A multifunctional synergistic filler and a green electricity-driven electrochemical groundwater remediation method

Abstract

This invention relates to the field of groundwater pollution remediation technology, specifically to a multifunctional synergistic filler and a green electricity-driven electrochemical groundwater remediation method. The filler uses attapulgite or montmorillonite-modified biomass pyrolytic carbon as a substrate, in-situ constructing a three-dimensional interconnected conductive network of graphene quantum dots and carboxylated carbon nanotubes. It anchors bifunctional catalytic sites composed of layered bimetallic hydroxides and defective metal oxides, possessing multiple functions including water permeability, adsorption and capture, electron transfer, and electrocatalytic reduction. Based on this filler, this invention constructs an e-PRB remediation wall, using solar green electricity to drive a fluctuating electric field to enhance the directional migration and in-situ fixation of heavy metals. An integrated multi-field coupling numerical model and dual intelligent control algorithm enable adaptive operation, simultaneously completing targeted heavy metal remediation, resource recovery, and in-situ regeneration of the filler. This method boasts high remediation efficiency, low carbon footprint, and environmental friendliness, making it suitable for various in-situ remediation scenarios for heavy metal pollution in groundwater.

Description

Technical Field

[0001] This invention relates to the field of groundwater pollution remediation technology, specifically to a multifunctional synergistic filler and a green electric-driven electrochemical groundwater remediation method. Background Technology

[0002] Heavy metals, as typical highly toxic and recalcitrant pollutants in groundwater environments, are prone to bioaccumulation through the food chain, seriously threatening drinking water safety, ecosystem health, and human living environment safety. Developing efficient, low-carbon, and in-situ controllable groundwater heavy metal remediation technologies is a core need and research hotspot in the field of water environment governance.

[0003] Currently, reactive permeable grids (PRBs) are the mainstream technology for in-situ remediation of heavy metals in groundwater. However, traditional PRBs rely solely on physical adsorption and chemical reactions to trap pollutants, resulting in low mass transfer efficiency, easy saturation of the packing material, and easy desorption and re-migration of heavy metals. While the e-PRB technology, coupled with electrochemical enhancement, combines the dual advantages of electric field-driven enhanced pollutant migration and directional transformation of the reaction medium, thus improving remediation efficiency to some extent, it still faces many engineering bottlenecks.

[0004] Existing e-PRB packing materials have limited functionality and cannot simultaneously meet the multiple requirements of permeable bearing capacity, electron transfer, targeted adsorption, and electrocatalytic reduction. They suffer from long and inefficient electron transfer paths and insufficient catalytically active sites. The systems are highly dependent on stable mains power, resulting in high energy consumption and carbon emissions. They are unsuitable for remote, grid-free, and polluted sites and have extremely poor compatibility with fluctuating green energy sources such as solar power. Furthermore, the lack of multi-field coupling prediction models and intelligent control strategies to adapt to fluctuating energy inputs makes them prone to fluctuations in remediation effectiveness and the risk of nighttime desorption of heavy metals. Additionally, the packing material requires excavation and replacement after saturation, leading to high maintenance costs and the potential for secondary pollution. Current technologies struggle to balance remediation efficiency, low-carbon operation, long-term stability, and resource recovery, severely hindering the large-scale engineering application of e-PRB technology. Summary of the Invention

[0005] Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a multifunctional synergistic filler and a green electric-driven electrochemical groundwater remediation method.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A multifunctional synergistic packing material of the present invention, wherein the packing material is a granular porous composite material, comprising a mineral biochar substrate, a three-dimensional interconnected conductive network in situ grown on the surface of the mineral biochar, and bifunctional catalytic active sites uniformly anchored on the surface of the conductive network. The mineral-type biochar is attapulgite or montmorillonite-modified biomass pyrolysis char, which has a hierarchical porous structure and serves as an environmentally compatible support framework and a heavy metal physical adsorption unit for the filler. The three-dimensional interconnected conductive network is a continuous conductive structure formed by in-situ hybridization of graphene quantum dots and carboxylated carbon nanotubes, which completely covers the inner wall and outer surface of the pores of mineral-type biochar, serving as an electron transport unit for the filler. The bifunctional catalytic active site is an ultrathin nanosheet structure formed by the composite of layered bimetallic hydroxide and oxygen vacancy defective metal oxide, which grows vertically in-plane on the surface of a three-dimensional interconnected conductive network, serving as a heavy metal ion targeted capture unit and an electrocatalytic reduction unit as filler.

[0007] Preferably, the biomass source of the mineral biochar is agricultural and forestry waste, the doping mass ratio of attapulgite or montmorillonite is 10%-25%, the pyrolysis preparation temperature is 550℃-750℃, the pyrolysis atmosphere is a nitrogen inert atmosphere, and the pyrolysis time is 2h-4h.

[0008] In a further preferred embodiment, in the three-dimensional interconnected conductive network, the mass ratio of graphene quantum dots to carboxylated carbon nanotubes is 1:3-1:8, the particle size of the graphene quantum dots is 2nm-10nm, and the diameter of the carboxylated carbon nanotubes is 8nm-15nm and the length is 5μm-20μm. After in-situ hybridization, a continuous and uninterrupted conductive coating layer is formed on the surface of mineral-type biochar.

[0009] Preferably, in the bifunctional catalytic active site, the layered bimetallic hydroxide is any one of Mg-AlLDH, Ni-FeLDH, and Zn-CrLDH, and the oxygen vacancy defective metal oxide is any one of defective manganese dioxide, defective ferric oxide, and defective cobalt tetroxide, and the composite mass ratio of the two is 2:1-5:1.

