A method for constructing and operating a permeable reaction barrier based on photocatalysis

Abstract

This invention provides a method for constructing and operating a photocatalytically regulated permeable reaction barrier, comprising: installing several permeable reaction modules in a trench to form a permeable reaction barrier; connecting the ultraviolet light bands of the permeable reaction modules; filling the gaps between the permeable reaction barrier and the trench; sequentially covering the top of the permeable reaction barrier with a geomembrane and a layer of cohesive soil, and compacting the layers; constructing monitoring wells downstream of the permeable reaction barrier and upstream of the pollution source; and during operation, regulating the opening and closing of the ultraviolet light bands in the permeable reaction barrier according to the monitoring parameters of the upstream and downstream groundwater. This invention provides a method for constructing and operating a photocatalytically regulated permeable reaction barrier, improving the operational efficiency of the permeable reaction barrier in sites with varying groundwater pollutant concentrations and reducing costs.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control and treatment technology, specifically, it relates to a method for constructing and operating a permeable reaction barrier based on photocatalysis. Background Technology

[0002] A permeable reactive barrier (PRB) is a device used for in-situ remediation of contaminated groundwater. It works by filling a strip of permeable material downstream of the groundwater flow, causing a series of physical and chemical reactions between the contaminated groundwater and the material, thereby removing or degrading pollutants and controlling the spread of the contamination plume. For groundwater containing high-concentration, constant-contamination groundwater, improving the adsorption efficiency of the material and increasing the frequency of material replacement significantly enhances the pollutant removal efficiency of PRBs, leading to their successful application in an increasing number of groundwater remediation projects at contaminated sites.

[0003] However, in the later stages of remediation of sites with high concentrations of organic contamination, the concentration of groundwater pollutants fluctuates significantly. For sites with operating enterprises, the concentration of groundwater pollutants is relatively low, and it varies considerably with seasonal and climatic changes. To ensure the removal of groundwater pollutants in such sites, engineers often optimize the selection of permeable reactive barriers (PRBs) and the design of their replacement cycles based on the highest groundwater pollutant concentration over a period of time (e.g., one year). This directly leads to increased operating costs of PRBs and lower operational efficiency of supporting facilities. Therefore, there is an urgent need to improve the operational efficiency of PRBs in sites with significant changes in groundwater pollutants through novel structural designs and control methods. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for constructing and operating a permeable reaction barrier based on photocatalytic regulation, thereby improving the operating efficiency of the permeable reaction barrier in sites with varying groundwater pollutant concentrations and reducing costs.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention provides a method for constructing and operating a photocatalytically regulated permeable reaction barrier, comprising the following steps:

[0007] Step 10: Based on the groundwater pollution investigation information of the contaminated site, determine the structural parameters of the permeability reaction barrier; the structural parameters include orientation, length, depth, and width;

[0008] Step 20: A trench is excavated downstream of the pollution source along the direction of the permeable reaction barrier to form a permeable reaction barrier. Several permeable reaction modules are installed in the trench to form the permeable reaction barrier. Each permeable reaction module includes a hollow shell with permeable mesh on two opposite hollow sides. The shell contains granular filler, and the granular filler contains an ultraviolet light strip. The granular filler includes transparent glass spheres and ceramic particles with titanium dioxide loaded on their surface. The ultraviolet light strip connects several permeable reaction modules and is equipped with a control switch for controlling the opening and closing of the ultraviolet light strip.

[0009] Step 30: Fill the gap between the permeable reactive barrier and the trench, and cover the top of the permeable reactive barrier with a geomembrane and a cohesive soil layer in sequence, and compact it.

[0010] Step 40: Construct monitoring wells downstream of the permeability reaction barrier and upstream of the pollution source; install monitoring devices in the monitoring wells below the lowest groundwater level to collect monitoring parameters of the upstream and downstream groundwater.

[0011] Step 50: Connect the monitoring device and control switch to the monitor;

[0012] Step 60: During operation, the monitor adjusts the opening and closing of the ultraviolet light band in the permeability reaction barrier based on the monitoring parameter data of the upstream and downstream groundwater collected by the monitoring device.

[0013] As a further improvement of the present invention, in each of the permeable reaction modules, the embedding length of the ultraviolet light band is determined according to equations (1) and (2):

[0014] Equation (1)

[0015] Equation (2)

[0016] In the formula, L This indicates the embedment length of the ultraviolet band, in cm. a This indicates the length of the permeability reaction barrier module, in cm. b Indicates the width of the permeability reaction barrier module, in cm; c This indicates the height of the permeability reaction barrier module, in cm. This represents the radial effective irradiation area of ​​a UV band, expressed in cm². 2 ; The reduction factor representing the radial effective irradiation area of ​​the ultraviolet band is dimensionless. This represents the bulk volume of a transparent glass sphere, expressed in cm³. 3 ; This represents the bulk volume of expanded clay aggregate, expressed in cm³. 3 ; RThe volume ratio of transparent glass spheres to ceramsite is a reference value, dimensionless; R The value range is 0.8 to 2.3.

