Construction and operation method for regulating permeable reaction barrier based on photocatalysis

Abstract

The invention provides a construction and operation method of a permeable reaction barrier based on photocatalytic regulation, which comprises the following steps: mounting a plurality of permeable reaction modules in a groove to form the permeable reaction barrier; the ultraviolet light band is connected with the plurality of permeable reaction modules; a gap between the permeable reaction barrier and the groove is filled, and the top of the permeable reaction barrier is sequentially covered with a geomembrane and a cohesive soil layer and compacted; respectively building monitoring wells at the downstream of the permeable reaction barrier and the upstream of the pollution source; during operation, opening and closing of the ultraviolet light band in the permeable reaction barrier are regulated according to monitoring parameters of upstream and downstream groundwater. According to the construction and operation method for regulating and controlling the permeable reaction barrier based on photocatalysis, the operation efficiency of the permeable reaction barrier in a groundwater pollutant concentration change site is improved, and the cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of water pollution control and treatment, and specifically relates to a method for constructing and operating a permeability reaction barrier based on photocatalytic regulation. Background Art

[0002] A permeable reactive barrier is a device used for in-situ remediation of contaminated groundwater. By filling the groundwater downstream with a strip of permeable filler material, the contaminated groundwater undergoes a series of physical and chemical reactions with the filler material, thereby removing or degrading pollutants and controlling the spread of the contamination plume. For groundwater containing high or constant concentrations of pollutants, the permeable reactive barrier significantly improves its removal efficiency by optimizing the filler material's adsorption efficiency and increasing the frequency of filler material replacement. This has led to its successful application in a growing number of groundwater remediation projects at contaminated sites.

[0003] However, in the later stages of remediation of high-concentration organic pollution sites, the concentration of groundwater pollutants changes significantly. For sites with active production enterprises, the concentration of groundwater pollutants is relatively low, and with seasonal and climatic changes, the concentration of groundwater pollutants varies greatly. In order to ensure the removal effect of groundwater pollutants in such sites, engineers often select the filler type of the permeable reaction barrier and optimize the design of the filler replacement cycle based on the highest groundwater pollutant concentration over a period of time (such as one year). This directly leads to an increase in the operating cost of the permeable reaction barrier and a low operating efficiency of the supporting facilities. Therefore, there is an urgent need to improve the operating efficiency of the permeable reaction barrier in sites where groundwater pollutants change significantly through new permeable reaction barrier structure design 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 changing groundwater pollutant concentrations and reducing costs.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: The present invention provides a method for constructing and operating a permeable reaction barrier based on photocatalytic regulation, comprising the following steps: Step 10: determining structural parameters of the permeability reaction barrier based on groundwater pollution survey information of the contaminated site; the structural parameters include direction, length, depth, and width; Step 20: excavating a trench downstream of the pollution source along the direction of the permeable reaction barrier, installing a plurality of permeable reaction modules in the trench to form a permeable reaction barrier; the permeable reaction module comprises a hollow shell, with water-permeable mesh provided on two opposite hollow sides of the shell; the shell contains a granular filler, and an ultraviolet light strip is provided inside the granular filler; the granular filler comprises light-transmitting glass balls and ceramsite with titanium dioxide loaded on its surface; connecting the ultraviolet light strips of the plurality of permeable reaction modules, and installing a control switch for turning the ultraviolet light strip on and off; Step 30, filling the gap between the permeable reaction barrier and the trench, covering the top of the permeable reaction barrier with a geomembrane and a clay layer in sequence, and compacting them; Step 40: construct monitoring wells downstream of the permeability reaction barrier and upstream of the pollution source; install monitoring components in the monitoring wells below the lowest groundwater level to collect monitoring parameters of the upstream and downstream groundwater; Step 50, connecting the monitoring element and the control switch to the monitor; Step 60: During operation, the monitor regulates the opening and closing of the ultraviolet light band in the permeability reaction barrier according to the monitoring parameter data of the upstream and downstream groundwater collected by the monitoring component.

[0006] As a further improvement of the present invention, in each of the permeability reaction modules, the embedding length of the ultraviolet light band is determined according to formula (1) and formula (2): Formula (1) Formula (2) Where, L Indicates the buried length of the UV light band in cm; a represents the length of the permeability reaction barrier module in cm; b represents the width of the permeability reaction barrier module in cm; c represents the height of the permeability reaction barrier module in cm; Indicates the radial effective irradiation area of ​​a UV light band, in cm 2 ; It represents the reduction factor of the radial effective irradiation area of ​​the ultraviolet light band, dimensionless; Indicates the stacking volume of light-transmitting glass balls, in cm 3 ; Indicates the bulk volume of ceramsite in cm 3 ; R It represents the reference value of the bulk volume ratio of transparent glass balls and ceramsite, dimensionless; R The value range is 0.8 to 2.3.

