Comprehensive evaluation method for long-term antifouling performance of clay separating wall of refuse landfill

Abstract

The invention relates to the field of underground environmental pollution prevention and control of refuse landfills, in particular to a comprehensive evaluation method for long-term antifouling performance of a clay separating wall of a refuse landfill, which comprises the following steps: S1, preparing clay separating wall materials with multiple proportions; s2, designing a test according to the long-term anti-fouling performance of the clay separation wall, and obtaining physical and chemical parameters of a clay separation wall material through the test; and S3, setting screening conditions according to the physicochemical parameters, and evaluating and screening the clay separation wall materials with multiple proportions by utilizing the screening conditions to obtain the clay separation wall material with long-term effective antifouling performance. According to the comprehensive evaluation method provided by the invention, the permeability of the clay separating wall, the chemical compatibility with the pollutants and the blocking time of the separating wall to the pollutants are comprehensively considered, so that the long-term antifouling property of the clay separating wall of the refuse landfill is more comprehensively judged, and the screened material can meet the long-term antifouling requirement; and the evaluation accuracy and reliability are greatly improved.

Description

Technical Field

[0001] The 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 acceleration of China's industrialization and urbanization, the output of urban domestic waste is increasing. my country mainly disposes of these urban domestic waste by landfill. After long-term physical, chemical and biological reactions, urban domestic waste will produce a large amount of leachate containing high concentrations of pollutants. Once these leachates leak, they will seriously pollute the environment. Therefore, it is necessary to build an anti-seepage system around the landfill. Among them, clay-based isolation walls are widely used in anti-pollution projects in landfills 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 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 scheme 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 above-mentioned simulation tank test device still mainly relies on the permeability coefficient for evaluation. Studies have shown that the composition of garbage leachate is complex and the concentration of pollutants is very high. High-concentration polluted liquid will reduce the chemical compatibility of the clay-based isolation wall and increase the permeability of the isolation wall. In addition, the migration of pollutants in low-permeability walls is mainly molecular diffusion, which can be transported to the outside of the isolation wall through molecular diffusion. These factors that are not considered in actual construction may cause the long-term anti-fouling performance of the isolation wall to decrease, or even cause the isolation wall to fail, thereby polluting the environment.

[0004] Therefore, it is crucial to comprehensively judge the long-term anti-pollution performance of the clay-based isolation wall in the landfill by comprehensively considering the permeability of the clay-based isolation wall, its chemical compatibility with pollutants, and the blocking time of the isolation wall on pollutants, in order to accurately evaluate the service life of the clay-based isolation wall. 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 index of isolation walls in the prior art is single and it is difficult to more comprehensively evaluate the long-term anti-fouling performance.

[0006] The technical solution of the present invention is implemented 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. Designing tests based on the long-term antifouling performance of clay-based isolation walls, and obtaining the physical and chemical parameters of clay-based isolation wall materials through the tests;

[0009] S3. Set screening conditions according to the physical and chemical parameters, and use 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 scheme, preferably, in step S2, the test includes indoor permeability test, chemical compatibility test, Batch adsorption test and soil column test, and the physicochemical parameters of the clay-based isolation wall material include permeability coefficient, chemical compatibility parameters, and solute migration parameters; the permeability coefficient is obtained according to the indoor permeability test, the chemical compatibility parameters are obtained according to the chemical compatibility test, and the solute migration parameters are obtained according to the Batch adsorption test and the soil column test.

[0012] On the basis of the above technical scheme, preferably, in step S2, the chemical compatibility parameters are divided into inorganic pollutant compatibility parameters and organic pollutant compatibility parameters, and the inorganic pollutant permeate and the organic pollutant permeate 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 of pollutants between soil and pore water, the effective diffusion coefficient and the mechanical diffusion coefficient.

[0014] On the basis of the above technical scheme, 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] Based on the above technical solution, preferably, in step S3, the first condition is k s ≤1.0×10 -9 m / s,k s This is the permeability coefficient obtained from the indoor permeability test.

[0016] Based on 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 the inorganic pollutant solution penetrates. r It is the permeability coefficient of the clay-based isolation wall material measured after penetration by organic pollutant solution.