[0010] Preferably, the multifunctional synergistic filler is a spherical particle with a particle size of 2mm-8mm.

[0011] More preferably, the surface of the mineral biochar is activated by acid and alkali treatment to introduce hydroxyl and carboxyl oxygen-containing functional groups, with a functional group content ≥1.2 mmol / g. The three-dimensional interconnected conductive network is grown in situ on the surface of the mineral biochar by hydrothermal method, and the bifunctional catalytic active sites are anchored on the surface of the conductive network by in-situ precipitation method.

[0012] A further preferred method for green electricity-driven electrochemical groundwater remediation includes the following steps: S1 remediation system construction: Downstream of the groundwater heavy metal pollution plume, a waterproof and seepage-proof curtain is constructed perpendicular to the groundwater flow direction. Upstream of the seepage-proof curtain, an e-PRB remediation wall is constructed in the polluted aquifer. The e-PRB remediation wall is divided into an anode zone, a functional filler reaction zone, and a cathode zone along the groundwater flow direction. The functional filler reaction zone is filled with the multifunctional synergistic filler. The anode zone and the cathode zone are filled with conductive graphite particles. The anode and cathode are connected to a green electric drive system via waterproof wires. S2 Green Electricity Drive System Construction: Construct a green electricity drive system including solar photovoltaic panels, energy storage supercapacitor modules, programmable fluctuation power supplies, and intelligent control units. The solar photovoltaic panels are the main power supply unit of the system. The energy storage supercapacitor modules are used to smooth out intraday fluctuations in photovoltaic power. The programmable fluctuation power supply is used to output sine wave or square wave fluctuation voltages that are adapted to the repair needs. The intelligent control unit has a built-in multi-field coupling numerical model and dual intelligent control algorithms. S3 Heavy Metal Targeted Remediation Operation: A fluctuating electric field is applied to the e-PRB remediation wall through a green electric drive system. Heavy metal ions in the groundwater migrate directionally to the functional filler reaction zone under the drive of the electric field. Through the physical adsorption, functional group targeted capture, and electrocatalytic reduction of the multifunctional synergistic filler, the heavy metals are fixed in situ and converted to non-toxic valence states. The treated groundwater is discharged through the seepage-proof curtain in compliance with standards. S4 Adaptive Intelligent Control: The intelligent control unit collects data on solar irradiance, influent pollutant concentration, internal potential or pH field distribution of the repair wall, and effluent water quality in real time. It dynamically adjusts electric field parameters and energy distribution through dual intelligent control algorithms to achieve stable and efficient repair under fluctuating green electricity input. S5 Heavy Metal Resource Recovery and Packing Material Regeneration: After the repair operation is set, a constant potential is applied to the e-PRB repair wall in reverse through the green electric drive system, which reduces and peels off the heavy metal elements fixed on the multifunctional synergistic packing material and collects them in a directional manner, thus realizing the recovery of heavy metal resources and in-situ regeneration of packing material at the same time.

[0013] Preferably, in step S1, the thickness of the e-PRB repair wall is 0.8m-3m, the wall depth covers the entire contaminated aquifer, the thickness of both the anode and cathode zones is 1 / 5-1 / 3 of the thickness of the functional filler reaction zone, and the distance between the anode and cathode is 0.5m-2.5m. More preferably, in step S2, the fluctuating voltage output range of the green electric drive system is 0.8V-5V, and the frequency is 0.1Hz-10Hz. In step S5, the range of the reverse constant potential is -0.8V to -2.5V, and the application time is 2h-6h.

[0014] Preferably, the dual intelligent control algorithm in step S4 includes a predictive buffer algorithm and a demand response algorithm; The predictive buffering algorithm combines a supercapacitor charge-discharge model with intraday solar irradiance time-series prediction data. The demand response algorithm dynamically adjusts the electric field output power and fluctuation mode based on real-time influent pollutant concentration and effluent water quality feedback. In step S4, the multi-field coupled numerical model built into the intelligent control unit is a high-fidelity numerical model that couples the unstable groundwater flow field, the fluctuating electric potential field, the heavy metal ion migration field, and the electrode reaction dynamics. It can simulate and predict the system's annual-scale repair efficiency and long-term operational stability.

[0015] (III) Beneficial Effects Compared with existing technologies, this invention provides a multifunctional synergistic filler and a green electrochemical groundwater remediation method, which has the following beneficial effects: The packing material developed in this technical solution uses agricultural and forestry waste-based mineral biochar as its framework, which is both environmentally friendly and has a high specific surface area. The three-dimensional conductive network of graphene quantum dots / carboxylated carbon nanotubes constructed in situ on its surface enables rapid cross-scale electron transfer. The vertically anchored LDH / oxygen vacancy metal oxide bifunctional active sites can simultaneously complete the targeted adsorption and electrocatalytic reduction of heavy metal ions, and the stationary state is stable with no risk of secondary release.

[0016] The system is powered entirely by solar energy, combining supercapacitor energy storage and programmable fluctuating power supply to convert intermittent photovoltaic power into a fluctuating electric field that adapts to the repair dynamics. The intelligent control unit optimizes the electric field parameters in real time based on a multi-field coupled numerical model and dual algorithms to ensure that the effluent meets the standards under fluctuating light conditions. The energy consumption is reduced by more than 40% compared to the traditional DC electrochemical method.

[0017] After the repair cycle is completed, a reverse constant potential of -0.8V to -2.5V is applied for 2–6 hours to selectively strip and recover heavy metal elements, and simultaneously regenerate the filler. After 5 cycles, the performance decay is less than 8%, which greatly reduces long-term operation and maintenance costs.

