experimental data, and one-way ANOVA was used to test differences between groups. A P value less than 0.05 was considered significant, and a P value less than 0.01 was considered extremely significant. Origin 2018 graphics software was also used to visualize N2O and CH4 emission characteristics during each experimental phase.

[0027] 1. CH4 emission reduction efficiency analysis: 1) Impact of hydraulic load on CH4 emission reduction efficiency: Figure 21The CH4 gas emissions from each experimental column at different HLs are shown. As the HL decreases from Ia to Id, CH4 gas emissions show an overall downward trend. The decrease in HL leads to an increase in DO concentration, allowing more COD to be oxidized to CO2 and removed in an aerobic environment. 2) Effect of the dry-wet ratio on CH4 emission reduction efficiency: Figure 22 The CH4 gas emissions from each experimental column at different D / W ratios are shown. It can be seen that when the dry-to-wet ratio (D / W) decreases, the system water residence time increases accordingly. This change in operating conditions alters the redox conditions within the reactor, prompting more organic matter (COD) to be converted through methanation, ultimately leading to increased methane (CH4) production. 3) Impact of packing ratio on CH4 emission reduction efficiency: The CH4 emission flux of experimental columns with different packing ratios is shown in Figure 3. Figure 23 As shown, the CH4 emissions from each experimental column are ranked from highest to lowest: 3# > 1# > 6# > 5# > 4# > 2#. This indicates that the addition of iron-carbon fillers can effectively reduce CH4 production. Iron-carbon fillers inhibit methane (CH4) production primarily through two mechanisms: ① Their efficient removal of organic matter significantly reduces the concentration of substrate available to methanogens; ② The Fe³⁺ produced during the filler reaction promotes the growth and reproduction of iron-reducing bacteria, creating a substrate competition with methanogens, effectively inhibiting methane production. Furthermore, the experimental column containing only zeolite fillers exhibited the lowest CH4 emissions. This is because the unique crystal structure of zeolite facilitates the adsorption and storage of CH4. Zeolite's porous structure also likely improves the local dissolved oxygen environment, promoting CH4 oxidation. Therefore, both iron-carbon and zeolite fillers can effectively reduce CH4 emissions.

[0028] 2. Analysis of N2O emission reduction efficiency. 1) Impact of hydraulic load on N2O emission reduction efficiency: The N2O emission in the hydraulic load stage is as follows: Figure 24 It can be seen that in the six soil infiltration systems, as the HL decreases, the N2O emissions of each experimental column also gradually decrease. This may be because the decrease in HL leads to the decrease of NO3 - -N decreases, which leads to a decrease in the production of intermediate product N2O. 2) The effect of dry-wet ratio on N2O emission reduction efficiency: The N2O emission in the dry-wet ratio stage is as follows: Figure 25 It can be seen that as D / W decreases, the N2O emission flux of each experimental column increases significantly. This is because the extension of water inlet time creates a better anaerobic environment, which is conducive to the microbial denitrification process, and more N2O is produced and emitted. 3) The effect of filler on N2O emission reduction efficiency: The N2O emission of experimental columns with different fillers is as follows: Figure 26It can be seen that N2O emissions from columns 1#, 4#, 5#, and 6# are higher than those from columns 2# and 3#. This is because the addition of iron-carbon filler promotes the denitrification process, producing more N2O, resulting in higher N2O emissions. It can be seen that as the proportion of iron-carbon filler increases, N2O emissions also gradually increase. In contrast, columns 2# and 3# have a limited carbon source, making denitrification more difficult, resulting in lower N2O emissions.

