Permeable reactive barrier repair method with in-situ blockage cleaning and microbial activation functions

Abstract

This invention discloses a method for repairing permeable reactive walls with in-situ unblocking and regeneration functions and microbial activation, belonging to the field of groundwater pollution remediation technology. The method uses a monitoring system to monitor and assess the status of the multi-media composite reactive wall in real time. When a blockage trend or a decline in treatment efficiency occurs, in-situ hydraulic disturbance, flushing and unblocking, and microbial activation are used to repair the multi-media composite reactive wall. This method uses permeability degradation as a trigger condition to synergistically implement in-situ unblocking and regeneration with the maintenance or dynamic activation of microbial activity in the repair of permeable reactive walls. By switching or coordinating the repair mode, unblocking mode, and activation mode under different operating conditions, it improves the engineering stability, repair sustainability, and full life-cycle operational reliability of permeable reactive walls without relying on specific reactive materials or strict environmental conditions.

Description

Technical Field

[0001] This invention relates to the field of groundwater pollution remediation technology, specifically to a method for remediating permeable reactive walls with in-situ decontamination, regeneration, and microbial activation functions. The method includes the operation, monitoring, decontamination, regeneration, and microbial activation of the permeable reactive wall system. This method is particularly suitable for multi-media permeable reactive wall devices with in-situ decontamination, regeneration, and microbial activation functions, enabling efficient operation and performance optimization of the device. Background Technology

[0002] Permeable reactive barriers (PRBs) are a typical in-situ groundwater remediation technology. The basic principle is to construct a reactive media wall of a certain thickness and permeability along the migration path of contaminated groundwater. Groundwater passively flows through the permeable reactive barrier under the influence of the natural hydraulic gradient, where it undergoes physical adsorption, chemical reactions, and biodegradation processes, achieving in-situ removal of pollutants. Compared with traditional groundwater remediation methods such as pump and treat, PRB technology has advantages such as not requiring long-term pumping, low energy consumption, and minimal surface disturbance, and has been applied in remediation projects for chlorinated organic pollutants, heavy metals, and some inorganic pollutants.

[0003] In complex contaminated sites like landfill leachate, groundwater typically exhibits high ammonia nitrogen concentrations, high organic loads, and high inorganic salt content, posing serious engineering stability challenges to PRB systems during long-term operation. Existing PRB operation methods also suffer from numerous technical deficiencies.

[0004] The invention patent application "A Method for In-situ Remediation of Cyanide-Containing Groundwater with a Permeable Reactive Wall" (CN107739083A), published on February 27, 2018, employs a two-stage reactive wall structure. By filling different catalysts with zeolite as a carrier into the two reaction sections respectively, cyanide is oxidized in stages under different pH conditions, which can solve the problem of in-situ remediation of cyanide-containing groundwater. However, it still has the following drawbacks: 1. The system has extremely strict requirements for pH control. If pH monitoring or adjustment fails, highly toxic products will be generated, posing a risk of secondary pollution. 2. The preparation process of oxide catalysts is complex, and the zeolite support requires acidification pretreatment. In practical engineering, large-scale production of the packing material is costly and requires frequent replacement. 3. Two-stage permeable reactive barriers rely on porous structures to maintain permeability, but during long-term operation, packing material caking or biofilm growth may reduce the permeability coefficient of the barrier and affect the efficiency of groundwater flow. The invention patent "Method for Remediating Groundwater Using a Permeable Reactive Wall" (CN110357241B), authorized on November 6, 2020, uses a composite slurry of nano-zero-valent iron and biochar to construct a reactive wall through layered injection technology to achieve in-situ remediation of chlorinated hydrocarbon pollution in groundwater. This can solve the problem that traditional open-cut permeable reactive walls are prone to pollutant diffusion, but it still has the following drawbacks: 1. Nano-zero valent iron is prone to agglomeration and passivation. Although biochar is used as a carrier to alleviate the agglomeration effect, it still has the problems of short migration distance and limited activity period under the action of groundwater flow, which affects the sustainability of remediation. 2. The injection process relies on precision equipment and requires high formation homogeneity. In sites with developed fissures or uneven clay layer thickness, the slurry distribution is prone to shift, resulting in discontinuity in the reactive wall structure. 3. The ecological risks of composite materials remaining underground for a long time are not clearly defined. For example, biochar may become a secondary source of pollution after adsorbing pollutants, and nano-zero-valent iron oxide products may change the chemical environment of groundwater.

[0005] The invention patent authorized on August 2, 2024, entitled "A Method for In-situ Remediation of Groundwater and Soil Using a Microbial Electrochemical Permeable Reactive Wall" (CN116475217B), employs a microbial electrochemical reactive wall structure. It delivers reagents to groundwater and soil through a control pipe, forming a redox potential gradient and utilizing a conductive reaction medium to achieve directional electron transport, replacing the traditional mass transfer process. This can solve problems such as low mass transfer efficiency, high cost, and easy secondary pollution in groundwater and soil remediation. However, it still has the following drawbacks: 1. The system is highly dependent on environmental conditions. The electron transport efficiency of the conductive reaction medium is significantly affected by the conductivity of groundwater, pH value and temperature fluctuations. Microbial activity decreases under low temperature or extreme pH conditions, which may lead to a decrease in remediation efficiency. 2. The control tube needs to continuously deliver reagents to maintain the redox gradient, which requires frequent operation and maintenance. The reagent consumption is large during long-term operation, and uneven reagent diffusion may cause local pollution rebound. 3. The electron transmission distance is limited by the resistivity of the conductive medium. When dealing with large-scale or deep pollution plumes, reaction units need to be densely deployed, which increases construction costs and deployment difficulty. 4. Conductive media exposed to groundwater for extended periods are prone to blockage due to suspended solids deposition or biofilm growth, resulting in decreased permeability and reduced flow capacity of the wall. Regular cleaning or replacement is required, leading to high maintenance costs. Summary of the Invention

