Pollution source downstream aeration zone perfluorinated and polyfluoroalkyl compound treatment system and method

Abstract

The invention discloses a pollution source downstream aeration zone perfluorinated and polyfluoroalkyl compound treatment system and method. The system comprises a low-permeability adsorption composite function barrier and an underground water remediation facility adjacent to the low-permeability adsorption composite function barrier. The composite functional barrier is formed by compounding a low-permeability material and a material with high adsorbability to PFAS, is arranged near a groundwater surface, and is used for changing a water flow path of an aeration zone above the groundwater surface, forcing the PFAS retained in the aeration zone to enter groundwater and adsorbing the flowing PFAS; the top of the composite function barrier is higher than the pollution plume of the downstream aeration zone of the pollution source and located above the groundwater annual fluctuation highest phreatic level, the bottom of the composite function barrier is located below the groundwater annual fluctuation lowest phreatic level, and the width of the composite function barrier is larger than that of the pollution plume. According to the method, the low-permeability adsorption composite functional barrier is constructed near the diving surface, the low permeability of the composite functional barrier forces PFAS enriched in a downstream aeration zone to enter underground water, and meanwhile, a high-adsorbability material in the composite functional barrier is used for effectively intercepting the flowing PFAS.

Description

Technical Field

[0001] This invention relates to a downstream treatment system and method for pollution sources, and more particularly to a system and method for treating perfluorinated and polyfluoroalkyl compounds in the vadose zone downstream of pollution sources. Background Technology

[0002] Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic persistent organic pollutants. PFAS are difficult to degrade naturally in the environment and have strong surface activity, readily adsorbing and accumulating at the air-water interface. When PFAS are leached into groundwater through the vadose zone, some PFAS migrate downstream via capillary water, leading to PFAS accumulation at the air-water interface in the downstream vadose zone. Under the influence of precipitation, groundwater level fluctuations, and other factors, PFAS in the downstream vadose zone will continue to pollute groundwater, becoming a major challenge in the remediation process.

[0003] Currently, mainstream remediation technologies for PFAS-contaminated groundwater primarily target dissolved pollutants migrating in the saturation zone, such as permeable adsorption walls and extraction-treatment systems. However, due to the low volatility of most PFAS and their strong adsorption characteristics at the air-water interface, traditional vadose zone soil treatment technologies, such as gas-phase extraction, are ineffective in treating PFAS adsorbed and retained in the vadose zone. Therefore, existing technologies lack targeted remediation methods for PFAS present in the vadose zone downstream of pollution sources, necessitating a new system and method that can effectively manage PFAS in the vadose zone downstream of pollution sources. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to propose a system and method for treating perfluorinated and polyfluoroalkyl compounds in the vadose zone downstream of a pollution source, in order to solve the problem that existing technologies are unable to effectively treat PFAS enriched in the vadose zone downstream of a pollution source, and to achieve synergistic treatment of PFAS pollution in the vadose zone and groundwater.

[0005] Technical solution: The present invention includes a low-permeability adsorption composite functional barrier and an adjacent groundwater remediation facility; the low-permeability adsorption composite functional barrier is composed of a low-permeability material and a material with high adsorption capacity for PFAS, and is deployed near the groundwater phreatic surface to change the flow path of water in the vadose zone above the phreatic surface, forcing PFAS retained in the vadose zone into the groundwater and adsorbing the flowing PFAS; the top of the low-permeability adsorption composite functional barrier is higher than the height of the pollution plume in the vadose zone downstream of the pollution source and is located above the highest phreatic surface of the interannual groundwater fluctuation, while the bottom is located below the lowest phreatic surface of the interannual groundwater fluctuation, and the width is greater than the width of the pollution plume.

[0006] The low-permeability material is at least one of bentonite, clay, or modified clay.

[0007] The material with high adsorption capacity for PFAS is at least one of activated carbon, ion exchange resin, modified biochar, or material with specific adsorption capacity for PFAS.

[0008] In the low-permeability adsorption composite functional barrier, the low-permeability material and the material with high adsorption capacity for PFAS are laid in alternating layers, uniformly mixed, or the low-permeability material is used as the core layer and the two sides are composed of high-adsorption materials.

[0009] The groundwater remediation facility is a permeable adsorption wall or an extraction-treatment system.