[0017] As a further improvement of the present invention, in step 40, the permeability reaction barrier is constructed at intervals downstream of the permeability reaction barrier along its direction. K A downstream monitoring well is constructed at intervals along the direction of the permeability reaction barrier upstream of the pollution source. K One upstream monitoring well, K One upstream monitoring well and K Each downstream monitoring well is deployed in a corresponding manner; K It is an integer greater than or equal to 3.

[0018] As a further improvement of the present invention, the permeability reaction barrier includes N The permeable reaction units are arranged sequentially along the direction of groundwater flow. Each permeable reaction unit includes several permeable reaction modules that are sequentially assembled on a vertical plane. The ultraviolet light bands of all permeable reaction modules in the same permeable reaction unit are connected in series. N The permeation reaction units are connected in parallel; each permeation reaction unit corresponds to a switch for controlling the opening and closing of the ultraviolet light band. N Each switch is connected to the monitor; N It is an integer greater than or equal to 3.

[0019] As a further improvement of the present invention, the control switches of the two permeation reaction units located at the upstream and downstream ends are always in the on state; the state of the control switches of the other permeation reaction units is controlled by a monitor.

[0020] As a further improvement of the present invention, the monitor uses equations (3) to (5) to control the state of the control switch of the permeation reaction unit:

[0021] (3)

[0022] (4)

[0023] (5)

[0024] In the formula, Indicates the first n The state of the control switch for the sheet permeation reaction unit: 0 indicates the off state, and 1 indicates the on state; This represents the maximum ratio of monitoring parameters for upstream and downstream groundwater, and is dimensionless. Indicates the first k The first monitoring parameter value of upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the firstk The first monitoring parameter value of downstream groundwater collected by the monitoring device in the downstream monitoring well; Indicates the first k The second monitoring parameter value of upstream groundwater collected by monitoring devices in an upstream monitoring well; Indicates the first k The second monitoring parameter value of downstream groundwater collected by monitoring devices in a downstream monitoring well; This represents the response threshold, which is dimensionless. This represents the monitoring well distance adjustment coefficient, which is dimensionless and ranges from 0.1 to 0.3. This indicates the distance between two adjacent monitoring wells located on the same side of the permeability reaction barrier, in meters (m).

[0025] As a further improvement of the present invention, the splicing gaps between the permeable reaction modules of two adjacent permeable reaction units are arranged in an alternating manner.

[0026] As a further improvement of the present invention, step 30, filling the gap between the permeable reaction barrier and the trench, specifically includes:

[0027] The gap between the lower sidewall of the permeable reactive barrier and the sidewall of the trench is filled with a cementitious material; the height of the gap filled with the cementitious material is 0.3 to 0.5 m.

[0028] Quartz sand was used to fill the gaps between the remaining sidewalls of the permeable reactive barrier and the sidewalls of the trench.

[0029] As a further improvement of the present invention, the top surface of the cohesive soil layer is 0.3 to 0.5 m higher than the ground surface.

[0030] As a further improvement of the present invention, the distance between the monitoring well located downstream of the permeability reaction barrier and the permeability reaction barrier is 2 to 3 m; the distance between the monitoring well located upstream of the pollution source and the pollution source is 2 to 5 m.

[0031] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0032] (1) The present invention provides a method for constructing and operating a permeable reaction barrier based on photocatalytic regulation. During construction, prefabricated permeable reaction modules are spliced ​​together to form a permeable reaction barrier. Ceramic particles loaded with titanium dioxide are placed in the permeable reaction modules to adsorb pollutants and degrade them through photocatalysis. An ultraviolet light band is set to introduce an external light source. When the ultraviolet light band is closed, pollutants are adsorbed and fixed in the permeable reaction module by the adsorption of the packing material when polluted groundwater flows through it. When the ultraviolet light band is open, pollutants are adsorbed and fixed in the permeable reaction module by the adsorption of the packing material, and the pollutants released from the desorption by the packing material are catalytically degraded by photocatalysis. After degradation, the pollutants adsorbed on the packing material diffuse back into the groundwater. When the concentration of pollutants in the groundwater changes frequently, the opening and closing state of the ultraviolet light band in the permeable reaction barrier is controlled according to the collected monitoring parameters of the upstream and downstream groundwater. This improves the permeability reaction effect, reduces the frequency of packing material replacement, enhances the operating efficiency of the permeable reaction barrier, and reduces operating costs.