[0006] The technical problem this invention aims to solve is that reactive walls in complex contaminated sites such as landfill leachate are prone to permeability degradation, reduced remediation efficiency, and difficulty in in-situ restoration after long-term operation. This invention provides a method for repairing permeable reactive walls that is based on operational status monitoring, uses permeability degradation as a triggering condition, and synergistically implements in-situ deblocking and regeneration with the maintenance or dynamic activation of microbial activity. By switching or coordinating the operation of remediation, deblocking, and activation modes under different operating conditions, this method improves the engineering stability, remediation sustainability, and overall life-cycle reliability of permeable reactive walls without relying on specific reactive materials or stringent environmental conditions.

[0007] The present invention adopts the following technical solution: A method for repairing a permeable reactive wall with in-situ unblocking, regeneration, and microbial activation functions. The repair device involved in the method includes a pollution source, a regulating tank, a multi-media composite reactive wall, a guide wall, a flushing fluid injection well, a microbial activation well, a nutrient solution storage tank, an extraction regulating well, and a monitoring system. The multi-media composite reactive wall includes a main body and a barrier wall on top of the main body. The main body includes a filtration zone, a heavy metal reaction removal zone, and an organic pollutant and nitrogen removal zone in sequence along the flow direction of the polluted groundwater. The heavy metal reaction removal zone and the organic pollutant and nitrogen removal zone are filled with reaction media. A reverse flushing channel is opened in the organic pollutant and nitrogen removal zone, and a reverse extraction channel is opened in the filtration zone. In-situ interception and remediation of contaminated groundwater using remediation devices deployed in underground aquifers; including the following steps: Step 1, Normal Operation Stage of the Media Composite Reaction Wall Under the action of the natural groundwater hydraulic gradient, the polluted groundwater flows through the multi-media composite reaction wall under the guidance of the guide wall, and successively completes the interception of suspended particles in the filtration zone, the removal of heavy metals in the heavy metal reaction removal zone, and the adsorption, transformation and biodegradation of organic pollutants and nitrogen pollutants in the organic pollutant and nitrogen removal zone. Step 2, Determining the state of the multi-media composite reactive barrier The monitoring system continuously collects water level, hydraulic gradient, permeability, and water quality parameters upstream, downstream, and inside the multi-media composite reactive wall. Based on the monitoring results, the following judgments are made: whether the multi-media composite reactive wall is blocked or its treatment efficiency is reduced; whether it is under a high-concentration organic pollution shock load condition. If it is under a high-concentration organic pollution shock load condition, nutrient solution or functional bacteria are added in a targeted manner to eliminate the high-concentration organic pollution state. If blockage or treatment efficiency reduction occurs, proceed to step 3. Step 3, In-situ hydraulic disturbance stage When monitoring results indicate that the multi-media composite reaction wall is showing signs of clogging or a decrease in treatment efficiency, flushing fluid is injected into the organic pollutant and nitrogen removal zone through the flushing fluid injection well and the reverse flushing pipeline to implement in-situ hydraulic disturbance of the reaction media. Step 4, Flushing and Unclogging Stage While or after in-situ hydraulic disturbance is being carried out, a local negative pressure hydraulic field is formed inside the multi-media composite reaction wall through the extraction regulating well and the reverse extraction channel, pointing towards the extraction regulating well. Fine particulate matter, sediment products, aging biofilm and pollutants generated by the disturbance are extracted and cleared by the flushing fluid. Step 5, Microbial Activation Stage After unblocking, nutrient solution or functional bacterial agent is added to the organic pollutant and nitrogen removal zone through microbial activation well to maintain or restore the activity of functional microorganisms in the reaction medium. Step 6: After confirming through the monitoring system that the permeability and pollutant removal capacity of the multi-media composite reactive barrier have been restored, return to Step 1 and enter the next operating cycle.

[0008] Preferably, the monitoring system includes a monitoring system and a central control unit; the monitoring system includes: a flow meter, a pressure gauge, and a dissolved oxygen sensor installed at the outlet of the nutrient solution storage tank; multiple sensors installed inside the organic pollutant and nitrogen removal zone to measure pore water pressure, flow rate, liquid level, pH, conductivity, and ammonia nitrogen value; a pressure gauge and a flow meter installed at the inlet of the backwash channel and at the outlet of the back extraction channel; the central control unit is used to receive monitoring data and automatically trigger a cleaning and regeneration program when abnormal hydraulic or water quality parameters of the reaction wall are detected.

[0009] Preferably, the criteria for determining the blockage trend or decreased processing efficiency in step 2 include one or more of the following: An early warning is issued when the average hydraulic gradient between the upstream and downstream of the multi-media composite reactive wall exceeds 1.5 times the average value during the initial stable operation period for 12 consecutive hours; and a clearing procedure is initiated when it exceeds 2.0 times. The unblocking procedure will be initiated when the pressure difference between any section between the filtration zone and the heavy metal reaction removal zone, or between the heavy metal reaction removal zone and the organic pollutant and nitrogen removal zone, increases by more than 30% within 4 hours. After excluding external shock load factors, the effluent pollutant concentration of the multi-media composite reactive barrier continued to approach 60% of the influent pollutant concentration; If any of the above conditions occur, it is determined that the multi-media composite reactive barrier has become clogged or its treatment efficiency has decreased.