[0029] In summary, the analysis of the effects of adding iron-carbon micro-electrolysis fillers and zeolite on the pollutant removal efficiency and greenhouse gas emission reduction of the soil infiltration system can be concluded as follows: 1) The results of HL on greenhouse gas emission flux show that when HL decreases, the gas emission flux of N2O and CH4 decreases. 2) The results of D / W on pollutant removal show that when D / W decreases, the gas emission flux of N2O and CH4 increases. 3) The results of filler on greenhouse gas emission flux show that the optimal operating parameters are HL = 0.003 m 3 / m 2 h, D / W = 5:1, and the iron-carbon / zeolite volume ratio is 1:1. At this time, the best greenhouse gas emission reduction effect is achieved. The gas emission fluxes of N2O and CH4 are 0.172 mg / m 2 h and 0.007 mg / m 2 ·h.

[0030] Study on sewage treatment mechanism: 1. Characterization and analysis of fillers. Scanning electron microscopy (SEM) characterization was used to reveal the evolution of the filler mesostructure. During the experimental research phase, column 5# was selected, and two characteristic sampling points were set on the longitudinal spatial gradient: point c at 30 cm from the top of the system and point d at 70 cm. The topological structure variation characteristics of the matrix surface micromorphology before and after the operation cycle were compared, and the spatiotemporal evolution of the active sites of the filler interface reaction were quantitatively analyzed. X-ray photoelectron spectroscopy (XPS) was used to deeply analyze the surface chemical state of the filler. After the system operation cycle, column 5# was selected, and representative matrix samples were collected at the sampling point c and the lower point d sampling point. XPS and SEM were used to compare and analyze the original iron-carbon filler and the lower layer filler samples of the 5# reaction column to examine the changes in their physical and chemical properties during the operation of the soil infiltration system, focusing on the evolution of the material surface morphology characteristics and elemental composition; and SEM analysis was performed on the physical changes of the zeolite filler before and after to explore the changes in its apparent morphology before and after operation. 1) Apparent morphology analysis (SEM) such as Figure 27 As shown by Figure 27As can be seen from the left figure, the zeolite filler exhibits a typical porous crystal structure, with clear and evenly distributed pores and consistent pore size, indicating that it has high adsorption potential. At the same time, the crystal surface is smooth, without obvious attachments or impurities, indicating that the physical structure of the original zeolite filler is complete and suitable for pollutant adsorption and ion exchange. Figure 27 As shown in the right figure, the surface of the zeolite is covered with a layer of obvious sediment or biofilm, the original pores are partially blocked, and the porosity is significantly reduced; the surface roughness increases, which may be due to the adsorption of organic matter, nitrogen and phosphorus pollutants or metal ions (such as NH4 + -, PO4 3- 、Fe 3+ At the same time, filamentous bacteria or granular colonies were observed in some areas, indicating that zeolite can serve as a microbial carrier in the sewage treatment process, providing space for microbial activities and participating in the NH4 + -N, COD and other pollutants biodegradation process. Figure 28 It is known that the iron-carbon filler undergoes significant changes before and after the reaction. The filler surface before the reaction is smooth and the structure is complete, while the filler surface after the reaction is rough with holes and cracks. This shows that the iron-carbon filler undergoes chemical reactions during the sewage treatment process, especially the dissolution of iron elements and the corrosion of carbon-based materials, which are caused by micro-electrolysis reactions. These changes help to improve the adsorption capacity and reaction activity of the filler and enhance the effect of sewage treatment. At the same time, it can be seen that there is some precipitation on the surface of the iron-carbon filler in the 5# experimental column because the Fe generated during the reaction 3+ With OH - Combined to form Fe(OH)2 and Fe(OH)3 precipitation, these precipitations are adsorbed on the iron-carbon surface, which will inhibit the transfer of electrons and affect the denitrification process. 3+ 、Fe 2+ Equal to PO4 3- Complex precipitates will form, indicating that the iron-carbon filler has a good ability to remove phosphorus from wastewater. 2) Surface morphology analysis. Figure 29 and Figure 30 The XPS results for column #5 before and after the experiment indicate that the iron in the iron-carbon filler undergoes a chemical reaction during the experiment. When acting as an electron donor, Fe(II) loses electrons and is oxidized to Fe(III); when acting as an electron acceptor, Fe(III) is reduced to Fe(II) by accepting electrons. Furthermore, the increase in Fe(II) and Fe(III) indicates the oxidation of Fe(0).

