Method for repairing heavy metals in groundwater of sloping field

Abstract

The invention discloses a slope groundwater heavy metal remediation method. Comprising the following steps: adding a heavy metal chelating agent into an injection well group of a collection area; after heavy metals are captured and removed by utilizing an active material filled in the permeable reactive barrier and arranged positive and negative electrode pairs, the heavy metals flow into a phytoremediation area; after heavy metal pollutants are continuously removed by utilizing the phytoremediation area, the water flows into the water storage circulation area; the water quality monitoring system is used for monitoring the water quality in real time in the water storage circulation area; the PLC control system controls opening and closing of the circulating pump and the control valve based on the water quality monitoring result. The device integrates pollution desorption and convergence, solidification and recovery, plant absorption, cyclic repair, deep purification and online monitoring, can efficiently and durably remove heavy metals, and solves the problems of difficult heavy metal treatment and low efficiency.

Description

A method for remediating heavy metals in groundwater on slopes Technical Field

[0001] This invention relates to a method for remediating heavy metals in groundwater on slopes. Background Technology

[0002] With rapid industrial development, heavy metal pollution in soil and groundwater has become increasingly serious, threatening human health and ecological security, and hindering sustainable economic development. The sources of heavy metal pollution in soil are complex, including atmospheric deposition, industrial wastewater, solid waste, mining, and the irrational use of pesticides and fertilizers. Heavy metal pollution is characterized by its diverse forms, high toxicity, and bioaccumulation, and can directly harm human health and the ecological environment through the food chain. Therefore, the remediation of heavy metal pollution in soil and groundwater is urgently needed.

[0003] Permeable reactive barriers (PRBs) are an emerging in-situ remediation technology that utilizes specific activated packing materials to intercept or remove pollutants from groundwater through adsorption, precipitation, and redox reactions. These include continuous wall PRBs, funnel-gate PRBs, and injection-type reactive barriers. The structural type of this technology largely determines the remediation effectiveness and cost of groundwater pollution, and the selection must be based on the hydrogeological characteristics of the contaminated site and the scale of the pollutants. PRBs filled with activated carbon treat heavy metals in groundwater, and the use of soil, ryegrass, and other vegetation to form a buffer zone can improve the removal of heavy metals from surface runoff and shallow pollution plumes.

[0004] Permeable reactive walls are constructed by excavating trenches and filling them with adsorbent materials to form an active material wall that intercepts pollutants. Based on adsorption and precipitation, heavy metals are removed, thus achieving the remediation and purification of groundwater pollution.

[0005] However, existing permeable reactive walls have the following main problems: (1) They are highly dependent on the extent of pollutants on the site. For example, continuous wall PRBs are suitable for treating situations with a small range of pollutants, while funnel-gate type reactive walls are suitable for treating groundwater with large areas of pollution. When the groundwater depth and the pollution range are large, the wall needs to cover the entire width and depth of the pollutants, which significantly increases the construction difficulty and installation cost. In addition, large-scale excavation of aquifers can easily disturb the groundwater flow field and affect the ecological environment; (2) For sites with severe heavy metal pollution, solidification / stabilization can only slowly reduce the concentration of heavy metals and is difficult to effectively and continuously remove pollutants, and cannot reduce the total amount of pollutants; (3) The leaching efficiency of existing heavy metal leaching agents is greatly affected by factors such as soil type, heavy metal type, and soil pH, and the reagent consumption is large, resulting in high operating costs. Therefore, single remediation technologies are difficult to effectively reduce the concentration of heavy metal pollution. Only by combining multiple technologies can the migration of heavy metals in the soil be controlled, and heavy metals be removed and recycled efficiently and permanently. Summary of the Invention

[0006] To address the above problems, this application provides a method for remediating heavy metals in groundwater on slopes, employing a chemical-physical approach. electric power Plant-coupled cyclic remediation technology utilizes the synergistic effects of chelation, adsorption, electrochemistry, plant enrichment, and microbial degradation to perform multi-stage enhanced treatment of heavy metals, achieving efficient and sustained removal of heavy metal pollutants from groundwater. This addresses the challenges and low efficiency of heavy metal remediation and offers advantages such as minimal disturbance to the groundwater flow field, simple construction, high remediation efficiency, easy replacement of fillers, strong applicability, and environmental friendliness.