[0010] Preferably, before flushing in step 4, the main flow rate into the multi-media composite reaction wall is reduced by adjusting the valve on the pipeline between the pollution source and the regulating tank, and some or all of the incoming water is temporarily stored in the regulating tank; the flushing liquid in step 4 is clean groundwater or treated effluent that meets the standards, and the flushing pressure is gradually increased, with an initial pressure of 0.3 MPa, which is then increased to 0.5 to 0.8 MPa, and in-situ flushing is carried out using an intermittent pulse operation mode.

[0011] Preferably, while performing in-situ hydraulic disturbance in step 3, the extraction regulating well is started, and the extraction flow rate is controlled to be 1.1 to 1.5 times the flushing fluid injection flow rate, so that a stable negative pressure zone is formed inside the multi-media composite reactive wall to suppress the diffusion of pollutants to the surrounding aquifer during the unblocking process; the extracted waste liquid is transported to the regulating tank, treated and reused for flushing or discharged in compliance with standards; when the monitoring results show that the hydraulic gradient of the multi-media composite reactive wall recovers to within 1.2 times the initial stable operating value and remains stable for 2 hours, the normal operation state is restored.

[0012] Preferably, the nutrient solution is transported from the nutrient solution storage tank to the microbial activation well via a metering pump, and enters the organic pollutant and nitrogen removal zone through the microbial activation holes set on the well wall. The nutrient solution includes a fast-acting carbon source, a phosphorus source, and trace elements. During the addition process, the dissolved oxygen in the nutrient solution is monitored by a dissolved oxygen sensor, and an inert gas is introduced when necessary to regulate the hypoxic environment.

[0013] Preferably, the microbial activation in step 5 includes a conventional maintenance mode and an enhanced activation mode; The conventional maintenance mode involves continuously or intermittently adding nutrient solution to the organic pollutant and nitrogen removal zone through microbial activation wells during the normal operation of the multi-media composite reactive barrier. The addition flow rate is 0.1% to 0.5% of the groundwater inflow. The enhanced activation mode is activated within 24 hours after unblocking, when the concentration of pollutants in the influent increases abnormally or the removal rate of the effluent continues to decline and is not caused by physical blockage. The nutrient solution dosage is increased to 2 to 3 times that of the conventional maintenance mode, and functional bacteria and carbon source are added.

[0014] Preferably, the process of judging and eliminating the high concentration organic pollution shock load condition in step 2 is as follows: when the monitoring results show that the concentration of organic pollutants in the influent increases significantly in a short period of time, while the overall hydraulic gradient, inter-regional pressure difference and permeability of the multi-media composite reaction wall are still within the normal range, it is judged to be a high concentration organic pollution shock load condition. Under this condition, the unblocking procedure is not initiated. Instead, nutrient solution or functional bacterial agent is added to the organic pollutant and nitrogen removal zone through microbial activation wells, and the addition frequency and amount are dynamically adjusted according to real-time monitoring data.

[0015] Preferably, the barrier wall is used in sites where groundwater flows in a dispersed manner or where the contaminated strata are buried at a large depth; specifically, in sites where groundwater flows in a dispersed manner or where the contaminated strata are buried at a large depth, when the guide wall guides the contaminated groundwater to flow into the multi-media composite reaction wall, the barrier wall restricts the flow of shallow groundwater and intercepts suspended particles and uniform water flow through the filter zone set on the water-facing side.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By setting a clearing trigger threshold to monitor changes in the performance and permeability of the permeable reactive wall, the clearing procedure is initiated before the hydraulic performance of the permeable reactive wall declines significantly, thus avoiding irreversible blockage and achieving preventive maintenance. This transforms the permeable reactive wall from a static repair system into a controllable and regenerative engineering system.

[0017] (2) The coordination relationship between the unblocking unit, the microbial activation unit and the core permeable reactive wall in terms of time sequence and space was clarified, so that the device can play its role as a whole system. The unblocking process was upgraded from a single physical operation to a systematic approach that combines hydraulic disturbance, pollutant recovery and biological reconstruction.

[0018] (3) By regularly and gently cleaning and activating microorganisms in situ, the expensive and destructive operation of replacing the reaction medium on a large scale due to long-term performance degradation is avoided, which significantly reduces the total life cycle cost.

[0019] (4) By forming a negative pressure hydraulic capture zone through directional extraction, the pollutants released during the regeneration process are collected and treated in a concentrated manner, thus preventing the pollutants from spreading to the surrounding groundwater environment. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the planar layout of the repair device in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the longitudinal cross-sectional structure of the repair device in an embodiment of the present invention.

[0022] Figure 3 This is a flowchart of the method of the present invention.