[0018] In summary, this technical solution achieves integrated high-efficiency removal, green energy supply, intelligent control, and resource recycling, and has outstanding environmental, economic, and engineering application value. The e-PRB wall structure is reasonable and has good permeability, making it suitable for various aquifer scenarios. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the hierarchical structure of the multifunctional synergistic filler of the present invention; Figure 2 This is a schematic diagram illustrating the working principle of the green electricity-driven electrochemical groundwater remediation system of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1-2 The present invention provides a multifunctional synergistic filler, wherein the filler is a granular porous composite material comprising a mineral biochar substrate, a three-dimensional interconnected conductive network grown in situ on the surface of the mineral biochar, and bifunctional catalytic active sites uniformly anchored on the surface of the conductive network. The mineral-type biochar is attapulgite or montmorillonite-modified biomass pyrolysis char, which has a hierarchical porous structure and serves as an environmentally compatible support framework and a heavy metal physical adsorption unit for the filler. The three-dimensional interconnected conductive network is a continuous conductive structure formed by in-situ hybridization of graphene quantum dots and carboxylated carbon nanotubes, which completely covers the inner wall and outer surface of the pores of mineral-type biochar, serving as an electron transport unit for the filler. The bifunctional catalytic active site is an ultrathin nanosheet structure formed by the composite of layered bimetallic hydroxide and oxygen vacancy defective metal oxide, which grows vertically in-plane on the surface of a three-dimensional interconnected conductive network, serving as a heavy metal ion targeted capture unit and an electrocatalytic reduction unit as filler.

[0022] This technical solution is divided into two main dimensions: On the materials side: Breaking through the bottleneck of the single function of traditional PRB fillers, through the hierarchical synergy of mineral-based biochar substrate, three-dimensional interconnected conductive network, and dual-functional catalytic active sites, single-particle fillers can simultaneously possess five core functions: water permeability and load-bearing, physical adsorption, targeted capture, electron transfer, and electrocatalytic reduction. The filler itself is a micro working electrode, completely opening up the entire pathway of heavy metal enrichment, electron transfer, and catalytic reduction, solving the core pain points of traditional e-PRB such as low electron transfer efficiency, poor mass transfer capacity, and easy desorption of heavy metals.

[0023] Methodologically: Breaking away from the dependence of traditional electrochemical remediation on stable mains power, this approach uses fluctuating solar green electricity as the sole energy source. It enhances the directional migration of heavy metals through fluctuating electric fields, and combines a multi-field coupled high-fidelity numerical model with dual intelligent control algorithms to achieve adaptive and stable system operation under fluctuating energy. Finally, it achieves heavy metal resource recovery and in-situ regeneration of fillers through reverse constant potential, forming a green closed loop of remediation, recovery, and regeneration, taking into account both environmental governance and resource recycling.

[0024] Mineral-based biochar substrates include an environmentally compatible support framework and physical adsorption units. Based on the pyrolytic char of agricultural and forestry waste, the biochar is modified with attapulgite or montmorillonite clay minerals to form a hierarchical porous structure, such as a gradient distribution of micropores, mesopores, and macropores. On the one hand, it achieves physical adsorption and retention of heavy metal ions with its ultra-high specific surface area; on the other hand, the layered structure of the clay minerals and its cation exchange capacity further enhance the heavy metal ion exchange efficiency. At the same time, the modified biochar has higher mechanical strength and stronger environmental compatibility. It is not easily broken under long-term scouring by groundwater and does not release toxic substances, making it the core load-bearing foundation of the packing material.

[0025] The clay mineral doping ratio is 10%-25%. When it is below 10%, the pore modification and ion exchange enhancement effects of clay minerals are insufficient. When it is above 25%, the carbon skeleton ratio decreases, the mechanical strength is greatly reduced, and it is easy to sinter and break during pyrolysis. This range is the optimal range that balances adsorption performance, mechanical strength and environmental stability.

[0026] Pyrolysis temperature 550℃-750℃, inert atmosphere pyrolysis 2h-4h: below 550℃, biomass carbonization is incomplete and pore structure is underdeveloped; above 750℃, the carbon skeleton is over-sintered, pores collapse, oxygen-containing functional groups decompose in large quantities, and adsorption sites are sharply reduced; pyrolysis time of 2h-4h can ensure complete carbonization and avoid damage to pore structure.

[0027] After acid-base activation, the oxygen-containing functional groups are ≥1.2 mmol / g: oxygen-containing functional groups such as hydroxyl and carboxyl groups can, firstly, undergo complexation reactions with heavy metal ions to enhance the targeted capture ability; secondly, they provide anchoring points for the in-situ growth of the three-dimensional conductive network, ensuring the chemical bonding between the conductive network and biochar and preventing long-term erosion and detachment. When the functional group content is less than 1.2 mmol / g, neither the complexation sites nor the anchoring points can meet the usage requirements.

[0028] The three-dimensional interconnected conductive network includes electron transport units and electric field enhancement units. To address the shortcomings of traditional e-PRB fillers, such as separation from the electrode, long electron transport paths, and high resistance, an in-situ hybridization of graphene quantum dots (GQDs) and carboxylated carbon nanotubes (CNTs) is employed to form a continuous conductive network with zero-dimensional nodes and a one-dimensional framework. The carboxylated carbon nanotubes overlap to form long-range conductive pathways, while the graphene quantum dots fill the gaps between the carbon nanotubes, completely eliminating conductive breaks and fully coating the inner walls and outer surfaces of the biochar pores, making the entire filler particle an integrated micro-working electrode. Electrons can be rapidly and without resistance within the filler, significantly improving the Faraday efficiency of electrocatalytic reduction. Simultaneously, the continuous conductive network strengthens the local electric field, further enhancing the directional migration efficiency of heavy metal ions to the filler surface.

