Design method of permeable reactive wall with different layout types based on antifouling performance

Abstract

The present invention discloses a design method for permeable reaction walls of different plane layout types based on anti-fouling performance, specifically, considering the migration of pollutants in the permeable reaction wall and the aquifer, comprehensively planning and optimizing the main relevant factors in the design of the permeable reaction wall in stages, designing various parts of the permeable reaction wall, and considering whether the pollutant concentrations at the pollution source and the aquifer monitoring point meet the standards at the design stage, and using the repair time at the pollution source as an evaluation index to obtain the optimal design parameter combination of the permeable reaction wall. Compared with the traditional permeable reaction wall design method, the design method adopted by the present invention can consider factors such as different wall layout types and aquifer influences to cope with different groundwater pollution situations, can obtain the permeable reaction wall parameter value combination with the best service performance under different working conditions and obtain the corresponding repair time, and the design method is reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental geotechnical engineering, and in particular is a design method of permeable reaction walls with different plane layout types based on anti-fouling performance. Background Art

[0002] Permeable reactive wall technology uses a wall made of reactive materials with good permeability. The wall is installed downstream of the pollution plume. When groundwater containing pollutants flows through, it will react with the active materials in the wall. The pollutants are precipitated, adsorbed, oxidized, reduced or degraded in the permeable reactive wall, thereby reducing the concentration of pollutants in the groundwater and achieving in-situ remediation of groundwater. The design of permeable reactive walls needs to consider many factors, including site hydrogeological conditions, pollutant distribution, physical and chemical properties of pollutants, groundwater chemical characteristics, required remediation time and economic feasibility. The design steps of permeable reactive walls can be summarized into the following six stages: (1) Preliminary assessment of economic and technical feasibility; (2) Investigation of factors such as on-site hydrogeological conditions, pollution conditions and groundwater chemical characteristics; (3) Selection of appropriate permeable reactive wall reaction media based on the chemical and physical properties of pollutants; (4) Design of reasonable thickness, location and permeability coefficient for the permeable reactive wall; (5) Selection of appropriate construction methods; and (6) Development of a monitoring and maintenance plan.

[0003] Fully understanding the on-site hydrogeological conditions is the key to designing a permeable reaction wall. For example, in order to ensure that the permeable reaction wall can be inserted below the aquifer, it is necessary to understand the groundwater level to design a reasonable permeable reaction wall size; the groundwater flow rate in the wall will affect the residence time of pollutants in the reaction medium of the permeable reaction wall, so it is necessary to understand the groundwater hydraulic gradient to design a reasonable permeability coefficient and thickness of the permeable reaction wall according to the residence time; in order to achieve effective treatment of the polluted plume, it is necessary to understand the distribution of pollutant concentrations in groundwater to design a reasonable permeable reaction wall size and plane layout. As a new type of groundwater pollution remediation and treatment technology, the permeable reaction wall technology started late in research and there is no systematic and complete design method. Usually, the most direct permeable reaction wall design method is to conduct field tests or model tests. Therefore, it is very necessary to propose a permeable reaction wall design method that can achieve effective groundwater remediation. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide a design method for permeable reactive walls with different plane layouts based on anti-fouling performance. The method is applied to the selection of permeable reactive wall parameter schemes for in-situ remediation of groundwater in actual cases, in order to provide a certain theoretical reference for the design of permeable reactive walls in actual projects.

[0005] The specific technical solutions adopted by the present invention are as follows:

[0006] Step 1): Construction of mathematical model of pollutant transport

[0007] Considering the migration of pollutants in the permeable reaction wall and aquifer, the mathematical model is as follows:

[0008]

[0009] Where: C A ——concentration of pollutants in the aquifer; C B ——Concentration of pollutants in the permeable reaction wall; D A ——Hydrodynamic diffusion coefficient of pollutants in aquifers; D B ——Hydrodynamic diffusion coefficient of pollutants in permeable reaction wall; λ A ——degradation rate of pollutants in aquifers; B ——degradation rate of pollutants in the permeable reaction wall; v A ——actual velocity of groundwater flow in the aquifer; v B ——actual groundwater flow velocity in the permeable reaction wall; x——the distance that pollutants migrate from the junction of the pollution source and the permeable reaction wall along the direction of maximum groundwater flow velocity.

