Description
As a result of the need to reduce dependency on imported oil and the complete or partial ban of methyl tert-butyl ether as a fuel oxygenate by several states, ethanol has emerged as a major component of gasoline. Accordingly, the use of ethanol in the U.S. is projected to increase sharply over the coming years. As ethanol becomes a major component of gasoline, it is certain that ethanol will become a major source of groundwater contamination. Ethanol is an organic solvent completely miscible in water and could affect the physicochemical properties of groundwater, soil surface chemistry, and the fate and transport of pollutants, such as heavy-metals, in the subsurface. The principal focus of this research is to investigate the influence of ethanol on the adsorption capacity and desorption kinetics of Cadmium (Cd), Zinc (Zn) and Lead (Pb) on the surface of soil. The adsorption results indicates that with an increase in ethanol content from 0 to 10%, the adsorption capacity (Kf) of Cd, Pb, and Zn on bentonite decreased by approximately 62, 4, and 97%, respectively. Beyond 10%, the Kf value increased significantly by 100, 330 and 1600% for 50% ethanol content for Cd, Pb, and Zn, respectively. Similarly in the case of kaolin, the Kf value of Cd, Pb, and Zn decreased from 0 upto 25% ethanol-water fraction by 62, 22, and 58%, respectively. As the ethanol content increased from 25 to 50%, the adsorption capacity of Cd, Pb, and Zn increased by 54, 4, and 187%, respectively. The results of desorption experiments show that as the ethanol content increased from 0 to 25%, the desorption rate of Cd from the surface of bentonite increased by 924%. The results indicate that the presence of ethanol in groundwater could adversely impact natural attenuation techniques which rely on adsorption to reduce the mass, toxicity, and mobility of heavy-metals in the subsurface to eliminate or lessen the risk to human health and the environment. In addition, the release of an ethanol-gasoline mixture at sites contaminated with heavy-metal compounds could remobilize the contaminants that had already been adsorbed on soil, potentially causing groundwater contamination.