[0017] On the basis of the above technical scheme, 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 transport 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 antifouling 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 comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills provided by the present invention comprehensively considers the permeability of clay-based isolation walls, chemical compatibility with pollutants, and the blocking time of pollutants by the isolation walls through indoor permeability tests, chemical compatibility tests, batch adsorption tests, soil column tests, and numerical calculations, so as to more comprehensively judge the long-term anti-fouling performance of clay-based isolation walls in landfills, ensure that the selected materials can meet the long-term anti-fouling requirements in all aspects, and greatly improve 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

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

[0023] Figure 2 Example 1 of the present invention is an inorganic polluted liquid (CaCl 2 Schematic diagram of the change in the permeability of the isolation wall material after the penetration of the solution;

[0024] Figure 3 This is a schematic diagram of the change in the 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 described embodiments 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 creative work 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. Designing tests based on the long-term antifouling performance of clay-based isolation walls, and obtaining the physical and chemical parameters of clay-based isolation wall materials through the tests;

[0030] S3. Set screening conditions according to the physical and chemical parameters, and use 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 performance testing and chemical compatibility evaluation, a clay-based isolation wall material ratio that not only meets the construction requirements but also has good long-term anti-fouling performance is screened out, laying the foundation for subsequent pollutant blocking time evaluation and final material selection.

[0032] Furthermore, the isolation wall material includes the original foundation soil at the construction site and clay with a particle size of less than 200 mesh, and the prepared isolation wall material meets the slump of 100-150 mm. Specifically, the original foundation soil at the construction site refers to the original soil at the landfill site. Clay includes bentonite, attapulgite, kaolin, etc. The fineness and uniformity of the material are ensured by limiting the particle size to less than 200 mesh. The slump is an indicator to measure the fluidity of the mixed material. The range of 100-150 mm ensures that the material has appropriate fluidity and workability.

[0033] Specifically, the clay-based isolation wall materials prepared in multiple proportions can have clay contents of 10%, 20%, 30%, 40%, 60%, 80% and 100%, respectively, and the corresponding contents of the original foundation soil at the construction site are 90%, 80%, 70%, 60%, 40%, 20% and 0%, respectively. The above are only preferred embodiments of the present invention and are 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) Taking into account the actual conditions of the landfill, the landfill leachate contains inorganic and organic pollutants, so a chemical compatibility test is selected. The chemical compatibility test includes the chemical compatibility of the isolation wall material with inorganic and organic pollutants to obtain chemical compatibility parameters. This is because the pollutants in the leachate will reduce the chemical compatibility of certain clay-based isolation walls (such as anti-seepage materials containing bentonite), increase the permeability coefficient of the isolation wall, and obtain chemical compatibility parameters. The chemical compatibility parameters are the permeability coefficient under inorganic pollutants and the permeability coefficient under organic pollutants. They are mainly used to determine whether the permeability coefficient of the isolation wall material will increase under the penetration of inorganic or organic pollutants.

[0037] Referring to the results of previous studies on the concentration of pollutants in leachate from typical landfills at home and abroad, we selected CaCl 2Solution and glucose solution (COD) were used as inorganic pollutant permeate and organic pollutant permeate to conduct 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, Ca 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 test and soil column test can simulate these complex migration processes. Batch adsorption test and soil column test 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, effective diffusion coefficient and mechanical diffusion coefficient. The distribution coefficient reflects the distribution of pollutants between solid phase and 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; 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 transport 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 material obtained in A1 is screened according to the second condition. 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 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 the inorganic pollutant solution penetrates. r is the permeability coefficient of the clay-based isolation wall material measured after penetration by an organic pollutant solution, where the inorganic pollutant solution can be CaCl 2 solution, NaCl solution, NH 4 The organic pollutant solution may be one or more of a Cl solution and other mixed salt solutions; the organic pollutant solution may be one or more of a glucose solution, a phenol solution, a humic acid solution, a landfill leachate, and an 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 are screened according to the third condition, which is the service time of the clay-based isolation wall materials in blocking the leakage of pollutants. The service time meets the years required by the 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 materials, and using the one-dimensional convection-diffusion control equation to simulate the penetration curve of pollutants in the clay-based isolation wall materials. A heavy metal pollutant is selected as a typical pollutant for the study of the blocking time of the clay-based isolation wall for pollutants, and batch adsorption tests and soil column tests are selected to detect and obtain the distribution coefficient, effective diffusion coefficient and mechanical diffusion coefficient of the pollutant between the soil and pore water, establish a one-dimensional convection-diffusion control equation, substitute the above parameters into the one-dimensional convection-diffusion control equation, simulate the penetration curve of heavy metal pollutants in the clay-based isolation wall materials through the convection-diffusion control equation, analyze and simulate the migration characteristics of typical pollutants in the isolation wall materials, and thus evaluate the anti-fouling performance and service time of the clay-based isolation wall.

