A PRB structural form for sustainable degradation of complex pollutants in groundwater

Abstract

This invention discloses a permeable reactive wall for treating multiple types of pollution in groundwater. The permeable reactive wall comprises multiple interconnected funnel-gate type structural units, each of which includes a funnel-shaped drainage head, a first conveying pipe, and a second conveying pipe. The first conveying pipe is filled with a first composite filler, and the second conveying pipe is filled with a second composite filler. The permeable reactive wall can continuously and efficiently treat complex pollution in shallow soil saturated aquifers.

Description

Technical Field

[0001] This invention relates to the field of groundwater environmental engineering, and more particularly to permeable reactive walls (PRBs) for treating multiple types of pollution in groundwater, and methods for using permeable reactive walls to treat complex pollution in shallow (1-50m) saturated aquifers. The fields covered by this invention include first-level disciplines such as geological resources and geological engineering, environmental science and engineering, and materials science and engineering. Background Technology

[0002] Current PRB (Plasma Reinforced Bioreactor) systems are predominantly large-scale reactors, primarily based on a circulating water multi-layer infiltration ex-situ treatment mechanism. In-situ PRB walls are typically constructed through extensive excavation and filling, or are large-scale shallow groundwater treatment units. When addressing pollutants, existing PRB packing materials are mostly designed for single pollutant forms. During the maintenance phase of the treatment process, re-excavation is usually required to replace the packing material and maintain performance. Furthermore, the packing materials are mostly adsorbent, with reactive packing materials targeting relatively singular pollutants. Existing products have relatively simple packing material fabrication methods and mature processes. The manufacturing and construction process of PRB structures is straightforward, generally involving material preparation, on-site excavation, material filling, and subsequent excavation, maintenance, and filling.

[0003] Large-scale reaction facilities often involve extraction-type off-site treatment, such as wastewater treatment plants. Due to the large surface space occupied by these facilities, their high construction costs, and the difficulty in site selection, most treatment plants treat groundwater and surface water pollution through off-site extraction and re-release, which is extremely costly among water pollution treatment methods.

[0004] There are also large-scale deep reaction devices, distinct from fixed treatment sites. While these offer some flexibility, the high proportion of ineffective volume in these large-scale devices results in high construction costs for practical applications. The preparation of adsorbent materials or fillers in the products mostly employs common methods for preparing mesoporous materials, generally involving raw material pretreatment followed by calcination. The preparation methods for reactive fillers are more diverse, but the types are fewer. The existing PRB unit structure layout is mostly carried out through excavation followed by backfilling. Existing unit structures are difficult to interconnect and form walls underground without excavation.

[0005] The main reason for the technical problems and defects in current PRB products is the high cost of applying and testing new materials or new fillers, which makes it difficult to conduct PRB application research and development. This limits the scope of contact and research methods for technical and testing personnel with new materials or new fillers. Reducing the production and application costs of materials is the main problem faced by PRB in field and indoor testing applications.

[0006] In particular, existing PRB permeable reactive wall fillers have at least one of the following drawbacks and problems:

[0007] 1. High cost of filler materials

[0008] In PRB (Permeable Reactive Barrier) technology, wall materials and excavation costs are the two primary cost sources to consider in engineering projects. Existing PRB technology suffers from material waste. Although relatively inexpensive and efficient infill materials exist, the cost of producing infill materials for a single wall infill layer is enormous when dealing with large-scale remediation areas. The exponential increase in costs due to the insurmountable scale makes the development of new materials difficult due to low production volume and high cost, making it even more difficult to apply most new materials to actual engineering sites. Even laboratory-scale PRB simulations are challenging. Since saturated aquifers in actual sites are often located deep below the surface, saving material costs is particularly important given the already high excavation costs.

[0009] 2. High PRB maintenance costs

[0010] For general PRB wall fillers, clogging is a decisive factor in the service life of PRB. Due to the large-scale excavation and the huge production cost of filler materials, when clogging occurs (usually due to metal salt precipitation or microbial proliferation), it is necessary to excavate again to replace the PRB filler. This doubles the application and maintenance costs of PRB in actual sites. Therefore, solving the clogging problem of PRB, extending the replacement cycle of filler, and reducing the number of engineering excavations are key to the large-scale application of this type of groundwater pollution treatment.

[0011] 3. It is difficult to reconcile high processing efficiency and high sustainability after material application.

[0012] For PRB wall filling work within a certain cost framework, selecting appropriate wall consumables is crucial. The selection criteria should prioritize low cost, high efficiency, and long service life. The filling material should also possess highly efficient treatment capabilities to address pollution migration issues in groundwater at the PRB construction site. The durability of this treatment effect is also an important reference for evaluating the material's suitability. Existing PRB filling structures primarily rely on physical adsorption and chemical reactions. For single or complex pollution forms, these structures suffer from low pollution treatment efficiency of adsorption materials and poor degradation sustainability of reaction materials. Furthermore, the migration of pollutants constantly residing in the saturation zone prevents existing filling structures from maintaining consistently high-efficiency pollutant degradation during cyclical operation.

[0013] 4. The material still has drawbacks when facing single or complex pollution.

[0014] In actual engineering sites, groundwater pollution presents challenges due to the diverse forms of pollution from both point and area sources, as well as the complex types of pollutants released. This includes both numerous single-type pollutants and the coexistence of multiple complex pollutants. Existing filler structures that degrade pollutants in groundwater based on chemical reactions are highly effective against single-type pollutants, but struggle to cope with the coexistence of multiple complex pollutants in groundwater. While materials primarily based on physical adsorption exhibit indiscriminate adsorption of various pollutants in groundwater, their limited adsorption capacity and desorption characteristics make them ill-suited to handle the continuous influx of pollutants into the groundwater.

[0015] 5. Existing materials are prone to secondary pollution.

[0016] When dealing with pollutants in groundwater, existing reactive PRB packing structures suffer from poor structural stability and high solubility when exposed to different pollutants, making the materials themselves a direct source of secondary pollution in groundwater. Furthermore, reactive materials exhibit incomplete reactions. While these issues can be addressed by increasing packing volume, improving packing composition, and optimizing wall parameters and reaction mechanisms, these methods are insufficient for achieving risk-free degradation of pollutants that readily produce intermediate products such as low / high valence state compounds or ions of the same element, or low-halogenated derivatives. The desorption characteristics of existing adsorbent PRB packing structures when the material reaches adsorption saturation are the primary cause of secondary pollution from this type of material.

[0017] 6. The raw materials required for the preparation of existing PRB fillers are difficult to obtain, and the preparation process is complex.

[0018] The existing reactive packing structures are not readily available, and the huge research and development costs of new materials lead to high application costs. The selection and production of PRB packings is the source of this form of groundwater pollution treatment. Most reactive packings have high research and development costs, resulting in huge costs for direct use. At the same time, there are problems such as the harsh preparation conditions of raw materials used to prepare certain special materials, which are difficult to obtain directly, and the immature preparation processes of raw materials.

[0019] 7. Existing PRB packing structures have poor environmental recyclability.