[0007] To achieve the above objectives, the present invention provides a method for heavy metal remediation of groundwater on slopes, wherein the method is implemented using a heavy metal remediation system for groundwater on slopes; wherein the heavy metal remediation system for groundwater on slopes includes a collection zone, a permeable reactive barrier, a phytoremediation zone, a water storage and circulation zone, and a hydraulic cutoff zone arranged sequentially within an aquifer; the collection zone is arranged along the flow direction of groundwater pollutants on the slope, and a group of injection wells is arranged in the collection zone and a heavy metal chelating agent is added to collect and allow heavy metals to enter the permeable reactive barrier; the permeable reactive barrier is filled with active material and equipped with anode and cathode pairs, and the permeable reactive barrier... The permeable reactive wall is connected to the phytoremediation area; the phytoremediation area consists of a pool, substrate, and plants, and the pool is connected to the water storage and circulation area; the water storage and circulation area consists of a pool, a circulation pump, and a water supply pipe, the water supply pipe being connected to the inlet side of the permeable reactive wall, and the pool is connected to the hydraulic cutoff area; a water quality monitoring system is installed in the water storage and circulation area; the hydraulic cutoff area consists of a pool, a water supply pipe, and control valves on the water supply pipe, used for controlled cutoff of groundwater flow; it also includes a PLC control system, which controls the opening and closing of the circulation pump and control valves based on the water quality monitoring results; The method includes the following steps: Adding a heavy metal chelating agent to the injection well group in the collection area desorbs heavy metals from the surface of soil particles, enhancing the mobility and solubility of heavy metals. All heavy metals are collected with groundwater and flow into the permeable reactive barrier. The active material filling the permeable reactive barrier and the anode and cathode electrodes are used to capture and remove heavy metals before they flow into the phytoremediation zone. The phytoremediation zone continuously removes heavy metal pollutants before the water flows into the water storage and circulation zone. In the water storage and circulation zone, a water quality monitoring system monitors the water quality in real time. If the heavy metal content exceeds the standard in the water quality monitoring results, the PLC control system outputs a control signal. The signal closes the control valve of the hydraulic cutoff zone, while simultaneously opening the circulating water pump and pipeline control valve of the water storage and circulation zone. Substandard water is transferred to the collection zone or the inlet side of the permeable reactive wall for circulation treatment. Through the synergistic effect of chelation-adsorption-electrochemical-plant enrichment, heavy metals are efficiently and persistently removed. If the water quality meets the standards, the circulating water pump and pipeline control valve of the water storage and circulation zone are closed, and the control valve of the hydraulic cutoff zone is opened. The effluent enters the aquatic plant purification zone, where aquatic plants further enhance the absorption of heavy metals, and microorganisms decompose and remove ammonia nitrogen pollutants, deeply purifying the water quality. The effluent then enters the underground environment through the highly permeable layer at the bottom of the pool and the outlet wall.

[0008] Furthermore, an aquatic plant purification zone is set up at the outlet of the water supply pipe in the hydraulic cutoff zone. The aquatic plant purification zone consists of a pool and aquatic plants, and is used to deeply purify the effluent water quality. The purified water flows out to the underground environment through the effluent pool.

[0009] Furthermore, the collection area is located on a slope with a certain gradient of 5-15°. The injection well group in the collection area consists of incomplete wells, located in a heavy metal-contaminated aquifer with a large hydraulic gradient, at a depth corresponding to the depth of the contaminated groundwater. A heavy metal chelating agent is added to the injection well group. The heavy metal chelating agent is one or a combination of aspartic acid-glutamic acid polymeric amino acid and iminodisuccinic acid, used to desorb heavy metals from the surface of soil particles, enhance the mobility and dissolution of heavy metals, and allow all heavy metals to flow into the permeable reactive barrier along with the groundwater.

[0010] Furthermore, the bottom of the permeable reactive wall is an impermeable layer with an inclination angle consistent with the hydraulic gradient, and its depth is 0.8~1.0m greater than the depth of the groundwater pollution plume; an impermeable guide wall is set at the front end of the impermeable layer, with a depth 1.0~1.5m greater than the depth of the impermeable layer; the water inlet wall of the permeable reactive wall is composed of a steel reinforcement skeleton and a permeable geotextile covering the steel reinforcement skeleton; an impermeable concrete barrier plate is also set on the upper part of the water inlet wall, with the bottom of the barrier plate level with the groundwater level and the top 0.3m above the ground; the water outlet wall of the permeable reactive wall is composed of an upper permeable wall and a lower water-resistant wall, with the length ratio of the permeable wall to the water-resistant wall being 1:1; a guide plate is set in the middle of the permeable reactive wall to divide the reaction area into two unit areas, and the guide plate is composed of an upper water-retaining wall and a lower grid filter, with the length ratio of the water-retaining wall to the grid filter being 1:1.

[0011] Furthermore, both the first and second units of the dual-unit zone are filled with reactive materials. The first unit is filled with adsorption filler, which is one or a composite filter material selected from activated zeolite, volcanic rock, and ceramsite, with a particle size of 2-5 mm. The lower part of the second unit is filled with adsorption filler, and the upper part is filled with activated biochar composite filler. The filler is spherical porous particles with a particle size of 2-4 mm. The width of each reaction unit is 1.5-2.5 m. The material filling is required to make the permeability coefficient of the wall and reaction zone 2-6 times higher than the permeability coefficient of the aquifer. An electrically operated repair anode and cathode electrode pair is provided in the first unit and / or the second unit.