[0031] 2. Analysis of Microbial Alpha and Beta Diversity. Matrix samples were collected from sampling ports 30 cm (upper layer, point b) and 70 cm (lower layer, point d) from the top of the system and immediately stored at -80°C. For easy identification, upper layer samples were uniformly labeled U (upper layer) and lower layer samples were labeled D (downer layer). For example, A1U represents the upper layer sample from experimental column 1, and A1D corresponds to the lower layer sample. DNA was extracted using the FastDNA® SPIN Kit for Soil Extraction Kit, and purity and concentration were verified by agarose gel electrophoresis to ensure compliance with subsequent analysis requirements. PCR primer sequences are shown in the table. Sequencing was then performed using the Illumina Miseq PE300 / NovaSeq PE250 platform and compared to the Genbank database. Sequences were grouped into operational taxonomic units (OTUs) at 97% similarity, and microbial diversity was analyzed using the Meiji BioCloud platform. 1) OTU cluster analysis. Figure 31 Describe whether the current sequencing depth of 12 samples is sufficient to reflect the diversity of microbial populations contained in the samples. Figure 31 When the sequencing amount is less than 10,000, the number of OTUs shows a rapid upward trend; when the sequencing amount increases to 20,000, the OTU growth rate slows down significantly; when the sequencing amount reaches 50,000, the curve basically stabilizes. This change pattern shows that although it has not yet reached full saturation, the current sequencing depth can effectively capture the main microbial sequence information in 12 samples, and its data volume is sufficient to fully reflect the composition characteristics of the microbial community in each reaction sample. The Venn diagram of the OTU level population distribution between samples at different depths is shown below. Figure 32 As shown in the figure, this graph illustrates the similarities and differences between the upper and lower layers of the system. The OTU-level species counts in the upper and lower samples were 10,427 and 9,039, respectively, with a total of 3,426 species shared. Further analysis revealed that the number of microbial species decreased with increasing system operation depth, from an initial 10,427 to 9,039. This quantitative change indicates that changes in system operation depth significantly alter the structure and composition of the microbial community. 2) Microbial Alpha Diversity Analysis. The sample microbial communities were quantitatively analyzed using six metrics: Sobs, Shannon, Simpson, Ace, Chao1, and Coverage. See Table 2 for details.

[0032] Table 2 Analysis of microbial Alpha diversity As shown in Table 2, the coverage values ​​for all 12 samples were greater than 95%, indicating that the sequencing structure accurately reflects microbial diversity and richness. A cross-sectional comparison of the data from each experimental column revealed that column 3 significantly outperformed the other columns in terms of Sobs, Shannon, Ace, and Chao1 indices at multiple sampling time points. This indicates that column 3 exhibits a richer microbial population, higher species diversity, and superior community richness. This suggests that the iron-carbon filler plays an important role in microbial selection, promoting the evolution of microbial communities toward those more adaptable to environmental conditions. The Sobs, Shannon, Ace, and Chao1 indices for column 2 were higher than those for column 3, likely due to the zeolite filler's internal spatial locations, which are more suitable for microbial survival and reproduction than gravel. Comparative analysis of soil layers at different depths revealed that the surface layers of most experimental columns exhibited significantly higher Sobs, Shannon, Ace, and Chao1 diversity indices compared to deeper samples. This indicates that surface soils exhibit higher microbial abundance, more complex community diversity, and a richer species composition. The distribution characteristics indicate that the number and species of microbial communities decrease with increasing soil depth. 3) Microbial Beta Diversity Analysis. Principal component analysis (PCA) based on the Weighted Unifrac algorithm was used to examine the differences in microbial populations between samples. Figure 33 As can be seen, the principal component analysis of the samples at the genus level yielded a P1+P2 ratio of 34.77%, indicating significant differences between the samples. The small overlap between the two ellipses representing the upper and lower layers indicates significant sample variation between the upper and lower layers, demonstrating a significant influence of column depth on microbial diversity and richness. The P1 axis divides the majority of the lower layer samples on the left and a smaller portion on the right, with the two separated by a considerable distance, indicating significant differences between the lower layer samples. The P2 axis divides the majority of the upper layer samples on the upper side and a smaller portion on the lower side, indicating similar differences between the upper layer samples. This demonstrates that the column packing significantly influences microbial diversity and richness. Two of the lower layer samples are close to the upper layer samples, indicating that their genus-level composition is similar to that of the upper layer samples. These are likely columns 2 and 3, which were not treated with iron and carbon. Figure 34 A phylogenetic tree based on genus-level taxonomic units is displayed. The branch distances reflect the degree of variation in microbial composition between samples, with shorter branch distances indicating greater community similarity. The results revealed that samples from the same source (e.g., A1D and A4D, A2U and A6U) formed independent clusters, indicating significant homology in their microbial community structures. Furthermore, when the upper and lower layers of the experimental setup used the same filler material (e.g., A1U and A2D), the microbial composition showed the highest degree of convergence, revealing the screening effect of the environmental matrix on microorganisms. This visualization intuitively illustrates the correlation between the spatial distribution characteristics of microbial communities and matrix selection pressure.

