Removal of arsenic from landfill leachate by natural soil adsorption for potential use as a permeable reactive barrier

Abstract

Landfills poses a potential threat to human health and environment due to detrimental effects of toxic pollutants. Leachate is one of the most serious environmental hazards associated with landfills. This study aims to identify the most significant heavy metal pollutant in leachate from landfills in Malaysia and to assess the potential of natural and locally available soil as reactive media for permeable reactive barrier (PRB) systems for leachate treatment. The data collection sites consist of seven landfills in Negeri Sembilan and Melaka. The leachate and soil from the seven landfills were analysed. The analyses of the leachate contamination potentials and environmental impacts of the landfills area involved the investigation of these indexes; quality rating scales (QRS), leachate pollution index (LPI), geo-accumulation index (Igeo), pollution index (PI) and integrated pollution index (IPI). In this study, ten types of locally available soil were screened for their capability to remove arsenic. Batch and column studies were conducted to determine the most effective soil for reactive media in PRB system in terms of adsorption capacity, retention and dispersion properties. Maximum QRS values of arsenic (787) and LPI of 15.28 in Ulu Maasop landfill denoted progressive deterioration of leachate contamination especially in non-sanitary landfills (dumpsites). The difference in IPI values for sanitary (IPI > 1) and for non-sanitary landfill soil (IPI < 1) confirmed advanced decline of the soil quality in non-sanitary landfills. Arsenic was identified as the pollutant of concern based on the contamination potential in leachate and the impacts to the soil in vicinity of the landfill. Ulu Maasop soil (UMS3) was selected based on high arsenic adsorption capacities (0.31 mg/g for initial concentration of 50 mg/L) and also removal of heavy metals in real leachate via batch adsorption test. From column studies, UMS3 soil showed to have retardation factor of 32.7 which may reduce mobility of arsenic in the contaminant plume. Mineral compounds such as hematite, baumite and calcite in UMS3 soil proved to have significant effects on arsenic removal. XPS findings revealed that mechanisms of arsenic adsorption onto UMS3 soil were probably via oxidation, surface complexation and ligand exchange with hydroxyl groups. Hence, UMS3 soil is a good candidate for reactive barrier system proposed for arsenic mitigation in landfill due to its high adsorption capacities, high retention and dispersive characteristics.