[0029] The mass ratio of GQDs to CNTs is 1:3-1:8: If the proportion of GQDs is too high, such as >1:3, the proportion of continuous conductive framework of carbon nanotubes is insufficient, and long-range conductive pathways cannot be formed; if the proportion is too low, such as <1:8, the overlap gaps of carbon nanotubes cannot be filled, there are breaks in the conductive network, and the conductivity decreases significantly; within this range, a continuous coating layer without breaks can be formed, ensuring that the overall conductivity of the filler is ≥120S / m.

[0030] GQDs have a particle size of 2nm-10nm, CNTs have a tube diameter of 8nm-15nm, and a tube length of 5μm-20μm. The particle size of GQDs matches the mesopore size of biochar, allowing it to penetrate deep into the pores and achieve full coverage of the inner wall for conductive coating. The size of the carbon nanotubes can form a stable and continuous network on the outer surface of biochar without clogging the pores of biochar, ensuring that the permeability coefficient of the filler meets the hydraulic flow requirements of PRB.

[0031] Hydrothermal in-situ growth: Compared with physical impregnation and mechanical mixing, the hydrothermal method can make the conductive network firmly bonded to the surface of biochar through the chemical bonding of oxygen-containing functional groups. It will not fall off under long-term scouring of groundwater and ensures that the conductivity decay rate is ≤8% after 180 days of continuous operation. Its long-term stability is far superior to that of the physical loading method.

[0032] Bifunctional catalytic active sites include targeted capture units and electrocatalytic reduction units. An ultrathin nanosheet structure, composed of layered double metal hydroxide (LDH) and oxygen vacancy defect type metal oxide, is vertically grown on the surface of a three-dimensional conductive network to achieve a synergistic effect of enrichment and reduction. Targeted capture function: The layered structure of LDH contains a large number of hydroxyl active sites and exchangeable interlayer anions, which can specifically capture divalent heavy metal ions, such as Pb, in groundwater through complexation and ion exchange. 2 +、Cd 2 +、Cu 2 + etc., to achieve the directional enrichment of heavy metals on the surface of the filler, and solve the problem of low contact probability between low concentration heavy metal ions and catalytic sites; Electrocatalytic reduction function: Oxygen vacancy defective metal oxides have abundant unsaturated active sites, which can significantly reduce the overpotential of heavy metal ion reduction. Electrons are rapidly transferred through the conductive network, removing enriched toxic high-valence heavy metals, such as Cr. 6 + Reduced to non-toxic, low-valence Cr 3 +, or reduce heavy metal ions to stable elements, completely solving the risk of heavy metal desorption and re-migration, including the desorption problem when there is no power supply at night; Structural advantages: The vertical growth of ultrathin nanosheets maximizes the exposure of active sites, avoids site waste caused by sheet stacking, and allows active sites to directly contact the conductive network, enabling unimpeded electron transfer and significantly improving the Faraday efficiency of catalytic reduction.

[0033] The mass ratio of LDH to defective metal oxide composites is 2:1-5:1. If the proportion of LDH is too high, such as >5:1, there are insufficient catalytic reduction sites, the enriched heavy metals cannot be stably fixed and are easily desorbed; if the proportion is too low, such as <2:1, there are insufficient targeted capture sites, the heavy metals cannot be effectively enriched and the catalytic efficiency drops significantly. This range perfectly balances the synergistic effect of capture and reduction.

[0034] Material selection and matching logic: Ni-FeLDH has the highest anion exchange capacity and the strongest ability to capture divalent heavy metals; defective manganese dioxide has the strongest ability to capture Cr. 6 + exhibits the best reduction catalytic activity, while defective ferric oxide shows the best reduction catalytic activity for Pb. 2 +、Cd 2 The + type offers the best restoration and fixation effect, and can be flexibly selected according to the type of site pollution, making it highly adaptable to different sites.

[0035] In-situ precipitation anchoring: The nanosheets form chemical bonds with the conductive network through in-situ precipitation, and do not fall off during long-term operation; the vertically grown structure does not block the pores of the filler, ensuring water permeability, while maximizing the exposure of active sites, and the catalytic efficiency is more than 3 times higher than that of planar loading.

[0036] Spherical particles with a diameter of 2mm-8mm: When the particle size is <2mm, the packing material is too dense, the permeability coefficient decreases, and it is easily blocked by groundwater suspended matter; when the particle size is >8mm, the specific surface area of ​​the packing material is sharply reduced, the adsorption and catalytic sites are insufficient, and the remediation efficiency decreases; this range takes into account the hydraulic flow capacity and reactivity required by PRB, with a permeability coefficient ≥5×10^-3cm / s, which fully meets the requirements of in-situ remediation.

[0037] Working principle of each step in the green electricity-driven electrochemical groundwater remediation method Step S1: Construction of the Repair System Core working principle: By forcibly blocking the downstream migration of the pollutant plume through a waterproof and seepage-proof curtain, the polluted groundwater is allowed to flow 100% through the e-PRB remediation wall, avoiding short-circuit flow and bypass flow. A three-section structure with an anode zone, a functional filler reaction zone, and a cathode zone is set along the groundwater flow direction. After being energized, a stable electric field is formed in the aquifer. Under the action of electromigration and electroosmosis, the heavy metal cations in the groundwater move directionally towards the cathode and are forced to pass through the functional filler reaction zone. Compared with the traditional PRB contact mode that relies solely on natural convection diffusion, the contact efficiency between heavy metals and fillers is increased by more than 10 times, fundamentally improving the remediation efficiency.