[0010] Step 2): Preliminary design of permeable reactive wall parameters

[0011] According to the type and concentration of pollutants in the groundwater, appropriate reaction materials in the wall are selected; the layout of the permeable reaction wall is determined according to the groundwater flow direction, flow velocity, aquifer thickness and distribution of pollution sources; and the aquifer scale, permeable reaction wall filling materials, permeability coefficient and thickness are preliminarily designed in combination with the groundwater pollution situation and calculation model.

[0012] The required thickness of the permeable reaction wall when the pollutants at the aquifer monitoring point reach different concentrations can be preliminarily designed using the following formula:

[0013]

[0014]

[0015] ——Ratio of pollutant concentration at the monitoring point in the aquifer to the initial source concentration; L B ——thickness of permeable reaction wall; L A ——The distance between the permeable reaction wall and the aquifer monitoring point; n A ——porosity of aquifer; n B ——porosity of permeable reactive wall; S——shape factor of permeable reactive wall system; Q A ——flow through the aquifer; Q B——Flow through a permeable reactive wall.

[0016] Step 3): Evaluation of the service performance of the permeable reactive wall

[0017] When the pollutant concentration at the aquifer monitoring point is less than or equal to the maximum pollutant concentration allowed by the environmental quality standards, the goal of controlling the spread of the pollution plume is achieved; when the pollutant concentration at the pollution source is less than or equal to the maximum pollutant concentration allowed by the environmental quality standards, the goal of in-situ remediation of groundwater is achieved.

[0018] After completing the construction of the mathematical model of pollutant migration in the permeable reaction wall and aquifer and the preliminary setting of parameters, the service performance of the preliminarily designed permeable reaction wall was evaluated by calculating the distribution of pollutant concentrations in the aquifer and the restoration time of the pollution source, combined with the control objectives and restoration objectives:

[0019] Step 3.1): Calculation method for the distribution of pollutant concentrations in aquifers

[0020] The pollutant concentration at each location in the aquifer after the pollution plume passes through the permeable reaction wall is calculated as follows:

[0021]

[0022] Where: ——Ratio of the pollutant concentration in the aquifer to the initial source concentration; C S ——pollutant concentration at the pollution source; X A —dimensionless distance in the aquifer;

[0023] Step 3.2): Calculation method for pollution source repair time

[0024] The restoration time required for the pollutant concentration at the pollution source to reach the restoration target is calculated as follows:

[0025]

[0026] Where: t——pollution source repair time; λ s ——the natural decay rate of pollutants at the pollution source; f ——The decay rate of pollutants at the pollution source caused by the pollutants entering the permeable reaction wall; C T —— Pollutant remediation target concentration; ——The ratio of the target concentration of pollutants to be repaired at the pollution source to the initial source concentration; A——The surface area of ​​the permeable reaction wall that receives the mass flux of pollutants; V——The water content of the area enclosed by the permeable reaction wall.

[0027] Step 4): Design solution confirmed

[0028] In order to compare the service performance of the permeable reactive wall under different permeable reactive wall parameter values, the pollutant concentration at the aquifer monitoring point after the pollution plume passes through the permeable reactive wall with different thicknesses is calculated according to step 3.1. According to the calculation results, the relationship between the pollutant concentration at the aquifer monitoring point and the thickness of the permeable reactive wall under different permeable reactive wall parameter values ​​can be obtained. The remediation target concentration is determined according to the "Groundwater Quality Standard" (GB / T14848-2017). According to step 3.2, the pollution source remediation time under different permeable reactive wall parameter values ​​is further compared by calculation;