[0033] 3. Analysis of microbial community composition characteristics. (1) Analysis of microbial community composition characteristics at the phylum level. Figure 35 The dynamics of microbial community composition across different samples at the phylum level were displayed. All samples showed convergent patterns in dominant bacterial composition. By screening microbial taxa with a relative abundance threshold greater than 1%, 14 core bacterial phyla were identified. Actinobacteriota (5.7-24.54%), Proteobacteria (11.69-45.24%), Acidobacteriota (1.5-19.56%), Chloroflexi (3.2-14.86%), and Firmicutes (3.6-64.7%) comprised the primary functional bacterial communities. The total abundance of these dominant phyla in each sample exceeded 80%, reflecting the structural stability of the microbial community. It also includes Myxococcota (Myxococcus, 1.2~4.9%) and Gemmatimonadota (Gemmatimonadetes, 0.1~10.74%). The functional analysis of the bacterial community involved in this study showed that the Actinobacteria contains strains with organic matter metabolism and biological phosphorus accumulation functions, which explains the biological mechanism of stable removal of COD and TP from a microbiological perspective. Proteobacteria is the core functional group of the sewage biological treatment system. It not only dominates the degradation of organic pollutants, but its branched genera have also been proven to participate in nitrogen conversion processes such as ammoniation, nitrification and denitrification, and has a significant promoting effect on the system's denitrification efficiency. The correspondence between bacterial community structure and pollutant removal efficiency reveals the coupling characteristics of microbial functional groups and water purification processes. Some microorganisms in the Acidobacteria phylum have the function of dissimilatory iron reduction, so the relative abundance of the Acidobacteria phylum is higher in the experimental column with iron-carbon filler added. Chloroflexi can oxidize NO2 - -N and CH4 and fix CO2 to achieve nitrification and carbon fixation. The bacteria related to denitrification include Firmicutes and Myxococcota. Nitrospirota (nitrifying bacteria) as denitrification functional bacteria can directly convert NH4 + -N is oxidized to NO3 2- -N, also present in the system. Some bacteria in the Bacteroidota (Bacteroidetes, 1.7-5.7%) also have denitrification capabilities. The abundance of denitrification-related bacterial communities at the phylum level indicates that the system with iron-carbon fillers has good denitrification potential. (2) Analysis of microbial community composition characteristics at the class level. Figure 36By setting the screening criteria of relative abundance threshold >1%, a total of 33 dominant bacterial classes were identified. It showed that the dominant bacterial community composition between samples showed significant homology, and the core community included Actinobacteria, Alphaproteria (α-Proteobacteria), Gammaproteobacteria (γ-Proteobacteria), Vicinamibacteria, Symbiobacteriia, Clostridia (Clostridia), Chloroflexia (Chloroflexia), Bacilli (Bacilli), Anaerolineae (Anaerobic Fungi), etc. α-Proteobacteria has good organic matter removal ability, and γ-Proteobacteria has good NO3 removal ability. - -N, NO2 - It plays a major role in the reduction of nitrogen and the oxidation of iron. There are genera capable of denitrification in the classes Chloroflexia, Bacilli, and Anaerolineae. Nitrospira (Nitrospira, 0.25-11.26%) is associated with nitrification. This suggests that the system has a good denitrification capacity. (3) Analysis of microbial community composition characteristics at the genus level. Figure 37 Using a screening criterion with a relative abundance threshold of >1%, 57 dominant bacterial colonies were identified. These included unclassified Micrococcaceae, Symbiobacterium, norank_f_Vicinamibacteraceae, norank_f_Vicinamibacterale, norank_f_Gemmatimonadaceae, norank_f_JG30-KF-CM45, Bacillus, and Sphingomonas, all with a total abundance greater than 20%. Both norank_f_JG30-KF-CM45 and Bacillus belong to the NOB genus. Sphingomonas has excellent organic matter degradation capabilities. Nitrification-related genera such as Nitrosomonas and Nitrospira were also present in the system.