[0023] Attached Figures: 1. Pollution Source; 2. Equalization Tank; 4. Multi-Media Composite Reaction Wall; 5. Guide Wall; 6. Flushing Fluid Injection Well; 8. Microbial Activation Well; 9. Nutrient Solution Storage Tank; 10. Extraction Equalization Well; 12. Surface Line; 13. Barrier Wall; 14. Filtration Zone; 15. Heavy Metal Removal Zone; 16. Organic Pollutant and Nitrogen Removal Zone; 17. Microbial Activation Hole; 18. Backflushing Flow Direction; 19. Backflushing Pipeline; 20. Backflushing Extraction Channel. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a schematic diagram of the planar arrangement of the repair device involved in the present invention. Figure 2 This is a schematic longitudinal cross-sectional view of the main body of the permeable reactive wall in an embodiment of the present invention. Figure 1 , Figure 2 As can be seen, the remediation device involved in this remediation method includes a pollution source 1, a regulating tank 2, a multi-media composite reaction wall 4, a guide wall 5, a flushing fluid injection well 6, a microbial activation well 8, a nutrient solution storage tank 9, an extraction regulating well 10, and a monitoring system. The multi-media composite reactive wall 4 includes a main body and a barrier wall 13 on top of the main body. The main body includes a filtration zone 14, a heavy metal reaction removal zone 15, and an organic pollutant and nitrogen removal zone 16 in sequence along the flow direction of the polluted groundwater. The heavy metal reaction removal zone 15 and the organic pollutant and nitrogen removal zone 16 are filled with reaction media. A reverse flushing channel 19 is opened in the organic pollutant and nitrogen removal zone 16, and a reverse extraction channel 20 is opened in the filtration zone 14. exist Figure 1 and Figure 2 In the diagram, 12 represents the surface, 17 is the microbial activation well, and 18 represents the reverse flushing flow direction. The microbial activation well 17 is located on the well wall of the organic pollutant and nitrogen removal zone 16 and is evenly distributed.

[0026] In this embodiment, the barrier wall 13 is used in sites where groundwater flows in a dispersed manner or where the contaminated strata are buried at a large depth. Specifically, in sites where groundwater flows in a dispersed manner or where the contaminated strata are buried at a large depth, when the guide wall 5 guides the contaminated groundwater to flow into the multi-media composite reaction wall 4, the barrier wall 13 restricts the flow of shallow groundwater and intercepts suspended particles and uniform water flow through the filter zone 14 set on the water-facing side.

[0027] Figure 3 This is a flowchart of the remediation method of the present invention. As shown in the figure, the present invention provides a permeable reactive barrier remediation method with in-situ decongestion, regeneration, and microbial activation functions, utilizing a remediation device deployed in an underground aquifer to intercept and remediate contaminated groundwater in situ; including the following steps: Step 1, Normal operation phase of the media composite reaction wall 4 Under the influence of the natural groundwater hydraulic gradient, the polluted groundwater flows through the multi-media composite reaction wall 4 under the guidance of the guide wall 5, and successively completes the interception of suspended particles in the filtration zone 14, the removal of heavy metals in the heavy metal reaction removal zone 15, and the adsorption, transformation and biodegradation of organic pollutants and nitrogen pollutants in the organic pollutant and nitrogen removal zone 16.

[0028] Step 2, Determining the state of the multi-media composite reactive wall.

[0029] The monitoring system continuously collects water level, hydraulic gradient, permeability, and water quality parameters upstream, downstream, and inside the multi-media composite reactive wall 4. Based on the monitoring results, the following judgments are made: whether the multi-media composite reactive wall 4 is blocked or its treatment efficiency is reduced; whether it is under a high-concentration organic pollution shock load condition. If it is under a high-concentration organic pollution shock load condition, nutrient solution or functional bacteria are added in a targeted manner to eliminate the high-concentration organic pollution state. If blockage or treatment efficiency reduction occurs, proceed to step 3.

[0030] In this embodiment, the criteria for determining the blockage trend or decreased processing efficiency in step 2 include one or more of the following: When the average hydraulic gradient between the upstream and downstream of the multi-media composite reactive barrier 4 exceeds 1.5 times the average value during the initial stable operation period for 12 consecutive hours, an early warning is issued; when it exceeds 2.0 times, the unblocking procedure is initiated. The unblocking procedure is initiated when the pressure difference between any section between the filtration zone 14 and the heavy metal reaction removal zone 15, or between the heavy metal reaction removal zone 15 and the organic pollutant and nitrogen removal zone 16, increases by more than 30% within 4 hours. After excluding external shock load factors, the effluent pollutant concentration of the multi-media composite reactive wall 4 continuously approached 60% of the influent pollutant concentration; If any of the above situations occur, it is determined that the multi-media composite reactive wall 4 has become blocked or its treatment efficiency has decreased.

[0031] Step 3, In-situ hydraulic disturbance stage

[0032] When monitoring results indicate that the multi-media composite reaction wall 4 shows a tendency to become clogged or its treatment efficiency decreases, flushing fluid is injected into the organic pollutant and nitrogen removal zone 16 through the flushing fluid injection well 6 and the backflushing pipe 19 to perform in-situ hydraulic disturbance on the reaction media.

[0033] In this embodiment, while performing in-situ hydraulic disturbance in step 3, the extraction regulating well 10 is started, and the extraction flow rate is controlled to be 1.1 to 1.5 times the flushing fluid injection flow rate, so that a stable negative pressure zone is formed inside the multi-media composite reactive wall 4 to suppress the diffusion of pollutants to the surrounding aquifer during the unblocking process; the extracted waste liquid is transported to the regulating tank 2, and after treatment, it is reused for flushing or discharged in compliance with standards; when the monitoring results show that the hydraulic gradient of the multi-media composite reactive wall 4 recovers to within 1.2 times the initial stable operating value and remains stable for 2 hours, the normal operation state is restored.

[0034] Step 4, Flushing and Unclogging Stage

[0035] Simultaneously or subsequently, a local negative pressure hydraulic field is formed inside the multi-media composite reaction wall 4, pointing towards the extraction regulating well 10, through the extraction regulating well 10 and the reverse extraction channel 20. Fine particulate matter, sediment products, aging biofilm and pollutants generated by the disturbance are directionally extracted with the flushing fluid and cleared.