[0029] On the premise of meeting both the control objectives and the restoration objectives, the economic and efficiency factors are comprehensively considered to determine the optimal parameter value combination of the permeable reactive wall and obtain the best design scheme of the permeable reactive wall.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention proposes a permeable reaction wall design scheme that can simultaneously meet the restoration goals of both the pollution source and the aquifer; by calculating the relationship between the pollution source restoration time and the thickness of the permeable reaction wall and the pollutant concentration in the aquifer, the present invention can simultaneously consider economic benefits and work efficiency during the permeable reaction wall design process, and obtain the optimal parameter value combination of the permeable reaction wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic flow chart of the design method of the present invention;

[0033] Figure 2 is a schematic cross-sectional view of a calculation model of a permeable reactive wall in an embodiment;

[0034] Figure 3 is a schematic plan view of a calculation model of a permeable reactive wall in an embodiment;

[0035] Figure 4 is a graph showing the relationship between the thickness of the permeable reaction wall and the pollutant concentration at the monitoring point of the aquifer obtained according to the calculation in the embodiment;

[0036] The reference numerals in the figure are: permeable reaction wall 1, impermeable barrier wall 2, aquifer 3, pollution source 4, groundwater flow 5, aquiclude 6 and aquifer monitoring point 7. DETAILED DESCRIPTION

[0037] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0038] Example

[0039] like Figure 2 As shown, it is a schematic diagram of a calculation model of a design method of a permeable reactive wall with different plane layout types based on anti-fouling performance, the model includes a permeable reactive wall 1, an impermeable barrier wall 2, an aquifer 3, a pollution source 4, a groundwater flow 5, an aquiclude 6 and an aquifer monitoring point 7;

[0040] like Figure 3 As shown, the permeable reaction wall 1 is arranged in the direction of maximum velocity of the groundwater flow 5, and the impermeable barrier wall 2 is used in other directions to separate the pollution source 4 and the aquifer 3;

[0041] This example uses dichloromethane as a pollutant in groundwater to further illustrate the concept of the present invention:

[0042] like Figure 3 As shown in the figure, the design method of permeable reaction wall with different plane layout types based on anti-fouling performance is implemented in four steps. Step 1 is to construct a mathematical model of pollutant migration in the permeable reaction wall 1 and the aquifer 3, and determine the migration parameters of the pollutant dichloromethane in the permeable reaction wall 1 and the aquifer 3, the concentration of the initial pollution source 4 of the pollutant dichloromethane, the scale and thickness of the aquifer 3, etc.; Step 2 is the preliminary design of the parameters of the permeable reaction wall 1, and the preliminary design of the parameters such as the layout type of the permeable reaction wall 1, the wall reaction material, and the wall permeability coefficient are performed; Step 3 is to evaluate the service performance of the permeable reaction wall 1, by calculating the distribution of pollutant concentrations in the aquifer 3 and the restoration time of the pollution source 4, and evaluating the service performance of the preliminarily designed permeable reaction wall 1 in combination with the control target and the restoration target; Step 4 is to determine the design scheme of the permeable reaction wall 1, and on the premise of meeting the control target and the restoration target at the same time, comprehensively consider the two factors of economy and efficiency, determine the optimal parameter value combination of the permeable reaction wall, and obtain the best design scheme of the permeable reaction wall.

[0043] Step 1: If Figure 1 As shown, the calculation model of the present invention includes a permeable reaction wall 1, an impermeable barrier wall 2, an aquifer 3, a pollution source 4, a groundwater flow 5, an aquiclude 6 and an aquifer monitoring point 7. Specific working conditions and parameter values: Natural attenuation rate of dichloromethane in pollution source 4 λ s =0.001d -1 ; Porosity of permeable reaction wall 1 n B =0.4; diffusion coefficient D in permeable reaction wall 1 0B =9.42×10 -5 m 2 / d; diffusion of permeable reaction wall 1 α = 0.01; bending factor of permeable reaction wall 1 τ B =0.5; distance L from permeable reaction wall 1 to aquifer outlet boundary A=50m; hydraulic gradient i in permeable reaction wall 1 = 0.01; groundwater velocity v in aquifer 3 A =0.1; porosity of aquifer 3 n A =0.4; diffusion coefficient of aquifer 3 D 0A =9.42×10 -5 m 2 / d; aquifer 3 dispersion α = 3; aquifer 3 bending factor τ A =0.5; Dichloromethane degradation rate λ in aquifer 3 A =0.001d -1 .