[0033] (2) The present invention provides a method for constructing and operating a permeable reaction barrier based on photocatalysis. By setting the embedding length of the ultraviolet light strip, quantitative data support can be provided for optimizing the service performance of the permeable reaction barrier. For example, when the particulate filler changes, the length of the ultraviolet light strip should also be adjusted accordingly. This can maximize the catalytic effect of the ultraviolet lamp and reduce energy input.

[0034] (3) The present invention provides a method for the construction and operation of a permeable reaction barrier based on photocatalytic regulation. The permeable reaction barrier is designed in sections, which on the one hand improves the mobility of on-site construction and maintenance of the permeable reaction barrier, and on the other hand can adjust the opening and closing state of the ultraviolet light band according to the changes in the concentration of pollutants in the groundwater upstream and downstream of the permeable reaction barrier in sections, thereby improving the efficiency of groundwater remediation and reducing the economic cost of remediation projects. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the permeable reaction barrier based on photocatalytic regulation constructed in the method of the embodiments of the present invention;

[0036] Figure 2 This is a schematic diagram of the permeability reaction module in the method of this embodiment of the invention;

[0037] Figure 3 This is a schematic diagram of the structure of the permeable reaction unit in the method of this embodiment of the invention;

[0038] Figure 4 This is a top view showing the layout of the permeability reaction barrier and monitoring well in the method of this embodiment of the invention;

[0039] Figure 5 This is a comparison chart of the changes in perfluorooctanoic acid concentration in Example 1, Comparative Example 1, and Comparative Example 2.

[0040] In the diagram: 1. Ground surface; 21. Lowest groundwater level; 22. Highest groundwater level; 3. Pollution source; 4. Trench; 5. Permeable reaction barrier; 50. Permeable reaction module; 51. Permeable reaction unit; 501. Shell; 502. Permeable mesh; 503. Ultraviolet light strip; 504. Transparent glass sphere; 505. Ceramsite; 7. Geomembrane; 61. Cementitious material; 62. Quartz sand; 7. Geomembrane; 8. Cohesive soil layer; 9. Monitoring well; 10. Monitoring device; 11. Monitor. Detailed Implementation

[0041] The technical solution of the present invention will be described in detail below.

[0042] This invention provides a method for constructing and operating a photocatalytically regulated permeable reaction barrier, such as... Figure 1 As shown, it includes the following steps:

[0043] Step 10: Determine the structural parameters of the permeability reaction barrier based on the groundwater pollution investigation information of the contaminated site; the structural parameters include orientation, length, depth and width.

[0044] Step 20: A trench 4 is excavated downstream of pollution source 3 along the direction of the permeable reaction barrier to form a trench 4. Several permeable reaction modules 50 are installed in the trench to form a permeable reaction barrier 5. The top of the permeable reaction barrier 5 is higher than the lowest groundwater level 21.

[0045] Among them, such as Figure 2 As shown, the permeable reaction module includes a hollow shell 501, with permeable mesh 502 on each of the two oppositely hollowed-out sides of the shell 501. Preferably, the porosity of the permeable mesh 502 is greater than 80%. The shell 501 contains granular filler, and an ultraviolet light strip 503 is provided inside the granular filler. The granular filler includes translucent glass spheres 504 and ceramic particles 505 with titanium dioxide loaded on their surface.

[0046] The ultraviolet light strip 503 is connected to several permeable reaction modules, and a control switch for controlling the opening and closing of the ultraviolet light strip is installed.

[0047] Step 30: Fill the gap between the permeable reactive barrier 5 and the trench 4, and cover the top of the permeable reactive barrier with geomembrane 7 and cohesive soil layer 8 in sequence, and compact them.

[0048] The geomembrane 7 can prevent the fine particles of the overburden from entering the quartz sand 62 and clogging the permeability reaction barrier 5. The compacted cohesive soil layer 8 can prevent rainwater from infiltrating and damaging the stability of the permeability reaction barrier 5 and the sidewall of the trench 4.

[0049] Step 40: Construct monitoring wells 9 downstream of the permeability reaction barrier 5 and upstream of the pollution source 3 respectively; install monitoring devices 10 in the monitoring wells 9 and below the lowest groundwater level 21 to collect monitoring parameters of the upstream and downstream groundwater.

[0050] Preferably, the monitoring parameters include at least one of pH, conductivity, and redox potential. Pollutants can inhibit the characteristics and quantity of microbial communities in groundwater, and changes in the characteristics and quantity of microbial communities can cause changes in pH, conductivity, and redox potential. Therefore, monitoring parameters such as pH, conductivity, and redox potential can characterize the concentration of pollutants in groundwater.

