Leaching ofMetals, Organic Carbon and Nutrients fromMunicipalWaste under Semi-Arid Conditions

A large portion of municipal waste, disposed in landfills, is organic in nature. This organicmaterial starts decomposing soon after the disposal in landfills. The decomposition leads to the generation of in situ leachate, and this leachate can contain substantial amounts of contaminants. Under arid conditions, leachate is solely generated by waste decomposition, as little input of external water occurs due to rain. The objective of this study was to characterize the in situ leachate from typical waste streams in Pakistan. Wecollected fresh municipal solid wastes typical of household, mixed, and restaurant waste, and analyzed the leachates for volume and water quality parameters. The wastes released up to 30% of their initial moisture as leachate and the leachate contained metals, organic carbon, and nutrients at concentrations many times higher than the environmental water quality standards for waste water discharge. As landfill leachate in Pakistan is usually not contained or collected, the in situ leachate is a source of surface and ground water contamination. Methods have to be developed and implemented to prevent leaching of contaminants into underlying soils and sediments, and subsequently into ground and surface waters.