[0044] According to the investigation of relevant domestic pollution sites, the present invention uses dichloromethane as the pollutant, and its initial source concentration C S By investigating the actual concentration of dichloromethane in domestic contaminated sites, 25000 μg / L was selected as the initial source concentration. The remediation target concentration C at 4 pollution sources and 7 aquifer monitoring points T According to the Class III standard of Groundwater Quality Standard (GB / T14848-2017), it is formulated as C T =60μg / L.

[0045] Step 2: Preliminary design of permeable reactive wall parameters

[0046] According to the distribution of pollutants, the shape factor of the permeable reaction wall 1 is set to S = 4; Fe-

[0047] Ni / Al2O3 is used as the reaction material in the permeable reaction wall 1, and the degradation rate of dichloromethane is λ B =23.76d -1 ; According to the thickness of the aquifer 3 and the shape parameter of the pollution source 4 A / V = 0.125; the permeability coefficient of the permeable reaction wall 1 is preliminarily set to K = 100m / d, and the thickness of the permeable reaction wall 1 is calculated according to formulas (3) to (5): B =0.6m.

[0048] Step 3: Evaluate the service performance of the permeable reactive wall 1

[0049] After preliminary design of the parameters of the permeable reaction wall 1, the relationship between the thickness of the permeable reaction wall and the pollutant concentration at the monitoring point of the aquifer was calculated by formulas (6) to (11). It was determined that when the permeability coefficient K = 100 m / d, the thickness of the permeable reaction wall should be 0.6 m. Then, according to formulas (12) to (14), the corresponding pollution source repair time was calculated to be 94 days.

[0050] Step 4: Determine the design

[0051] Further comparison is made when the permeability coefficient of the permeable reaction wall is 150 and 200 m / d. According to step 3, the relationship between the thickness of the permeable reaction wall and the pollutant concentration at the monitoring point of the aquifer under different parameter values ​​is obtained, as shown in Figure 2. Figure 4 As shown in the figure, the required thickness of the permeable reaction wall is 0.9 and 1.2 m respectively. Further calculation shows that the pollution source repair time is 66 and 51 days respectively. According to the above calculation results, if economic benefits are given priority, the permeable reaction wall permeability coefficient K = 100 m / d and thickness L B =0.6m design; if work efficiency is given priority, a permeable reaction wall with a permeability coefficient of K = 200m / d and a thickness of L B =1.2m design plan.

[0052] The calculation model used in the design process of the present invention mainly considers the migration of pollutants in the permeable reaction wall and the aquifer, and comprehensively plans and optimizes the main relevant factors in the permeable reaction wall design in stages, designs various parts of the permeable reaction wall, such as wall reaction materials, wall thickness, wall permeability coefficient, wall layout type, etc., and considers whether the pollutant concentrations at the pollution source and the aquifer monitoring point meet the standards at the design stage, and uses the repair time at the pollution source as an evaluation index to obtain the optimal design parameter combination of the permeable reaction wall. Compared with the traditional permeable reaction wall design method, the design method adopted by the present invention can consider different factors such as wall layout types and aquifer influences to cope with different groundwater pollution situations, and can obtain the permeable reaction wall parameter value combination with the best service performance under different working conditions and obtain the corresponding repair time, and the design method is reliable.

