A comprehensive evaluation method for the long-term antifouling performance of clay-based isolation walls in landfills

Abstract

The present invention relates to the field of underground environmental pollution prevention and control in landfills, and specifically to a comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills, comprising the following steps: S1, preparing multiple proportions of clay-based isolation wall materials; S2, designing a test based on the long-term anti-fouling performance of the clay-based isolation wall, and obtaining the physicochemical parameters of the clay-based isolation wall materials through the test; S3, setting screening conditions based on the physicochemical parameters, and using the screening conditions to evaluate and screen the multiple proportions of clay-based isolation wall materials to obtain clay-based isolation wall materials with long-term effective anti-fouling performance. The comprehensive evaluation method provided by the present invention comprehensively considers the permeability of the clay-based isolation wall, its chemical compatibility with pollutants, and the blocking time of the isolation wall for pollutants, and more comprehensively judges the long-term anti-fouling performance of the clay-based isolation wall in the landfill, ensuring that the screened materials can meet the long-term anti-fouling requirements, thereby greatly improving the accuracy and reliability of the evaluation.

Description

Technical Field

[0001] The present invention relates to the field of underground environmental pollution prevention and control in landfills, and in particular to a comprehensive evaluation method for the long-term anti-pollution performance of clay-based isolation walls in landfills. Background Art

[0002] With the accelerated pace of industrialization and urbanization in China, the production of municipal solid waste (MSW) is increasing. Landfills are the primary method of disposal in my country. Through long-term physical, chemical, and biological reactions, MSW produces large quantities of leachate containing high concentrations of pollutants. Leakage of this leachate can severely pollute the environment. Therefore, it is necessary to construct anti-seepage systems around landfills. Clay-based isolation walls are widely used in landfill anti-pollution projects due to their low cost and low permeability.

[0003] At present, most projects only use the single indicator of whether the permeability coefficient meets the anti-seepage requirements as the criterion for determining whether the clay-based isolation wall can be used in landfills. For example, the existing patent CN201911221187.7 discloses a simulation tank test device and test method for underground anti-seepage walls, which intuitively simulates the anti-seepage and anti-fouling performance of different flexible anti-seepage walls under large deformation conditions. Combined with the previous measurement of various engineering properties of wall materials, including slump, compressive strength and permeability coefficient, it can more comprehensively and accurately evaluate the practicality of different materials as anti-seepage walls. The above technical solution simulates the anti-seepage and anti-fouling performance of different anti-seepage walls under large deformation conditions through a simulation tank test device, which can effectively reduce the failure rate of experimental construction of underground anti-seepage walls made of new materials, thereby indirectly saving a lot of economic costs and natural resources. However, the aforementioned simulation tank test device still primarily relies on permeability coefficients for evaluation. Studies have shown that leachate, with its complex composition and high pollutant concentrations, can reduce the chemical compatibility of clay-based isolation walls, increasing their permeability. Furthermore, the migration of pollutants through low-permeability walls is primarily through molecular diffusion, allowing them to migrate outside the walls. These factors, often unaccounted for during actual construction, can reduce the long-term anti-fouling performance of isolation walls, or even lead to their failure, thereby polluting the environment.

[0004] Therefore, it is crucial to comprehensively judge the long-term anti-pollution performance of clay-based isolation walls in landfills by comprehensively considering the permeability of clay-based isolation walls, their chemical compatibility with pollutants, and the blocking time of pollutants by the isolation walls, in order to accurately evaluate the service life of clay-based isolation walls. Summary of the Invention

[0005] In view of this, the present invention proposes a comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills to solve the problem that the anti-fouling performance evaluation indicators of isolation walls in the existing technology are single and it is difficult to evaluate the long-term anti-fouling performance more comprehensively.

[0006] The technical solution of the present invention is achieved as follows: The present invention provides a comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills, comprising the following steps:

[0007] S1. Prepare clay-based isolation wall materials with multiple proportions;

[0008] S2. Design a test based on the long-term antifouling performance of the clay-based isolation wall and obtain the physicochemical parameters of the clay-based isolation wall material through the test;

[0009] S3. Setting screening conditions according to the physical and chemical parameters, and using the screening conditions to evaluate and screen clay-based isolation wall materials with multiple ratios to obtain clay-based isolation wall materials with long-term and effective anti-fouling performance.