[0045] In order to obtain the analytical solution of 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 related 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 a 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 mode considers convection, molecular diffusion, mechanical dispersion, adsorption and degradation.

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

[0047]

[0048]

[0049]

[0050] In the formula, 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 blocking factor, K d It is the distribution coefficient of pollutants between soil and pore water.

[0051] The breakdown time, i.e., the moment t in the present invention, refers to the time required for the migration of pollutants to break through the anti-pollution and anti-seepage barrier, which 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), i.e., the required service life of the construction design, which is usually 50 years. The Technical Specification for Geotechnical Engineering of Municipal Solid Waste Sanitary Landfill (CJJ 176-2012) takes the target pollutant concentration C out,10 The original concentration of pollutants C 0 The ratio C out,10 / C 0 = 0.1 corresponding to the time t 10 is the breakdown time.

[0052] Comprehensive consideration is given to isolation wall materials that meet the permeability coefficient requirements of landfill isolation walls, isolation wall materials that have good chemical compatibility with pollutants, and materials that can block pollutants for a time that meets the service life of the isolation wall, and ultimately 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. Screening a plurality of clay-based isolation wall materials according to the first condition, the first condition being the same as A1;

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

[0056] B3, screening multiple clay-based isolation wall materials according to the third condition, the third condition 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 judged by a comprehensive evaluation index, wherein the calculation formula of the comprehensive evaluation index includes:

[0058] CEI=W 1 ×S 1 +W 2 ×S 2 +W 3 ×S 3

[0059]

[0060] If k s ≤1.0×10 -9 m / s, then S 1 =1; otherwise S 1 =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 ≥ the required years of construction design, then S 3 =1; otherwise S 3 =0;

[0064] Among them, CEI represents the comprehensive evaluation index, W 1 is the weight coefficient of the first condition, W 1 The value is 0.3-0.4; W 2 is the weight coefficient of the second condition, W 2 The value is 0.3-0.4; W 3 is the weight coefficient of the third condition, W 3 The value is 0.2-0.3; W 1 +W 2 +W 3 =1;S 1 is the score of the first condition, S 2 is the score of the second condition, S 2i S is the score for inorganic pollutants, 2r S is the score for organic pollutants, 3is the score for the third condition.

[0065] The value range of CEI 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 threshold of CEI is set to 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 embodiments.

[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 is composed of Fujian standard sand and powdered attapulgite (particle size below 200 mesh). A total of seven groups of isolation wall material ratios were designed, namely ① 10 parts of attapulgite and 90 parts of Fujian standard sand are evenly mixed (recorded as C10F90); ② 20 parts of attapulgite and 80 parts of Fujian standard sand are evenly mixed (recorded as C20F80); ③ 30 parts of attapulgite and 70 parts of Fujian standard sand are evenly mixed (recorded as C30F70); ④ 40 parts of attapulgite and 60 parts of Fujian standard sand are evenly mixed (recorded as C40F60); ⑤ 60 parts of attapulgite and 40 parts of Fujian standard sand are evenly mixed (recorded as C60F40); ⑥ 80 parts of attapulgite and 20 parts of Fujian standard sand are evenly mixed (recorded as C80F20); ⑦ 100 parts of attapulgite and 0 parts of Fujian standard sand are evenly mixed (recorded 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, and obtain the isolation wall material proportion that meets the permeability coefficient requirements of the landfill isolation wall;

