•pH has significant effect on membrane behaviors, especially on alkaline condition.•Acidic solution shows the existence of erosion effect on membrane behaviors.•Bentonite amended Fukakusa clay possess excellent buffer capacity to resist pH change.•Enhancing pH will cause the larger soil cluster and narrower permeable paths.•The mechanisms of the membrane performance change were discussed.Bentonite has been proven to be effective in enhancing the membrane behavior of clay, by which landfill liners can have better barrier performance toward the migration of contaminants. In this study, sodium bentonite amended locally available natural clay (Fukakusa clay) was investigated for its membrane behavior. The chemico-osmotic efficiency coefficient, ω, was obtained under different concentrations of KCl solution (1, 5, 10, and 50 mM) at pH ranging from 4.0 to 11.0. It was found that ω continually decreased as the KCl concentration increased, which is consistent with Gouy–Chapman theory. pH values were found to have a significant effect on membrane behaviors, especially on the alkaline condition. According to the results, the membrane behavior under alkaline condition was 1.2–2.5 times higher than that under acidic conditions. The similarity of membrane behavior between 4.0 and 7.0 reflect the existence, but very slight erosion effect, of acidic solution. It was further found that bentonite amended Fukakusa clay possess excellent buffer capacity to resist pH change. The mechanisms of the membrane performance change were discussed with the assistance of X-ray Diffraction patterns (XRD), free swelling results, X-ray Fluorescence results (XRF), scanning electron microscope (SEM) and camera images.

Well injection depth extraction (WIDE) is used to remediate contaminated fine-grained soil with low hydraulic conductivity. The flow path is short because the prefabricated vertical wells (PVW) are closely installed in the WIDE system. The current analytical solution that considers the infinite extraction boundary is not suitable to describe the close distance between the injection PVWs (IPVW) and the extraction PVWs (EPVW). A Neumann boundary is proposed as an extraction boundary that can reflect the characteristics of the WIDE system. A flux-type boundary is proposed as an injection boundary to meet the requirements for mass conservation. An analytical solution for a simplified planar two-dimensional model of the WIDE system is presented to take into account the proposed extraction and injection boundaries. Moreover, the initial concentration that is exponentially distributed along the depth is taken into account. The results are consistent with those obtained from the finite-difference method and the experimental data. The results indicate that the Neumann boundary is better than the infinite extraction boundary, and the analytical solution with the infinite boundary is a special case of the proposed solution. The proposed analytical solution is relatively simple and can be used for a quick preliminary calculation to evaluate the experimental results and to evaluate more complex numerical methods.

Lysimeters are always utilized to simulate the landfill environmental conditions due to their relatively low expense and the short duration of the research. However, lysimeters tend to be operated with various geometrical characteristics (e.g. height/width ratio and height) which can result in changes to the physical and thermodynamic characteristics, and affect the waste decomposition rates and leaching behavior. Considering these points, in this study, the lysimeter test was conducted using six lysimeters to evaluate the size effect on leachate generation and leaching behavior of construction and demolition waste residue (C&D waste). According to the lysimeter test results, increasing the width of the lysimeter can reduce the potential of side-edge-wall flow, and the filtration water can have a perfect flushing inside lysimeters with shorter lengths. Increasing the height merely results in an increase in upper loading, and results in waste with a denser micro-structure and with closer cohesion at the bottom of the lysimeters, which was not suitable for the leaching out of soluble constituents or heavy metals. The lysimeters with low height/width ratio can promote the leaching behavior and accelerate the dilution of landfill leacahte. In addition, the emission behaviors of some inorganic ions indicate microbial activity can have a significant effect on leaching behavior, which cannot be neglected when researching landfill waste. It is suggested that lysimeters with lower height and a lower H/W ratio are a better choice when investigating leaching behavior or microbial activity. These results contribute to establishing standardized feasible designs for laboratory-scale lysimeter tests.