[0036] In this embodiment, before flushing in step 4, the main flow rate into the multi-media composite reaction wall 4 is reduced by adjusting the valve on the pipeline between pollution source 1 and regulating tank 2, and some or all of the incoming water is temporarily stored in regulating tank 2; the flushing liquid in step 4 is clean groundwater or treated effluent that meets the standards, and the flushing pressure is gradually increased, with an initial pressure of 0.3 MPa, which is then increased to 0.5 to 0.8 MPa, and in-situ flushing is carried out using an intermittent pulse operation mode.

[0037] Step 5, Microbial Activation Stage

[0038] After clearing the blockage, nutrient solution or functional bacterial agent is added to the organic pollutant and nitrogen removal zone 16 through microbial activation well 8 to maintain or restore the activity of functional microorganisms in the reaction medium.

[0039] In this embodiment, the nutrient solution is transported from the nutrient solution storage tank 9 to the microbial activation well 8 via a metering pump, and enters the organic pollutant and nitrogen removal zone 16 through the microbial activation hole 17 set on the well wall. The nutrient solution includes a fast-acting carbon source, a phosphorus source and trace elements. During the addition process, the dissolved oxygen in the nutrient solution is monitored by a dissolved oxygen sensor, and an inert gas is introduced when necessary to regulate the hypoxic environment.

[0040] Step 6: After confirming through the monitoring system that the permeability and pollutant removal capacity of the multi-media composite reactive wall 4 have been restored, return to step 1 and enter the next operating cycle.

[0041] In this embodiment, the monitoring system includes a monitoring system and a central control unit. The monitoring system includes: a flow meter, a pressure gauge, and a dissolved oxygen sensor installed at the outlet of the nutrient solution storage tank 9; multiple sensors installed inside the organic pollutant and nitrogen removal zone 16 to measure pore water pressure, flow rate, liquid level, pH, conductivity, and ammonia nitrogen value; a pressure gauge and a flow meter installed at the inlet of the backwash channel 19 and at the outlet of the back extraction channel 20; the central control unit is used to receive monitoring data and automatically trigger a cleaning and regeneration program when abnormal hydraulic or water quality parameters of the reaction wall are detected.

[0042] In this embodiment, the microbial activation in step 5 includes a conventional maintenance mode and an enhanced activation mode; The conventional maintenance mode involves continuously or intermittently adding nutrient solution to the organic pollutant and nitrogen removal zone 16 through the microbial activation well 8 during the normal operation of the multi-media composite reactive barrier 4, with the addition flow rate being 0.1% to 0.5% of the groundwater inflow. The enhanced activation mode is activated within 24 hours after unblocking, when the concentration of pollutants in the influent increases abnormally or the removal rate of the effluent continues to decline and is not caused by physical blockage. The nutrient solution dosage is increased to 2 to 3 times that of the conventional maintenance mode, and functional bacteria and carbon source are added.

[0043] In this embodiment, the process of judging and eliminating the high concentration organic pollution shock load condition is as follows: when the monitoring results show that the concentration of organic pollutants in the influent increases significantly in a short period of time, while the overall hydraulic gradient, inter-regional pressure difference and permeability of the multi-media composite reaction wall 4 are still within the normal range, it is judged to be a high concentration organic pollution shock load condition. Under this condition, the unblocking procedure is not initiated. Instead, nutrient solution or functional bacteria are added to the organic pollutant and nitrogen removal zone 16 through the microbial activation well 8, and the addition frequency and amount are dynamically adjusted according to the real-time monitoring data.

[0044] To better illustrate the technical effects of the present invention, it was put into practice in specific engineering projects according to different geological conditions, pollution layer locations and pollution sources, resulting in specific embodiments 1-5.

[0045] Example 1

[0046] The remediation target was groundwater contaminated with leachate from a landfill with relatively simple geological conditions and shallow contamination layers. During remediation, under the influence of the natural groundwater hydraulic gradient, the contaminated groundwater flowed upstream to the multi-media composite reactive barrier 4. After being homogenized in the equalization tank 2, the contaminated groundwater entered the main body of the multi-media composite reactive barrier 4 and flowed sequentially through the filtration zone 14, the heavy metal reaction removal zone 15, and the organic pollutant and nitrogen removal zone 16. In each functional zone, suspended particulate matter interception, heavy metal reaction removal, and adsorption, transformation, and biodegradation of organic and nitrogen pollutants were completed respectively.

[0047] In this embodiment, during system operation, the monitoring system continuously collects data on groundwater levels, hydraulic gradients, changes in equivalent permeability coefficients, pressure differences between functional zones, and influent and effluent water quality parameters upstream, downstream, and inside the multi-media composite reactive barrier 4 to determine the real-time operating status of the multi-media composite reactive barrier 4. Under normal operating conditions, nutrient solution is continuously or intermittently supplied to the organic pollutant and nitrogen removal zone 16 through the nutrient solution storage tank 9 to provide basic metabolic conditions for microorganisms in the reaction medium, allowing functional microorganisms to grow naturally on the surface of the reaction medium and form a stable biofilm.

[0048] When monitoring results indicate that the hydraulic gradient of the multi-media composite reactive barrier 4 shows a continuous upward trend but has not yet reached the severe clogging threshold, the system initiates a preventative regeneration operation. Specifically, the main flow rate entering the multi-media composite reactive barrier 4 is reduced, and clean groundwater or treated effluent that meets standards is injected into the target area through the flushing fluid injection well 6 to create a low-intensity, short-cycle hydraulic disturbance to the reactive media. Simultaneously, the extraction regulating well 10 is activated, creating a negative pressure hydraulic field within the multi-media composite reactive barrier 4 pointing towards the extraction regulating well 10. This allows the disturbed fine particulate matter and aging biofilm to be directionally extracted and centrally recovered and treated with the flushing fluid. After the preventative regeneration is completed, the normal influent flow rate is restored, and nutrient solution is continuously replenished, allowing the system to enter the next operating cycle.