[0010] On the basis of the above technical solution, preferably, in step S1, the isolation wall material includes in-situ foundation soil at the construction site and clay with a particle size of less than 200 mesh, and the isolation wall material meets the slump of 100-150 mm.

[0011] On the basis of the above technical solution, preferably, in step S2, the test includes an indoor permeability test, a chemical compatibility test, a batch adsorption test and a soil column test, and the physicochemical parameters of the clay-based isolation wall material include a permeability coefficient, a chemical compatibility parameter, and a solute migration parameter; the permeability coefficient is obtained according to the indoor permeability test, the chemical compatibility parameter is obtained according to the chemical compatibility test, and the solute migration parameter is obtained according to the batch adsorption test and the soil column test.

[0012] Based on the above technical solution, preferably, in step S2, the chemical compatibility parameters are divided into inorganic pollutant compatibility parameters and organic pollutant compatibility parameters, and the inorganic pollutant penetrant and the organic pollutant penetrant are used to perform a chemical compatibility test on the clay-based isolation wall material.

[0013] On the basis of the above technical solution, preferably, the solute transport parameters include the distribution coefficient, effective diffusion coefficient and mechanical diffusion coefficient of the pollutants between the soil and pore water.

[0014] On the basis of the above technical solution, preferably, in step S3, the screening conditions include a first condition, a second condition and a third condition, the first condition is set based on the permeability coefficient of the clay-based isolation wall material; the second condition is set based on the chemical compatibility of the clay-based isolation wall material; the third condition is set based on the service time of the clay-based isolation wall material in blocking the leakage of pollutants, wherein the service time of the clay-based isolation wall material in blocking the leakage of pollutants is calculated based on the solute migration parameters of the clay-based isolation wall material.

[0015] On the basis of the above technical solution, preferably, in step S3, the first condition is k s ≤1.0×10 -9 m / s,k s The permeability coefficient is obtained from the indoor permeability test.

[0016] On the basis of the above technical solution, preferably, in step S3, the second condition is K i ≤1.0×10 -9 m / s, and K r ≤1.0×10 -9 m / s, K i K is the permeability coefficient of the clay-based isolation wall material measured after penetration by the inorganic pollutant solution, r It is the permeability coefficient of the clay-based isolation wall material measured after penetration by the organic pollutant solution.

[0017] On the basis of the above technical solution, preferably, in step S3, the third condition is the service time of the clay-based isolation wall material in blocking the leakage of pollutants, and the service time meets the required years of construction design. The service time is calculated by establishing a one-dimensional convection-diffusion control equation based on the solute migration parameters of the clay-based isolation wall material, and the one-dimensional convection-diffusion control equation is used to simulate the penetration curve of pollutants in the clay-based isolation wall material.

[0018] The comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills of the present invention has the following beneficial effects compared with the prior art:

[0019] (1) The present invention provides a comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills. By comprehensively considering the permeability of the clay-based isolation walls, the chemical compatibility with pollutants, and the blocking time of the isolation walls for pollutants through indoor permeability tests, chemical compatibility tests, batch adsorption tests, soil column tests, and numerical calculations, the method provides a more comprehensive assessment of the long-term anti-fouling performance of clay-based isolation walls in landfills, ensuring that the selected materials meet the long-term anti-fouling requirements in all aspects, thereby greatly improving the accuracy and reliability of the evaluation.