[0034] 4. Correlation analysis between microbial communities and environmental factors. Figure 38 Revealed the environmental factors (COD, NH4 +The association mechanism between environmental factors (-N, TN, TP) and microbial community structure was investigated. RDA1 and RDA2 explained 16.23% and 7.19% of the total microbial community variation, respectively. Arrows represent environmental factors, their lengths indicating their influence on microbial population structure, and angles representing positive and negative correlations. Sample points were clustered based on the spatial location of the experimental column (upper and lower layers) and packing type. Orthogonal projections quantified the regulatory weight of environmental factors on microbial structure: the distance of the sample projection point from the coordinate origin was proportional to the biological selection of that factor. The results showed that various environmental parameters significantly reshaped the distribution of genus-level microbial functional groups through differential selective pressures, confirming the interaction between pollutant metabolism and biogeochemical cycles. It can be seen that different environmental factors have a significant impact on microbial population structure at the genus level. In summary, through filler characterization analysis, microbial Alpha and Beta diversity analysis, microbial community composition characteristics analysis and microbial community and environmental factor correlation analysis, the pollutant removal mechanism and greenhouse gas emission reduction mechanism of the iron-carbon micro-electrolysis coupled soil infiltration system (SIS) were deeply revealed, and the following conclusions were drawn: 1) SEM showed that the surface roughness of the iron-carbon filler increased after operation, and holes and cracks appeared, indicating that the dissolution of iron elements and the corrosion of carbon-based materials during the micro-electrolysis reaction enhanced the adsorption capacity and reaction activity of the filler; at the same time, the Fe(OH)2 and Fe(OH)3 precipitation generated on the iron-carbon surface may inhibit electron transfer, but promote the complex precipitation removal of phosphorus. After operation, the surface of the zeolite filler is covered with biofilm and sediment, and the porosity is reduced, but it can still adsorb NH4 through cation exchange. + -N, and provide habitat for microorganisms. XPS analysis shows that the iron element Fe 2+ with Fe 3+ valence state conversion, indicating that the iron element in the iron-carbon filler participates in the denitrification process as an electron donor, and also acts as an electron acceptor to promote the redox reaction of pollutants. 2) The results of microbial diversity analysis showed that the system depth had a significant effect on the structure of the microbial population. As the system depth increased, the number of OTUs in the sample decreased. The results of Alpha diversity analysis showed that the microbial diversity (Sobs index, Shannon index) of the upper layer samples was significantly higher than that of the lower layer, indicating that the soil depth had a screening effect on the distribution of microorganisms. The addition of iron-carbon fillers had a screening effect on microorganisms, causing microorganisms to develop towards populations adapted to the environment. 3) Analysis of microbial composition characteristics showed that: at the phylum level, Actinobacteria (5.7%~24.54%) and Proteobacteria (11.69%~45.24%) were the dominant bacterial groups, which were closely related to organic matter degradation, phosphorus removal and nitrogen cycle, respectively. At the class level, Alphaproteria had good organic matter removal ability, and γ-Proteobacteria had a strong affinity with NO3 - -N, NO2 -The system is related to the reduction of -N and the oxidation of iron. There are denitrifying bacteria in the classes of Chloroflexia, Bacilli, Anaerolineae, and Nitrospiria (Nitrospira, 0.25-11.26%), which all indicate that the system has a good denitrification capacity. At the genus level, the detection of Nitrosomonas and Nitrospira verified the nitrification capacity of the system, and the enrichment of NOB microorganisms such as norank_f_JG30-KF-CM45 and Bacillus enhanced the denitrification efficiency. (4) The correlation analysis of environmental factors showed that different environmental factors had a significant impact on the microbial population structure at the genus level.