[0010] A method for treating perfluorinated and polyfluoroalkyl compounds in the vadose zone downstream of a pollution source specifically includes the following steps:

[0011] S1: Obtain hydrogeological parameters and pollutant parameters of the treatment area. The hydrogeological parameters include annual groundwater level variation data, saturated permeability coefficient, and soil characteristic parameters. The pollutant parameters include PFAS physicochemical properties, leakage pollution amount, soil and groundwater concentration, solid phase adsorption coefficient, air-water interface area, and interface adsorption parameters.

[0012] S2: Based on the aforementioned hydrogeological parameters and pollutant parameters, determine the remediation targets, design low-permeability adsorption composite functional barriers and groundwater remediation facilities, and clarify the material ratio, structural dimensions and layout location of the low-permeability adsorption composite functional barriers;

[0013] S3: Establish a numerical model of the coupled vadose zone-groundwater and solve the groundwater flow in the variable saturation zone. Add the solid adsorption term of PFAS and the air-water interface adsorption term to the convection-dispersion equation, evaluate and verify the synergistic treatment effect of low-permeability adsorption composite functional barrier and groundwater remediation facility, and optimize the design scheme.

[0014] S4: Construct a low-permeability adsorption composite functional barrier and groundwater remediation facilities downstream of the pollution source according to the optimized design scheme.

[0015] In step S1, high-resolution sampling is performed on the downstream vadose zone, the water table, and the groundwater below the water table to determine the soil and groundwater concentrations of PFAS; representative soil samples are collected to determine the solid phase adsorption coefficient and air-water interface area, and groundwater samples are collected to determine the interface adsorption parameters.

[0016] In step S1, the soil concentration data is divided into grids and spatially interpolated. The soil concentration of the grid is multiplied by the grid volume to obtain the total mass of the downstream vadose zone PFAS.

[0017] In step S3, the assessment and verification include the total amount of PFAS introduced into the groundwater by the multifunctional barrier, the retention time of PFAS in the barrier, and the treatment capacity of the downstream groundwater remediation facilities for the total pollution load.

[0018] In step S3, the optimization includes the material ratio, thickness or layered structure of the low-permeability adsorption composite functional barrier, as well as the key parameters of the groundwater remediation facility; when the groundwater remediation facility is a permeable reactive wall, its thickness and the amount of adsorbent material filling are optimized; when the groundwater remediation facility is an extraction-treatment system, its extraction well layout and treatment scale are optimized.

[0019] Beneficial effects: This invention constructs a low-permeability adsorption composite functional barrier near the water table. The low permeability of the composite functional barrier forces PFAS enriched in the downstream vadose zone into the groundwater, while the highly adsorbent material in the composite functional barrier effectively intercepts the flowing PFAS. By working in conjunction with groundwater remediation facilities, a joint treatment system for the downstream vadose zone and groundwater is formed. It can effectively remove stubborn pollutants remaining in the vadose zone, significantly reduce the load on groundwater remediation measures, and extend their service life. It also has the advantages of low construction difficulty and convenient maintenance, and is particularly suitable for sites with a thin vadose zone. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the treatment of perfluorinated and polyfluoroalkyl compounds in the downstream vadose zone of the pollution source according to the present invention.

[0021] Figure 2 The simulation results show the treatment effect of using a low-permeability adsorption composite functional barrier: Figure 2 a represents the total mass of PFAS within the downstream vadose zone; Figure 2 b represents the total mass of PFAS within the multifunctional barrier region. Detailed Implementation

[0022] The invention will now be further described with reference to the accompanying drawings.

[0023] Example 1

[0024] like Figure 1 As shown, the downstream vadose zone perfluorinated and polyfluoroalkyl compounds treatment system of this embodiment includes a low-permeability adsorption composite functional barrier 1 as a pretreatment unit and a groundwater remediation facility 2. The low-permeability adsorption composite functional barrier 1 is composed of a low-permeability material and a material with high adsorption capacity for PFAS. It is deployed near the groundwater phreatic surface 3. That is, the top of the low-permeability adsorption composite functional barrier 1 is higher than the height of the pollution plume in the downstream vadose zone of the pollution source and is located above the highest phreatic surface of the interannual groundwater fluctuation, while the bottom is located below the lowest phreatic surface of the interannual groundwater fluctuation, and the width is greater than the width of the pollution plume.