[0049] Example 2

[0050] Example 2 is an improvement on Example 1, applicable to site conditions where groundwater flow is dispersed and side flow channels are well-developed. During remediation, a guide wall 5 is installed on at least one side of the multi-media composite reactive barrier 4. The guide wall 5 extends along the main flow direction of groundwater to block non-target groundwater flow and reconstruct the local hydraulic field, allowing the originally dispersed or side-flowing polluted groundwater to enter the multi-media composite reactive barrier 4 more fully under the action of the natural hydraulic gradient.

[0051] In this embodiment, contaminated groundwater is guided by guide wall 5 into the multi-media composite reactive wall 4, and flows sequentially through filtration zone 14, heavy metal reaction removal zone 15, and organic pollutant and nitrogen removal zone 16, thereby improving the interception rate and treatment efficiency of contaminated groundwater. When monitoring results show that there is a local blockage trend in a certain area, targeted reverse flushing and extraction recovery are carried out in that area through flushing fluid injection well 6 and extraction regulating well 10 to maintain the stability of the overall hydraulic conditions of the multi-media composite reactive wall 4.

[0052] Example 3

[0053] Example 3 addresses engineering conditions where the contaminated strata are at considerable depth and the primary remediation targets are located in deep aquifers. In this example, a multi-media composite reactive barrier 4 is integrally embedded in the deep strata where the contaminated groundwater is mainly distributed. A barrier wall 13 is installed on top of the barrier, and a filtration zone 14 is installed on the water-facing side. During remediation, the barrier wall 13 restricts the disorderly seepage of overlying groundwater, reducing the disturbance of shallow water to the deep reactive zone; the filtration zone 14 intercepts suspended particles and homogenizes the incoming water flow, thereby creating stable operating conditions for the subsequent heavy metal removal zone 15 and the organic pollutant and nitrogen removal zone 16.

[0054] In this embodiment, nutrient solution from nutrient solution storage tank 9 is directed to the depth of organic pollutant and nitrogen removal zone 16 via microbial activation well 8 to replenish the carbon, phosphorus, and trace elements required for microbial metabolism. When necessary, functional microbial agents can also be added simultaneously to enhance the activity and quantity of microorganisms in organic pollutant and nitrogen removal zone 16. During operation, when monitoring results indicate a decrease in the removal efficiency of organic pollutants in the deep wall while the overall permeability remains within the normal range, the system prioritizes initiating the microbial activation program. When this is accompanied by a simultaneous increase in local pressure differential or a decrease in the equivalent permeability coefficient, the flushing fluid injection well 6 and extraction regulating well 10 are further activated to clear blockages.

[0055] Example 4

[0056] Example 4 addresses the challenges of landfill leachate quality fluctuations, high instantaneous organic pollution loads, and limited thickness and hydraulic retention time in single applications due to constraints on the thickness of the multi-media composite reactive barrier 4. During remediation, the synergistic effect of the guide wall 5, barrier wall 13, and multi-media composite reactive barrier 4 allows contaminated groundwater to be first directed towards the multi-media composite reactive barrier 4 by the guide wall 5 under the influence of the natural hydraulic gradient. Then, under the hydraulic constraint of the barrier wall 13, sideflow and bypass flow are reduced, thereby extending the effective path of the contaminated groundwater near the multi-media composite reactive barrier 4. Subsequently, the contaminated groundwater flows sequentially through the filtration zone 14, the heavy metal reaction removal zone 15, and the organic pollutant and nitrogen removal zone 16, achieving in-situ reduction within the reaction medium.

[0057] During operation of this embodiment, the monitoring system continuously collects data on water level, hydraulic gradient, equivalent permeability coefficient changes, and influent and effluent water quality parameters, focusing on monitoring organic pollutant concentrations, ammonia nitrogen concentrations, and related indicative water quality indicators. When monitoring results show a significant increase in influent organic pollutant concentration within a short period, while the effluent removal efficiency of the multi-media composite reactive wall 4 shows a downward trend, but the overall hydraulic gradient, pressure difference, and permeability remain within the normal range, the system determines that the current operating condition is a high-concentration organic pollution shock load, rather than physical blockage. Under this condition, the system does not initiate hydraulic unblocking operations. Instead, it uses microbial activation well 8 to directionally add nutrient solution and / or functional bacterial agents to the organic pollutant and nitrogen removal zone 16, dynamically adjusting the addition frequency and dosage based on real-time monitoring data to improve the metabolic activity and unit volume reaction capacity of the functional microorganisms. When monitoring results indicate that the effluent organic pollutant concentration of the multi-media composite reactive wall 4 returns to the design control range and the removal efficiency remains stable, the nutrient solution addition level is gradually reduced, allowing the system to return to normal operating conditions.

[0058] Example 5

[0059] Example 5 is a comprehensive and synergistic remediation method developed based on Examples 2 to 4. It is applicable to scenarios where multiple adverse factors coexist, such as complex hydrogeological conditions, large depth of contaminated strata, and significant fluctuations in leachate quality. During remediation, a guide wall 5 is set on at least one side of the multi-media composite reaction wall 4 to guide contaminated groundwater into the multi-media composite reaction wall 4 when groundwater flow is dispersed and side flow channels are developed. A barrier wall 13 is set on the upper part of the multi-media composite reaction wall 4 to constrain the flow path of overlying groundwater and stabilize the hydraulic environment of the deep reaction zone. Nutrients are supplied and microbial communities are enhanced in the organic pollutant and nitrogen removal zone 16 under different operating conditions through the microbial activation well 8 and the nutrient solution storage tank 9.