[0038] Technical logic of the preferred technical solution: Wall thickness 0.8m-3m: When the thickness is <0.8m, the contact time between groundwater and filler is insufficient, and heavy metals cannot be fully adsorbed and reduced; when the thickness is >3m, the hydraulic resistance is too large, the energy consumption of the electric field is significantly increased, and the economic efficiency is reduced; it can be flexibly adjusted according to the pollution concentration and groundwater flow rate to adapt to different site requirements.

[0039] The thickness of the anode and cathode regions should be 1 / 5 to 1 / 3 of that of the functional regions, and the electrode spacing should be 0.5m to 2.5m. If the anode and cathode regions are too thick, they will occupy the effective reaction space of the functional packing. If the electrode spacing is too small, local short circuits in the electric field are likely to occur. If the electrode spacing is too large, the electric field strength will be insufficient, and the directional migration effect of heavy metals will be poor. This parameter range can maximize the reaction space of the functional packing while ensuring the electric field driving effect and reducing the operating energy consumption.

[0040] Step S2: Green Electric Drive System Setup Using solar photovoltaic panels as the sole primary power source, the system achieves zero dependence on grid power and zero carbon emissions, making it suitable for the remediation needs of remote, grid-free, and polluted sites. Compared to lithium batteries, the energy storage supercapacitor module offers faster charging and discharging speeds and longer cycle life, quickly mitigating intraday fluctuations in photovoltaic power, such as those caused by cloud cover, overcast skies, or lack of sunlight at night, ensuring stable electric field output. The programmable fluctuating power supply can output sine and square wave voltages tailored to remediation requirements. Compared to constant voltage power supply, fluctuating voltage enhances the migration dynamics of heavy metal ions while suppressing electrode polarization and reducing energy consumption. The intelligent control unit, serving as the system's brain, incorporates a multi-field coupling model and dual intelligent algorithms to achieve fully automated control throughout the entire process.

[0041] Technical logic of the preferred technical solution: Fluctuating voltage 0.8V-5V, frequency 0.1Hz-10Hz: When the voltage is <0.8V, the electric field strength is insufficient, and the directional migration effect of heavy metals is poor; when the voltage is >5V, water electrolysis is intensified, the pH of the aquifer fluctuates drastically, which can easily lead to the precipitation of heavy metal hydroxides that clog the pores of the filler, and even trigger the desorption of fixed heavy metals; the frequency of 0.1Hz-10Hz can match the migration rate of heavy metal ions, enhance the interfacial reaction kinetics, and suppress electrode polarization, reducing energy consumption by more than 40% compared with constant voltage power supply.

[0042] Step S3: Heavy Metal Targeted Repair Operation Core working principle: Through the synergistic effect of electric field-driven directional migration, physical adsorption and retention, functional group targeted capture, and electrocatalytic reduction and fixation, high-efficiency removal and stabilization of heavy metals are achieved. A fluctuating electric field drives heavy metal cations to move directionally toward the cathode and force them to pass through the functional packing reaction zone, thus solving the problem of low mass transfer efficiency of low-concentration heavy metals. The hierarchical porous structure of mineral biochar traps heavy metals through physical adsorption, while LDH achieves targeted enrichment of heavy metals through complexation and ion exchange, significantly increasing the heavy metal concentration on the surface of the filler. The three-dimensional conductive network rapidly transfers electrons to the catalytic active site, reducing the enriched heavy metal ions to non-toxic valence states or stable elements, forming insoluble solid products, and completely eliminating the risk of desorption and re-migration of heavy metals. The treated groundwater that meets the standards is discharged downstream through the impermeable curtain, achieving efficient in-situ remediation of the pollution.

[0043] Step S4 Adaptive Intelligent Control Core working principle: To address the industry pain point of unstable system repair effects under fluctuating green electricity input, the system achieves adaptive and stable operation through mechanism model prediction and dual-algorithm closed-loop control.

[0044] Multi-field coupled high-fidelity numerical model: Coupled with four core fields: unsteady groundwater flow field, fluctuating electric potential field, heavy metal ion migration field, and electrode reaction kinetics, it can accurately simulate the remediation effect of the system under different solar irradiance and pollution load. After importing the annual solar irradiance time series data, it can predict the long-term operating efficiency on an annual scale, predict the risk of heavy metal desorption in advance, and optimize operating parameters.

[0045] Dual-intelligent control algorithm technology logic: Predictive buffering algorithm: Combining the supercapacitor charging and discharging model with intraday solar irradiance time-series prediction data, the charging and discharging strategy is optimized in advance: When the irradiance is high during the day and the photovoltaic power is excessive, the supercapacitor is controlled to charge and store energy; when the irradiance is insufficient in the evening, on cloudy days, or at night, the supercapacitor is controlled to discharge and supply power, thus smoothing the fluctuation of photovoltaic power and ensuring that the system can still operate stably under 72 hours of no sunlight, avoiding the desorption of heavy metals caused by voltage fluctuations.

[0046] Demand response algorithm: Based on real-time influent pollutant concentration and effluent water quality feedback, the output power and fluctuation mode of the electric field are dynamically adjusted: the power is increased during high pollution load to enhance the repair effect; the power is reduced during low pollution load to achieve on-demand repair and avoid ineffective energy consumption. The overall operating energy consumption is reduced by more than 50% compared with the fixed parameter mode.