[0012] Furthermore, the bottom surface of the phytoremediation area pool is an impermeable layer, and the bottom surface is flush with the top of the permeable reactive wall on the water outlet side. The water outlet side wall is composed of a steel frame and permeable geotextile. The phytoremediation area pool is filled with one or a combination of gravel, sand, zeolite, waste wood blocks, corn cob particles, and biochar, and plants are planted on the upper part of the substrate. The particle size of the inorganic fillers such as gravel, sand, and zeolite is 3~8mm, and the particle size of the organic fillers such as waste wood blocks, corn cob particles, and biochar is 2~6mm. The particle size of the fillers in the substrate layer gradually increases from top to bottom.

[0013] Furthermore, the lower part of the water inlet side of the water storage and circulation area is a water-proof wall, and its top surface is flush with the bottom surface of the plant restoration area pool; the bottom surface of the water storage and circulation area pool is an impermeable layer, which is flush with the bottom of the impermeable layer of the permeable reactive wall; the water outlet side is a water-proof wall, and the side wall is provided with multiple openings for installing water supply pipes.

[0014] Furthermore, the hydraulic cutoff zone pool is surrounded by water-proof walls, and multiple water supply pipes are installed inside the walls. Each water supply pipe is equipped with a control valve, and the water supply pipes connect the upstream water storage and circulation zone and the downstream aquatic plant purification zone.

[0015] Furthermore, the bottom surface of the aquatic plant purification area pool is composed of an impermeable bottom plate and a highly permeable layer arranged at intervals of 0.5m. The upper part of the pool bottom is filled with matrix filler, and emergent and submerged plants are selected and planted on the filler according to the water depth to deeply purify the effluent water quality. The effluent side wall is composed of a steel frame and permeable geotextile, and the pool width is 0.8~1.2m.

[0016] Furthermore, the permeable reactive wall is equipped with an electrically conductive repair cathode and anode pair. The cathode electrode is a graphite rod, and the anode electrode is any one of titanium, stainless steel, or a conductive metal-organic framework material. Under the action of a DC electric field, charged heavy metals migrate to the oppositely charged cathode electrode via electrodynamic force, undergo a reduction reaction, and accumulate on the electrode surface. Subsequently, the electrodes are centrally processed to separate the heavy metals.

[0017] Furthermore, the planted plants are heavy metal hyperaccumulators, exhibiting extremely high tolerance to heavy metals such as Cr, Pb, Cu, and Cd, including one or more of the following: carnations, coreopsis, alfalfa, Leymus chinensis, pokeweed, violetia baoshanense, marigold, ryegrass, and centipede grass; the emergent plants include plants with strong wastewater purification capabilities such as reeds, cattails, irises, loosestrife, canna lilies, and others; the submerged plants include one or more of the following: Vallisneria natans, hornwort, foxtail grass, hydrangea, and water lilies.

[0018] The present application has the following advantages: (1) The present invention sets up a collection area, a permeable reactive wall, a plant remediation area, a water storage and circulation area, a hydraulic cut-off area and an aquatic plant purification area, forming a slope groundwater heavy metal remediation system and method that integrates pollution desorption and aggregation, solidification and recycling, plant absorption, circulation remediation, deep purification and online monitoring. Through multi-level enhanced treatment with the synergistic effect of adsorption, electrochemistry, plant enrichment and microbial degradation, heavy metals are removed efficiently and persistently, and pollutants such as COD and ammonia nitrogen are removed at the same time, solving the problems of difficulty and low efficiency in heavy metal treatment.

[0019] (2) The present invention sets up a heavy metal collection area, injects chelating agent into the soil to leach heavy metal contaminated soil in situ through non-complete wells, so that heavy metals are desorbed from the surface of soil particles, and then the heavy metals are adsorbed and stabilized by the active adsorption packing in the reaction zone. Combined with the action of electrodynamics, the heavy metals are enriched on the electrode surface for recovery. The electrode is recycled, which can completely remove heavy metals and ensure the stability of groundwater pollution remediation.

[0020] (3) The heavy metal chelating agent selected in this invention is one or more of aspartic acid-glutamic acid polymeric amino acids and iminodisuccinic acid, which can rapidly chelate and desorb heavy metal ions such as cadmium, chromium, and lead on the soil surface, thereby achieving efficient leaching of heavy metal contaminated soil; in addition, the above materials are environmentally friendly, insensitive to changes in environmental pH, highly adaptable, and the leaching waste liquid can be utilized by plants and microorganisms without causing secondary pollution.

[0021] (4) The present invention utilizes the natural hydraulic gradient to realize the operation of the device, with little disturbance to the groundwater flow field. The permeable reaction wall is set up to collect pollutants, thereby reducing the range of pollution diffusion. The active filler in the reaction zone has a large specific surface area and porosity, good permeability, and can efficiently adsorb and solidify heavy metals. The pollutants are transferred to the reaction zone for circulation treatment through a group of circulating pumps, so that the pollutants are in full contact with the filler, improving the utilization rate of the filler and the efficiency of pollutant remediation, significantly saving energy and reducing operating costs. Attached Figure Description

[0022] Figure 1 is a plan view of the slope groundwater heavy metal remediation system involved in this method.