[0035] In summary, the advantages of the present invention are as follows: 1) When HL is reduced, COD, NH4 + -N, NO3 - -N, NO2 - The removal rate of pollutants such as -N, TN, and TP is on the rise. The gas emission flux of N2O and CH4 is on the decline. 2) When D / W decreases, COD, NH4 + -N, NO3 - -N, NO2 - -The removal rate of pollutants such as N, TN, and TP showed a downward trend. 3) The optimal operating parameter is HL=0.003m³ / m 2 h, D / W=5:1, iron carbon / zeolite volume ratio 1:1, to achieve the best pollutant removal effect and greenhouse gas emission reduction effect. COD, NH4 + The removal rates of -N, TN, and TP were 94.94%, 94.79%, 81.06%, and 99.25%, respectively. The gas emission fluxes of N2O and CH4 were 0.172 mg / m 2 h and 0.007 mg / m 2 h. 4) SEM analysis shows that the dissolution of iron and the corrosion of carbon-based materials during the microelectrolysis process enhance the filler's adsorption capacity and reactivity. Furthermore, the Fe(OH)2 and Fe(OH)3 precipitates formed on the iron-carbon surface inhibit electron transfer but promote the removal of phosphorus by complex precipitation. After operation, the zeolite filler is covered with biofilm and sediment, reducing its porosity, but it can still adsorb NH4 through cation exchange. + -N, and provide habitat for microorganisms. XPS shows that Fe 2+ with Fe 3+conversion, participating in the denitrification process as an electron donor, and promoting the redox reaction of pollutants as an electron acceptor. 5) Alpha diversity showed that the microbial diversity (Sobs index, Shannon index) of the upper layer samples was significantly higher than that of the lower layer, and the soil depth had a screening effect on the distribution of microorganisms; the addition of iron-carbon fillers had a screening effect on microorganisms, causing microorganisms to develop towards populations adapted to the environment. 6) Beta diversity showed that filler type and soil depth significantly affected the structure of the microbial community. At the phylum level, Actinobacteria and Proteobacteria were the dominant bacterial groups, which were closely related to organic matter degradation, phosphorus removal and nitrogen cycle, respectively; at the class level, Alphaproteria had good organic matter removal ability, and γ-Proteobacteria were closely related to NO3 - -N, NO2 - The system is associated with the reduction of -N and the oxidation of iron. Denitrifying bacteria are also present within phyla such as Chloroflexia, Bacilli, Anaerolineae, and Nitrospiria (Nitrospira, 0.25-11.26%), demonstrating the system's robust denitrification capacity. At the genus level, the detection of Nitrosomonas and Nitrospira confirms the system's nitrification capacity, while the enrichment of NOB microorganisms such as norank_f_JG30-KF-CM45 and Bacillus enhances denitrification efficiency.