[0020] (2) By introducing a one-dimensional convection-diffusion control equation to simulate the penetration curve of pollutants in clay-based isolation wall materials, this method can accurately predict the long-term service performance of isolation wall materials in blocking pollutant leakage. This long-term performance prediction based on a theoretical model greatly improves the scientific nature and foresight of the evaluation method, and provides a reliable basis for the selection and design of isolation wall materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a flow chart of the comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills according to the present invention;

[0023] Figure 2 Schematic diagram of the change in permeability of the isolation wall material after infiltration by an inorganic polluting liquid (CaCl2 solution) in Example 1 of the present invention;

[0024] Figure 3 This is a schematic diagram of the change in permeability of the isolation wall material after penetration by organic pollutant liquid (COD) in Example 1 of the present invention;

[0025] Figure 4 This is a schematic diagram of the breakdown time of the heavy metal pollutant Cd at a depth of 1 m in the isolation wall according to Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, the present invention provides a comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills, comprising the following steps:

[0028] S1. Prepare clay-based isolation wall materials with multiple proportions;

[0029] S2. Design a test based on the long-term antifouling performance of the clay-based isolation wall and obtain the physicochemical parameters of the clay-based isolation wall material through the test;

[0030] S3. Setting screening conditions according to the physical and chemical parameters, and using the screening conditions to evaluate and screen clay-based isolation wall materials with multiple ratios to obtain clay-based isolation wall materials with long-term and effective anti-fouling performance.

[0031] In the present invention, through systematic material preparation, permeability testing and chemical compatibility evaluation, a clay-based isolation wall material ratio that not only meets construction requirements but also has good long-term anti-fouling performance is screened out, laying the foundation for subsequent pollutant retention time evaluation and final material selection.

[0032] Furthermore, the isolation wall material includes in-situ foundation soil from the construction site and clay with a particle size of less than 200 mesh, and the formulated isolation wall material meets the slump requirement of 100-150 mm. Specifically, the in-situ foundation soil from the construction site refers to the original soil at the landfill site. Clays include bentonite, attapulgite, kaolin, etc. The particle size is limited to less than 200 mesh to ensure the fineness and uniformity of the material. The slump is an indicator of the fluidity of the mixed material, and a range of 100-150 mm ensures the material has appropriate fluidity and workability.

[0033] Specifically, the clay-based isolation wall material can be prepared in multiple proportions, with clay contents of 10%, 20%, 30%, 40%, 60%, 80%, and 100%, respectively, corresponding to the clay contents of the in-situ foundation soil at the construction site of 90%, 80%, 70%, 60%, 40%, 20%, and 0%, respectively. The above is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention.

[0034] Furthermore, step S2 specifically includes:

[0035] (1) Considering the basic anti-seepage performance of the isolation wall, an indoor permeability test was selected to obtain the permeability coefficient.

[0036] (2) Considering the actual conditions of the landfill, the landfill leachate in the landfill involves inorganic pollutants and organic pollutants, and a chemical compatibility test is selected. The chemical compatibility test includes the chemical compatibility of the isolation wall material with inorganic pollutants and organic pollutants, and obtains the chemical compatibility parameters. Because the pollutants in the leachate will reduce the chemical compatibility of certain clay-based isolation walls (such as anti-seepage materials containing bentonite), the permeability coefficient of the isolation wall will increase, and the chemical compatibility parameters are obtained. The chemical compatibility parameters are the permeability coefficient under inorganic pollutants and the permeability coefficient under organic pollutants, which are mainly used to determine whether the permeability coefficient of the isolation wall material will increase under the penetration of inorganic pollutants or organic pollutants.

[0037] With reference to the results of previous studies on the concentration of pollutants in leachate from typical landfills at home and abroad, we selected CaCl2 solution and glucose solution (COD) as the inorganic pollutant permeate and organic pollutant permeate respectively to conduct permeation tests on the isolation wall materials to analyze the chemical compatibility of the isolation wall materials with organic and inorganic pollutants. In addition, in order to simulate the concentration of pollutants in the worst environment, CaCl2 solution was used as the inorganic pollutant permeate and glucose solution (COD) as the organic pollutant permeate. 2+ The concentrations of COD are designed to be 0 mg / L (deionized water)-40000 mg / L respectively.