[0020] Since the cost of using PRB (Plasma Reclaimed Water) is already relatively high, environmentally friendly recycling is an important means of saving costs for most existing fillers. Non-renewable fillers still require repeated excavation and refilling with new materials after a certain period following the initial landfilling, which increases the application cost of PRB. The number of regeneration cycles for recyclable fillers also tends to be low due to the properties of the filler itself and groundwater movement. The implementation of regeneration methods for recyclable fillers usually involves excavation or extraction followed by the corresponding regeneration operation, which is also a major expenditure item.

[0021] 8. The layout of large-scale PRB units lacks flexibility and practicality.

[0022] Existing PRB (Potentially Respiratory Barrier) layouts often employ large-scale reactors, which require highly skilled construction personnel for unified and coordinated construction. Furthermore, the disassembly and assembly of large reactors are less flexible. In addition, the geological strata of groundwater contamination aquifers at actual sites are more complex, especially in deep saturated aquifers. When large rock strata are found in the soil, the construction of large-scale reactors and reaction pools is not very applicable. The lack of flexibility in dealing with rock strata of complex shapes and sizes means that pollutants in the groundwater can still bypass the reactor walls through huge gaps, which reduces the effectiveness of PRB in treating groundwater pollutants.

[0023] Therefore, PRB and its application methods still need improvement in at least one of the above aspects. Summary of the Invention

[0024] In view of the shortcomings of the prior art, the purpose of the invention is to provide a permeable reactive wall (PRB) for treating various types of pollution in groundwater and a method for using the permeable reactive wall.

[0025] Specifically, the present invention provides a permeable reactive barrier (PRB) for treating various types of pollution in groundwater, comprising multiple interconnected funnel-gate type structural units, wherein each funnel-gate type structural unit includes a funnel-shaped drainage head, a first delivery pipe, and a second delivery pipe. The funnel-shaped drainage head includes a first opening and a second opening opposite each other, and an impermeable sidewall surrounding the first and second openings. The area of ​​the first opening is larger than the area of ​​the second opening. The first delivery pipe is sealed to the second opening, and the second delivery pipe is connected to the first delivery pipe on the side away from the drainage head. The first delivery pipe is filled with a first composite filler, and the second delivery pipe is filled with a second composite filler. The first composite filler comprises biochar, adsorbent layered double hydroxide LDH1, catalytic layered double hydroxide LDH2, and nano-zero-valent iron (nZVI). The second composite filler comprises the biochar, adsorbent layered double hydroxide LDH1, and catalytic layered double hydroxide LDH2.

[0026] The present invention also provides a method for treating complex pollution in shallow soil saturated aquifers using the aforementioned permeable reactive wall, comprising arranging multiple sets of funnel-gate type structural units in the site according to the actual site's pollutant migration depth, span, speed and pollution source type, in order to construct the permeable reactive wall (PRB).

[0027] The beneficial effects of this invention are as follows:

[0028] 1. Significantly reduces the application cost of filler materials used in PRB.

[0029] Regarding the packing structure, the composite packing structure used reduces the application cost of the packing structure used in PRB due to its higher degradation efficiency, stronger site contamination adaptability, longer degradation cycle, and superior recyclability. In terms of application form, this funnel-gate type PRB arrangement, with its flexible assembly and disassembly and small-volume application units forming a reactive wall, is suitable for complex spaces in deep saturated aquifers. The rational arrangement of individual PRB reaction units significantly reduces ineffective material usage and improves material utilization per unit space. Simultaneously, the water-guiding structural design is also suitable for the effective collection and centralized treatment of contaminants in groundwater, further reducing application costs through its arrangement.

[0030] 2. It improves the application efficiency of the packing structure and expands the scope of application of the PRB packing structure for pollution control.

[0031] This invention benefits from the convenient and low-cost acquisition of materials in the PRB packing structure, and is suitable for adsorbent LDH1 and catalytic LDH2 (layered bimetallic hydroxide series: MgAl-Cl) materials other than biochar-based materials. - &CO3 2- -LDHs, NiFe-Cl - &CO3 2- The preparation methods for LDHs, nZVI, and PMS are quite mature, and the reactants used in their preparation are easy to obtain. The composite material combines the advantages of each material, fully filling the practical application gaps required for PRB (Potentially Reducing Biochar). It combines PMS and / or nZVI to achieve oxidation and reduction removal of pollutants in groundwater, providing a more efficient and rational approach to addressing the coexistence of multiple pollutants in groundwater at contaminated sites, and achieving highly efficient removal of complex pollutants. Simultaneously, this packing structure enables continuous and efficient degradation of pollutants in groundwater. Catalytic LDH2 (NiFe-LDHs) is combined with nZVI and PMS to catalyze and promote oxidation-reduction reactions. Furthermore, the addition of BC (biochar) significantly increases the adsorption capacity. Utilizing the excellent slow-release properties of LDHs, the adsorbed pollutants are slowly released into the reaction packing, ensuring a complete reaction and reducing secondary pollution caused by incomplete reactions.

[0032] 3. Reduced construction and maintenance costs during PRB structure application.

[0033] When treating pollutants in groundwater using this invention, a large-scale underground reactive barrier (PRB) can be constructed by selectively choosing modular wall units. The unit structure can incorporate treatment materials tailored to the migration characteristics of specific pollutants, positioned at different depths or spans within the wall. Based on groundwater pollutant migration simulation software, the PRB is configured with appropriate reaction units within the corresponding pollutant migration range, adjusting the internal packing structure and unit wall arrangement to achieve coordinated degradation of various pollutants. This effectively addresses the challenges of multiple layers and large thicknesses in PRB construction. Regarding PRB structure maintenance, leveraging the stability and structural memory effect of LDHs (Laminated Hydrochloric Acids), this ultrathin crystalline material with catalytic and adsorption properties is highly stable and resistant to dissolution. For certain organic solvent-based pollutants, the structure can be reconstructed quickly after dissolution due to the interlayer structural memory effect. The ion exchange capacity of LDHs allows for recycling and renewal. Contact with a high-concentration, non-polluting inorganic salt solution allows for the reintercalation of anions in the intermediate layers, resulting in material renewal and sustainable recyclability. Meanwhile, due to its ability to inhibit the proliferation of bacteria, LDHs materials themselves have self-cleaning properties, which distinguishes them from other mesoporous PRB fillers that are easily clogged by microorganisms. This innovative portable PRB application structure also increases the effective number of LDHs cycles and the effective usage time within the cycle.

[0034] 4. Enhanced the applicability of deploying PRB for groundwater pollution treatment.

[0035] Due to the uncertainty of the underground environment, the saturated aquifers in actual engineering sites often contain heterogeneous and diverse porous media, and are usually located at considerable depths. Based on basic stratigraphic data and pollution patterns, the pollutant migration paths (depth and span) generated by simulation software can reasonably predict whether each pollutant will enter the saturated aquifer in the actual strata, thereby determining the setting parameters and location of the PRB (Plasma Receptacle Block). This structural unit-combined PRB form uses a grid-based division of the overall structure, enabling more detailed, efficient, accurate, economical, and environmentally friendly treatment of various pollutants in groundwater. Furthermore, leveraging the various advantages of LDHs (Local Debris Heating Devices) and their portable recycling capabilities, this PRB form is more suitable for treating complex groundwater pollution. In addition, thanks to its highly detailed and flexible miniaturized processing unit modules, it is more suitable for complex and varied underground soil environments. It can also avoid irregular rock strata of different volumes that are unavoidable in actual sites, thereby reducing the pain point of difficulty in arranging large reaction devices due to complex geological conditions. This makes the PRB method of treating groundwater pollution more applicable to various geological conditions. Brief description of the attached figures

[0036] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0037] Figure 1 This is a schematic diagram of the structure of a funnel-guide gate type PRB unit according to some embodiments of the present invention, where A is a side view and B is a top view;

[0038] Figure 2 Examples of individual arrangements of funnel-gate type PRB units for permeable reactive wall (PRB) are shown, with A being a rigid material arrangement and B being a flexible material arrangement.