[0025] The low-permeability adsorption composite functional barrier 1 has a permeability coefficient lower than that of the surrounding natural vadose zone and aquifer soil. It alters the flow path of water in the vadose zone above the water table, forcing PFAS retained in the vadose zone into the groundwater and adsorbing flowing PFAS. The groundwater remediation facility 2 employs a permeable adsorption wall or an extraction-treatment system to remediate the PFAS introduced into the groundwater by the composite functional barrier and the existing PFAS contaminants in the groundwater. The low-permeability adsorption composite functional barrier 1 and the groundwater remediation facility 2 work together to form a joint treatment system for the downstream vadose zone and groundwater.

[0026] The low-permeability adsorption composite functional barrier 1 includes at least one of bentonite, clay, or modified clay as the low-permeability material; and at least one of activated carbon, ion exchange resin, modified biochar, or materials with specific adsorption capacity for PFAS as the high-permeability adsorption material. The low-permeability material and the high-permeability adsorption material for PFAS are combined in a layered alternating manner, uniformly mixed, or with the low-permeability material as the core layer and the high-permeability material on both sides.

[0027] Above the groundwater level 3 is the vadose zone, and below it is groundwater, which mainly flows in direction 4. Under the influence of rainfall infiltration 5, PFAS surface pollution sources enter the vadose zone and groundwater, forming a PFAS pollution plume 6. The PFAS pollution plume 6 includes the pollution source portion 601, vadose zone pollutants 602 downstream of the pollution source, and groundwater pollutants 603. Due to the low permeability of the low-permeability adsorption composite functional barrier 1, local vadose zone and groundwater flow are bypassed, changing the flow direction to direction 7. This causes the vadose zone pollutants 602, originally concentrated in the vadose zone, to enter the groundwater and, together with the existing groundwater pollutants 603, are treated in the groundwater remediation facility 2. Ultimately, the water flow 605, achieving the remediation target, flows out of the remediation area. Meanwhile, under the influence of weak convection, diffusion and hydrodynamic dispersion, some of the pollutants 602 in the vadose zone enter the interior of the low-permeability adsorption composite functional barrier 1, forming a plume 604. Under the strong adsorption effect of the composite functional barrier 1, the plume 604 is effectively blocked within the low-permeability adsorption composite functional barrier 1, reducing the intensity of pollutant discharge into groundwater.

[0028] Example 2

[0029] The method for treating perfluorinated and polyfluoroalkyl compounds in the downstream vadose zone of the pollution source in this embodiment includes the following steps:

[0030] S1: Obtain hydrogeological and pollutant parameters of the treatment area, including the physical and chemical characteristics of PFAS and the amount of leakage pollution. Hydrogeological parameters specifically include annual groundwater level variation data, saturated permeability coefficient, and soil characteristic parameters. Obtaining the pollutant parameters requires high-resolution sampling of the downstream vadose zone, water table, and groundwater below the water table to determine the soil and groundwater concentrations of PFAS. Representative soil samples are collected to determine the solid-phase adsorption coefficient and air-water interface area, and groundwater samples are collected to determine relevant interfacial adsorption parameters. Higher PFAS soil concentration in the vadose zone indicates more severe pollution in the downstream vadose zone. The soil concentration data is divided into grids and spatially interpolated. Multiplying the soil concentration in each grid by the grid volume yields the total mass of PFAS in the downstream vadose zone.

[0031] S2: Obtain hydrogeological and pollutant parameters to determine remediation targets and simultaneously design groundwater remediation facilities and low-permeability adsorption composite functional barriers. Based on the remediation targets, select and design permeable reactive barriers or extraction-treatment systems to ensure they can treat PFAS introduced into the groundwater by the composite functional barrier, as well as existing pollutants in the groundwater. Determine the material composition, structural dimensions (such as thickness and height), and placement location of the low-permeability adsorption composite functional barrier based on the downstream vadose zone PFAS pollution level, total amount, and hydrogeological conditions. The low-permeability adsorption composite functional barrier is composed of low-permeability materials and materials with high PFAS adsorption capacity, layered alternately, uniformly mixed, or with a low-permeability material as the core layer and high-adsorption materials on both sides. The top of the barrier must be higher than the downstream vadose zone pollution plume height and located above the highest interannual groundwater level, while its bottom is below the lowest interannual groundwater level, with a width greater than the pollution plume width, to ensure its hydraulic control and retention effectiveness.