[0007] As a further improvement of the present invention, in step 40, the following steps are constructed at intervals along the direction of the permeable reaction barrier downstream of the permeable reaction barrier: K Downstream monitoring wells are constructed at intervals upstream of the pollution source along the direction of the permeability reaction barrier. K Upstream monitoring wells, K upstream monitoring wells and K Each downstream monitoring well is laid out in a one-to-one correspondence; K is an integer greater than or equal to 3.

[0008] As a further improvement of the present invention, the permeable reaction barrier comprises N The permeability reaction units are arranged in sequence along the direction of groundwater flow. Each permeability reaction unit includes a number of permeability reaction modules spliced ​​in sequence on a vertical plane. The ultraviolet light bands of all the permeability reaction modules in the same permeability reaction unit are connected in series in sequence. N The permeability reaction units are connected in parallel; each permeability 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 is an integer greater than or equal to 3.

[0009] As a further improvement of the present invention, the control switches of the two permeability reaction units located at the most upstream and the most downstream are always in the open state; the states of the control switches of the other permeability reaction units are controlled by the monitor.

[0010] 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 permeability reaction unit: (3) (4) (5) Where, Indicates the n The state of the control switch of the sheet permeability reaction unit, 0 means closed state, 1 means open state; It represents the maximum ratio of monitoring parameters of upstream and downstream groundwater, dimensionless; Indicates the k The first monitoring parameter value of the upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the k The first monitoring parameter value of the downstream groundwater collected by the monitoring device in the downstream monitoring well; Indicates the k The second monitoring parameter value of the upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the kThe second monitoring parameter value of the downstream groundwater collected by the monitoring device in the downstream monitoring well; represents the response threshold, dimensionless; It represents the monitoring well distance adjustment coefficient, dimensionless, ranging from 0.1 to 0.3; It represents the distance between two adjacent monitoring wells located on the same side of the permeability reaction barrier, in meters.

[0011] As a further improvement of the present invention, the splicing gaps between the permeability reaction modules of two adjacent permeability reaction units are arranged in a staggered manner.

[0012] As a further improvement of the present invention, in step 30, filling the gap between the permeable reaction barrier and the groove specifically includes: The gap between the lower side wall of the permeable reaction barrier and the side wall of the trench is filled with a cementitious material; the height of the gap filled with cementitious material is 0.3 to 0.5 m; The gap between the remaining sidewalls of the permeable reaction barrier and the sidewalls of the trench is filled with quartz sand.

[0013] As a further improvement of the present invention, the top surface of the clay layer is 0.3 to 0.5 m higher than the ground surface.

[0014] 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 meters; the distance between the monitoring well located upstream of the pollution source and the pollution source is 2 to 5 meters.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The present invention provides a method for constructing and operating a permeability reaction barrier based on photocatalytic regulation. During construction, prefabricated permeability reaction modules are spliced ​​to form a permeability reaction barrier. Ceramsite with a surface loaded with titanium dioxide that can adsorb pollutants and degrade pollutants through photocatalysis is set in the permeability reaction module, and an ultraviolet light band is set to introduce an external light source. When the ultraviolet light band is turned off, when the contaminated groundwater flows through the permeability reaction module, the pollutants are adsorbed and fixed in the permeability reaction module through the adsorption effect of the filler; when the ultraviolet light band is turned on, when the contaminated groundwater flows through the permeability reaction module, on the one hand, the pollutants are adsorbed and fixed in the permeability reaction module through the adsorption effect of the filler, and on the other hand, the pollutants released by desorption from the filler are catalytically degraded through the photocatalytic effect. After degradation, the pollutants adsorbed on the filler diffuse back to the groundwater; when the concentration of groundwater pollutants changes frequently, the on-off state of the ultraviolet light band in the permeability reaction barrier is regulated according to the monitoring parameter data of the upstream and downstream groundwater collected, so as to improve the permeability reaction effect, reduce the frequency of filling replacement, improve the operating efficiency of the permeability reaction barrier, and reduce the operating cost.