[0047] Step S5: Heavy Metal Resource Recovery and In-situ Regeneration of Packing Material Addressing the shortcomings of traditional PRB packing materials, such as the need for excavation and replacement after saturation, high costs, easy secondary pollution, and inability to recover heavy metals, this invention applies a reverse constant potential, using the functional packing material as a cathode to reduce the solid heavy metal products fixed on the packing surface into soluble ions. These ions are then stripped into an aqueous solution and collected directionally, achieving resource recovery of heavy metals. Simultaneously, after the heavy metals are stripped, the adsorption and catalytic sites of the packing material are fully restored, achieving in-situ regeneration without the need for excavation and replacement, significantly reducing operation and maintenance costs and avoiding secondary pollution.

[0048] Technical logic of the preferred technical solution: Reverse constant potential -0.8V to -2.5V, application time 2h-6h: When the absolute value of the potential is <0.8V, the heavy metal stripping is insufficient and the recovery rate is <60%; when the absolute value of the potential is >2.5V, water electrolysis is violent, which will destroy the conductive network and catalytic sites of the packing and cause irreversible performance damage; within this parameter range, the heavy metal stripping recovery rate can be ≥90%, and the packing adsorption capacity recovery rate can be ≥95%, and it can be recycled ≥5 times.

[0049] All materials, processes, equipment, and construction methods in this solution are mature and universal technologies in the fields of environmental remediation and material preparation. No special customization or development is required. Ordinary environmental engineering companies and material processing plants can achieve mass production and project implementation, making it fully industrial-grade feasible.

[0050] Feasibility of multifunctional synergistic packing Raw materials are readily available and costs are controllable: biomass raw materials are agricultural and forestry waste such as corn stalks and wheat stalks, which are widely available and extremely low in cost; attapulgite, montmorillonite, graphene quantum dots, carboxylated carbon nanotubes, LDH precursors and other materials are all mature commercial products on the market, with sufficient procurement channels, and no need for laboratory self-production.

[0051] The preparation process is mature and can be mass-produced on a large scale: biochar pyrolysis, acid-base activation, hydrothermal reaction, in-situ precipitation, and granulation are all conventional processes in the powder and carbon materials industry. Tube furnaces, hydrothermal reactors, and disc granulators are all general industrial equipment, which can achieve seamless scale-up from laboratory pilot to industrial mass production without technical barriers.

[0052] Stable performance and meets engineering requirements: The prepared filler material fully meets the engineering specifications for e-PRB in-situ remediation in terms of permeability, adsorption capacity, conductivity, mechanical strength and long-term stability. It releases no toxic or harmful substances and meets the environmental safety standards for groundwater remediation.

[0053] Feasibility of green electric drive-based repair methods The engineering construction technology is mature and can be implemented quickly: the waterproof and seepage-proof curtain adopts cement mixing piles / high-pressure jet grouting piles, and the e-PRB wall adopts continuous wall groove in-situ filling. These are all conventional construction technologies in the field of groundwater pollution control, with hundreds of engineering application cases in China. The construction team has mature technology and can quickly realize the project implementation.

[0054] The equipment system is mature and can be directly integrated: the solar photovoltaic panels, energy storage supercapacitors, programmable power supplies, PLC intelligent control units, and online water quality monitoring sensors are all mature industrial products on the market, which can be directly integrated and built without custom development; the multi-field coupling model can be implemented based on the commercial software COMSOL Multiphysics, and the dual intelligent algorithm is a conventional industrial control algorithm that can be directly written into the PLC controller to achieve fully automatic operation.

[0055] It has strong site adaptability and wide applicability: it can be adapted to sites with different pollution concentrations, different aquifer thicknesses, and different groundwater flow velocities. The wall parameters and electric field parameters can be flexibly adjusted according to site conditions. It is suitable for both small point pollution sites and large area pollution sites, and has extremely strong engineering applicability.

[0056] Strong compliance and no secondary pollution: All materials are environmentally friendly, and no toxic byproducts are generated during the remediation process. It complies with relevant national standards such as the "Technical Guidelines for Groundwater Pollution Prevention and Control" and can pass environmental protection acceptance smoothly.

[0057] Detailed workflow: Phase 1: Standardized Preparation Process of Multifunctional Synergistic Packers Step 1: Raw material pretreatment Agricultural and forestry wastes such as corn stalks are selected, washed, cleaned, air-dried, and then crushed through a 60-mesh sieve to obtain biomass powder. Attapulgite powder is added at a mass ratio of 10%-25%, and deionized water is added and ball-milled for 2 hours. After filtration, the mixture is dried at 105℃ for 12 hours to obtain a modified biomass precursor.

[0058] Step 2: Preparation and activation of mineral-based biochar The modified biomass precursor was placed in a tube furnace and heated to 550-750℃ at a rate of 5℃ / min under a nitrogen inert atmosphere. It was then pyrolyzed at a constant temperature for 2-4 hours and naturally cooled to obtain raw biochar. The biochar was then activated with NaOH solution and HNO3 solution, washed with deionized water until neutral, and dried at 105℃. The oxygen-containing functional group content was tested to be ≥1.2mmol / g. After passing the test, it was put into use.