[0051] Preferably, the permeability reaction barrier 5 is constructed at intervals along its direction downstream of the permeability reaction barrier 5. K One downstream monitoring well was constructed at intervals along the direction of the permeability reaction barrier upstream of pollution source 3. K One upstream monitoring well, K One upstream monitoring well and K Each downstream monitoring well is deployed in a corresponding manner; K The value is an integer greater than or equal to 3. Preferably, the distance between two adjacent upstream monitoring wells is 10–40 m. The concentration of groundwater pollutants will change to some extent along the direction of the permeability reaction barrier. In order to ensure monitoring accuracy and operational effectiveness, it is necessary to monitor the concentration of groundwater pollutants upstream and downstream through multiple sets of monitoring wells, and an appropriate distance should be set between adjacent monitoring wells.

[0052] Step 50: Connect the monitoring device and control switch to the monitor.

[0053] Step 60: During operation, the monitoring unit 10 sends the collected monitoring parameter data of the upstream and downstream groundwater to the monitor 11. The monitor 11 adjusts the corresponding control switch to regulate the opening and closing of the ultraviolet light band in the permeability reaction barrier 5 based on the monitoring parameter data of the upstream and downstream groundwater.

[0054] During operation, contaminated groundwater passes through the permeable reaction module, through the permeable mesh 502 on one side, and flows into the inner cavity of the shell 501. It then flows through the granular packing material and exits from the permeable mesh 502 on the other side. During this process, the granular packing material adsorbs pollutants from the contaminated groundwater, thereby purifying it. When the ultraviolet light band 503 is activated, the granular packing material, comprising transparent glass spheres 504 and ceramic particles 505 with titanium dioxide loaded on their surface, emits ultraviolet light. This ultraviolet light irradiates the surface of the titanium dioxide loaded on the ceramic particles 505, generating electron-hole pairs that react with the water molecules in contact to generate hydroxyl radicals. These hydroxyl radicals gradually degrade organic pollutants into small molecule intermediates through oxidation, ultimately mineralizing them into CO2 and H2O. Because the ceramic particles 505 are opaque, the propagation distance of ultraviolet light within the permeable reaction barrier is very short, with a maximum distance approximately five times the diameter of the granular packing material. Therefore, in this embodiment of the invention, by adding transparent glass spheres 504 to the filler, ultraviolet light can pass through the transparent glass spheres 504 and be refracted on the surface of the transparent glass spheres 504, thereby greatly increasing the irradiation area of ​​the ultraviolet light and the ceramic particles 505. For example, after mixing ceramic particles 505 and transparent glass spheres 504 in a volume ratio of 1:1, the axial irradiation area of ​​a single ultraviolet light band 503 can be increased by about 7 times, greatly improving the catalytic efficiency of the light source.

[0055] This invention, through the addition of a packing material to a permeable reaction module that adsorbs and photocatalytically degrades pollutants, introduces an external light source. When the ultraviolet light band 503 is off, polluted groundwater flowing through the permeable reaction module is adsorbed and fixed within the module by the packing material. When the ultraviolet light band 503 is on, as more pollutants flow through the module, they are again adsorbed and fixed within the module, while simultaneously photocatalytically degrading pollutants released from the packing material. The degraded pollutants diffuse back into the groundwater, reducing the frequency of packing material replacement. In particular, when used in sites where groundwater organic pollutants fluctuate frequently, this permeable reaction barrier enhances its operational efficiency.

[0056] The permeable reactive barrier in this invention serves two purposes: first, it adsorbs pollutants from groundwater; second, it degrades and removes pollutants that were previously adsorbed on the packing material and might be released back into the groundwater through ultraviolet light catalysis. In other words, to prevent released pollutants from migrating downstream again, this invention proposes a permeable reactive barrier with photocatalytic regulation function. After pollutants are desorbed from the packing material, they are catalytically degraded, preventing them from returning to the water flow. Thus, the packing material in the permeable reactive barrier unit can not only adsorb pollutants from groundwater but also degrade them and prevent their release back into the groundwater.

[0057] Preferably, in each permeable reaction module, the embedding length of the ultraviolet light band 503 is determined according to equations (1) and (2):

[0058] Equation (1)

[0059] Equation (2)

[0060] In the formula, L This indicates the embedment length of the ultraviolet band 503, in cm; a This indicates the length of the permeability reaction barrier module, in cm. b Indicates the width of the permeability reaction barrier module, in cm; c This indicates the height of the permeability reaction barrier module, in cm. This represents the radial effective irradiation area of ​​a UV band 503, expressed in cm². 2 ; The reduction factor representing the radial effective irradiation area of ​​ultraviolet band 503 is dimensionless. This represents the bulk volume of the 504 transparent glass spheres, expressed in cm³. 3 ; This represents the bulk volume of expanded clay granules 505, in cm³. 3 ; R The reference value representing the bulk volume ratio of transparent glass sphere 504 and ceramsite 505 is dimensionless. R The value range is 0.8 to 2.3.