[0016] (2) The present invention provides a method for constructing and operating a permeable reaction barrier based on photocatalytic regulation. By setting the embedded length of the UV light strip, it can provide quantitative data support for optimizing the service performance of the permeable reaction barrier. For example, when the granular filler changes, the length of the UV light strip must also be adjusted accordingly. This can maximize the catalytic effect of the UV light and reduce energy input.

[0017] (3) The present invention provides a method for constructing and operating a permeable reaction barrier based on photocatalytic regulation. The permeable reaction barrier is designed in segments. On the one hand, it 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 the concentration of groundwater pollutants upstream and downstream of the permeable reaction barrier in units of segments, thereby improving the efficiency of contaminated groundwater remediation and reducing the economic cost of the remediation project. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the permeable reaction barrier based on photocatalytic regulation constructed in the embodiment method of the present invention; Figure 2 Schematic diagram of the structure of the permeability reaction module in the method of the embodiment of the present invention; Figure 3 Schematic diagram of the structure of the permeability reaction unit in the method of the embodiment of the present invention; Figure 4 1 is a top view of the arrangement of the permeable reaction barrier and the monitoring wells in the method according to the embodiment of the present invention; Figure 5 This is a comparison chart of the changes in perfluorooctanoic acid concentration in Example 1, Comparative Example 1 and Comparative Example 2.

[0019] In the figure: ground surface 1, lowest groundwater level 21, highest groundwater level 22, pollution source 3, trench 4, permeability reaction barrier 5, permeability reaction module 50, permeability reaction unit 51, shell 501, permeable gauze 502, ultraviolet light strip 503, transparent glass ball 504, ceramsite 505, geomembrane 7, cementitious material 61, quartz sand 62, geomembrane 7, clay layer 8, monitoring well 9, monitoring element 10, monitor 11. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail below.

[0021] The embodiment of the present invention provides a method for constructing and operating a permeable reaction barrier based on photocatalytic regulation, such as Figure 1 As shown, the following steps are included: Step 10: Determine the structural parameters of the permeability reaction barrier based on the groundwater pollution survey information of the contaminated site; the structural parameters include direction, length, depth and width.

[0022] In step 20, a trench 4 is excavated downstream of the pollution source 3 along the direction of the permeability reaction barrier, and a plurality of permeability reaction modules 50 are installed in the trench to form a permeability reaction barrier 5. The top of the permeability reaction barrier 5 is higher than the lowest groundwater level 21.

[0023] Among them, such as Figure 2 As shown, the permeability reaction module includes a hollow housing 501, with water-permeable mesh 502 positioned on each of the two opposite sides of the housing 501. Preferably, the porosity of the water-permeable mesh 502 is greater than 80%. The housing 501 is filled with granular filler, within which a UV light strip 503 is positioned. The granular filler includes translucent glass balls 504 and ceramic particles 505 with a surface load of titanium dioxide.

[0024] Connect the ultraviolet light strips 503 of several permeability reaction modules, and install a control switch for controlling the opening and closing of the ultraviolet light strips.

[0025] Step 30: Fill the gap between the permeable reaction barrier 5 and the trench 4, and cover the top of the permeable reaction barrier with a geomembrane 7 and a clay layer 8 in sequence, and compact them.

[0026] The geomembrane 7 can prevent the upper layer of fine particles from entering the quartz sand 62 and blocking the permeable reaction barrier 5. The compacted clay layer 8 can prevent precipitation from infiltrating and destroying the stability of the permeable reaction barrier 5 and the side wall of the trench 4.

[0027] Step 40: construct monitoring wells 9 downstream of the permeability reaction barrier 5 and upstream of the pollution source 3; install monitoring components 10 in the monitoring wells 9 and below the lowest groundwater level 21 to collect monitoring parameters of the upstream and downstream groundwater.

[0028] Preferably, the monitoring parameters include at least one of pH, conductivity, and redox potential. Pollutants can inhibit the characteristics and quantity of microbial flora in groundwater, and changes in the characteristics and quantity of microbial flora can cause changes in pH, conductivity, and redox potential. Therefore, these monitoring parameters can represent the concentration of groundwater pollutants.