[0039] Figure 3 The diagram shows the layout of a permeable reactive wall combined with underground engineering components, where A represents a single pipe connection and B represents a double pipe connection.

[0040] Figure 4 A schematic diagram showing a longitudinally aligned site layout of multiple funnel-guide gate type PRB units is provided.

[0041] Figure 5 A schematic diagram showing the longitudinal arc-shaped site layout of multiple funnel-guide gate type PRB units is shown.

[0042] Figure 6 A schematic diagram showing a vertically aligned site layout of multiple funnel-guide gate type PRB units is provided.

[0043] Figure 7 This is a schematic diagram of the annular (non-full arc) site layout of multiple funnel-guide gate type PRB units.

[0044] Figure 8 This is a schematic diagram of the annular (full arc) site layout for multiple funnel-guide gate type PRB units.

[0045] Figure 9 The images show scanning electron microscope (SEM) images of a first composite filler (A) and a second composite filler (B) prepared according to an embodiment of the present invention. Detailed Implementation

[0046] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings.

[0047] One aspect of the invention provides a permeable reactive wall (PRB) for treating various types of contamination in groundwater, comprising multiple interconnected funnel-gate type structural units. For example... Figure 1As shown in A and B, each funnel-gate type structural unit includes a funnel-shaped drain head ⑥, a first delivery pipe, and a second delivery pipe. The funnel-shaped drain head ⑥ includes a first opening and a second opening opposite each other, and non-permeable sidewalls surrounding the first and second openings. The area of ​​the first opening is larger than that of the second opening. The first delivery pipe is sealed to the second opening, and the second delivery pipe is connected to the first delivery pipe on the side away from the drain head. The first delivery pipe is filled with a first composite packing material ②, and the second delivery pipe is filled with a second composite packing material ①. The first composite packing material comprises biochar, adsorbent layered double hydroxide LDH1, catalytic layered double hydroxide LDH2, and nano-zero valent iron nZVI. The second composite packing material comprises the biochar, adsorbent layered double hydroxide LDH1, and catalytic layered double hydroxide LDH2. The second composite packing material may also contain persulfate PMS as an oxidant. The amount of PMS added is 1-10% of the total weight of the second composite packing material, and it is added in solution form during PRB maintenance.

[0048] Preferably, the PRB includes multiple sets of funnel-guide gate type structural units, with four interconnected funnel-guide gate type structural units forming a group. In each group, each funnel-guide gate type structural unit is interconnected by a sealed connecting strip ⑦ set at the top of the non-permeable sidewall.

[0049] Preferably, the first and second conveying pipes further include a 200-400 mesh bidirectional permeation filter screen ③ disposed therein. The first and second composite packing materials are respectively housed within the bidirectional permeation filter screen. The bidirectional permeation filter screen can be a 300 mesh bidirectional permeation nylon filter screen.

[0050] In one embodiment, the length of the second conveying pipe is greater than that of the first conveying pipe, and a maintenance interface ④ is provided on the side wall of the second conveying pipe for replenishing the consumed PMS.

[0051] In another embodiment, the first and second conveying pipes are connected by a flow stabilizer joint ⑤.

[0052] Preferably, LDH1 and LDH2 are represented by the following formula:

[0053] ([M 1-x 2+ M x 3+ (OH)2] x+ [A] n- ]· z H2O)

[0054] For LDH1, M 2+ Mg 2+ M3+ For Al 3+ For LDH2, M 2+ For Ni 2+ M 3+ For Fe 3+ X is the molar ratio M 3+ / ( M 2+ + M 3+ (0.2 to 0.4), A n- For containing Cl - and CO3 2- The interlayer anions, n is the number of negative charges (2-4), and z is the number of water molecules in the interlayer structure (2-5 water molecules).

[0055] like Figure 2 As shown, according to one embodiment of the permeable reactive wall of the present invention, at least three sets of funnel-gate type structural units are individually arranged together using either a rigid non-building material (A) or a flexible material (B). Each set of funnel-gate type structural units is interconnected by a sealed connecting strip ⑦ located at the top of the impermeable sidewall of adjacent funnel-gate type structural units. Impermeable strong adhesive tape is used to bond the edges together on the funnel plane of the unit's water-facing side, ensuring good sealing within the PRB structure and allowing groundwater in the saturated zone to flow evenly and rationally towards the filler structure.

[0056] Figure 3 This diagram illustrates the layout of a permeable reactive wall system integrated with underground engineering components, where A represents a single pipe connection and B represents a double pipe connection. Therefore, as... Figure 3 As shown, at least three sets of funnel-guide gate type structural units can also be arranged together through inherent building underground engineering components, wherein each set of funnel-guide gate type structural units is connected to each other by a sealed connecting strip set at the top of the non-permeable sidewall of the adjacent structural unit.

[0057] Preferably, the rigid non-building material can be selected from at least one of stainless steel, polyethylene, and polyacrylic acid. The flexible material can be selected from at least one of waterproof fabric and waterproof curtain. The building's underground engineering components can be made of concrete and / or cement and / or mortar.

[0058] In one embodiment, biochar (BC) can be obtained from at least one selected from reeds, calamus, shrubs, leaves, seaweed, phytoplankton, seed husks, fruit pericarps, and corn stalks by acid washing, alkali washing, drying, and hot milling. The specific surface area of ​​biochar is 600-1100 m². 2 / g, with a porosity of 30-70%, a particle size of 50-200 mesh, and an average pore diameter of 3-50nm.

[0059] In particular, the PRB of the present invention has at least the following features and advantages:

[0060] 1. Highly efficient and long-lasting form of pollutant degradation

[0061] 1) Packing structure

[0062] In a preferred embodiment, the filler structure used in the structural unit PRB of the present invention is two types of composite filler, namely MgAl-Cl - &CO3 2- -LDH1, NiFe-Cl - &CO3 2- -LDH2 is compounded with zero-valent iron and biochar, and adsorbed as MgAl-Cl - &CO3 2- -LDH1, catalytic NiFe-Cl - &CO3 2- -LDH2 is directly compounded with biochar. The particle size of the biochar should be selected based on the actual porous media conditions of the site. Since the permeability coefficient K of the material medium does not change significantly after modification, the packing structure should be set at 2-10 times the permeability coefficient of the porous media of the actual site. When treating the corresponding pollution, BC can be indiscriminately adsorbed and captured by both LDH1 and LDH2. LDH1 and LDH2 exchange interlayer ions and achieve temporary sequestration during adsorption. Compared with the adsorption and desorption process of biochar, it has a significantly milder trend. The modified LDH-nZVI@BC or LDH@BC has a slow-release property, which makes the contact between the reactive degrading oxidant PMS and the reducing agent nZVI and the pollutants more complete per unit time, improving the reaction efficiency and avoiding secondary pollution caused by incomplete reaction. At the same time, the increased specific surface area and refined pore structure further improve the adsorption capacity of the material. Consumables nZVI and PMS can be transported through the infusion pipeline connected to the reaction unit to achieve a replenishment effect and extend the service life of the single packing structure. Simultaneously, due to the reduction and oxidation reactions, the consumed nZVI is converted into Fe. 2+ Fe 3+The form of nZVI exists within the packing structure, further promoting the catalytic reaction while forming new LDH structures with the injected alkaline NaOH and Na₂CO₃. This process can be carried out when the degradation efficiency decreases to near the effect of simple adsorption. Alternatively, the material can be re-intercalated and rebuilt using Na₂SO₄, Na₂CO₃, and NaCl solutions, achieving renewal. However, this process must be carried out while nZVI and PMS still possess oxidizing or reducing properties. For the replenishment of the oxidant (PMS), the LDH intercalation structure is renewed simultaneously with its replenishment. In summary, replenishing PMS can simultaneously achieve oxidant replenishment and LDH intercalation renewal. When the reducing agent nZVI is replenished, its reacted ferrous and ferrous ions can form novel single-element LDH structures in situ with the newly injected alkaline solution. This renewal method provides a reasonable approach for the recycling and utilization of materials in pollution treatment.

[0063] 2) Funnel-guide gate type structural unit and load-bearing wall

[0064] The funnel-guide gate type PRB structural unit design in this invention significantly reduces the ineffective volume of filler within a unit volume space. Compared to reaction methods that simply stack large amounts of filler, it saves material usage, reduces material filling costs, and improves the rational utilization of material space and the contact area between reactants and filler. The delivery pipe material of the structural unit is selected based on actual site conditions, using common, high-strength, low-cost application-grade pipe materials such as stainless steel, PVC, and PMMA, ensuring durability and resistance to deformation. The connecting wall material can be the concrete and cement mortar material used for foundation beams in individual or combined underground engineering projects, or a material similar to that of the funnel-guide gate PRB unit structure, ensuring integrity in underground applications and extending service life. In addition to commonly used rigid materials, using non-permeable soft materials to load-bearing PRB structural units allows for more flexible handling of complex stress conditions in underground spaces and saves on the cost of load-bearing wall construction. The selection of load-bearing wall materials must consider application durability and the flexural deformation caused by the complex physicochemical fields in the underground space, ensuring that they will not overturn or slide within the design life, thus reducing the effective contact area between the PRB structural unit's water-facing surface and the groundwater flow line, thereby weakening the PRB's reaction and removal effect on groundwater pollutants. The design of the unit-type PRB structure used in the wall, by refining the cross-section to form a treatment grid wall, ensures sufficient contact between pollutants and the filler. The funnel-gate type structural unit, mainly composed of a water-collecting water-facing surface and a load-bearing delivery pipe of appropriate length, can increase the effective reaction time in the pollutant seepage path and improve reaction efficiency.

[0065] 3) Site layout

[0066] The arrangement of PRB unit walls in the treatment site can be adopted based on the actual depth, span, velocity of pollutant migration, and type of pollution source in the site. Figure 4 and Figure 5 The longitudinal arrangement of the multi-column walls shown (including) Figure 5 The arc type shown and Figure 4 (as shown in the vertical type) Figure 6 The vertical arrangement shown (including curved and straight types) and Figure 7 and 8 The annular cylindrical type shown (including) Figure 8 The full arc shown Figure 7 The non-full arc layout shown ensures the efficient and durable construction of the PRB. In addition, the gap filling and water diversion adopted during the deployment process reasonably increase the effectiveness of pollution treatment.

[0067] 2. Economical, environmentally friendly, and with low maintenance costs

[0068] 1) Packing structure

[0069] In the filler structure of this invention, the biochar in the composite material is widely available and can be flexibly selected from various biological wastes (fruit shells, plant straw, etc.), is inexpensive, and has a simple preparation process. The raw materials for preparing LDH1 and LDH2 can be industrial wastewater or other solutions containing metal ions (this invention can use solutions containing Ni). 2+ Fe 3+ Mg 2+ Al 3+The process involves the addition, mixing, and drying of industrial wastewater (or low-cost metal salts) with strong alkalis and interlayer growth inhibitors under high temperature and pressure. The process is simple and mature, with low material costs, and the interlayer growth inhibitors used can be reused after material filtration. For practical composite material applications, high-temperature composites can be performed using single or double-stage composite methods, with a simple and convenient operation process. For commonly used oxidants PMS and reductants nZVI, batches of finished products made from recycled industrial solid waste can be selected. These two substances can be purchased in large quantities from relevant industrial manufacturers and through normal e-commerce channels. They can also be prepared in-house when equipment conditions permit, as the preparation method is simple. Their direct cost as daily PRB maintenance consumables is low. During PRB maintenance, the excellent renewal and reconstruction characteristics of LDH1 and LDH2 can increase the number of material recycling cycles. Simultaneously, the pore structure is further refined after composite with BC as a carrier, enhancing the adsorption performance per unit volume of material with minimal impact on the permeability of raw materials. During maintenance, iron ion reconstruction of LDH can also solve the clogging problems caused by iron ion circulation and iron compound precipitation that are difficult to address in nZVI applications. In addition, the alkali and non-polluting metal salts added during the anion intercalation and structural reconstruction of LDH1 and LDH2 have a certain inhibitory effect on microbial growth. Simultaneously, due to the inherent antibacterial properties of LDHs materials, the growth of porous microorganisms is significantly improved after composite biochar, ensuring the self-cleaning property of the material system and extending the single-use cycle of the packing structure. The packing structure of the invention avoids the high maintenance costs of PRB materials caused by repeated excavation and replacement of packing. The packing structure and maintenance materials used in the invention are all environmentally friendly substances, causing no secondary pollution before or after the pollution removal reaction. Furthermore, the use of maintenance materials achieves multiple benefits, ensuring efficient and thorough degradation of pollutants by the reaction packing, updating the performance of catalytic, slow-release, and adsorption materials, and increasing the number of material recycling cycles with a lower-cost maintenance method. The invented packing structure not only efficiently and persistently degrades pollutants but also extends the application cycle of the first round of materials. In addition, apart from the necessary electrical energy consumption, all reagents used in the preparation process are recyclable and have minimal environmental impact.

[0070] 2) Funnel-guide gate type structural unit and load-bearing wall

[0071] The funnel-guide gate structural unit is made of common, high-strength, low-cost application-grade pipe materials such as stainless steel, PVC, and PMMA, selected according to actual site conditions to ensure durability and prevent deformation. The connecting wall materials can be concrete and cement mortar materials used in foundation beams of underground engineering projects, or materials similar to those used in the funnel-guide gate PRB unit structure, ensuring integrity in underground applications and extending service life. In addition to commonly used rigid materials, using non-permeable soft materials to support the PRB structural units can significantly reduce the cost of supporting wall construction. In this invention, the delivery pipes of each funnel-guide gate structural unit are crucial; they are key to ensuring the efficient and long-lasting degradation of pollutants by the packing structure. Material selection must consider chemical and mechanical properties such as alkali resistance, durability, strength, and temperature stress. The presence of the delivery pipes provides a foundation for the in-situ continuous renewal and efficient maintenance of the packing structure, greatly reducing PRB maintenance costs. The selection of load-bearing wall materials must take into account the application durability and the flexural deformation caused by the complex physical and chemical fields in the underground space, to ensure that it will not slip or overturn within the design life, thereby reducing the effective contact area between the water-facing surface of the PRB structural unit and the groundwater flow line, which would weaken the PRB's reaction and removal effect on groundwater pollutants. Under the condition that the material selection can ensure long-term application, the corresponding maintenance costs are reduced.