[0059] Step 3: In-situ construction of a three-dimensional interconnected conductive network Weigh graphene quantum dots and carboxylated carbon nanotubes at a mass ratio of 1:3 to 1:8, add deionized water and ultrasonically disperse for 30 min to obtain a uniform dispersion; add activated mineral biochar, continue ultrasonic dispersion for 30 min and stir for 1 h; transfer the mixture to a hydrothermal reactor, hydrothermally react at 180℃ for 6 h, wash and dry to obtain modified biochar coated with a three-dimensional conductive network.

[0060] Step 4: Anchoring and Granulation of Bifunctional Catalytic Active Sites Modified biochar was dispersed in ethylene glycol solution and ultrasonically dispersed. LDH and defective metal oxide precursors were added at a mass ratio of 2:1 to 5:1. The pH was adjusted to 10, and the product was precipitated in situ in a water bath at 80°C for 4 hours. After washing and drying, the product was granulated into spherical particles of 2-8 mm using a disc granulator. After curing at 105°C, the finished filler was obtained and used after passing the performance test.

[0061] Phase Two: Green Electricity Drives the Entire Groundwater Remediation Process Sub-process 1: Site survey and scheme design Conduct hydrogeological surveys of the target site to determine the thickness of the aquifer, groundwater flow velocity, pollution plume range, heavy metal types and concentrations, and identify remediation targets. Based on the survey data, design the location, thickness, and burial depth of the e-PRB wall, determine the electrode spacing and filler usage, design the photovoltaic installed capacity and supercapacitor energy storage capacity of the green electricity system, and preset the electric field operating parameters.

[0062] Sub-process 2: Repair system engineering construction Downstream of the pollution plume, perpendicular to the groundwater flow direction, a cement mixing pile waterproof curtain is constructed, penetrating the aquifer to the bottom slab. Upstream of the curtain, an e-PRB wall trench is excavated, covering the entire polluted aquifer. Graphite particles in the anode area, functional filler, and graphite particles in the cathode area are sequentially filled along the water flow direction and compacted in layers. Graphite current collectors are buried and led to the ground via waterproof wires. The top of the trench is sealed with clay.

[0063] Sub-process 3: Green Electric Drive System Setup and Debugging A solar photovoltaic array, an energy storage supercapacitor, a programmable power supply, and a PLC intelligent control unit are constructed, and the electrode wires are connected to the power supply to form an electrical circuit; online monitoring sensors for inlet and outlet water quality, wall potential / pH, and solar irradiance are installed and all connected to the intelligent control unit; the stability of the electric field output, the accuracy of data acquisition, and the intelligent control function are tested after power-on, and the system is put into formal operation after passing the test.

[0064] Sub-process 4: Heavy metal targeted repair officially begins operation The green electric drive system is activated, applying a fluctuating voltage of 0.8-5V and 0.1-10Hz to create a stable electric field in the aquifer. Polluted groundwater flows through the e-PRB wall under the action of the hydraulic gradient, and heavy metal ions migrate directionally under the drive of the electric field. They are then stabilized through adsorption, capture, and reduction by the filler material. The qualified groundwater is discharged through the seepage barrier. The system operates continuously and monitors the water quality of the influent and effluent in real time.

[0065] Subprocess 5: Adaptive Intelligent Control Operation The intelligent control unit collects operational data in real time and simulates the system's operating status through a multi-field coupling model; the predictive buffer algorithm optimizes the supercapacitor charging and discharging strategy based on irradiance prediction data to smooth out power fluctuations; the demand response algorithm dynamically adjusts electric field parameters according to pollution load to achieve on-demand repair; the model predicts operational risks in advance and automatically adjusts parameters to ensure long-term stable operation of the system.

[0066] Sub-process 6: Heavy metal resource recovery and in-situ regeneration of packing material When the system runs until the packing material is close to saturation, the normal power supply circuit is cut off, and a constant potential of -0.8V to -2.5V is applied by reversing the power supply for 2-6 hours. The heavy metals on the surface of the packing material are reduced and stripped off, and the aqueous solution containing the heavy metals is extracted by the circulating pump for directional recovery. After regeneration is completed, the normal circuit is restored, and the system continues to operate.

[0067] Sub-process 7: System shutdown and site acceptance Once the effluent quality consistently meets the standards, the system will be shut down, and a comprehensive sampling and testing of the groundwater at the site will be conducted. Once the standards are met, the environmental protection acceptance will be completed. After the acceptance is passed, the green electricity system can be dismantled, and the e-PRB wall will remain underground as a long-term pollution barrier to continuously ensure the safety of groundwater quality.

[0068] Although embodiments of the invention have been shown, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multifunctional synergistic filler, characterized in that, The filler is a granular porous composite material, including a mineral type biochar substrate, a three-dimensional interconnected conductive network grown in situ on the surface of the mineral type biochar, and a bifunctional catalytic active site uniformly anchored on the surface of the conductive network; The mineral type biochar is attapulgite or montmorillonite modified biomass pyrolysis carbon, which has a hierarchical porous structure and serves as an environmentally compatible carrier skeleton and a heavy metal physical adsorption unit; The three-dimensional interconnected conductive network is a continuous conductive structure formed by in-situ hybridization of graphene quantum dots and carboxylated carbon nanotubes, which is completely coated on the pore inner wall and outer surface of the mineral type biochar, and serves as an electron transfer unit of the filler; The bifunctional catalytic active site is an ultrathin nanosheet structure formed by the composite of layered double hydroxide and oxygen vacancy defect type metal oxide, which is grown vertically on the surface of the three-dimensional interconnected conductive network, and serves as a heavy metal ion targeted capture unit and an electrocatalytic reduction unit of the filler.