[0029] Preferably, the downstream of the permeable reaction barrier 5 is spaced apart along the direction of the permeable reaction barrier. K Downstream monitoring wells were constructed at intervals upstream of pollution source 3 along the direction of the permeability reaction barrier. K Upstream monitoring wells, K upstream monitoring wells and K Each downstream monitoring well is laid out in a one-to-one correspondence; Kis an integer greater than or equal to 3. Preferably, the spacing between two adjacent upstream monitoring wells is 10 to 40 meters. Groundwater pollutant concentrations vary along the direction of the permeability reaction barrier. To ensure monitoring accuracy and operational effectiveness, it is necessary to monitor upstream and downstream groundwater pollutant concentrations using multiple groups of monitoring wells, with appropriate spacing between adjacent monitoring wells.

[0030] Step 50: Connect the monitoring device and the control switch to the monitor.

[0031] Step 60, during operation, the monitoring component 10 sends the collected monitoring parameter data of the upstream and downstream groundwater to the monitor 11, and the monitor 11 adjusts the corresponding control switch to adjust the opening and closing of the ultraviolet light band in the permeability reaction barrier 5 according to the monitoring parameter data of the upstream and downstream groundwater.

[0032] During operation, contaminated groundwater passes through the permeable mesh 502 on one side of the permeable reaction module and flows into the inner cavity of the housing 501. It then flows through the granular filler and exits through the permeable mesh 502 on the other side. During this process, the granular filler absorbs pollutants from the contaminated groundwater, thereby purifying the groundwater. When the UV light band 503 is turned on, the granular filler comprises transparent glass spheres 504 and ceramic granules 505 with titanium dioxide on their surfaces. After the UV light band 303 emits ultraviolet light, it strikes the titanium dioxide surface of the ceramic granules 105, generating electron-hole pairs that react with contacting water molecules to form hydroxyl radicals. These hydroxyl radicals gradually degrade organic pollutants through oxidation into small molecular intermediates, ultimately mineralizing into CO2 and H2O. Because the ceramic granules 505 are opaque, the UV light travels a very short distance within the permeable reaction barrier, with a maximum distance of approximately five times the diameter of the granular filler. Therefore, by adding transparent glass balls 504 to the filler, the embodiment of the present invention allows ultraviolet light to pass through the transparent glass balls 504 and refract on their surfaces, thereby greatly increasing the irradiation area of ​​the ultraviolet light and the ceramsite 505. For example, after mixing the ceramsite 505 and transparent glass balls 504 in a volume ratio of 1:1, the axial irradiation area of ​​a single ultraviolet light strip 503 can be increased by approximately 7 times, greatly improving the catalytic efficiency of the light source.

[0033] The embodiment of the present invention adds a filler that can adsorb pollutants and degrade pollutants through photocatalysis into the permeability reaction module, and introduces an external light source. When the ultraviolet light band 503 is turned off, when the contaminated groundwater flows through the permeability reaction module, the pollutants are adsorbed and fixed in the permeability reaction module through the adsorption effect of the filler. When the ultraviolet light band 503 is turned on, when the contaminated groundwater flows through the permeability reaction module, on the one hand, the pollutants are adsorbed and fixed in the permeability reaction module through the adsorption effect of the filler, and on the other hand, the pollutants released by desorption from the filler are catalytically degraded through the photocatalytic effect. After degradation, the pollutants adsorbed on the filler diffuse back to the groundwater, reducing the frequency of filling replacement. In particular, when used in sites where organic pollutants in groundwater change frequently, the permeability reaction barrier of this embodiment improves the operating efficiency of the permeability reaction barrier.

[0034] The permeable reaction barrier of the embodiment of the present invention has two functions: one is to adsorb pollutants in the groundwater; the other is to degrade and remove pollutants that were previously adsorbed on the filler and may be released into the groundwater again through the catalytic effect of ultraviolet light. In other words, in order to prevent the released pollutants from migrating downstream again, the embodiment of the present invention proposes a permeable reaction barrier with photocatalytic regulation function, which catalytically degrades the pollutants after they are desorbed from the filler, preventing the pollutants from returning to the water flow. In this way, the filler in the permeable reaction barrier unit can not only adsorb pollutants in the contaminated groundwater, but also degrade the pollutants and release them into the groundwater again.