[0023] Figure 2 is a cross-sectional view of Figure 1.

[0024] Figure 3 is a cross-sectional view of the slope groundwater heavy metal remediation system of Embodiment 3 of this application.

[0025] Figure 4 is a schematic diagram of the reaction packing and metal unit frame inside the reaction wall.

[0026] In the diagram: 1. Collection area; 11. Injection well group; 2. Permeable reaction wall; 21. Anode and cathode pair; 22. Guide wall; 23. Barrier plate; 24. Permeable wall; 25. Water-blocking wall; 26. Water-retaining wall; 27. Grille filter; 28. Adsorption packing; 29. ​​Biochar composite packing; 291. Reaction pack; 292. Metal unit frame; 293. Hanging lug; 3. Phytoremediation area; 31. Substrate; 4. Water storage and circulation area; 41. Circulation pump group; 42. Water quality monitoring system; 5. Hydraulic cutoff area; 51. Control valve; 6. Aquatic plant purification area; 61. Impermeable layer; 62. Highly permeable layer. Detailed Implementation

[0027] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0029] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] Example 1 The method in this example is based on the slope groundwater heavy metal remediation system shown in Figures 1-2, which includes a collection zone 1, a permeable reactive wall 2, a phytoremediation zone 3, a water storage and circulation zone 4, a hydraulic cutoff zone 5, and an aquatic plant purification zone 6 set in the aquifer, and each zone is connected in sequence.

[0032] The method of this embodiment will now be further explained in conjunction with the system: Collection area 1 is set along the flow direction of groundwater pollutants on the slope, with a slope of 5~15°. Injection well group 11 is arranged on the slope. The injection wells are set in the heavy metal polluted aquifer with a large hydraulic gradient, at a depth at the depth of the polluted groundwater. The injection well 11 is a non-complete unconfined well. The filter of the non-complete well is set in segments along the well wall at intervals, with a spacing of 3~5 times the diameter of the well wall. The injection well 11 is used to add a heavy metal chelating agent, which is one or a combination of aspartic acid-glutamic acid polymeric amino acid and iminodisuccinic acid. After injection, the chelating agent diffuses evenly along the filter in the polluted aquifer, increasing the contact range with heavy metals, enhancing the migration and dissolution of heavy metals, thereby desorbing heavy metals from the surface of soil particles and collecting them with the groundwater into the permeable reactive barrier 2.

[0033] The bottom of the permeable reactive barrier 2 is an impermeable layer with an inclination angle consistent with the hydraulic gradient, and its depth is 0.8~1.0m greater than the depth of the groundwater pollution plume. An impermeable guide wall 22 is installed in front of the impermeable layer, with a depth 1.0~1.5m greater than the depth of the impermeable layer. The inlet side of the reactive barrier consists of a steel reinforcement frame and permeable geotextile. The steel reinforcement frame is covered with permeable geotextile, and the permeability coefficient of the permeable geotextile is greater than 1.0. 10 3 ~5.0 10 3 The flow rate is m / s; the steel reinforcement frame is made of multiple solid stainless steel pipes welded longitudinally and transversely, with a pipe diameter of 15~20mm and a frame width of 35~50cm. An impermeable concrete barrier plate 23 is also installed on the upper part of the inlet side wall. The bottom of the barrier plate is flush with the groundwater level, and the top is 0.3m above the ground, used to intercept debris. The outlet side wall of the reaction wall consists of an upper permeable wall 24 and a lower impermeable wall 25, with a length ratio of 1:1. A flow guide plate is installed in the middle of the reaction wall to divide the reaction zone into two unit zones. The flow guide plate consists of an upper retaining wall 26 and a lower grid filter 27, with a length ratio of 1:1. The flow guide plate causes the water to deflect, increasing the hydraulic residence time and increasing the contact between pollutants and the filler material, thus enabling a full reaction. The retaining wall consists of a steel reinforcement frame and multiple layers of impermeable geotextile, with a permeability coefficient of less than 5.0. 10 7 m / s; the grid filter is made of stainless steel pipes welded longitudinally and transversely into a perforated grid, with a pipe diameter of 8-10 mm and a hole spacing of 2-3 cm. Specifically, both the first and second units of the dual-unit zone are filled with reactive materials. The first unit is filled with adsorption filler 28, which is one or a composite filter material selected from activated zeolite, volcanic rock, and ceramsite, with a particle size of 2-5 mm. The lower part of the second unit is filled with adsorption filler 28, and the upper part is filled with activated biochar composite filler 29. The filler is spherical porous particles with a particle size of 2-4 mm. The width of each reaction unit is 1.5-2.5 m, and the material filling should ensure that the permeability coefficient of the wall and reaction zone is 2-6 times higher than that of the aquifer. The biochar composite filler composition includes 50%-60% bentonite-modified biochar, 10%-15% clay, 10%-15% diatomaceous earth, and 5%-10% ammonium bicarbonate. Clay is used as a binder, diatomaceous earth as a high-permeability material, and ammonium bicarbonate as a pore-forming agent, which can be obtained through existing technologies.