[0060] In this embodiment, polluted groundwater, guided by the natural groundwater hydraulic gradient, first flows into the multi-media composite reactive barrier 4 under the guidance of guide wall 5 and the constraint of barrier wall 13. Then, it flows sequentially through filtration zone 14, heavy metal reaction removal zone 15, and organic pollutant and nitrogen removal zone 16, completing the interception, reaction removal, and biodegradation of pollutants. During system operation, the monitoring system continuously collects groundwater level, hydraulic gradient, equivalent permeability coefficient changes, pressure difference between zones, and influent and effluent water quality parameters. The real-time monitoring data is compared and analyzed with the initial stable operation period data to determine whether the multi-media composite reactive barrier 4 is in normal operating condition.

[0061] When monitoring results show that the overall permeability is normal but the concentration of organic pollutants has increased significantly, the system determines that it has entered a high-load operation state. At this time, nutrient solution and / or functional bacterial agents are preferentially added to the organic pollutant and nitrogen removal zone 16 through the microbial activation well 8 to enhance the metabolic activity of the reaction medium per unit volume. When the monitoring results further show that the local hydraulic gradient or inter-regional pressure difference has a continuous upward trend, it indicates that the risk of blockage has begun to appear inside the wall. At this time, the system reduces the main flow rate into the multi-media composite reaction wall 4 and injects clean groundwater or treated effluent that meets the standards into the target area through the flushing fluid injection well 6 and the backwash pipe 19 to implement low-intensity or enhanced hydraulic flushing of the reaction medium. At the same time, the extraction regulating well 10 is activated, and a negative pressure hydraulic field is formed pointing to the extraction regulating well 10 through the backwash channel 20, so that the disturbed fine particulate matter, sediment products and aged biofilm are directionally extracted and centrally recovered and treated with the backwash flow 18. After the blockage is cleared, nutrient solution is replenished through microbial activation of well 8 to promote biofilm reconstruction and recovery of the reaction system. Once monitoring results confirm that the permeability and pollutant removal capacity of the multi-media composite reactive wall 4 have stabilized, the system enters the next operating cycle.

Claims

1. A permeable reactive wall repair method with in-situ cleaning, regeneration and microbial activation functions. The repair device involved in the repair method includes a pollution source (1), a regulating tank (2), a multi-media composite reactive wall (4), a guide wall (5), a flushing fluid injection well (6), a microbial activation well (8), a nutrient solution storage tank (9), an extraction regulating well (10) and a monitoring system. The multi-media composite reactive wall (4) includes a main body and a barrier wall (13) on top of the main body. The main body includes, in sequence along the flow direction of the polluted groundwater, a filtration zone (14), a heavy metal reaction removal zone (15), and an organic pollutant and nitrogen removal zone (16). The heavy metal reaction removal zone (15) and the organic pollutant and nitrogen removal zone (16) are filled with reaction media; a backwashing channel (19) is opened in the organic pollutant and nitrogen removal zone (16), and a back extraction channel (20) is opened in the filtration zone (14). Its characteristic is that it utilizes a remediation device deployed in an underground aquifer to intercept and remediate contaminated groundwater in situ; including the following steps: Step 1, Media Composite Reaction Wall (4) Normal Operation Stage Under the action of the natural groundwater hydraulic gradient, the polluted groundwater flows through the multi-media composite reaction wall (4) under the guidance of the guide wall (5), and completes the interception of suspended particles in the filtration zone (14), the heavy metal reaction removal zone (15), and the adsorption, transformation and biodegradation of organic pollutants and nitrogen pollutants in the organic pollutant and nitrogen removal zone (16). Step 2, Determining the state of the multi-media composite reactive wall (4) The monitoring system continuously collects water level, hydraulic gradient, permeability and water quality parameters of the upstream, downstream and inside of the multi-media composite reactive wall (4), and makes the following judgments based on the monitoring results: whether the multi-media composite reactive wall (4) is blocked or its treatment efficiency is reduced, and whether it is under high concentration organic pollution shock load conditions. If it is under high concentration organic pollution shock load conditions, nutrient solution or functional bacteria are added in a targeted manner to eliminate the high concentration organic pollution state; if blockage or treatment efficiency is reduced, proceed to step 3. Step 3, In-situ hydraulic disturbance stage When the monitoring results show that the multi-media composite reaction wall (4) is showing a clogging trend or a decrease in treatment efficiency, flushing fluid is injected into the organic pollutant and nitrogen removal zone (16) through the flushing fluid injection well (6) and the back flushing pipe (19) to implement in-situ hydraulic disturbance of the reaction medium; Step 4, Flushing and Unclogging Stage At the same time or after the in-situ hydraulic disturbance is implemented, a local negative pressure hydraulic field pointing towards the extraction regulating well (10) is formed inside the multi-media composite reaction wall (4) through the extraction regulating well (10) and the reverse extraction channel (20), so that the fine particulate matter, sediment products, aging biofilm and pollutants generated by the disturbance are extracted and cleared with the flushing liquid. Step 5, Microbial Activation Stage After unblocking, nutrient solution or functional bacterial agent is added to the organic pollutant and nitrogen removal zone (16) through the microbial activation well (8) to maintain or restore the activity of functional microorganisms in the reaction medium; Step 6: After confirming the recovery of the permeability and pollutant removal capacity of the multi-media composite reactive wall (4) through the monitoring system, return to step 1 and enter the next operating cycle.