[0035] Preferably, in each permeability reaction module, the embedded length of the ultraviolet light strip 503 is determined according to formula (1) and formula (2): Formula (1) Formula (2) Where, L represents the embedded length of the UV light tape 503 in cm; a represents the length of the permeability reaction barrier module in cm; b represents the width of the permeability reaction barrier module in cm; c represents the height of the permeability reaction barrier module in cm; Indicates the radial effective irradiation area of ​​a UV light band 503, in cm 2 ; represents the reduction coefficient of the radial effective irradiation area of ​​the ultraviolet light band 503, dimensionless; Indicates the stacking volume of the light-transmitting glass balls 504, in cm 3 ; Indicates the bulk volume of ceramsite 505, in cm 3 ;R represents the reference value of the stacking volume ratio of the transparent glass balls 504 and the ceramsite 505, dimensionless; R The value range is 0.8 to 2.3.

[0036] In the preferred embodiment described above, by adjusting the embedded length of the UV light strip 503, quantitative data support can be provided for optimizing the performance of the permeable reaction barrier. For example, when the granular filler material changes, the length of the UV light strip should also be adjusted accordingly. This maximizes the catalytic effect of the UV light and reduces energy input.

[0037] Preferably, Figure 4 As shown, the permeable reaction barrier 5 comprises N The permeability reaction units 51 are arranged in sequence along the groundwater flow direction. Each permeability reaction unit includes a number of permeability reaction modules 50 sequentially spliced ​​on a vertical surface. Figure 3 As shown. Among them, N is an integer greater than or equal to 3.

[0038] In the above preferred embodiment, several permeability reaction modules are spliced ​​along the groove direction and along the vertical surface to form a permeability reaction unit, and then the permeability reaction modules are spliced ​​along the groundwater flow direction. N The permeability reaction units are connected and arranged to form a permeability reaction barrier. The permeability reaction barrier is designed in pieces and modules. On the one hand, it improves the mobility of on-site construction and maintenance of the permeability 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 in pieces or modules, thereby improving the efficiency of contaminated groundwater remediation and reducing the economic cost of the remediation project.

[0039] Preferably, the ultraviolet light bands of all the permeability reaction modules in the same permeability 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 11. That is, the opening or closing of the ultraviolet light bands of all the permeability reaction modules in the same permeability reaction unit is consistent, while the opening or closing of the ultraviolet light bands in different permeability reaction units are controlled by their own control switches, and the states may be different.

[0040] In this preferred embodiment, the UV light strip is turned on or off on a per-sheet basis. First, using per-sheet as a unit allows for precise control of the length of the UV light strip embedded in the filler, facilitating construction quality control. Second, setting and installing permeable reaction barriers along the groundwater flow direction on a per-sheet basis enables cascade control of UV photocatalysis, quantitatively controlling the number of UV light sources turned on based on the concentration differences of upstream and downstream pollutants. Furthermore, during the operation of the permeable reaction barrier, changes in formation pressure, groundwater level, and other factors can cause filler blockage and damage. After the permeable reaction barrier is designed and installed in sections, the damaged permeable reaction unit can be partially replaced, avoiding damage to the UV light strip caused by excavation of the entire barrier.

[0041] Preferably, the control switches of the most upstream and most downstream osmotic reaction units 51 are always in the open state, and the states of the control switches of other osmotic reaction units 51 are controlled by the monitor.

[0042] Typically, groundwater flow is slow, and contaminants in the groundwater migrate through the pores of a permeability barrier by convection and diffusion. While contaminant migration by convection aligns with the groundwater flow, diffusional migration is directional and can be either aligned with, perpendicular to, or opposite to the groundwater flow. When the groundwater concentration decreases after entering the permeability barrier, contaminants adsorbed on the filler material desorb and re-release into the groundwater, releasing the adsorbed contaminants into the downstream groundwater environment. Therefore, to degrade contaminants migrating upstream by diffusion, the control switch of the upstreammost permeability barrier is always kept open. Furthermore, concentrated rainfall over a short period of time can cause short-term changes in the groundwater flow field, even causing flow to reverse the main flow direction. Therefore, to minimize the possibility of reverse groundwater flow caused by rainfall, which could lead to the re-migration of released contaminants upstream, the control switch of the upstreammost permeability barrier is always kept open. The reason for keeping the control switch of the downstreammost permeability barrier always open is to prevent contaminants desorbed from the filler material from being released into the downstream groundwater environment when the groundwater is stagnant.