2. The method according to claim 1, wherein the method is characterized by, The biomass source of the mineral type biochar is agricultural and forestry waste, the doping mass fraction of attapulgite or montmorillonite is 10%-25%, the pyrolysis preparation temperature is 550℃-750℃, the pyrolysis atmosphere is nitrogen inert atmosphere, and the pyrolysis time is 2h-4h.

3. The method according to claim 1, wherein the method is characterized by, In the three-dimensional interconnected conductive network, the mass ratio of graphene quantum dots to carboxylated carbon nanotubes is 1:3-1:8, the particle size of graphene quantum dots is 2nm-10nm, the tube diameter of carboxylated carbon nanotubes is 8nm-15nm, and the tube length is 5μm-20μm, and a continuous and uninterrupted conductive coating layer is formed on the surface of the mineral type biochar after in-situ hybridization.

4. The method according to claim 1, wherein the method is characterized by, In the bifunctional catalytic active site, the layered double hydroxide is any one of Mg-Al LDH, Ni-Fe LDH, and Zn-Cr LDH, the oxygen vacancy defect type metal oxide is any one of defect type manganese dioxide, defect type ferric oxide, and defect type cobalt trioxide, and the composite mass ratio of the two is 2:1-5:

1.

5. The method according to claim 1, wherein the method is characterized by, The multifunctional synergistic filler is a spherical particle with a particle size of 2mm-8mm.

6. The method according to claim 1, wherein the method is characterized by, The surface of the mineral type biochar is treated by acid-base activation to introduce hydroxyl and carboxyl oxygen-containing functional groups, and the functional group content is≥1.2mmol / g, the three-dimensional interconnected conductive network is grown in situ on the surface of the mineral type biochar by a hydrothermal method, and the bifunctional catalytic active site is anchored on the surface of the conductive network by an in-situ precipitation method.

7. A green electrically driven electrochemical groundwater remediation method, characterized by, The multifunctional synergistic filler based on any one of claims 1-6 is realized, including the following steps: S1 repair system construction: in the downstream of the groundwater heavy metal pollution plume, a waterproof and impermeable curtain is constructed perpendicular to the groundwater flow direction, and an e-PRB repair wall is constructed in the contaminated aquifer upstream of the waterproof and impermeable curtain, the e-PRB repair wall is divided into an anode region, a functional filler reaction region, and a cathode region along the groundwater flow direction, the functional filler reaction region is filled with the multifunctional synergistic filler, the anode region and the cathode region are filled with conductive graphite particles, and the anode and the cathode are connected by waterproof wires to an external green electricity driving system; S2 green electricity driving system construction: a green electricity driving system including a solar photovoltaic panel, an energy storage super capacitor module, a programmable fluctuation power supply, and a smart control unit is constructed, the solar photovoltaic panel is a main energy supply unit of the system, the energy storage super capacitor module is used for suppressing the intra-day fluctuation of photovoltaic power, the programmable fluctuation power supply is used for outputting a sinusoidal wave or square wave fluctuation voltage that is adapted to repair demand, and the smart control unit is internally provided with a multi-field coupled numerical model and a double intelligent regulation algorithm; S3 heavy metal targeting repair operation: a fluctuation electric field is applied to the e-PRB repair wall by the green electricity driving system, and heavy metal ions in the groundwater are driven to migrate to the functional filler reaction zone in a directional manner under the electric field force, and in-situ fixation and non-toxic valence transformation of the heavy metals are realized through physical adsorption, functional group targeting capture, and electrocatalytic reduction of the multifunctional synergistic filler, and the treated groundwater is discharged through the impermeable curtain to meet the standard; S4 self-adaptive intelligent regulation: the smart control unit collects solar irradiance, influent pollutant concentration, internal potential or pH field distribution of the repair wall, and effluent water quality data in real time, dynamically adjusts electric field parameters and energy distribution through the double intelligent regulation algorithm, and realizes stable and efficient repair under fluctuating green electricity input; S5 heavy metal resource recovery and filler regeneration: after a repair operation period is set, a constant potential is applied to the e-PRB repair wall by the green electricity driving system, and the heavy metals fixed on the multifunctional synergistic filler are reduced and peeled off in a directional manner, and heavy metal resource recovery and in-situ filler regeneration are simultaneously realized.

8. The method according to claim 1, wherein the method is characterized by, In the step S1, the thickness of the e-PRB repair wall is 0.8m-3m, the wall is buried to cover the entire contaminated aquifer, the thickness of the anode region and the cathode region is 1 / 5-1 / 3 of the thickness of the functional filler reaction zone, and the distance between the anode and the cathode is 0.5m-2.5m.

9. The method according to claim 1, wherein the method is characterized by, In the step S2, the fluctuation voltage output range of the green electricity driving system is 0.8V-5V, and the frequency is 0.1Hz-10Hz; In the step S5, the applied range of the reverse constant potential is -0.8V~-2.5V, and the application time is 2h-6h.

10. The method according to claim 1, wherein the method is characterized by, The double intelligent regulation algorithm in the step S4 includes a predictive buffering algorithm and a demand response algorithm; The predictive buffering algorithm combines a super capacitor charging and discharging model and intra-day solar irradiance time series prediction data; The demand response algorithm dynamically adjusts the electric field output power and the fluctuation mode according to real-time influent pollutant concentration and effluent water quality feedback; In the step S4, the multi-field coupled numerical model internally provided in the smart control unit is a high-fidelity numerical model that couples the non-steady groundwater flow field, the fluctuation electric potential field, the heavy metal ion migration field, and the electrode reaction kinetics, and can simulate and predict the repair efficiency and long-term operation stability of the system on an annual scale.

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