[0061] In the above preferred embodiment, by setting the embedding length of the ultraviolet light strip 503, quantitative data support can be provided for optimizing the service performance of the permeable reaction barrier. For example, when the particulate filler changes, the length of the ultraviolet light strip must also be adjusted accordingly. This can maximize the catalytic effect of the ultraviolet lamp and reduce energy input.

[0062] Preferred, such as Figure 4 As shown, the permeability reaction barrier 5 includes N The permeable reaction units 51 are arranged sequentially along the direction of groundwater flow. Each permeable reaction unit includes several permeable reaction modules 50 sequentially assembled on a vertical plane, such as... Figure 3 As shown. Among them, N It is an integer greater than or equal to 3.

[0063] In the preferred embodiment described above, several permeable reaction modules are spliced ​​together along the trench direction and along the vertical plane to form a permeable reaction unit, and then along the direction of groundwater flow... NThe permeable reaction units are connected to form a permeable reaction barrier. The permeable reaction barrier is designed in sections and modules, which improves the mobility of on-site construction and maintenance of the permeable reaction barrier. On the other hand, it can adjust the opening and closing state of the ultraviolet light band according to the changes in groundwater pollution concentration, either in sections or in modules, thereby improving the efficiency of groundwater remediation and reducing the economic cost of remediation projects.

[0064] Preferably, the ultraviolet light bands of all permeable reaction modules in the same permeable reaction unit are connected in series. N The permeation reaction units are connected in parallel. Each permeation reaction unit corresponds to a switch for controlling the opening and closing of the ultraviolet light band. N Each switch is connected to monitor 11. That is, the opening or closing of the ultraviolet light strip of all permeation reaction modules in the same permeation reaction unit is consistent, while the opening or closing of the ultraviolet light strip in different permeation reaction units is controlled by their respective control switches, and the states may be different.

[0065] In this preferred embodiment, the opening and closing of the ultraviolet light band is controlled on a piece-by-piece basis. First, this piece-by-piece approach allows for precise control of the embedding length of the ultraviolet light band within the packing material, which is beneficial for construction quality control. Second, setting and installing the permeable reaction barrier on a piece-by-piece basis along the direction of groundwater flow enables tiered control of ultraviolet photocatalysis, that is, quantitatively controlling the number of ultraviolet light units activated based on the concentration differences of pollutants upstream and downstream. Furthermore, during the operation of the permeable reaction barrier, changes in factors such as formation pressure and groundwater level can cause blockage and damage to the packing material. After segmented design and installation, damaged permeable reaction units can be locally replaced, avoiding damage to the ultraviolet light band caused by the excavation and construction of the entire barrier.

[0066] Preferably, the control switches of the upstream and downstream permeation reaction units 51 are always in the on state, while the state of the control switches of other permeation reaction units 51 is controlled by a monitor.

[0067] Groundwater flow is typically slow, and pollutants migrate within the pores of permeable reactive barriers via convection and diffusion. Convective migration follows the same direction as groundwater flow, while diffusion migration is random, potentially occurring in the same, perpendicular, or opposite direction. When the groundwater concentration decreases upon entering the permeable reactive barrier, pollutants adsorbed on the packing material desorb and are released back into the groundwater, thus releasing the adsorbed pollutants into the downstream groundwater environment. Therefore, to degrade pollutants migrating upstream via diffusion, the control switch of the upstreamst permeable reactive unit is always kept on. Furthermore, concentrated rainfall over short periods can cause temporary changes in the groundwater flow field, even resulting in flow opposite to the main flow direction. Therefore, to reduce the risk of pollutants migrating upstream again due to reverse groundwater flow caused by rainfall, the control switch of the upstreamst permeable reactive unit is always on. The reason for keeping the control switch of the downstreamst permeable reactive unit on is to prevent the release of desorbed pollutants from the packing material into the downstream groundwater environment when the groundwater is stagnant.