[0043] Preferably, the monitor 11 controls the state of the control switch of the permeability reaction unit using equations (3) to (5): (3) (4) (5) Where, Indicates the n The state of the control switch of the sheet permeability reaction unit, 0 means closed state, 1 means open state; It represents the maximum ratio of monitoring parameters of upstream and downstream groundwater, dimensionless; Indicates the k The first monitoring parameter value of the upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the k The first monitoring parameter value of the downstream groundwater collected by the monitoring device in the downstream monitoring well; Indicates the k The second monitoring parameter value of the upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the k The second monitoring parameter value of the downstream groundwater collected by the monitoring device in the downstream monitoring well; represents the response threshold, dimensionless; It represents the monitoring well distance adjustment coefficient, dimensionless, ranging from 0.1 to 0.3; Represents the distance between two adjacent monitoring wells located on the same side of the permeability barrier, in meters. The first monitoring parameter is pH and the second is conductivity; or, the first monitoring parameter is redox potential and the second is conductivity.

[0044] The embodiment of the present invention adjusts the second to the first slices according to the monitoring parameters of the upstream and downstream groundwater. N -The state of the control switch of 1 permeability reaction unit, that is, the opening and closing of the ultraviolet light band. When the concentration of groundwater pollutants upstream of the permeability reaction barrier increases, the effect of the filler in the permeability reaction barrier on adsorbing pollutants decreases. An appropriate number of ultraviolet light bands are turned on, and the catalytic effect of the ultraviolet light bands is used to make up for the defect of insufficient physical adsorption of the filler; when the concentration of groundwater pollutants upstream decreases again, the pollutants adsorbed by the filler in the permeability reaction barrier will be released into the groundwater again. At this time, an appropriate number of ultraviolet light bands are turned on, and the adsorbed pollutants are degraded through the catalytic effect of the ultraviolet light bands, making up for the defect that the traditional permeability reaction barrier cannot completely remove pollutants. The embodiment of the present invention adjusts the number of ultraviolet light bands that are turned on according to the concentration of upstream pollutants, which can improve the working performance of the permeability reaction barrier, save energy consumption, and reduce costs.

[0045] Preferably, the joint gaps between the permeability reaction modules of two adjacent permeability reaction units 51 are arranged in a staggered manner, which effectively prevents the contaminated groundwater from flowing through the joint gaps instead of passing through the permeability reaction modules.

[0046] Preferably, in step 30, filling the gap between the permeable reaction barrier and the groove specifically includes: The gap between the lower sidewall of the permeable reactive barrier and the trench sidewall is filled with a cementitious material 61 (e.g., cement, lime, slag, or a mixture thereof). The height of the gap filled with cementitious material is 0.3 to 0.5 m. The gaps between the remaining sidewalls of the permeable reactive barrier and the trench sidewall are filled with quartz sand 62.

[0047] Because the soil at the bottom of the excavated trench 4 is prone to deformation and even collapse due to concentrated ground stress, this embodiment uses a cementitious material to fill the trench 4, creating a strong structure that prevents soil deformation from causing the permeable reaction barrier 5 to tilt or shift between different units. Filling the remaining gaps with quartz sand maintains the permeable reaction barrier 5 in a vertical position, preventing tilt and maintaining good water permeability.

[0048] Preferably, the top surface of the clay layer 8 is 0.3 to 0.5 m higher than the ground surface 1. This can effectively prevent water from accumulating on the upper part of the permeable reaction barrier after construction, thereby changing the local groundwater flow field and affecting the working performance of the permeable reaction barrier.

[0049] Preferably, the distance between the monitoring well 9 downstream of the permeability reaction barrier 5 and the permeability reaction barrier 5 is 2 to 3 meters. The distance between the monitoring well 9 upstream of the pollution source 3 and the pollution source 3 is 2 to 5 meters. Improving the accuracy of monitoring data can achieve precise control of the activation time or quantity of the ultraviolet light band in the permeability reaction unit, improve energy efficiency, and reduce repair costs.

[0050] 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 the comparative examples are all simulation experiments in the laboratory. Example

[0051] In the experiment, the perfluorooctanoic acid concentration in the upstream contaminated groundwater was set at 100 μg / L, and the solid-liquid ratio of ceramsite to contaminated groundwater was 1:10. The particle size of the ceramsite ranged from 1 to 2.5 cm. The volume of the transparent glass ball was the same as that of the ceramsite, with a diameter of 1.5 cm. Titanium dioxide powder was evenly loaded on the surface of the ceramsite, and the mass ratio of titanium dioxide to ceramsite was 1:100. After the ceramsite and the transparent glass ball were evenly mixed, they were poured into a polyethylene bottle and placed in an opaque shaker for shaking. During the experiment, three ultraviolet light strips were evenly installed in the polyethylene bottle and turned on so that the ultraviolet light could fully irradiate the surface of the ceramsite. Each ultraviolet light strip was 10 cm long and had a power of 0.1 W.