[0034] Specifically, as shown in Figure 4, the adsorption filler and activated biochar composite filler are uniformly filled into the permeable geotextile reaction pack 291 to prevent water flow impact and loss. The geotextile permeability coefficient is greater than 1.0. 10 3 ~5.0 10 3 The reaction packing material has a speed of m / s and is cylindrical, with a diameter of 0.3~0.6m and a length of 0.8m. The reaction packing material is placed within a stainless steel metal unit frame 292 for easy replacement. The diameter of the metal unit frame is 0.1m larger than the reaction packing material, and its length matches that of the permeable wall reaction unit. Lifting lugs 293 are installed at both ends of the top of the metal frame. The reaction packing material can be filled with active filler on the ground and sealed before being installed in the unit frame. Each packing material is then hoisted and stacked into the wall using ground lifting equipment, thus completing the loading of the entire filler material.

[0035] Specifically, the permeable reactive wall contains 21 pairs of electro-repairing cathode and anode electrodes, with a distance of less than 30 cm between each pair. The cathode electrode is a graphite rod, and the anode electrode is made of any one of titanium, stainless steel, or a conductive metal-organic framework material. The low-voltage DC power supply uses a solar photovoltaic device. When a DC voltage is applied to the electrodes, a DC electric field is formed between the electrodes, driving the electro-repairing process within a voltage range of 0–50V.

[0036] Heavy metals flow into the reaction zone of the permeable reactive barrier. Some heavy metals are adsorbed by the packing material, while some charged heavy metals migrate to the cathode electrode under the influence of the electric field, undergoing a reduction reaction and accumulating on the electrode surface. The electrode is then centrally treated to separate the heavy metals and remove some pollutants. The pre-treated groundwater enters the phytoremediation zone 3.

[0037] The phytoremediation zone 3 consists of a pool, a substrate 31, and plants. The bottom of the pool is an impermeable layer, flush with the top of the permeable reactive barrier 25 on the effluent side. The effluent side wall is composed of a steel frame and permeable geotextile. The pool width is 1.0~1.5m. The pool is filled with one or a combination of gravel, sand, zeolite, waste wood blocks, corn cob particles, and biochar. The particle size of inorganic fillers such as gravel, sand, and zeolite is 3~8mm, while the particle size of organic fillers such as waste wood blocks, corn cob particles, and biochar is 2~6mm. The particle size of the fillers in the substrate layer gradually increases from top to bottom. Plants, which are heavy metal hyperaccumulators, are planted on the upper part of the substrate. They are highly resistant to heavy metals such as Cr, Pb, Cu, and Cd. The plants continuously remove heavy metal pollutants through absorption. The primary effluent enters the storage and circulation zone 4.

[0038] The water storage and circulation zone 4 consists of a pool, a circulation pump group 41, water supply pipelines, and a water quality monitoring system 42. The water supply pipelines of the circulation pump group 41 are connected to the inlet side of the first unit of the permeable reactive wall 2, used to lift water with excessive heavy metals into the permeable reactive wall for circulation treatment. The bottom surface of the pool is an impermeable layer, flush with the bottom of the impermeable layer of the permeable reactive wall; the lower part of the inlet side is a water-resistant wall, the top surface of which is flush with the bottom surface of the pool in the plant restoration zone 3; the outlet side is a water-resistant wall with multiple openings in the sidewall for installing water supply pipelines.

[0039] The hydraulic cutoff zone 5 consists of a pool body, water supply pipes, and control valves 51. The pool body is surrounded by water-resistant walls, within which multiple water supply pipes and control valves 51 are installed, connecting the upstream water storage and circulation zone 4 and the downstream aquatic plant purification zone 6. Based on water quality monitoring results, when the heavy metal content in the water storage and circulation zone 4 exceeds the standard, control valve 51 is closed to cut off the groundwater flow. Simultaneously, the circulating water pump 41 and the pipe control valves are opened, transferring the substandard water to the permeable reactive wall reaction zone for circulation treatment. Through the synergistic effect of chelation, adsorption, electrochemistry, and plant enrichment, heavy metals are efficiently and persistently removed. Once the water quality meets the standard, the circulating water pump 41 and the pipe control valves are closed, and control valve 51 is opened, allowing the effluent to enter the aquatic plant purification zone 6.