2. The method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions according to claim 1, characterized in that, The monitoring system includes a monitoring system and a central control unit. The monitoring system includes: a flow meter, a pressure gauge and a dissolved oxygen sensor installed at the outlet of the nutrient solution storage tank (9); multiple sensors installed inside the organic pollutant and nitrogen removal zone (16) to measure pore water pressure, flow rate, liquid level, pH, conductivity and ammonia nitrogen value; a pressure gauge and a flow meter installed at the inlet of the backwash channel (19) and at the outlet of the back extraction channel (20); the central control unit is used to receive monitoring data and automatically trigger the unblocking and regeneration program when abnormal hydraulic or water quality parameters of the reaction wall are detected.

3. The method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions according to claim 1, characterized in that, The criteria for determining the clogging trend or decreased processing efficiency in step 2 include one or more of the following: When the average hydraulic gradient between the upstream and downstream of the multi-media composite reactive wall (4) exceeds 1.5 times the average value of the initial stable operation period for 12 consecutive hours, an early warning is issued; when it exceeds 2.0 times, the unblocking procedure is initiated. The unblocking procedure is initiated when the pressure difference between the filtration zone (14) and the heavy metal reaction removal zone (15) or between the heavy metal reaction removal zone (15) and the organic pollutant and nitrogen removal zone (16) increases by more than 30% within 4 hours. After excluding external shock load factors, the effluent pollutant concentration of the multi-media composite reactive wall (4) continued to approach 60% of the influent pollutant concentration; If any of the above situations occur, it is determined that the multi-media composite reactive wall (4) has become blocked or its treatment efficiency has decreased.

4. The method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions according to claim 1, characterized in that, Before flushing in step 4, the main flow rate into the multi-media composite reaction wall (4) is reduced by adjusting the valve on the pipeline between the pollution source (1) and the regulating tank (2), and some or all of the incoming water is temporarily stored in the regulating tank (2); the flushing liquid in step 4 is clean groundwater or treated effluent that meets the standards. The flushing pressure is gradually increased, with an initial pressure of 0.3 MPa, which is then increased to 0.5 to 0.8 MPa, and in-situ flushing is carried out using an intermittent pulse operation mode.

5. A method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions as described in claim 1 or 4, characterized in that, While implementing the in-situ hydraulic disturbance in step 3, the extraction regulating well (10) is started, and the extraction flow rate is controlled to be 1.1 to 1.5 times the flushing fluid injection flow rate, so that a stable negative pressure zone is formed inside the multi-media composite reaction wall (4) to suppress the diffusion of pollutants to the surrounding aquifer during the unblocking process; the extracted waste liquid is transported to the regulating tank (2), and after treatment, it is reused for flushing or discharged in compliance with standards; when the monitoring results show that the hydraulic gradient of the multi-media composite reaction wall (4) recovers to within 1.2 times the initial stable operating value and remains stable for 2 hours, the normal operation state is restored.

6. The method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions according to claim 1, characterized in that, The nutrient solution is transported from the nutrient solution storage tank (9) to the microbial activation well (8) by a metering pump, and enters the organic pollutant and nitrogen removal zone (16) through the microbial activation hole (17) set on the well wall. The nutrient solution includes fast-acting carbon source, phosphorus source and trace elements. During the addition process, the dissolved oxygen of the nutrient solution is monitored by a dissolved oxygen sensor, and an inert gas is introduced when necessary to regulate the hypoxic environment.

7. A method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions as described in claim 1 or 6, characterized in that, Step 5 describes microbial activation, which includes a conventional maintenance mode and an enhanced activation mode. The conventional maintenance mode involves continuously or intermittently adding nutrient solution to the organic pollutant and nitrogen removal zone (16) through the microbial activation well (8) during the normal operation of the multi-media composite reactive barrier (4), with the addition flow rate being 0.1% to 0.5% of the groundwater inflow flow rate; The enhanced activation mode is activated within 24 hours after unblocking, when the concentration of pollutants in the influent increases abnormally or the removal rate of the effluent continues to decline and is not caused by physical blockage. The nutrient solution dosage is increased to 2 to 3 times that of the conventional maintenance mode, and functional bacteria and carbon source are added.

8. A method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions as described in claim 1 or 6, characterized in that, The process of judging and eliminating the high concentration organic pollution shock load condition described in step 2 is as follows: When the monitoring results show that the concentration of organic pollutants in the influent increases significantly in a short period of time, while the overall hydraulic gradient, inter-regional pressure difference and permeability of the multi-media composite reaction wall (4) are still within the normal range, it is judged to be a high concentration organic pollution shock load condition. Under this condition, the unblocking procedure is not started, but nutrient solution or functional bacteria are added to the organic pollutant and nitrogen removal zone (16) through the microbial activation well (8), and the addition frequency and amount are dynamically adjusted according to the real-time monitoring data.

9. A method for repairing a permeable reactive wall with in-situ deblocking, regeneration, and microbial activation functions as described in claim 1 or 6, characterized in that, The barrier wall (13) is used in sites where groundwater flows in a dispersed manner or where the contaminated layer is buried at a large depth. Specifically, in sites where groundwater flows in a dispersed manner or where the contaminated layer is buried at a large depth, when the guide wall (5) guides the contaminated groundwater to flow into the multi-media composite reaction wall (4), the barrier wall (13) restricts the shallow groundwater from flowing over and intercepts suspended particles and uniform water flow through the filter zone (14) set on the water-facing side.

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