[0052] The solution was collected at intervals of 3 hours, and the concentration of perfluorooctanoic acid was tested. After 12 hours of the adsorption test, perfluorooctanoic acid reached adsorption saturation on the surface of the ceramsite. Then, the simulated groundwater with some pollutants removed from the polyethylene bottle was taken out, and refilled with simulated contaminated groundwater with a perfluorooctanoic acid concentration of 30μg / L, and then placed on a shaker for shaking. The solution was collected at intervals of 3 hours, and the concentration of perfluorooctanoic acid was tested. This test simulates the removal of perfluorooctanoic acid in groundwater under the condition that the ultraviolet light bands of the upstream, second and downstream permeability reaction units along the groundwater flow direction are in the turned-on state. The simulated changes in perfluorooctanoic acid concentration in downstream groundwater are shown in Figure 5 .

[0053] Comparative Example 1 The ceramsite in Example 1 was replaced with ceramsite that was not loaded with titanium dioxide powder (i.e., the ceramsite used in the traditional method), and no UV light strip was installed in the polyethylene bottle during the test. The pollutant concentration, sampling time, and pollutant testing methods in the other steps of the test were the same as those in Comparative Example 1. This test simulates the removal effect of a traditional permeable reaction barrier (without UV light strip) on perfluorooctanoic acid contaminated groundwater under the same conditions as the permeable reaction barrier with four permeable reaction units in Example 1. The simulated changes in perfluorooctanoic acid concentration in downstream groundwater are shown in Figure 5 .

[0054] Comparative Example 2 During the test, four UV light strips were evenly installed in the polyethylene bottle and all turned on. The pollutant concentration, sampling time, and pollutant testing methods in the other steps of the test were the same as those in Comparative Example 1. This test simulates the removal effect of PFOA in groundwater under the condition that a permeable reaction barrier with four permeable reaction units and the UV light strips of the four permeable reaction units are all turned on. The simulated changes in the concentration of PFOA in the downstream groundwater are shown in Figure 2. Figure 5 .

[0055] from Figure 5 From the changes in the perfluorooctanoic acid concentrations in Comparative Example 1 and Example 1, it can be seen that in Example 1, by turning on three ultraviolet light bands (corresponding to the ultraviolet light bands of three units in the four permeability reaction units being in the on state), the perfluorooctanoic acid adsorbed on the filler no longer migrates to the downstream groundwater after the perfluorooctanoic acid concentration in the groundwater changes from high to low, and the removal effect is obvious.

[0056] from Figure 5The changes in pollutants in Comparative Example 2 and Example 1 show that when the upstream groundwater PFOA concentration is constant, the number of UV light strips activated within the permeability reaction unit reaches an optimal value. As the number of activated UV light strips increases, the groundwater PFOA concentration no longer changes significantly. Therefore, the present invention optimizes the number of UV light strips activated within the permeability reaction unit based on the difference in PFOA concentrations in the upstream and downstream groundwater, achieving both excellent removal efficiency and reduced energy consumption.

[0057] The basic principles, main features, and advantages of the present invention are shown and described above. 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 only intended to further illustrate the principles of the present invention. Various changes and improvements are possible without departing from the spirit and scope of the present invention, and such changes and improvements fall within the scope of the invention as claimed.

Claims

1. A method for constructing and operating a permeable reaction barrier based on photocatalytic regulation, characterized in that: The following steps are involved: Step 10: determining structural parameters of the permeability reaction barrier based on groundwater pollution survey information of the contaminated site; the structural parameters include direction, length, depth, and width; Step 20, excavating a trench (4) downstream of the pollution source (3) along the direction of the permeable reaction barrier, installing a plurality of permeable reaction modules (50) in the trench to form a permeable reaction barrier (5); the permeable reaction module (50) includes a hollow shell (501), and two opposite hollow sides of the shell (501) are respectively provided with a permeable mesh (502); the shell (501) is filled with a granular filler, and an ultraviolet light strip (503) is arranged inside the granular filler; the granular filler includes a translucent glass ball (504) and a ceramsite (505) with titanium dioxide loaded on the surface; connecting the ultraviolet light strips of the plurality of permeable reaction modules, and installing a control switch for controlling the opening and closing of the ultraviolet light strip; Step 30, filling the gap between the permeable reaction barrier (5) and the trench (4), covering the top of the permeable reaction barrier with a geomembrane (7) and a clay layer (8), and compacting them; Step 40, constructing monitoring wells (9) downstream of the permeability reaction barrier (5) and upstream of the pollution source (3); installing monitoring components (10) in the monitoring wells (9) below the lowest groundwater level (21) to collect monitoring parameters of the upstream and downstream groundwater; Step 50, connecting the monitoring element and the control switch to the monitor; Step 60: During operation, the monitor regulates the opening and closing of the ultraviolet light band in the permeability reaction barrier (5) according to the monitoring parameter data of the upstream and downstream groundwater collected by the monitoring element (10).

2. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 1, characterized in that: In each of the permeability reaction modules, the embedding length of the ultraviolet light band (503) is determined according to formula (1) and formula (2): Formula (1) Formula (2) Where, L represents the buried length of the ultraviolet light band (503), in cm; a represents the length of the permeability reaction barrier module in cm; b represents the width of the permeability reaction barrier module in cm; c represents the height of the permeability reaction barrier module in cm; Indicates the radial effective irradiation area of ​​a UV band (503), in cm 2 ; represents the reduction factor of the radial effective irradiation area of ​​the ultraviolet light band (503), dimensionless; Indicates the stacking volume of the light-transmitting glass balls (504), in cm 3 ; Indicates the bulk volume of ceramsite (505), in cm 3 ; R represents the reference value of the stacking volume ratio of the light-transmitting glass balls (504) and the ceramsite (505), dimensionless; R The value range is 0.8 to 2.

3.

3. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 1, characterized in that: In the step 40, the permeable reaction barrier (5) is formed at intervals along the direction of the permeable reaction barrier downstream. K Downstream monitoring wells are constructed at intervals along the direction of the permeability reaction barrier upstream of the pollution source (3). K Upstream monitoring wells, K upstream monitoring wells and K Each downstream monitoring well is laid out in a one-to-one correspondence; K is an integer greater than or equal to 3.

4. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 3, characterized in that: The permeable reaction barrier comprises N The permeability reaction units (51) are arranged in sequence along the groundwater flow direction, and each permeability reaction unit includes a plurality of permeability reaction modules (50) spliced ​​in sequence on a vertical surface; the ultraviolet light bands of all the permeability reaction modules in the same permeability reaction unit are connected in series in sequence. N The permeability reaction units are connected in parallel; each permeability 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 is an integer greater than or equal to 3.

5. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 4, characterized in that: The control switches of the two permeability reaction units (51) located at the most upstream and the most downstream are always in the open state; the states of the control switches of the other permeability reaction units (51) are controlled by the monitor.

6. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 5, characterized in that: The monitor uses equations (3) to (5) to control the state of the control switch of the permeability reaction unit: （3） （4） （5） Where, Indicates the n The state of the control switch of the sheet permeability reaction unit, 0 means closed state, 1 means open state; It represents the maximum ratio of monitoring parameters of upstream and downstream groundwater, dimensionless; Indicates the k The first monitoring parameter value of the upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the k The first monitoring parameter value of the downstream groundwater collected by the monitoring device in the downstream monitoring well; Indicates the k The second monitoring parameter value of the upstream groundwater collected by the monitoring device in the upstream monitoring well; Indicates the k The second monitoring parameter value of the downstream groundwater collected by the monitoring device in the downstream monitoring well; represents the response threshold, dimensionless; It represents the monitoring well distance adjustment coefficient, dimensionless, ranging from 0.1 to 0.3; It represents the distance between two adjacent monitoring wells located on the same side of the permeability reaction barrier, in meters.

7. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 4, characterized in that: The splicing gaps between the permeability reaction modules of two adjacent permeability reaction units are arranged in a staggered manner.

8. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 1, characterized in that: In step 30, filling the gap between the permeable reaction barrier and the groove specifically includes: The gap between the lower side wall of the permeable reaction barrier and the side wall 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) is used to fill the gap between the remaining side walls of the permeable reaction barrier and the side walls of the trench.

9. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation according to claim 1, characterized in that: The top surface of the clay layer (8) is 0.3 to 0.5 m higher than the ground surface (1).

10. The method for constructing and operating a permeable reaction barrier based on photocatalytic regulation 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 meters; the distance between the monitoring well (9) located upstream of the pollution source (3) and the pollution source (3) is 2 to 5 meters.

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