[0032] S3: Establish a numerical model of the coupled vadose zone and groundwater to simulate, evaluate, and verify the remediation scheme designed in S2, in order to optimize the design scheme. Specifically, the numerical model uses the Richards equation to solve the groundwater flow in the variable saturation zone. Solid-phase adsorption terms for PFAS and air-water interface adsorption terms are added to the convection-dispersion equation. The air-water interface area can be determined using thermodynamic estimation or empirical coefficient methods. The evaluation and verification mainly include: the total amount of PFAS introduced into the groundwater by the composite functional barrier, the retention time of PFAS in the barrier, and the treatment capacity of downstream groundwater remediation facilities for the total pollution load. Optimize the material ratio, thickness, or layered structure of the composite functional barrier, and the thickness of the permeable reactive barrier, the amount of adsorbent material filling, or the layout and treatment scale of the extraction wells in the extraction-treatment system of the downstream groundwater remediation facilities to ensure long-term effective treatment of the groundwater pollution introduced by the composite functional barrier and the existing groundwater pollution.

[0033] S4: Following the optimized design scheme of step S3, construct the low-permeability adsorption composite functional barrier and the groundwater remediation facility in sequence at the optimized layout location downstream of the pollution source area.

[0034] To illustrate the role of the composite functional barrier, a two-dimensional profile numerical simulation is presented below. The water flow simulation is based on the Richards equation, while the solute transport simulation employs a convection-dispersion equation that includes adsorption terms at the PFAS solid phase and the air-water interface. The air-water interface area is calculated using a thermodynamic method based on the soil VG model. This simulation uses perfluorooctanesulfonic acid (PFOS) as an example.

[0035] The model area is 20 m long and 6 m high. The left side is a constant head boundary (water level 3 m high), and the right side is also a constant head boundary (water level 2.9 m high). The pollution source is 5 m long, and the composite functional barrier is located 5 m downstream of it, with a barrier length of 10 m. The aquifer is considered homogeneous and isotropic, with a saturated permeability coefficient of 75 cm / h, longitudinal and lateral dispersion of 45 cm and 5 cm respectively, and a solid-phase adsorption coefficient of 0.1 cm. 3 / g. The adsorption coefficient of PFOS at the air-water interface is 0.016 cm. The saturation permeability coefficient of the composite functional barrier is set to 4 cm / h, and the solid-phase adsorption coefficient is 10 cm³ / g. A PFOS injection point with a concentration of 400 μg / L is set at 5 cm above the water surface, and continuous injection is carried out for 10 days, with a total simulation duration of 4 years.

[0036] Simulation results are as follows Figure 2 As shown. Figure 2 The total mass of PFAS in the downstream vadose zone was compared under two scenarios: with and without a composite functional barrier. Figure 2 a) and the total mass of PFAS within the composite functional barrier area ( Figure 2 The changes in b) are shown in the figure. The masses in the figure have been dimensionless (i.e., the actual mass divided by the total injected mass). Figure 2 (a) The results show that, without remediation measures, the peak mass of PFAS in the downstream vadose zone reaches 0.27 due to the strong adsorption of PFOS at the air-water interface. However, after the composite functional barrier was installed, the peak mass dropped to 0.19, indicating that a large amount of PFAS entered the groundwater from the vadose zone under the action of the barrier. Figure 2 (b) shows that even four years after the barrier was installed, a large amount of PFAS remained trapped within the barrier area, significantly reducing the PFAS emission flux to groundwater remediation facilities. Although the model used in this embodiment is relatively generalized and the barrier parameters were not optimized, the above results fully demonstrate the significant potential of this method in controlling downstream vadose zone PFAS pollution.

[0037] This invention utilizes a low-permeability adsorption composite functional barrier near the groundwater phreatic surface to allow PFAS retained in the vadose zone to enter the groundwater and adsorb flowing PFAS. It works in synergy with groundwater remediation facilities to effectively remove pollutants in the vadose zone downstream of the pollution source and reduce the load on groundwater remediation measures. It is also easy to construct and maintain, and is particularly suitable for sites with a thin vadose zone.

Claims

1. A system for treating perfluorinated and polyfluoroalkyl compounds in the vadose zone downstream of a pollution source, characterized in that, It includes a low-permeability adsorption composite functional barrier and an adjacent groundwater remediation facility; the low-permeability adsorption composite functional barrier is composed of a low-permeability material and a material with high adsorption capacity for PFAS, and is deployed near the groundwater phreatic surface, with a permeability coefficient lower than that of the surrounding natural vadose zone and aquifer soil; the top of the low-permeability adsorption composite functional barrier is higher than the height of the pollution plume in the vadose zone downstream of the pollution source and is located above the highest phreatic surface of the interannual groundwater fluctuation, while the bottom is located below the lowest phreatic surface of the interannual groundwater fluctuation, and the width is greater than the width of the pollution plume.