[0040] The aquatic plant purification zone 6 consists of a pool and aquatic plants. The effluent sidewall is constructed of a reinforced steel frame and permeable geotextile. The pool width is 0.8–1.2 m. The bottom of the pool is alternately arranged with an impermeable layer 61 and a highly permeable layer 62, spaced 0.5 m apart. The upper part of the pool bottom is filled with a substrate. The highly permeable layer 62 is a composite filter layer composed of coarse sand, gravel, and pebbles. The coarse sand particle size is 2–5 mm, the gravel particle size is 10–30 mm, and the pebbles particle size is 20–50 mm, with a thickness of 0.5–0.6 m. The substrate is a composite filler of coarse sand, zeolite, and biological ceramic particles, with a particle size of 2–6 mm and a thickness of 0.3–0.5 m. Emergent and submerged plants are planted on top of the filler according to the water depth. The aquatic plants further enhance the absorption of heavy metals, and microorganisms decompose and remove ammonia nitrogen pollutants, deeply purifying the water. The secondary effluent enters the underground environment through the highly permeable layer at the bottom of the pool and the effluent wall.

[0041] Specifically, heavy metal hyperaccumulating plants include one or more of the following: carnation, coreopsis, alfalfa, Leymus chinensis, pokeweed, violet, marigold, ryegrass, and centipede grass; emergent plants include plants with strong wastewater purification capabilities such as reeds, cattails, irises, loosestrife, canna lilies, and others; and submerged plants include one or more of the following: Vallisneria natans, hornwort, foxtail grass, hydrangea, and water lilies.

[0042] Based on Example 1, as shown in Figure 2, Example 2 is equipped with a water quality monitoring system 42 in the permeable reactive wall inlet / outlet side 2, the water storage and circulation area 4, and the aquatic plant purification area 6. Through multi-level automated collection, detection, and analysis of water quality, the operating status of the permeable reactive wall and the heavy metal remediation process are determined.

[0043] The water quality monitoring system 42 is a multi-functional automatic water quality detection and analysis device, including a multi-parameter water quality sensor and a heavy metal ion concentration detector. It uses two sensor probes to detect the physical and chemical parameters of the water. The physical parameter sensor probe has six measurement channels to detect pH, dissolved oxygen, conductivity, temperature, redox potential, and turbidity. The chemical parameter sensor probe has three measurement channels to detect COD, NH3-N, and microbial (BOD). The heavy metal ion concentration detector uses a fully automated anodic stripping voltammetry method, determining the concentrations of Cd, Pb, and Cr ions through a process of enrichment followed by leaching. Sampling ports are set up in sections within the monitoring well, with sensors and detectors deployed at different depths to form a water quality monitoring network. All monitoring points are connected to a data acquisition unit at the wellhead via an RS485 bus, and the acquisition unit has a built-in 5G communication module for remote data transmission.

[0044] The injection well group 11, circulating pump group 41, and water quality monitoring system 42 are all automatically controlled by a PLC system, achieving automated and intelligent operation. Water quality monitoring information is transmitted to the workstation and input into the PLC control system via an A / D converter, allowing for real-time adjustment of reagent dosing parameters such as concentration, flow rate, pressure, and time. Simultaneously, the system evaluates the remediation effect of heavy metals in the contaminated groundwater and determines the replacement cycle of the permeable reactive barrier packing. Specifically, the PLC control system automatically adjusts the injection well group 11 based on the monitored heavy metal concentration. If the heavy metal concentration on the influent side of the permeable reactive barrier reaction zone 2 is lower than the concentration detected in the soil sample, it indicates that the heavy metals are adsorbed on the surface of soil particles, requiring leaching and desorption. Initially, the concentration, flow rate, and pressure of the injected reagent should be increased. Once the heavy metal concentration increases and becomes similar to the concentration detected in the soil sample, the concentration, flow rate, and pressure of the injected reagent should be reduced, and the reagent should be injected intermittently based on the concentration monitoring data to save reagent consumption. The PLC control system also automatically regulates the circulating pump group 41 and control valves. If the water quality monitoring system 42 shows that the water quality meets the standards, it indicates that the pollutant remediation has been completed. The control valve 51 of the hydraulic cutoff zone 5 is opened, and the effluent enters the aquatic plant purification zone 6. If the water quality does not meet the standards, the control valve 51 of the hydraulic cutoff zone 5 is closed, and the circulating water pump 41 and pipeline control valves are opened simultaneously to transfer the substandard water to the permeable reactive wall reaction zone 2 for circulation treatment until the effluent water quality meets the standards. When the pollutant removal effect is poor, the difference in removal rate between adjacent circulation cycles is less than 5%, and the packing material usage time reaches the maximum time limit, the packing material in the reaction zone and the plant remediation zone is replaced, and new plants are planted to improve the remediation efficiency.