[0038] (3) Considering the diffusion and migration of pollutants in landfills, pollutants in landfills migrate in soil and groundwater through a variety of mechanisms, including convection, mechanical diffusion, molecular diffusion and adsorption. Batch adsorption tests and soil column tests can simulate these complex migration processes. Batch adsorption tests and soil column tests are selected to detect and obtain solute transport parameters, among which the solute transport parameters include the distribution coefficient of pollutants between soil and pore water, the effective diffusion coefficient and the mechanical diffusion coefficient. The distribution coefficient reflects the distribution of pollutants between the solid phase and the liquid phase, the effective diffusion coefficient characterizes the diffusion ability of pollutants in porous media, and the mechanical diffusion coefficient describes the diffusion of pollutants caused by uneven fluid velocity.

[0039] Furthermore, in step S3, the screening conditions include a first condition, a second condition and a third condition. The first condition is set based on the permeability coefficient of the clay-based isolation wall material; the second condition is set based on the chemical compatibility of the clay-based isolation wall material; and the third condition is set based on the service time of the clay-based isolation wall material in blocking the leakage of pollutants, wherein the service time of the clay-based isolation wall material in blocking the leakage of pollutants is calculated based on the solute migration parameters of the clay-based isolation wall material.

[0040] In one embodiment, step S3 specifically includes:

[0041] A1. Screen multiple clay-based isolation wall materials according to the first condition. The first condition is set based on the permeability coefficient of the clay-based isolation wall material, that is, the first condition is k s ≤1.0×10 -9 m / s, where k s The permeability coefficient is obtained from the indoor permeability test. The clay-based isolation wall materials that meet the first condition will enter the next step of screening.

[0042] A2. The clay-based isolation wall materials obtained in A1 are screened according to the second condition, which is set based on the chemical compatibility of the clay-based isolation wall materials. Clay-based isolation wall materials that meet the second condition proceed to the next step of screening.

[0043] The second condition is K i≤1.0×10 -9 m / s, and K r ≤1.0×10 -9 m / s, K i K is the permeability coefficient of the clay-based isolation wall material measured after penetration by the inorganic pollutant solution, r It is the permeability coefficient of the clay-based isolation wall material measured after penetration by an organic pollutant solution, wherein the inorganic pollutant solution can be one or more of CaCl2 solution, NaCl solution, NH4Cl solution and other mixed salt solutions, and the organic pollutant solution can be one or more of glucose solution, phenol solution, humic acid solution, landfill leachate, and organic solvent. The present invention does not limit the specific types and concentrations of the organic pollutant solution and the inorganic pollutant solution.

[0044] A3. The clay-based isolation wall materials obtained in A2 were screened based on the third condition: the service life of the clay-based isolation wall material in preventing pollutant leakage. This service life met the design requirements. This service life was calculated by establishing a one-dimensional convection-diffusion governing equation based on the solute transport parameters of the clay-based isolation wall material. The contaminant's penetration curve in the clay-based isolation wall material was simulated using this one-dimensional convection-diffusion governing equation. A heavy metal pollutant was selected as a representative pollutant for studying the retention time of the clay-based isolation wall. Batch adsorption tests and soil column tests were performed to determine the distribution coefficient, effective diffusion coefficient, and mechanical diffusion coefficient of the pollutant between the soil and pore water. A one-dimensional convection-diffusion governing equation was established. These parameters were substituted into the one-dimensional convection-diffusion governing equation. The penetration curve of the heavy metal pollutant in the clay-based isolation wall material was simulated using this convection-diffusion governing equation. The migration characteristics of the representative pollutant in the isolation wall material were analyzed and simulated, thereby evaluating the anti-fouling performance and service life of the clay-based isolation wall.

[0045] In order to obtain an analytical solution for the one-dimensional migration of organic pollutants in stratified media when considering convection-diffusion-adsorption-degradation, the following basic assumptions are made with reference to existing theories and relevant experimental studies: ① The isolation wall material is homogeneous, isotropic, and in a saturated state; ② The migration process of pollutants is one-dimensional and follows Fick's second law; ③ Under the leachate head, the seepage process has reached a stable seepage state; ④ The diffusion coefficient of pollutants is a constant, and the diffusion coefficient does not change with time and space; ⑤ The adsorption of pollutants by isolation wall materials is isothermal linear adsorption, and all have reached an equilibrium state; ⑥ A first-order degradation model is used to consider the impact of degradation on the migration process; ⑦ Considering a single pollutant, the migration modes include convection, molecular diffusion, mechanical dispersion, adsorption and degradation.