[0073] The permeability coefficient k of seven groups of clay-based isolation wall materials with different proportions was determined by a variable water 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 requirement 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. It can be seen from Table 1 that, except for C10F90 and C20F80, the other 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 the polluted liquid, and selects CaCl 2 Solution and glucose solution (COD) were used as inorganic pollutant permeate and organic pollutant permeate to conduct 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, Ca 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 It shows that the inorganic contamination liquid (CaCl 2 The change in the permeability of the isolation wall material after the penetration of the solution, Figure 3 The figure shows the change in the permeability of the isolation wall material after penetration by organic pollutant (COD). Figure 2 It can be seen that the influence of inorganic pollutant 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 landfill's requirements for isolation wall permeability, which means that the isolation wall has failed. 2+ When the concentration is less than 10000 mg / L, the chemical compatibility of the isolation wall material is good. 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, the 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 has no adverse effect on the permeability coefficients of the three groups of isolation wall materials in this embodiment, but reduces the permeability coefficients of the isolation wall, indicating that the chemical compatibility of the isolation wall materials in this embodiment with organic pollutants is good. However, it does not mean that other types of clay-based isolation wall materials will have the same change pattern. Therefore, the chemical compatibility of other types of clay-based isolation wall materials should be judged by relevant tests.

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

[0083] Considering that the chemical compatibility of the three groups of isolation wall materials C30F70, C40F60 and C60F40 with the organic and inorganic pollutants in the leachate is similar in step 3, these three groups of materials are still selected in this step for batch adsorption test and soil column test, 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 the study of the blocking time of clay-based isolation walls on pollutants. Relevant researchers can also select typical pollutants according to their own needs and the types and characteristics of pollutants in the leachate of the landfill involved.

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

[0086] The one-dimensional convection-dispersion 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 dis 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 control equation 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 4 It is the breakdown time of heavy metal pollutants Cd at 1m depth of the three isolation walls of C30F70, C40F60 and C60F40, assuming that 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. It can be seen from the figure that the breakdown time t 10 They are 71, 78 and 100 years respectively, which meet the service life requirements of the isolation wall. The service life and breakdown time are calculated according to the specific design requirements of the landfill.

[0093] In summary, after comprehensive judgment of the first condition, the second condition and the third condition, the clay-based isolation walls C30F70, C40F60 and C60F40 meet the long-term antifouling performance of the clay-based isolation walls, that is, the 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 the judgment of this embodiment is only for the selected isolation wall material ratio, and the long-term antifouling performance of the unselected ratio needs to be specifically analyzed.

[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 protection scope 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 tests based on the long-term antifouling performance of clay-based isolation walls, and obtaining the physicochemical parameters of clay-based isolation wall materials through the tests; S3. Set screening conditions according to the physical and chemical parameters, and use 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.

2. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in 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 to 150 mm.

3. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 1, characterized in that: In step S2, the test includes indoor permeability test, chemical compatibility test, batch adsorption test and soil column test, and the physicochemical parameters of the clay-based isolation wall material include permeability coefficient, chemical compatibility parameters, and solute migration parameters; the permeability coefficient is obtained according to the indoor permeability test, the chemical compatibility parameters are obtained according to the chemical compatibility test, and the solute migration parameters are obtained according to the batch adsorption test and soil column test.

4. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 3, 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 permeate and the organic pollutant permeate are used to perform a chemical compatibility test on the clay-based isolation wall material.

5. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 3, characterized in that: Solute transport parameters include the distribution coefficient of pollutants between soil and pore water, effective diffusion coefficient and mechanical diffusion coefficient.

6. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 5, characterized in that: 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.

7. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 6, characterized in that: In step S3, the first condition is k s ≤1.0×10 -9 m / s,k s This is the permeability coefficient obtained from the indoor permeability test.

8. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 6, 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 K is the permeability coefficient of the clay-based isolation wall material measured after the inorganic pollutant solution penetrates. r It is the permeability coefficient of the clay-based isolation wall material measured after penetration by organic pollutant solution.

9. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 6, characterized in that: 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 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.

10. A comprehensive evaluation method for the long-term anti-fouling performance of clay-based isolation walls in landfills as claimed in claim 9, characterized in that: The one-dimensional convection-dispersion governing equation is: in, 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 blocking factor, K d It is the distribution coefficient of pollutants between soil and pore water.

Images