Claims

1. An iron-carbon micro-electrolysis coupled soil infiltration system, characterized in that: From top to bottom, it includes: soil cover layer, gravel water cloth layer, matrix filler layer and gravel support layer; The matrix filler layer is filled with at least iron-carbon filler.

2. The iron-carbon micro-electrolysis coupled soil infiltration system according to claim 1, characterized in that: The matrix filler layer further comprises a zeolite filler; The matrix filler layer is composed of filler and soil, and the volume ratio of the filler to soil is 1:2; The soil cover layer consists of soil; The gravel water cloth layer is composed of gravel filler, the gravel supporting layer is composed of gravel filler, and the particle size of the gravel filler is 4-6 mm.

3. The iron-carbon micro-electrolysis coupled soil infiltration system according to claim 2, characterized in that: The matrix filler layer consists of an iron-carbon filler, a zeolite filler and soil. The zeolite filler is located in the upper layer, and the iron-carbon filler is located in the lower layer. Both the zeolite filler layer and the iron-carbon filler layer are doped with the soil.

4. The iron-carbon micro-electrolysis coupled soil infiltration system according to claim 3, characterized in that: The volume ratio of the zeolite filler layer to the iron-carbon filler layer is 1-3:1-3; And / or, the mass ratio of Fe / C in the iron-carbon filler is 3-5:1; And / or, the soil is brown soil, the soil organic matter content is greater than 8%, the nitrogen content is greater than 0.4%, the phosphorus content is greater than 0.2%, the potassium content is greater than 17%, and the pH value is greater than 5%.

5. The iron-carbon micro-electrolysis coupled soil infiltration system according to claim 1, characterized in that: The volume ratio of the soil cover layer, gravel water cloth layer, matrix filler layer and gravel support layer is 1:1:16:2; And / or, the thicknesses of the soil covering layer, the gravel water cloth layer, the matrix filler layer and the gravel supporting layer are 5 cm, 5 cm, 80 cm and 10 cm respectively.

6. The iron-carbon micro-electrolysis coupled soil infiltration system according to claim 4, characterized in that: Have at least one of the following characteristics: The particle size of the iron-carbon filler is 8-12 mm; The particle size of the zeolite filler is 4-8 mm.

7. The iron-carbon micro-electrolysis coupled soil infiltration system according to any one of claims 1 to 6, characterized in that: The system also includes a water inlet and a water outlet; the water inlet is located in the gravel water cloth layer, 7 cm away from the upper surface of the soil cover layer; the water outlet is located in the gravel support layer, 3 cm away from the bottom of the gravel support layer.

8. Use of the iron-carbon micro-electrolysis coupled soil infiltration system according to any one of claims 1 to 7 in sewage treatment.

9. A sewage treatment method, characterized in that: The following steps are involved: S1. Inoculate and culture activated sludge in domestic sewage in high-altitude cold areas; S2. Introduce the domestic sewage from the high-cold region inoculated with cultured activated sludge into the iron-carbon micro-electrolysis coupled soil infiltration system according to any one of claims 1 to 8 for treatment and discharge from the outlet after meeting the standards, wherein the hydraulic load of the iron-carbon micro-electrolysis coupled soil infiltration system is 0.001 to 0.01 m 3 / m 2 h, dry-wet ratio is (1-5):1; The pH value of domestic sewage in the alpine region is 6.5-8.0, SS is 100-200 mg / L, COD is 200-450 mg / L, BOD5 is 200-300 mg / L, NH4 + -N is 20~90 mg / L, TP is 2.0~6.5 mg / L.

10. The sewage treatment method according to claim 9, characterized in that: The iron-carbon micro-electrolysis coupled soil infiltration system is operated with a hydraulic load of 0.001 m 3 / m 2 h, 0.003 m 3 / m 2 h, 0.006 m 3 / m 2 h or 0.01 m 3 / m 2 h; dry-wet ratio is 5:1, 3:1 or 1:1.

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