Exploring the Theoretical Effects of Landfill based Microplastic Accumulation on the Hydro-Mechanical Properties of Porous Soil Media

In recent years, landfill has emerged as one of the major sources of MPs. The interaction of MPs with the porous soil media beneath landfill is not known. Therefore, through this minireview we make an attempt to explore the theoretical changes in soil hydro-mechanical properties of landfill liner material that are likely to be induced by MPs accumulation. The aim is two-fold: first, we review the current state of the art on characterization of MPs in landfill leachate based on its concentration, polymer type, morphology, and sampling conditions. Second, we discuss the changes in hydro-mechanical properties of porous media brought about by MPs accumulation by considering the changes in phase diagram, unsaturated soil properties and shear strength model. The possible changes in barrier clay due to MPs accumulation is discussed based on “diffused double layer theory”, which include the negative changes that can be brought about by nano-plastics in engineered clay barriers. The last section briefly discusses some possible future research directions that could help in improving current design guidelines for landfill liner system. © 2022 Elsevier B.V

Influence of plasticity and porewater salinity on shrinkage and water retention characteristics of biochar-engineered clays

Funding Information: The first author is grateful for the support by USDOE (United States Department of Education) GAANN (Graduate Assistance in Areas of National Need). The corresponding author acknowledges the startup research grant provided by the School of Engineering, Aalto University for supporting this research work. Publisher Copyright: © 2023 The Authors. Soil Science Society of America Journal published by Wiley Periodicals LLC on behalf of Soil Science Society of America.Clay-engineered barriers might be subjected to soil salinization issues under climate change. A recently emerged desalinization method is achieved by modifying clays using biochar. However, unsaturated soil responses of biochar-engineered clays in saline environments under drought conditions remain unknown. This study aims to investigate soil shrinkage and water retention characteristics of biochar-amended kaolin and bentonite under saline conditions. Soil shrinkage and water retention tests were conducted on clays (with and without biochar addition) with various porewater salinity (i.e., 0%–10%). Physiochemical properties (including zeta potential and porewater pH) were measured to interpret particle–fluid interactions. Shrinkage characteristics of kaolin and bentonite exhibited sensitivity and insensitivity to the porewater salinity, respectively. This phenomenon was explained by hydrogen-sodium ion exchange and deprotonation phenomenon occurring on kaolin and bentonite, respectively. Biochar significantly alleviated the salinity-induced shrinkage of clays by increasing the shrinkage limit of kaolin and bentonite by 6%–14% and 50%–107%, respectively (p < 0.05). This was attributed to the porous structure and hydrophilic functionality of biochar that immobilized sodium ions through ion exchange and protonation reactions. The air entry value of clays significantly increased with porewater salinity and biochar addition due to the reduction of void ratio and enhanced capillarity, respectively. An empirical equation was proposed to predict the shrinkage limit of clay in various saline conditions. It highlighted that the application of biochar-engineered clays could contribute to the desalination and the improvement of resistance to shrinkage damage in hydro-chemical barriers.Peer reviewe

A feasibility study of Indian fly ash-bentonite as an alternative adsorbent composite to sand-bentonite mixes in landfill liner

Multi-layered engineered landfill consists of the bottom liner layer (mainly bentonite clay (B)) upon which the hazardous wastes are dumped. In current practice, sand (S) is mixed with bentonite to mitigate the adverse effects of using bentonite alone in the liner layer. Incorporation of waste and unutilized fly ash (FA) as an amendment material to B has been explored in terms of its hydro-mechanical properties, but not gauged its adsorption potential. Indian subcontinent primarily relies on the thermal power source, and FA dumps have already reached its full capacity. The objective of this study is to explore the adsorption characteristics of four B-FA composite mixes sourced within India, considering Pb2+ as a model contaminant. The effect of fly ash type, fly ash amendment rate and adsorbate concentration was explored in the current study and juxtaposed with B-S mixes, based on 960 batch adsorption tests. Both B-FA and B-S mixes reached equilibrium adsorption capacity within 65 min. At higher adsorbate concentrations (commonly observed in the liner), B-FA mixes exhibited superior adsorption capacity, mainly one mixed with Neyvelli fly ash (NFA). The effect of higher amendment rate had little impact on the adsorption capacity at different concentration, but gradually decreased the percentage removal of Pb2+. The B-S mix showed a drastic decrease in percentage removal at higher adsorbate concentration among all tested mixes. Systematic characterization including geotechnical properties, microstructure and chemical analysis was also done to interpret the obtained results. Both Freundlich and Langmuir models fitted the isotherm data well for all B-FA mixes. The maximum adsorption capacity from the isotherm was correlated to easily measurable Atterberg limits by two empirical relationships