[0046] Based on the above assumptions and the law of conservation of mass, the calculation formula for the one-dimensional convection-diffusion control equation of pollutants considering convection, molecular diffusion, mechanical dispersion, adsorption and degradation is:

[0047]

[0048]

[0049]

[0050] Where, is the pollutant mass concentration of the permeate along the X-axis of the isolation wall material at time t, v s is the seepage velocity, k is the permeability coefficient, i is the hydraulic gradient, and n is the soil porosity; ρ d is the dry density of soil particles; D m is the mechanical diffusion coefficient; D * is the effective diffusion coefficient; R d is the retardation factor, K d It is the distribution coefficient of pollutants between soil and pore water.

[0051] The breakdown time, or t in this invention, refers to the time required for pollutants to migrate and break through the anti-pollution and anti-seepage barrier. It should be greater than the service life of the anti-pollution and anti-seepage barrier (the sum of the landfill operation period and the solid waste stabilization period), that is, the required service life of the construction design, which is usually 50 years. The Technical Specification for Geotechnical Engineering of Municipal Waste Sanitary Landfills (CJJ 176-2012) takes the target pollutant concentration outside the outflow wall as C out,10 The ratio C to the original concentration of pollutants C0 out,10 / C0=0.1 corresponding time t 10 is the breakdown time.

[0052] Comprehensive consideration is given to the isolation wall materials that meet the permeability coefficient requirements of the landfill isolation wall, the isolation wall materials that have good chemical compatibility with pollutants, and the materials whose pollutant blocking time meets the service life of the isolation wall, and finally the isolation wall materials that meet the long-term anti-pollution performance requirements of the landfill are screened and determined.

[0053] In another embodiment, step S3 specifically includes:

[0054] B1. Screen multiple clay-based isolation wall materials according to the first condition, which is the same as A1;

[0055] B2. Screening multiple clay-based isolation wall materials according to the second condition, the second condition being the same as B2;

[0056] B3. Screen multiple clay-based isolation wall materials according to the third condition, which is the same as B3;

[0057] B4. Based on the screening results of the first, second, and third conditions, the long-term antifouling performance of the clay-based isolation wall material is determined by a comprehensive evaluation index. The calculation formula for the comprehensive evaluation index includes:

[0058] CEI=W1×S1+W2×S2+W3×S3

[0059]

[0060] If k s ≤1.0×10 -9 m / s, then S1=1; otherwise S1=0

[0061] If Ki≤1.0×10 -9 m / s, then S 2i =1, otherwise S 2i =0;

[0062] If K r ≤1.0×10 -9 m / s, then S 2r =1, otherwise S 2r =0;

[0063] If the service time is greater than or equal to the required years of construction design, then S3 = 1; otherwise, S3 = 0;

[0064] Among them, CEI represents the comprehensive evaluation index, W1 is the weight coefficient of the first condition, and the value of W1 is 0.3-0.4; W2 is the weight coefficient of the second condition, and the value of W2 is 0.3-0.4; W3 is the weight coefficient of the third condition, and the value of W3 is 0.2-0.3; W1+W2+W3=1; S1 is the score of the first condition, S2 is the score of the second condition, S 2i S is the score for inorganic pollutants, 2r is the score of organic pollutants, and S3 is the score of the third condition.

[0065] The CEI value range is 0-1. The closer the CEI is to 1, the better the long-term antifouling performance of the clay-based isolation wall material. The CEI threshold is set at 0.8. Materials above this threshold can be considered to have good long-term antifouling performance.

[0066] The technical solution of the present invention is further illustrated by the following examples.