[0053] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A design method for permeable reactive walls with different plane layouts based on antifouling performance, characterized in that The following steps are involved: S1: Construct a mathematical model of pollutant transport based on the transport of pollutants in permeable reaction walls and aquifers with different layouts; S2: Based on the mathematical model of pollutant migration, a quantitative expression of the thickness of the permeable reaction wall and the pollution source repair time is proposed to make a preliminary design of the permeable reaction wall; S3: Based on the pollutant transport mathematical model and the preliminary design results of the permeable reactive wall parameters, the required permeable reactive wall thickness and pollution source repair time are calculated, and the service performance of the preliminarily designed permeable reactive wall is evaluated in combination with the control objectives and repair objectives; S4: Based on the distribution of pollutant concentrations in the aquifer obtained by permeable reaction walls of different thicknesses, a relationship diagram between the pollutant concentration at the monitoring point of the aquifer and the thickness of the permeable reaction wall under different permeable reaction wall parameter values ​​is obtained, and the remediation target concentration is determined according to industry specifications, and then the pollution source remediation time under different permeable reaction wall parameter values ​​is further compared; on the premise of simultaneously meeting the control target and the remediation target, the optimal parameter value combination of the permeable reaction wall is determined to obtain the best design scheme of the permeable reaction wall; The pollutant transport mathematical model is as follows: Where: C A —Concentration of pollutants in aquifers; C B —Concentration of pollutants in permeable reaction wall; D A —Hydrodynamic diffusion coefficient of pollutants in aquifers; D B —Hydrodynamic diffusion coefficient of pollutants in permeable reaction wall; A —Degradation rate of pollutants in the aquifer; B —Degradation rate of pollutants in the permeable reactive wall; v A —actual velocity of groundwater flow in the aquifer; v B —actual groundwater flow velocity in the permeable reaction wall; x—the distance that the pollutant migrates from the junction of the pollution source and the permeable reaction wall in the direction of maximum groundwater flow velocity; The permeable reaction wall thickness refers to the permeable reaction wall thickness required when the pollutants at the monitoring point of the aquifer reach different concentrations. The calculation method is as follows: C p R —Ratio of pollutant concentration at the monitoring point in the aquifer to the initial source concentration; L B —Thickness of permeable reaction wall; L A —The distance between the permeable reaction wall and the aquifer monitoring point; n A —Porosity of aquifer; n B — porosity of permeable reactive wall; S—shape factor of permeable reactive wall system; Q A —flow through the aquifer; Q B —Flow through permeable reaction walls; The distribution of pollutant concentration in the aquifer refers to the pollutant concentration at various locations in the aquifer after the pollution plume passes through the permeable reaction wall. The calculation method is as follows: Where: C A R —Ratio of the pollutant concentration in the aquifer to the initial source concentration; C S — Pollutant concentration at the pollution source; X A —dimensionless distance in the aquifer; The pollution source repair time refers to the repair time required for the pollutant concentration at the pollution source to reach the repair target. The calculation method is as follows: Where: t—pollution source repair time; λ s —Natural decay rate of pollutants at pollution sources; λ f —The decay rate of pollutants at the source due to the entry of pollutants into the permeable reaction wall; C T — Pollutant remediation target concentration; C T R —Ratio of the target concentration of pollutant remediation at the pollution source to the initial source concentration; A—Surface area of ​​the permeable reaction wall receiving the mass flux of pollutants; V—Water content of the area enclosed by the permeable reaction wall; —Peclet number; The industry standards include GB / T14848-2017 "Groundwater Quality Standards".

2. The permeable reactive wall design method according to claim 1, characterized in that: The step S2 is specifically as follows: selecting the reaction material in the wall according to the type and concentration of pollutants in the groundwater, determining the layout type of the permeable reaction wall according to the groundwater flow direction, flow velocity, aquifer thickness and distribution of pollution sources, and making a preliminary design of the aquifer scale, permeable reaction wall filling material, permeability coefficient and thickness in combination with the groundwater pollution situation and the mathematical model of pollutant migration.

3. The permeable reactive wall design method according to claim 1, characterized in that: In step S3, when the pollutant concentration at the aquifer monitoring point is less than or equal to the maximum pollutant concentration allowed by the environmental quality standards, the goal of controlling the spread of the pollution plume is achieved; when the pollutant concentration at the pollution source is less than or equal to the maximum pollutant concentration allowed by the environmental quality standards, the goal of in-situ remediation of groundwater is achieved.

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