[0072] 3) Site layout

[0073] By utilizing groundwater pollution migration simulation software, a gridded model of groundwater pollution at a site is constructed to predict the migration paths of inert and non-inert solutes in saturated groundwater aquifers. Combined with existing geomagnetic methods, the feasibility of the proposed solution is assessed and adjusted. Then, a suitable PRB (Pollution-Related Landing Array) layout is adopted for the severely polluted underground areas. For known pollution sources, the PRB can be deployed at the depth of the corresponding high-concentration polluted strata to prevent further diffusion after entering the soil. When existing pollution exists, the software predicts pollution migration paths based on groundwater flow lines. The PRB layout is then placed at the intersection of the migration path and the PRB structural unit wall (the optimal contact surface for pollutant collection is a 90° intersection). The layout method is rationally selected based on the existing pollution source type and pollution migration characteristics, reducing the high application costs caused by blind and random site layout.

[0074] 3. Applicable to a wide range of complex aquifers

[0075] 1) Funnel-guide gate type structural unit and load-bearing wall

[0076] By refining the saturated aquifer with a grid-type funnel-guide gate PRB device, it is more suitable for the micro-remediation of large-scale contaminated sites. When dealing with complex rock strata in the deployment area, waterproof soft materials and restrictive filler bags should be considered for filling the gaps between the PRB unit structure or the load-bearing wall and the large rock strata, which improves the applicability of the original highly flexible unit structure layout to the saturated aquifer.

[0077] 2) Site layout

[0078] When targeting known pollution sources, PRBs can be deployed at the depth of high-concentration contaminated strata in the corresponding saturation zone to prevent further diffusion after entering deeper soil layers. In cases of existing pollution, PRBs can be placed at the intersection of the migration path and the PRB structural unit wall (the optimal contact surface for pollutant collection is a 90° intersection). The deployment method should be rationally selected based on the existing pollution source type and pollution migration characteristics. For example, when facing severe non-point source pollution in a small, shallow saturation zone, a vertical deployment can be used to prevent non-point source infiltration; when facing pollution in a large, deep saturation zone, a vertical column deployment can be used to treat existing or newly migrated pollutants. The angle and curvature of the vertical deployment are determined based on the pollutant migration characteristics and the spatial position of the deployed PRBs in the pollutant migration path to better adapt to complex saturated aquifers. Furthermore, when facing shallower saturated aquifers with pollution patterns similar to point sources, an arc-shaped deployment can be used, employing a zone-enclosing and treatment approach. The PRB deployment method mentioned in the invention further enhances the applicability of this funnel-gate type structural unit PRB in treating various pollutants in complex underground aquifers.

[0079] 4. Mature material production and low application costs

[0080] 1) Packing structure

[0081] The LDH1 and LDH2 series (MgAl-Cl) used in the packing structure of this invention - &CO3 2- -LDH1, NiFe-Cl - &CO3 2-LDHs (Laminated Dihydrogen Hydrogen Hydrogen), biochar, nZVI, and PMS all have mature and complete production processes and preparation procedures, and are commercially available. The preparation of LDHs materials does not require high-end equipment conditions; synthesis is generally carried out at 100℃ for 4 hours using grinding, centrifugation, and stirring equipment. Good equipment sealing is required. A typical streamlined preparation method involves a combination of a colloid mill and a high-pressure homogenizer to prepare MgAl-LDH1, which has the main adsorption effect. When preparing NiFe-LDH2, which has catalytic effects, attention should be paid to sealing during the preparation process, and an inert gas should be used to displace the original gas in the reactor; other requirements are the same. These two types of LDHs materials exhibit outstanding adsorption and catalytic characteristics among the LDHs series. The raw materials required for the reaction preparation (metal salts, NaOH, etc.) are simple, readily available, and inexpensive, with simple production requirements and low production costs. Biochar, a common mesoporous adsorbent material, is produced from various biomass sources through pretreatment followed by calcination. Its raw materials are widely available, the preparation process is simple and mature, and the application cost is low. It can be used as a widely applicable, low-cost adsorbent packing material. Combining it with LDHs combines the advantages of each material while optimizing the packing structure at a lower cost. The reducing agent nZVI and the oxidizing agent PMS used in the packing material have mature production processes, enabling mass production. Application costs can be controlled artificially based on monitoring of the actual contaminated site remediation process.

[0082] 2) Funnel-guide gate type structural unit and load-bearing wall

[0083] The funnel-gate type PRB unit structure can use common, high-strength, low-cost application-grade piping materials such as stainless steel, PVC, and PMMA. The walls can be made of concrete, cement mortar, stainless steel, PVC, PMMA, or non-permeable soft materials, resulting in low-cost wall material selection and even cost savings when used in conjunction with underground engineering projects.

[0084] 3) Site layout

[0085] When deploying devices within the actual contaminated site area, the deployment should be based on the simulation results of groundwater solute migration software. Corresponding treatment arrangements should be adopted for the corresponding contaminated areas in the grid division. Treatment should be carried out before new pollution becomes uncontrollable. When deploying PRBs, they should be placed as close as possible to the soil near the pollution source. When facing the migration of existing pollution, the migration depth should be predicted. Based on the actual pollution distribution, the devices should be deployed near the protected area. By combining the analysis method of simulation software with the actual pollution situation, most of the PRB application costs can be saved.

[0086] 5. Wide range of applicable types of pollution degradation

[0087] 1) Packing structure

[0088] The packing structure in this invention is applicable to various single-phase and complex types of pollution. Mesoporous adsorbent materials can adsorb and degrade various pollutants in water, but the pollution capture mechanism is temporary. The packing structure utilizes LDH1 and LDH2 micropores to refine the pores of biochar, and the adsorption capacity can be enhanced through LDH-nZVI@BC or LDH@BC composite materials. When using the packing for reactive degradation, LDHs can serve as a fixed, slow-release material for various forms of pollution: ① In treating metal ions, this can be achieved through surface functional group complexation, interlayer anion co-precipitation, crystal surface electrostatic attraction, and surface co-precipitation. ② In treating inorganic anions, this can be achieved through interlayer anion intercalation adsorption exchange, electrostatic adsorption, and ligand exchange. ③ In treating organic pollution, electron transition energy can be used to achieve oxidation reactions on the surface, degrading low-valence organic pollutants. nZVI and PMS can act as reducing and oxidizing agents, respectively, to initiate redox reactions. Under the conditions of capture and slow release by adsorbent material LDH1 and participation of catalytic LDH2, the degradation efficiency of various pollutants per unit time is improved. Simultaneously, due to the slow-release performance, the reaction time of the same amount of pollutants flowing through the packing structure is increased, ensuring a thorough and complete reaction and reducing the possibility of secondary pollution. This combined mechanism can redox degrade most organic pollutants, inorganic anionic pollutants, and some heavy metal pollutants that require adjustment of valence to reduce their pollution. Furthermore, in addition to serving as supplementary materials to maintain the catalytic performance of each PRB unit, the iron ions generated by the reacted nZVI can further catalyze the degradation reaction. By injecting alkaline substances, single-element LDHs are regenerated to continue the catalytic reaction, reducing blockage caused by metal precipitation in the material. The injection of PMS, after the oxidation reaction is completed, can renew the interlayer of the original composite LDHs with anions, restoring the adsorption and slow-release capacity of the LDHs. The packing structure system of this invention can achieve long-term and efficient degradation of various pollutants in complex saturated aquifer groundwater.

