Anaerobic Sediments Decrease the Leaching of Trace Metals to Groundwater

The increased deterioration of water resources in Lebanon from progressive urbanization, agricultural activities and development of industries is, according to the natural authorities, a major critical problem by the year 2010. At our study site, at Al-Ghadir River, aqueous solutions containing heavy metals are extensively released from many industries directly to the river. Sediments and soil, at these sites became contaminated with these elements and their potential mobility is of particular concern since downward leaching of the heavy metals may result in the contamination of the groundwater. The objective of the present work was to investigate the bioleaching of heavy metals from the sediments of Al-Ghadir River to underground water using ex-situ column experiments. In order to conciliate the field conditions and the laboratory constraints, we have chosen to experiment the heavy metal leaching from long-term contaminated and non-destructured sediments. Sediments were incubated under anaerobic conditions and enriched with nutrients to stimulate microbial metabolism. The evolution of carbon metabolism and metals leached from the incubated sediment columns were followed over time and the effect of leaching on the distribution of metals as a function of depth was also studied. Results obtained showed that after a phase of mobilization of the heavy metals and which was enhanced by the bacterial activity, the study of the distribution profile of the heavy metals showed that they were highly readsorbed at the surface of the sediment column and their readsorption was found to decrease with depth.