[0067] Example 1

[0068] This embodiment provides a comprehensive evaluation method for the long-term anti-fouling performance of a clay-based isolation wall in a landfill, comprising the following steps:

[0069] Step 1: Prepare clay-based isolation wall materials:

[0070] The clay-based isolation wall material consists of Fujian standard sand and powdered attapulgite (particle size below 200 mesh). Seven sets of isolation wall material ratios were designed: ① 10 parts attapulgite mixed evenly with 90 parts Fujian standard sand (denoted as C10F90); ② 20 parts attapulgite mixed evenly with 80 parts Fujian standard sand (denoted as C20F80); ③ 30 parts attapulgite mixed evenly with 70 parts Fujian standard sand (denoted as C30F70); ④ 40 parts attapulgite mixed evenly with 60 parts Fujian standard sand (denoted as C40F60); ⑤ 60 parts attapulgite mixed evenly with 40 parts Fujian standard sand (denoted as C60F40); ⑥ 80 parts attapulgite mixed evenly with 20 parts Fujian standard sand (denoted as C80F20); and ⑦ 100 parts attapulgite mixed evenly with 0 parts Fujian standard sand (denoted as C100). They represent clay-based isolation wall materials with attapulgite contents of 10%, 20%, 30%, 40%, 60%, 80% and 100% respectively.

[0071] Tap water was added to seven groups of clay-based isolation wall materials to obtain clay-based isolation wall materials with different attapulgite contents that met the construction requirements of slump (100-150 mm).

[0072] Step 2: Conduct an indoor permeability test to test the permeability of clay-based isolation wall materials with different proportions to obtain the isolation wall material proportion that meets the permeability coefficient requirements of the landfill isolation wall;

[0073] The permeability coefficients k of seven groups of clay-based isolation wall materials with different proportions were determined by a variable head permeability test. The test results are shown in Table 1.

[0074] Table 1 Permeability coefficient of isolation wall materials

[0075] Clay-based isolation wall materials Attapulgite content (%) Permeability coefficient k(m / s) C10F90 10 <![CDATA[5.9×10 -9 ]]> C20F80 20 <![CDATA[3.0×10 -9 ]]> C30F70 30 <![CDATA[6.4×10 -10 ]]> C40F60 40 <![CDATA[4.9×10 -10 ]]> C60F40 60 <![CDATA[2.3×10 -10 <!-- 6 -->]]> C80F20 80 <![CDATA[1.3×10 -10 ]]> C100 100 <![CDATA[9.7×10 -11 ]]>

[0076] It can be seen from Table 1 that when the attapulgite content in the isolation wall material is not less than 30%, the permeability coefficient of the isolation wall is less than 1.0×10 -9 m / s, meeting the permeability coefficient requirements of landfill isolation walls.

[0077] Step 3: Conduct a chemical compatibility test to evaluate the chemical compatibility between the clay-based isolation wall material and the landfill leachate.

[0078] The material ratios that meet the permeability coefficient requirements of the landfill isolation wall in step 2 are selected for chemical compatibility testing. As shown in Table 1, except for C10F90 and C20F80, the remaining isolation wall materials meet the permeability coefficient requirements. In this embodiment, three groups of isolation wall materials, C30F70, C40F60 and C60F40, are selected for chemical compatibility testing.

[0079] The chemical compatibility test of this embodiment focuses on the change of the permeability of the isolation wall material under the penetration of pollutant liquid. CaCl2 solution and glucose solution (COD) are selected as the inorganic pollutant penetration liquid and organic pollutant penetration liquid respectively to conduct the penetration test on the isolation wall material to analyze the chemical compatibility of the isolation wall material with organic pollutants and inorganic pollutants. In addition, in order to simulate the pollutant concentration in the worst environment, CaCl2 solution is used as the inorganic pollutant penetration liquid and glucose solution (COD) as the organic pollutant penetration liquid. 2+ The concentrations of COD were designed to be 0 mg / L (deionized water), 1250 mg / L, 2500 mg / L, 5000 mg / L, 10000 mg / L, 20000 mg / L and 40000 mg / L, respectively.