[0089] 2) Funnel-guide gate type structural unit and load-bearing wall

[0090] The funnel-guide gate type PRB structural unit and wall materials are mainly non-reactive inert materials to ensure that they will not undergo secondary reactions to generate other forms of pollution when facing various pollutants in groundwater, thus increasing the difficulty of remediation.

[0091] 3) Site layout

[0092] The invention utilizes simulation software to reasonably predict the migration pathways of various pollutants in various site layouts. The path prediction for inert pollutants is more consistent with the groundwater flow line. However, the migration of non-inert pollutants, such as nitrogen and some heavy metal ions, requires the construction of a model that is more consistent with the actual migration and transformation of pollutants, based on the clear possible transformation pathways. The types and composition ratios of the corresponding fillers are designed according to the actual migration and potential transformation forms of pollutants and the corresponding pollution status.

[0093] 6. Improved construction efficiency

[0094] 1) Packing structure

[0095] The filler structure of this invention primarily utilizes composite material addition as the filling method. The composite material can be obtained at the appropriate preparation site, and the procurement of nZVI, PMS, and common maintenance reagents is readily available. During the monitoring of the PRB system's operation, if the treatment efficiency is found to be lower than expected for the same period, necessary maintenance measures can be taken. Before construction, the types, specifications, and models of the required materials are determined and transported to the construction site after preparation. The PRB unit filler is pre-filled, and mixing and stirring are performed during addition. The material is then discharged into the fixed filter bag of the PRB unit.

[0096] 2) Funnel-guide gate type structural unit and load-bearing wall

[0097] Funnel-gate type PRB structures can be manufactured and assembled in the factory, transported to the actual site for material filling, and then the walls and PRB units are installed and assembled when the site is excavated to the pre-designed contamination treatment area where the PRB is buried in the saturated aquifer. This can be combined with underground engineering construction (…). Figure 3 (A and B) The placement of PRB units should correspond to the actual locations of building components. Segmented casting should be carried out after the corresponding unit positions are set. After the unit materials are filled, the PRB units and walls can also be pre-assembled on a small scale. The assembled PRB walls are placed in batches at the pre-designed elevation. When the walls are not yet fully installed but have reached a certain height, the arranged walls can be pre-filled to ensure wall stability. If building components from underground engineering are used, casting should wait until the overall unit placement is completed. Separate wall placement ( Figure 2 When A and B), when the bottom surface of the wall comes into contact with the uneven soil layer below, use waterproof soft material or small filler bags for flexible filling to reduce the voids on the contact surface between the PRB and the boundary soil layer, improve the integrity of the soil layer layout, and reduce the phenomenon of pollution bypassing the gaps of the edge wall.

[0098] 3) Site layout

[0099] In this invention, the layout of the PRB site should be comprehensively considered in conjunction with the target pollutant, the type of pollution source, the simulated migration and transformation path, and the actual saturated water-bearing strata of the site. The layout form mainly relies on the shape and specifications of the load-bearing walls. Overall, the site layout of the funnel-gate type structural unit and the load-bearing walls does not require high professional comprehensive skills from the construction personnel. The prefabricated construction method makes the overall construction less difficult. The overall PRB construction process is clear and the construction process can be flexibly controlled.

[0100] A second aspect of the present invention provides a method for treating complex pollution in shallow soil saturated aquifers using the aforementioned permeable reactive wall, comprising arranging multiple sets of funnel-gate type structural units in the site according to the actual site's pollutant migration depth, span, speed, and pollution source type to construct the permeable reactive wall.

[0101] Preferably, the multiple funnel-guide gate type structural units adopt at least one of the following arrangements: vertical arrangement of multiple columns of walls (including arc type and straight type), vertical arrangement (including arc type and straight type), and ring arc cylinder type (including full arc and non-full arc).

[0102] Preferably, the method further includes connecting a delivery pipe to the maintenance interface for replenishing consumed nZVI and PMS, or delivering alkaline NaOH and Na2CO3 to form new single-element LDH structures in the composite filler, or delivering a solution containing Na2SO4, Na2CO3 and / or NaCl for intercalation reconstruction of LDH1 and LDH2, provided that nZVI and PMS still have redox properties.

[0103] The structure, shape, and connection relationship of the PRB unit-type funnel-guide gate device of this invention differ from existing technologies. This PRB structure uses miniaturized unit-type funnel-guide gate devices combined into regular or irregular PRB walls. The funnel-guide gate and unitized design concept significantly reduces the ineffective volume of filler within a unit volume space. Compared to reaction methods that simply stack large amounts of filler, it saves material usage, reduces material filling costs, and improves the rational utilization of material space. Furthermore, compared to the difficulty in site selection for large PRB reactors, this grid-refined design improves the applicability and flexibility of PRB reactors in dealing with complex aquifers. The connection method adopts a fixed wall opening connection, with corresponding hole forms designed in the unit structure. This type of connecting wall is compatible with underground building engineering and can also be deployed independently, offering excellent flexibility. The wall material can be concrete used in combined building engineering and inexpensive PVC (polyvinyl chloride), PMMA (plexiglass), impermeable fabric, or steel used independently. The selection of wall material needs to be considered in conjunction with the actual depth of the stratum and the form of contamination.

[0104] Furthermore, the application of the PRB material structure in this invention satisfies the key considerations for PRB construction: high efficiency, durability, environmental friendliness, economy, convenience, and broad applicability to pollution. It is an environmentally friendly green technology. The high efficiency and durability of the PRB packing in this invention are reflected in the enhanced coupling ability of pollution retention and degradation, and a significant extension of the single-use cycle of the packing. Environmental friendliness is mainly reflected in the minimal impact of the materials used in the packing structure on the ecological environment in terms of raw materials, preparation process, application, and maintenance. Economic efficiency is mainly reflected in the significant reduction of material production costs, and the antibacterial properties of the packing structure and the more convenient maintenance methods further reduce maintenance costs. Simultaneously, the convenient material acquisition methods and mature, streamlined material production processes make this multi-type composite packing structure possess good environmental applicability. The invention's broad applicability to pollution is reflected in the fact that the packing structure used in the invention can degrade a variety of common pollutants in groundwater (including most inorganic salts, heavy metals, and organic pollutants). In addition to improved basic adsorption capacity, it can degrade multiple types of pollutants and transform them into environmentally friendly substances. Compared with traditional packing materials, this greatly expands the applicability of the packing material to groundwater pollution.