[0045] Example 3, based on Example 1, as shown in Figure 3, further includes electrokinetic remediation electrode pairs 21 in collection area 1. The distance between each electrode pair is less than 30 cm. The cathode electrode is a graphite rod, and the anode electrode is any one of titanium, stainless steel, or a conductive metal-organic framework material. Heavy metals adsorbed on soil particles gain electrons at the cathode, undergoing an in-situ reduction reaction. Simultaneously, a heavy metal chelating agent is added to injection well 11, desorbing the heavy metals from the soil particle surface. The heavy metals then electromigrate to the cathode electrode, gain electrons, and undergo a reduction reaction, forming elemental enrichment on the electrode surface. The electrodes are periodically recovered, and the heavy metals are separated. The treated electrodes are recycled. The positions of the anode and cathode in collection area 1 and reaction area 2 are adjusted, with the electrodes positioned centrally where the original anode and cathode were, to enhance electrokinetic remediation and remove heavy metals. A low-voltage DC power supply using a solar photovoltaic device is employed. When a DC voltage is applied to the electrodes, a DC electric field is formed between them, driving the electrokinetic remediation process within a voltage range of 0–50 V.

[0046] Example 4, based on Example 1, as shown in Figure 3, further includes a microbial agent device in the aquatic plant purification zone 6. This device is used to add microbial agents to the water for further purification of ammonia nitrogen, COD, etc. The microbial agents include nitrifying bacteria and nutrients, including carbon sources, nitrogen sources, phosphorus sources, metal ions, and essential nutrients for microorganisms. The nitrifying bacteria and nutrients are stored separately in PVC solution tanks. Nutrients are periodically added to the aquatic plant purification zone to promote microbial growth and reproduction, thereby improving pollutant degradation efficiency. The microbial agent device is controlled by a PLC system for automated and intelligent operation. If the water quality monitoring system 42 shows that COD and NH3-N levels exceed the standards, and the microbial (BOD) level is below the standard, it indicates that the microbial content in the water is insufficient. The system will automatically open the microbial agent dosing pump and control valve to add nitrifying bacteria and nutrients to the water to promote microbial growth and decompose pollutants such as COD and NH3-N. If COD and NH3-N levels exceed the standards, but the microbial (BOD) level is within the standards, the system will periodically open the nutrient dosing pump and control valve to supply microbial nutrient solution to the water. If COD, NH3-N, and microbial (BOD) levels are all within the standards, the system will close the dosing pump and control valve to stop the dosing of microbial agents. The system is intelligently controlled by the PLC system to save on the amount of microbial agents used.

[0047] The present invention has been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described above. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Many other changes and modifications made without departing from the concept and scope of the present invention should be considered within the scope of protection of the present invention.

[0048] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0049] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for remediating heavy metals in groundwater on slopes, characterized in that, The method described is implemented using a slope groundwater heavy metal remediation system. This system comprises, in sequence, a collection zone, a permeable reactive barrier, a phytoremediation zone, a water storage and circulation zone, and a hydraulic cutoff zone within an aquifer. The collection zone is positioned along the flow direction of groundwater pollutants on the slope, and a group of injection wells is arranged within it. The permeable reactive barrier is filled with active material and equipped with anode and cathode pairs, and is connected to the phytoremediation zone. The phytoremediation zone consists of a pool, a substrate, and plants, and is connected to the water storage and circulation zone. The circulation zone is interconnected; the water storage and circulation zone consists of a tank, a circulation pump, and a water delivery pipeline, the water delivery pipeline being connected to the inlet side of the permeable reactive wall, and the tank being connected to the hydraulic cutoff zone; a water quality monitoring system is installed in the water storage and circulation zone; the hydraulic cutoff zone consists of a tank, a water delivery pipeline, and control valves on the water delivery pipeline; it also includes a PLC control system, which controls the opening and closing of the circulation pump and control valves based on the water quality monitoring results; the method includes the following steps: adding a heavy metal chelating agent to the injection well group in the collection area to remove heavy metals. The heavy metals are desorbed from the surface of soil particles, enhancing their mobility and solubility. All heavy metals are then collected with groundwater and flow into the permeable reactive barrier. The active materials filling the permeable reactive barrier and the anode and cathode electrodes capture and remove the heavy metals before they flow into the phytoremediation zone. The phytoremediation zone continues to remove heavy metal pollutants before the remaining heavy metals flow into the water storage and circulation zone. In the water storage and circulation zone, a water quality monitoring system monitors the water quality in real time. If the heavy metal content exceeds the standard, the PLC control system outputs a control signal to close the control valve in the hydraulic cutoff zone. Open the circulating water pump and pipeline control valve in the water storage and circulation zone to transfer substandard water to the collection zone or the inlet side of the permeable reactive wall for circulation treatment. Through the synergistic effect of chelation-adsorption-electrochemical-plant enrichment, heavy metals are efficiently and persistently removed. If the water quality meets the standards, close the circulating water pump and pipeline control valve in the water storage and circulation zone, open the control valve in the hydraulic cutoff zone, and the effluent enters the aquatic plant purification zone. The aquatic plants further enhance the absorption of heavy metals, and microorganisms decompose and remove ammonia nitrogen pollutants, deeply purifying the water quality. The effluent enters the underground environment through the highly permeable layer at the bottom of the pool and the outlet wall.