[0080] Figure 2 The figure shows the change in the permeability of the isolation wall material after penetration by an inorganic pollutant (CaCl2 solution). Figure 3 The figure shows the change of the permeability of the isolation wall material after the penetration of organic pollutant (COD). Figure 2 It can be seen that the influence of inorganic pollutant liquid on the permeability coefficient of the three groups of isolation wall materials is roughly the same. 2+ When the concentration is lower than 10000 mg / L, the permeability coefficient of the isolation wall material does not change much and is still less than 1.0×10 -9 m / s, when Ca 2+ When the concentration is greater than 10000 mg / L, the permeability coefficient of the isolation wall material increases and is greater than 1.0×10 -9 m / s, the isolation wall at this time no longer meets the requirements of the landfill for the isolation wall permeability coefficient, which means that the isolation wall has failed. 2+ When the concentration is less than 10000 mg / L, the isolation wall material has good chemical compatibility with it. 2+ When the concentration exceeds 10,000 mg / L, the chemical compatibility between the isolation wall material and the inorganic pollutant liquid is poor. Therefore, when designing the actual construction, relevant units should also consider the impact of the type and concentration of pollutants in the landfill leachate on the permeability of the isolation wall.

[0081] from Figure 3 It can be seen that the penetration of organic pollutants did not adversely affect the permeability coefficients of the three groups of isolation wall materials in this embodiment. Instead, it reduced the permeability coefficients of the isolation wall materials, indicating that the isolation wall materials in this embodiment have good chemical compatibility with organic pollutants. However, this does not mean that other types of clay-based isolation wall materials will exhibit the same behavior. Therefore, further testing is needed to determine the chemical compatibility of other types of clay-based isolation wall materials.

[0082] Step 3: Conduct batch adsorption tests and soil column tests to calculate the blocking time of pollutants by the clay-based isolation wall and evaluate the anti-pollution performance of the clay-based isolation wall.

[0083] Given that the chemical compatibility of the three groups of isolation wall materials, C30F70, C40F60, and C60F40, with the organic and inorganic pollutants in the landfill leachate is similar in step 3, these three groups of materials are still selected in this step for batch adsorption tests and soil column tests, and the blocking time of these three groups of materials on pollutants is evaluated by calculating the pollutant transport control equation.

[0084] The pollutant composition in landfill leachate is complex. In this case, the heavy metal pollutant Cd was selected as a typical pollutant for studying the retention time of clay-based isolation walls on pollutants. Relevant researchers can also select typical pollutants based on their own needs and the types and characteristics of pollutants in the landfill leachate involved.

[0085] The penetration curve of heavy metal pollutant Cd in clay-based isolation wall materials was simulated by convection-diffusion control equation, and the service time of clay-based isolation wall in blocking the leakage of heavy metal pollutant Cd was analyzed.

[0086] The one-dimensional convection-diffusion governing equation for pollutant transport in the presence of four solute transport processes, namely convection, mechanical dispersion, molecular diffusion, and adsorption, is as follows:

[0087]

[0088]

[0089]

[0090] Among them, v s is the seepage velocity, k is the permeability coefficient, i is the hydraulic gradient, and n is the soil porosity; ρ d is the dry density of soil particles; D m is the mechanical diffusion coefficient; D * is the effective diffusion coefficient; R d is the retardation factor, and Kd is the distribution coefficient of pollutants between soil and pore water.

[0091] Substituting the solute transport parameters (Kd, D*, and Dm) obtained from batch adsorption tests and soil column tests into the convection-diffusion governing equations can effectively simulate the migration characteristics of typical pollutants in isolation wall materials, thereby evaluating the anti-fouling performance and service life of clay-based isolation walls.

[0092] Figure 4Assuming the water head difference h on both sides of the isolation wall is 0.3m, the wall width B is 0.8m, and the isolation wall depth is 30m, the breakdown time of heavy metal pollutants Cd at a depth of 1m in the three isolation walls of C30F70, C40F60 and C60F40 can be seen from the figure. 10 The service life of the barrier is 71, 78, and 100 years, respectively, meeting the service life requirements for the barrier. The service life and breakdown time are calculated based on the specific design requirements of the landfill.