2. The system for the remediation of per- and polyfluoroalkyl substances in the zone of aeration downstream of a pollution source according to claim 1, characterized in that, The low-permeability material is at least one of bentonite, clay, or modified clay.

3. The system for the remediation of PFAS in the zone of aeration downstream of a pollution source according to claim 1, characterized in that, The material with high adsorption capacity for PFAS is at least one of activated carbon, ion exchange resin, modified biochar, or material with specific adsorption capacity for PFAS.

4. The system for the remediation of PFAS in the zone of aeration downstream of a contamination source according to claim 1, wherein, In the low-permeability adsorption composite functional barrier, the low-permeability material and the material with high adsorption capacity for PFAS are laid in alternating layers, uniformly mixed, or the low-permeability material is used as the core layer and the two sides are composed of high-adsorption materials.

5. The downstream vadose zone perfluorinated and polyfluoroalkyl compound treatment system according to claim 1, characterized in that, The groundwater remediation facility is a permeable adsorption wall or an extraction-treatment system.

6. A method for treating perfluorinated and polyfluoroalkyl compounds in the vadose zone downstream of a pollution source, characterized in that, This method is used to implement the downstream vadose zone perfluorinated and polyfluoroalkyl compounds treatment system of any one of claims 1 to 5, and specifically includes the following steps: S1: Obtain hydrogeological parameters and pollutant parameters of the treatment area. The hydrogeological parameters include annual groundwater level variation data, saturated permeability coefficient, and soil characteristic parameters. The pollutant parameters include PFAS physicochemical properties, leakage pollution amount, soil and groundwater concentration, solid phase adsorption coefficient, air-water interface area, and interface adsorption parameters. S2: Based on the aforementioned hydrogeological parameters and pollutant parameters, determine the remediation targets, design low-permeability adsorption composite functional barriers and groundwater remediation facilities, and clarify the material ratio, structural dimensions and layout location of the low-permeability adsorption composite functional barriers; S3: Establish a numerical model of the coupled vadose zone-groundwater and solve the groundwater flow in the variable saturation zone. Add the solid adsorption term of PFAS and the air-water interface adsorption term to the convection-dispersion equation, evaluate and verify the synergistic treatment effect of low-permeability adsorption composite functional barrier and groundwater remediation facility, and optimize the design scheme. S4: Construct a low-permeability adsorption composite functional barrier and groundwater remediation facilities downstream of the pollution source according to the optimized design scheme.

7. The method for treating perfluorinated and polyfluoroalkyl compounds in the downstream vadose zone of a pollution source according to claim 6, characterized in that, In step S1, high-resolution sampling is performed on the downstream vadose zone, the water table, and the groundwater below the water table to determine the soil and groundwater concentrations of PFAS; representative soil samples are collected to determine the solid phase adsorption coefficient and air-water interface area, and groundwater samples are collected to determine the interface adsorption parameters.

8. The method for treating perfluorinated and polyfluoroalkyl compounds in the downstream vadose zone of a pollution source according to claim 6, characterized in that, In step S1, the soil concentration data is divided into grids and spatially interpolated. The soil concentration of the grid is multiplied by the grid volume to obtain the total mass of the downstream vadose zone PFAS.

9. The method for treating perfluorinated and polyfluoroalkyl compounds in the downstream vadose zone of a pollution source according to claim 6, characterized in that, In step S3, the assessment and verification include the total amount of PFAS introduced into the groundwater by the multifunctional barrier, the retention time of PFAS in the barrier, and the treatment capacity of the downstream groundwater remediation facilities for the total pollution load.

10. The method for treating perfluorinated and polyfluoroalkyl compounds in the downstream vadose zone of a pollution source according to claim 6, characterized in that, In step S3, the optimization includes the material ratio, thickness or layered structure of the low-permeability adsorption composite functional barrier, as well as the key parameters of the groundwater remediation facility; when the groundwater remediation facility is a permeable reactive wall, its thickness and the amount of adsorbent material filling are optimized; when the groundwater remediation facility is an extraction-treatment system, its extraction well layout and treatment scale are optimized.

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