2. The method for remediating heavy metals in groundwater on slopes according to claim 1, characterized in that, An aquatic plant purification zone is set up at the outlet of the water supply pipe in the hydraulic cutoff zone. The aquatic plant purification zone consists of a pool and aquatic plants, and is used to deeply purify the effluent water quality. The purified water flows out to the underground environment through the effluent pool.

3. The method for remediating heavy metals in groundwater on slopes according to claim 1, characterized in that, The collection area is located on a slope with a certain gradient of 5-15°. The injection well group in the collection area consists of incomplete wells, located in a heavy metal-contaminated aquifer with a large hydraulic gradient, at a depth similar to that of the contaminated groundwater. A heavy metal chelating agent is added to the injection well group. The heavy metal chelating agent is one or a combination of aspartic acid-glutamic acid polymeric amino acid and iminodisuccinic acid, used to desorb heavy metals from the surface of soil particles, enhance the mobility and dissolution of heavy metals, and allow all heavy metals to flow into the permeable reactive barrier along with the groundwater.

4. The method for remediating heavy metals in groundwater on slopes according to claim 1, characterized in that, The bottom of the permeable reactive wall is an impermeable layer with an inclination angle consistent with the hydraulic gradient, and its depth is 0.8~1.0m greater than the depth of the groundwater pollution plume. An impermeable guide wall is set at the front end of the impermeable layer, with a depth 1.0~1.5m greater than the depth of the impermeable layer. The water inlet wall of the permeable reactive wall is composed of a steel skeleton and a permeable geotextile covering the steel skeleton. An impermeable concrete barrier plate is also set on the upper part of the water inlet wall. The bottom of the barrier plate is level with the groundwater level, and the top is 0.3m above the ground. The water outlet wall of the permeable reactive wall is composed of an upper permeable wall and a lower water-resistant wall, with a length ratio of 1:

1. A guide plate is set in the middle of the permeable reactive wall to divide the reaction area into two unit areas. The guide plate is composed of an upper water-retaining wall and a lower grid filter, with a length ratio of 1:

1.

5. A method for remediating heavy metals in groundwater on slopes according to claim 4, characterized in that, Both the first and second units of the dual-unit zone are filled with reactive materials. The first unit is filled with adsorption filler, which is one or a composite filter material of activated zeolite, volcanic rock, and ceramsite, with a particle size of 2-5 mm. The lower part of the second unit is filled with adsorption filler, and the upper part is filled with activated biochar composite filler. The filler is spherical porous particles with a particle size of 2-4 mm. The width of each reaction unit is 1.5-2.5 m. The material filling should make the permeability coefficient of the wall and reaction zone 2-6 times higher than the permeability coefficient of the aquifer. An electrically operated repair anode and cathode electrode pair is provided in the first unit and / or the second unit.

6. The method for remediating heavy metals in groundwater on slopes according to claim 1, characterized in that, The bottom surface of the phytoremediation area pool is an impermeable layer, and the bottom surface is flush with the top of the permeable reactive wall on the water outlet side. The water outlet side wall is composed of a steel frame and permeable geotextile. The phytoremediation area pool is filled with one or a combination of gravel, sand, zeolite, waste wood blocks, corn cob particles, and biochar. Plants are planted on the upper part of the substrate. The particle size of the inorganic fillers such as gravel, sand, and zeolite is 3~8mm, and the particle size of the organic fillers such as waste wood blocks, corn cob particles, and biochar is 2~6mm. The particle size of the fillers in the substrate layer gradually increases from top to bottom.

7. The method for remediating heavy metals in groundwater on slopes according to claim 1, characterized in that, The lower part of the water inlet side of the water storage and circulation area is a water-proof wall, and its top surface is flush with the bottom surface of the plant restoration area pool. The bottom surface of the water storage and circulation area pool is an impermeable layer, which is flush with the bottom of the impermeable layer of the permeable reactive wall. The water outlet side is a water-proof wall with multiple openings on the side wall for installing water supply pipes.

8. The method for remediating heavy metals in groundwater on slopes according to claim 1, characterized in that, The hydraulic cutoff zone pool is surrounded by water-proof walls, inside which multiple water supply pipes are installed. Each water supply pipe is equipped with a control valve, and the water supply pipes connect the upstream water storage and circulation zone and the downstream aquatic plant purification zone.

9. A method for remediating heavy metals in groundwater on slopes according to claim 1, characterized in that, The bottom of the aquatic plant purification area pool is composed of an impermeable bottom plate and a highly permeable layer arranged at intervals of 0.5m. The upper part of the pool bottom is filled with matrix filler, and emergent and submerged plants are selected and planted on the filler according to the water depth to deeply purify the effluent water quality. The effluent side wall is composed of a steel frame and permeable geotextile, and the pool width is 0.8~1.2m.

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