[0068] Preferably, the monitor 11 uses equations (3) to (5) to control the state of the control switch of the permeation reaction unit:

[0069] (3)

[0070] (4)

[0071] (5)

[0072] In the formula, Indicates the first n The state of the control switch for the sheet permeation reaction unit: 0 indicates the off state, and 1 indicates the on state; This represents the maximum ratio of monitoring parameters for upstream and downstream groundwater, and is dimensionless. Indicates the first k The first monitoring parameter value of upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the first k The first monitoring parameter value of downstream groundwater collected by the monitoring device in the downstream monitoring well; Indicates the first k The second monitoring parameter value of upstream groundwater collected by monitoring devices in an upstream monitoring well; Indicates the first k The second monitoring parameter value of downstream groundwater collected by monitoring devices in a downstream monitoring well; This represents the response threshold, which is dimensionless. This represents the monitoring well distance adjustment coefficient, which is dimensionless and ranges from 0.1 to 0.3. This indicates the distance between two adjacent monitoring wells located on the same side of the permeability barrier, in meters (m). The first monitoring parameter is pH, and the second is conductivity; or, the first monitoring parameter is redox potential, and the second is conductivity.

[0073] According to the monitoring parameters of the upstream and downstream groundwater, the second to the third [section / section] are adjusted. N The control switch for the -1 permeable reaction unit controls the opening and closing of the ultraviolet (UV) light band. When the concentration of pollutants in the upstream groundwater increases, the adsorption effect of the packing material in the permeable reaction barrier decreases. Opening an appropriate number of UV light bands allows the catalytic effect of the UV light to compensate for the insufficient physical adsorption of the packing material. When the concentration of pollutants in the upstream groundwater decreases again, the pollutants adsorbed by the packing material in the permeable reaction barrier are released back into the groundwater. At this time, opening an appropriate number of UV light bands degrades the adsorbed pollutants through the catalytic effect of the UV light, thus overcoming the limitation of traditional permeable reaction barriers in completely removing pollutants. This embodiment of the invention adjusts the number of UV light bands opened according to the concentration of upstream pollutants, which can improve the working performance of the permeable reaction barrier, save energy, and reduce costs.

[0074] Preferably, the splicing gaps between the permeable reaction modules of two adjacent permeable reaction units 51 are staggered. This effectively prevents contaminated groundwater from flowing through the permeable splicing gaps without passing through the permeable reaction modules.

[0075] Preferably, in step 30, filling the gap between the permeable reactive barrier and the trench specifically includes:

[0076] The gap between the lower sidewall of the permeable reactive barrier and the sidewall of the trench is filled with a cementitious material 61 (e.g., cement, lime, slag, and mixtures thereof). The height of the gap filled with the cementitious material is 0.3–0.5 m. The gaps between the remaining sidewalls of the permeable reactive barrier and the sidewalls of the trench are filled with quartz sand 62.

[0077] Because the bottom of the excavated trench 4 is prone to soil deformation and even collapse due to concentrated ground stress, this embodiment uses a cementitious material to fill the trench 4, forming a structure with a certain strength to prevent soil deformation from causing the permeability reaction barrier 5 to tilt or misalignment between different units. The remaining gaps are filled with quartz sand to keep the permeability reaction barrier 5 vertical and prevent tilting, while maintaining good permeability.

[0078] Preferably, the top surface of the cohesive soil layer 8 is 0.3 to 0.5 m higher than the ground surface 1. This effectively prevents water accumulation on the top of the permeability reactive barrier after construction, which could alter the local groundwater flow field and affect the working performance of the permeability reactive barrier.

[0079] Preferably, the distance between the monitoring well 9 located downstream of the permeability reaction barrier 5 and the permeability reaction barrier 5 is 2-3m. The distance between the monitoring well 9 located upstream of the pollution source 3 and the pollution source 3 is 2-5m. Improving the accuracy of monitoring data enables precise control of the activation time or quantity of ultraviolet light bands within the permeability reaction unit, thereby improving energy utilization efficiency and reducing remediation costs.

[0080] An embodiment and two comparative examples are provided to verify the performance of the method of the embodiment of the present invention. The embodiment and comparative examples are all simulation experiments conducted in the laboratory. Example

[0081] In the experiment, the concentration of perfluorooctanoic acid (PFOA) in the upstream contaminated groundwater was set at 100 μg / L, and the solid-liquid ratio of the expanded clay aggregate (ECA) to the contaminated groundwater was 1:10. The particle size of the ECA ranged from 1 to 2.5 cm. The volume of the transparent glass spheres was the same as that of the ECA, with a diameter of 1.5 cm. Titanium dioxide powder was uniformly loaded onto the surface of the ECA, and the mass ratio of titanium dioxide to ECA was 1:100. After the ECA and transparent glass spheres were mixed evenly, the mixture was poured into a polyethylene bottle and placed in an opaque shaker. During the experiment, three ultraviolet (UV) light strips were evenly installed inside the polyethylene bottle and turned on to ensure that the UV light could fully irradiate the surface of the ECA. Each UV light strip was 10 cm long and had a power of 0.1 W.