[0093] In summary, after comprehensive evaluation based on the first, second, and third conditions, the clay-based isolation walls C30F70, C40F60, and C60F40 meet the long-term antifouling performance requirements for clay-based isolation walls. This means that clay-based isolation walls with a ratio of 30% attapulgite and 70% Fujian standard sand, 40% attapulgite and 60% Fujian standard sand, and 60% attapulgite and 40% Fujian standard sand meet the anti-seepage requirements. It should be noted that this evaluation in this example only applies to the selected isolation wall material ratios; the long-term antifouling performance of unselected ratios requires specific analysis.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills, characterized by: The following steps are involved: S1. Prepare clay-based isolation wall materials with multiple proportions; S2. Designing a test for the long-term antifouling performance of a clay-based isolation wall and obtaining the physicochemical parameters of the clay-based isolation wall material through the test; in step S2, the test includes an indoor permeability test, a chemical compatibility test, a batch adsorption test, and a soil column test; the physicochemical parameters of the clay-based isolation wall material include a permeability coefficient, a chemical compatibility parameter, and a solute transport parameter; the permeability coefficient is obtained from the indoor permeability test, the chemical compatibility parameter is obtained from the chemical compatibility test, and the solute transport parameter is obtained from the batch adsorption test and the soil column test; S3. Setting screening conditions based on the physicochemical parameters, and using the screening conditions to evaluate and screen clay-based isolation wall materials with multiple ratios to obtain a clay-based isolation wall material with long-term and effective antifouling performance; In step S3, the screening conditions include a first condition, a second condition, and a third condition. The first condition is set based on the permeability coefficient of the clay-based isolation wall material. Clay-based isolation wall materials that meet the first condition enter the second condition screening. The second condition is set based on the chemical compatibility of the clay-based isolation wall material. The clay-based isolation wall material that meets the second condition enters the third condition screening. The third condition is the service time of the clay-based isolation wall material in blocking the leakage of pollutants. The service time meets the required years of construction design. The service time is calculated by establishing a one-dimensional convection-diffusion control equation based on the solute transport parameters of the clay-based isolation wall material, and using the one-dimensional convection-diffusion control equation to simulate the penetration curve of pollutants in the clay-based isolation wall material.

2. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills according to claim 1, characterized in that: In step S1, the isolation wall material includes in-situ foundation soil at the construction site and clay with a particle size of less than 200 meshes, and the isolation wall material meets the slump of 100-150 mm.

3. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills according to claim 1, characterized in that: In step S2, the chemical compatibility parameters are divided into inorganic pollutant compatibility parameters and organic pollutant compatibility parameters, and the inorganic pollutant penetrant and the organic pollutant penetrant are used to perform a chemical compatibility test on the clay-based isolation wall material.

4. The comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills according to claim 1, characterized in that: Solute transport parameters include the distribution coefficient of pollutants between soil and pore water, effective diffusion coefficient and mechanical diffusion coefficient.

5. The comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills according to claim 1, characterized in that: In step S3, the first condition is , The permeability coefficient is obtained from the indoor permeability test.

6. The comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills according to claim 1, characterized in that: In step S3, the second condition is K i ≤1.0×10 -9 m / s, and K r ≤1.0×10 -9 m / s, K i is the permeability coefficient of the clay-based isolation wall material measured after penetration by the inorganic pollutant solution, K r It is the permeability coefficient of the clay-based isolation wall material measured after penetration by the organic pollutant solution.

7. The comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills according to claim 1, characterized in that: The one-dimensional convection-diffusion governing equation is: in, is the pollutant mass concentration of the permeate along the X-axis of the isolation wall material at time t, is the seepage velocity, k is the permeability coefficient, i is the hydraulic gradient, and n is the soil porosity; is the dry density of soil particles; is the mechanical diffusion coefficient; is the effective diffusion coefficient; is the blocking factor, K d It is the distribution coefficient of pollutants between soil and pore water.

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