[0105] Furthermore, the PRB unit structure device of this invention has low manufacturing cost and a relatively simple equipment manufacturing process. It can be rationally customized and prefabricated in the factory based on actual site conditions. This involves determining the types and proportions of internal filler structures, the structural proportions of the PRB unit equipment and large-scale walls, and the material selection for the PRB structural units and even the large-scale load-bearing walls. The structural units are customized and pre-assembled in the factory, and then deployed on-site. Factory pre-assembly reduces construction difficulty, shortens the construction cycle, and does not place high demands on the proportion, quantity, or overall quality of construction personnel. When the unit-type PRB of this invention is deployed on-site, its fine grid structure units can flexibly avoid rock masses in complex saturated aquifers, solving the problem of difficulty in site selection and deployment of large-scale PRB devices in previous projects. Gaps between the unit-type PRB and the contacting rock layers can be addressed by using water-stop curtains or filler materials. The flexibility of the unit-type walls varies depending on the materials used; when used alone, highly flexible impermeable fabric, steel with good rigidity, or concrete and cement mortar commonly used in underground engineering can be used. Whether to use it in conjunction with underground engineering projects depends on the actual site conditions. During the maintenance of unit-configuration PRBs, the adsorption, slow-release, antibacterial, and catalytic properties of LDH1 and LDH2 in the packing material are restored due to their memory and remodeling characteristics. This remodeling can be categorized into non-polluting inorganic salt intercalation renewal and in-situ generation of new LDH structures (intercalation renewal via injection of Na2SO4, Na2CO3, and NaCl, and in-situ remodeling via injection of Na2CO3, NaOH, and stabilizers, respectively). Both methods restore the characteristics of LDHs, making maintenance easier. nZVI and PMS in the packing structure are consumable substances. To maintain the high efficiency and longevity of single-unit pollution treatment within the saturated aquifer within the pollution plume, they are periodically replenished. Both oxidants and reductants are common environmentally friendly substances. This periodic replenishment method avoids frequent excavation work during PRB engineering material performance maintenance, saving significant maintenance costs. Example

[0106] -Preparation of the first composite filler

[0107] Under N2 protection, LDH1 powder (purchased from Xi'an Qiyue Biotechnology Co., Ltd.) and nZVI (spherical zero-valent iron with a diameter of approximately 500 nm) were added to a grinding and stirring machine heated to 40°C at a mass ratio of nZVI:LDH1 of 35:1. The mixture was stirred for 1.5 hours under nitrogen protection to obtain a final product. This mixture was then poured into a flask, sealed, and heated to 120°C with stirring for 6 hours to obtain the LDH1-nZVI reaction product. Biochar BC (straw biochar, approximately 100 mesh) was dried and pulverized, then added to a flask at a mass ratio of BC:LDH1-nZVI of 25:1 (the mass of LDH1-nZVI was determined by taking 10 ml of the slurry from the corresponding batch, drying it, and then converting the slurry volume to the product mass). The mixture was stirred and reacted for another 8 hours under nitrogen protection. The reaction product was washed, centrifuged, dried, and then ground to obtain the first composite filler, LDH1-nZVI@BC.

[0108] Under nitrogen protection, LDH2 powder (purchased from Xi'an Huirui Biotechnology Co., Ltd.) and nZVI (spherical zero-valent iron with a diameter of approximately 500 nm) were added to a grinding and stirring machine heated to 40°C at a mass ratio of nZVI:LDH2 of 32:1. The mixture was stirred for 1.5 hours under nitrogen protection to obtain a final product. This mixture was then poured into a flask, sealed, and heated to 120°C with stirring for 6 hours to obtain the LDH2-nZVI reaction product. Biochar BC (straw biochar, approximately 100 mesh) was dried and pulverized, then added to a flask at a mass ratio of BC:LDH2-nZVI of 20:1 (the mass of LDH2-nZVI was determined by taking 10 ml of the slurry from the corresponding batch, drying it, and then converting the slurry volume to the product mass). The mixture was stirred and reacted for another 8 hours under nitrogen protection. The reaction product was washed, centrifuged, dried, and then ground to obtain the first composite filler, LDH2-nZVI@BC.

[0109] The prepared LDH1-nZVI@BC and LDH2-nZVI@BC were mixed and added to obtain the first composite filler. Figure 9 A shows a SEM image of the first composite filler prepared.

[0110] -Preparation of the second composite filler

[0111] The biochar BC (straw biochar, about 100 mesh) was dried and pulverized, and added to a grinding and stirring machine heated to 40°C. Then, under N2 protection, LDH1 powder (purchased from Xi'an Qiyue Biotechnology Co., Ltd.) was added at a mass ratio of BC:LDH1=25:1. The mixture was heated to 120°C and stirred for 6 hours under N2 protection. The reaction product was washed, centrifuged, heated, dried and ground to obtain LDH1@BC.

[0112] The biochar BC (straw biochar, about 100 mesh) was dried and pulverized, and added to a grinding and stirring machine heated to 40°C. Then, under N2 protection, LDH2 powder (purchased from Xi'an Huirui Biotechnology Co., Ltd.) was added at a mass ratio of BC:LDH2=20:1. The mixture was heated to 120°C and stirred for 6 hours under N2 protection. The reaction product was washed, centrifuged, heated, dried and ground to obtain LDH2@BC.

[0113] The prepared LDH1@BC and LDH2@BC were mixed and added to obtain the second composite filler. Figure 9 B shows an SEM image of the prepared second composite filler.

[0114] - Install PRB walls

[0115] The saturated aquifer of groundwater contaminated by a steel plant was revealed by geophysical electromagnetic exploration to be located at a depth of 5-8 meters. Actual sampling and testing revealed the presence of heavy metals such as lead, carbamazepine, phosphate, and nitrogen. Multiple preliminary samplings of groundwater in the designed remediation area showed the following: 1. Average lead concentration: 0.174 mg / L; 2. Average CBZ concentration: 0.132 µg / L; 3. Average total phosphorus concentration: 11.37 mg / L; 4. Average total nitrogen concentration: 43.52 mg / L. Preliminary geological surveys revealed that the soil in the designed remediation area of ​​the industrial park is mainly silty sand, a low-permeability medium with good particle size distribution, minimal karst development, and few rock layers and gravel. Therefore, according to… Figure 2 Arrangement A involves the separate deployment of PRB walls. Based on simulations of groundwater-related pollution migration, the corresponding burial depth for the designated area is 5.4m-3.4m underground. The supporting walls for the assembled PRB wall units are made of stainless steel, and the basic carrier for the filler is biochar with a permeability coefficient approximately three times that of the original soil layer.

[0116] The deployed PRB wall consists of 40 PRB units, each composed of four funnel-gate type units. The PRB units and groups are interconnected via sealing rubber strips on adjacent sidewalls of the funnel-shaped water-facing side. The PRB units are made of PVC, with the first delivery pipe being 0.2m long and the second delivery pipe 0.6m long. The prepared first and second composite packing materials are respectively loaded into 300-mesh bidirectional permeable nylon filters and then placed in the first and second delivery pipes. For the second composite packing material in the second delivery pipe, PMS solution is injected at a flow rate of 80 ml / d and a concentration of 1 mmol / L during maintenance. At the outlet end of the deployed area, close to and parallel to the wall, three observation wells are drilled at equal intervals using perforated PVC pipes and a handheld oil pump-type small drilling machine. Each observation well is equidistant from the wall surface to facilitate groundwater sampling and observation of groundwater level changes.