[0082] Solution samples were collected at 3-hour intervals, and the perfluorooctanoic acid (PFOA) concentration was tested. After 12 hours of adsorption, PFOA reached adsorption saturation on the ceramic particle surface. Then, the simulated groundwater, after partial removal of contaminants from the polyethylene bottle, was removed and replaced with simulated contaminated groundwater containing 30 μg / L PFOA, and placed on a shaker. Solution samples were collected at 3-hour intervals, and the PFOA concentration was tested. This experiment simulated the removal effect of PFOA from groundwater under the condition that the ultraviolet light bands of the upstream, second, and downstream permeable reaction units along the groundwater flow direction were open, using a permeable reaction barrier with four permeable reaction units. The simulated downstream groundwater PFOA concentration changes are shown in [Figure showing the PFOA concentration changes]. Figure 5 .

[0083] Comparative Example 1

[0084] The expanded clay particles in Example 1 were replaced with expanded clay particles without titanium dioxide powder loading (i.e., the expanded clay particles used in the conventional method), and no ultraviolet light strip was installed inside the polyethylene bottle during the experiment. The pollutant concentration, sampling time, and pollutant testing methods in all other steps of the experiment were the same as in Comparative Example 1. This experiment simulated the removal effect of a conventional perfluorooctanoic acid (PFOA) from contaminated groundwater under the same conditions as the thickness of the permeable reaction barrier with four permeable reaction units as in Example 1 (without an ultraviolet light strip). The simulated changes in downstream groundwater PFOA concentration are shown in [Figure 1]. Figure 5 .

[0085] Comparative Example 2

[0086] During the experiment, four ultraviolet (UV) light strips were uniformly installed inside a polyethylene bottle and all were turned on. The contaminant concentration, sampling time, and contaminant testing methods were identical to those in Comparative Example 1 for all other steps of the experiment. This experiment simulated the removal effect of perfluorooctanoic acid (PFOA) from groundwater under the condition that the UV light strips of all four permeable reaction units were turned on, using a permeable reaction barrier with four permeable reaction units. The simulated changes in downstream groundwater PFOA concentration are shown in [Figure showing the effect]. Figure 5 .

[0087] from Figure 5 The changes in perfluorooctanoic acid (PFOA) concentration in Comparative Example 1 and Example 1 show that, in Example 1, by turning on three ultraviolet light bands (corresponding to the ultraviolet light bands of three units within the four permeable reaction units being in the on state), the PFOA concentration in the groundwater can be changed from high to low, and the PFOA adsorbed on the packing material will no longer migrate to the downstream groundwater, resulting in a significant removal effect.

[0088] from Figure 5 The changes in pollutants observed in Comparative Example 2 and Example 1 show that when the concentration of perfluorooctanoic acid (PFOA) in the upstream groundwater is constant, the optimal number of UV lamps activated within the permeable reaction unit is found. As the number of activated lamps increases further, the PFOA concentration in the groundwater no longer changes significantly. Therefore, this embodiment of the invention optimizes the number of UV lamps activated within the permeable reaction unit based on the difference in PFOA concentration between upstream and downstream groundwater, achieving both excellent removal efficiency and reduced energy consumption.

[0089] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the specific embodiments described above. The specific embodiments and descriptions in the specification are merely for further illustrating the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for constructing and operating a photocatalytically regulated permeable reaction barrier, characterized in that, Includes the following steps: Step 10: Based on the groundwater pollution investigation information of the contaminated site, determine the structural parameters of the permeability reaction barrier; the structural parameters include orientation, length, depth, and width; Step 20: A trench (4) is excavated downstream of the pollution source (3) along the direction of the permeable reaction barrier. Several permeable reaction modules (50) are installed in the trench to form a permeable reaction barrier (5). The permeable reaction module (50) includes a hollow shell (501), and two permeable meshes (502) are respectively provided on the two hollow sides of the shell (501). The shell (501) is filled with granular filler, and an ultraviolet light strip (503) is set inside the granular filler. The granular filler includes a light-transmitting glass ball (504) and ceramic particles (505) with titanium dioxide loaded on the surface. The ultraviolet light strips of several permeable reaction modules are connected, and a control switch for controlling the opening and closing of the ultraviolet light strips is installed. Step 30: Fill the gap between the permeable reactive barrier (5) and the trench (4), and cover the top of the permeable reactive barrier with a geomembrane (7) and a cohesive soil layer (8) in sequence, and compact it; Step 40: Construct monitoring wells (9) downstream of the permeability reaction barrier (5) and upstream of the pollution source (3); install monitoring devices (10) in the monitoring wells (9) below the lowest groundwater level (21) to collect monitoring parameters of the upstream and downstream groundwater. Step 50: Connect the monitoring device and control switch to the monitor; Step 60: During operation, the monitor adjusts the opening and closing of the ultraviolet light band in the permeable reaction barrier (5) based on the monitoring parameter data of the upstream and downstream groundwater collected by the monitoring device (10).

2. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 1, characterized in that, In each of the aforementioned permeable reaction modules, the embedding length of the ultraviolet light band (503) is determined according to equations (1) and (2): Equation (1) Equation (2) In the formula, L The buried length of the ultraviolet band (503) is indicated in cm; a This indicates the length of the permeability reaction barrier module, in cm. b Indicates the width of the permeability reaction barrier module, in cm; c This indicates the height of the permeability reaction barrier module, in cm. This represents the radial effective irradiation area of ​​a UV band (503), expressed in cm². 2 ; The reduction factor representing the radial effective irradiation area of ​​the ultraviolet band (503) is dimensionless; This represents the bulk volume of the transparent glass sphere (504), in cm³. 3 ; This represents the bulk volume of expanded clay aggregate (505), in cm³. 3 ; R The reference value representing the bulk volume ratio of transparent glass spheres (504) and ceramsite (505) is dimensionless; R The value range is 0.8 to 2.

3.

3. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 1, characterized in that, In step 40, the permeability reaction barrier (5) is constructed downstream along the direction of the permeability reaction barrier at intervals. K Each downstream monitoring well is constructed at intervals along the direction of the permeability reaction barrier upstream of the pollution source (3). K One upstream monitoring well, K One upstream monitoring well and K Each downstream monitoring well is deployed in a corresponding manner; K It is an integer greater than or equal to 3.

4. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 3, characterized in that, The permeability reaction barrier includes N The permeable reaction units (51) are arranged sequentially along the direction of groundwater flow. Each permeable reaction unit includes several permeable reaction modules (50) that are sequentially spliced ​​on a vertical plane. The ultraviolet light bands of all permeable reaction modules in the same permeable reaction unit are connected in series. N The permeation reaction units are connected in parallel; each permeation reaction unit corresponds to a switch for controlling the opening and closing of the ultraviolet light band. N Each switch is connected to the monitor; N It is an integer greater than or equal to 3.

5. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 4, characterized in that, The control switches of the two permeation reaction units (51) located at the upstream and downstream ends are always in the on state; the status of the control switches of the other permeation reaction units (51) is controlled by the monitor.

6. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 5, characterized in that, The monitor uses equations (3) to (5) to control the state of the control switch of the permeation reaction unit: （3） （4） （5） In the formula, Indicates the first n The state of the control switch for the sheet permeation reaction unit: 0 indicates the off state, and 1 indicates the on state; This represents the maximum ratio of monitoring parameters for upstream and downstream groundwater, and is dimensionless. Indicates the first k The first monitoring parameter value of upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the first k The first monitoring parameter value of downstream groundwater collected by the monitoring device in the downstream monitoring well; Indicates the first k The second monitoring parameter value of upstream groundwater collected by monitoring devices in an upstream monitoring well; Indicates the first k The second monitoring parameter value of downstream groundwater collected by monitoring devices in a downstream monitoring well; This represents the response threshold, which is dimensionless. This represents the monitoring well distance adjustment coefficient, which is dimensionless and ranges from 0.1 to 0.

3. This indicates the distance between two adjacent monitoring wells located on the same side of the permeability reaction barrier, in meters (m).

7. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 4, characterized in that, The splicing gaps between the permeable reaction modules of two adjacent permeable reaction units are arranged in an alternating pattern.

8. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 1, characterized in that, In step 30, filling the gap between the permeable reaction barrier and the trench specifically includes: The gap between the lower sidewall of the permeable reaction barrier and the sidewall of the trench is filled with a cementitious material (61); the height of the gap filled with the cementitious material is 0.3 to 0.5 m. Quartz sand (62) was used to fill the gap between the remaining sidewalls of the permeable reactive barrier and the sidewalls of the trench.

9. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 1, characterized in that, The top surface of the cohesive soil layer (8) is 0.3 to 0.5 m higher than the ground surface (1).

10. The method for constructing and operating a photocatalytically regulated permeable reaction barrier according to claim 1, characterized in that, The distance between the monitoring well (9) located downstream of the permeability reaction barrier (5) and the permeability reaction barrier (5) is 2 to 3 m; the distance between the monitoring well (9) located upstream of the pollution source (3) and the pollution source (3) is 2 to 5 m.

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