[0117] The concentration of pollutants in the treated groundwater was measured at the outlet side of the PRB wall system after 30, 60, 67, 90 and 97 days of stable operation. The results showed that the PRB wall had a good removal effect on a variety of pollutants. After one month of operation, the average removal rates of heavy metal lead, carbamazepine, total phosphorus and total nitrogen were 87.2%, 96.4%, 89.6% and 91.7%, respectively. Two months later, sampling tests revealed a significant decrease in the system's effectiveness in treating heavy metal lead and phosphate contaminants, with corresponding average removal rates of 73.8%, 93.7%, 79.4%, and 90.2%, respectively. Therefore, Na₂CO₃ and NaOH solutions were replenished via the delivery pipe (concentrations of 1 mol / L NaOH and 0.2 mol / L Na₂CO₃, with an injection flow rate of 500 ml per wall unit). Re-sampling and testing one week later showed improved average removal rates for heavy metal lead, total phosphorus, and total nitrogen. The average removal rate for carbamazepine contamination decreased slightly, and the system packing could not be restored to its initial contamination removal state. At this point, the average removal rates for each contaminant were 82.8%, 93.4%, 85.1%, and 90.6%, respectively. In the third month, groundwater samples were tested, and the average removal rates of heavy metals lead, carbamazepine, total phosphorus, and total nitrogen all decreased, to 70.5%, 92.3%, 74.7%, and 89.6%, respectively. The concentration changes of heavy metals lead and total phosphorus were more pronounced, which is similar to the trend of pollutant concentration changes after treatment by the PRB system in the second month. The PRB packing material was removed, soaked in a high-concentration NaCl solution, dried, refilled, buried, and put into operation. One week later, groundwater samples were tested, and the average removal rates of heavy metals lead, carbamazepine, total phosphorus, and total nitrogen all improved to some extent, to 80.4%, 92.6%, 82.3%, and 89.8%, respectively, indicating that the PRB system packing material has good recycling potential. Overall, the PRB system demonstrated sustained and efficient removal of several major pollutants from groundwater during operation at the site, exhibiting long-term stable and reliable applicability. In addition, its low cost of packing material preparation and application, along with ease of construction, makes it more promising for application. During operation and maintenance, the PRB system can maintain the efficient degradation of complex and diverse pollutants in groundwater in a more cost-effective and convenient manner, and it also exhibits good recyclability of the packing material structure.

[0118] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be covered within the protection scope of the present invention.

Claims

1. A permeable reactive wall (PRB) for treating multiple types of contamination in groundwater, characterized in that... It includes multiple interconnected funnel-guide gate type structural units. Each funnel-gate type structural unit includes a funnel-shaped guide head, a first conveying pipe, and a second conveying pipe. The funnel-shaped guide head includes a first opening and a second opening opposite each other, and non-permeable sidewalls surrounding the first and second openings. The area of ​​the first opening is larger than the area of ​​the second opening. The first conveying pipe is sealed to the second opening, and the second conveying pipe is connected to the first conveying pipe on the side away from the guide head. The first conveying pipe is filled with a first composite packing material, and the second conveying pipe is filled with a second composite packing material. The first composite packing material comprises biochar (BC), adsorbent layered double hydroxide (LDH1), catalytic layered double hydroxide (LDH2), and nano-zero-valent iron (nZVI). The second composite packing material comprises the biochar, the adsorbent layered double hydroxide (LDH1), the catalytic layered double hydroxide (LDH2), and persulfate (PMS) as an oxidant. The adsorbent layered double hydroxide LDH1 and the catalytic layered double hydroxide LDH2 are represented by the following formula: ([M 1-x 2+ M x 3+ (OH)2] x+ [A n- ]·zH2O) For LDH1, M 2+ Mg 2+ M 3+ For Al 3+ For LDH2, M 2+ For Ni 2+ M 3+ For Fe 3+ , X represents the molar ratio M. 3+ / ( M 2+ + M 3+ ), A n- For containing Cl - and CO3 2- The interlayer anions, where n is the number of negative charges and z is the number of water molecules in the interlayer structure.

2. The permeable reactive wall PRB according to claim 1, characterized in that, The amount of PMS added accounts for 1-10% of the total weight of the second composite filler, and it is added in solution form during PRB maintenance.

3. The permeable reactive wall PRB according to claim 1, characterized in that... It includes multiple sets of funnel-guide gate type structural units. Every four interconnected funnel-guide gate type structural units form a group, where the first opening is the water-facing side. In each group, adjacent funnel-guide gate type structural units are interconnected by a sealed connecting strip set on the water-facing side.

4. The permeable reactive wall PRB according to claim 2, characterized in that, The first conveying pipe and the second conveying pipe further include a 200-400 mesh bidirectional permeation filter screen disposed therein, wherein the first composite packing and the second composite packing are respectively contained in the bidirectional permeation filter screen. The second delivery pipe is longer than the first delivery pipe. A maintenance interface is provided on the side wall of the second delivery pipe for replenishing consumed nZVI and PMS, or for introducing NaOH, Na₂CO₃, Na₂SO₄, and NaCl to update the interlayer ions of LDH1 or LDH2 or reconstruct the LDH structure, ensuring the oxidation or reduction reaction proceeds fully. The first conveying pipeline and the second conveying pipeline are connected by a flow stabilizer joint.

5. The permeable reactive wall PRB according to claim 3, characterized in that, At least three sets of funnel-guide gate type structural units are individually arranged together using rigid non-building materials or flexible materials.

6. The permeable reactive wall PRB according to claim 3, characterized in that, At least three sets of funnel-gate type structural units are arranged together through inherent underground building engineering components. Each funnel-guide gate type structural unit is interconnected by a sealed connecting strip set on the water-facing side of adjacent funnel-guide gate type structural units.

7. The permeable reactive wall PRB according to claim 5, characterized in that, The rigid non-building material is selected from at least one of stainless steel, polyethylene, and polyacrylate, or the flexible material is selected from at least one of waterproof fabric and waterproof curtain.

8. The permeable reactive wall PRB according to claim 6, characterized in that, The underground engineering components of the building are made of concrete and / or cement and / or mortar.

9. A method for treating complex pollution in shallow soil saturated aquifers using a permeable reactive wall as described in any one of claims 1 to 8, characterized in that... This involves arranging multiple funnel-gate type structural units in the site according to the actual migration depth, span, speed of pollutants and the type of pollution source in the site, in order to construct the permeable reactive wall (PRB).

10. The method according to claim 9, characterized in that, The multi-group funnel-guide gate type structural unit adopts at least one of the following arrangements: vertical arrangement of multiple rows of walls, vertical arrangement, and ring-arc cylinder type.

11. The method according to claim 9 or 10, characterized in that, The method also includes connecting a delivery pipe to a maintenance interface for replenishing consumed nZVI and PMS, or delivering alkaline NaOH and Na2CO3 to form new single-element LHD structures in the composite filler, or delivering a solution containing Na2SO4, Na2CO3 and / or NaCl for intercalation reconstruction of LDH1 and LDH2, provided that nZVI and PMS still have redox properties.

12. The method according to claim 10, characterized in that, The vertical arrangement of the multi-column walls includes curved and straight types, the vertical arrangement includes curved and straight types, and the annular cylindrical type includes full arc and non-full arc.

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