Journal of Environmental Sciences 2011, 23(11) 1865–1872 Modeling the influence of ethanol on the adsorption and desorption of selected BTEX compounds on bentonite and kaolin Temesgen Garoma ∗ , Lacy Skidmore Department of Civil, Construction, and Environmental Engineering, San Diego State University, San Diego, CA 92182, USA. E-mail: tgaroma@mail.sdsu.edu Received 24 December 2010; revised 21 March 2011; accepted 05 May 2011 Abstract The influence of ethanol on the adsorption capacity and desorption kinetics of benzene and toluene on bentonite and kaolin through modeling and experimental study was investigated. The results showed that the adsorption capacity of both soils for the target compounds decreased as ethanol content increased. As ethanol content increased from 0 to 50%, the adsorption capacity for benzene and toluene on bentonite decreased from 3.6 to 0.54 μg n+1 /(L n ·g) (by 85%) and 1.91 to 0.01 μg n+1 /(L n ·g) (by 99.5%), respectively. For benzene and toluene adsorption on kaolin, the adsorption capacity decreased by 86.5% (from 0.26 to 0.04 μg n+1 /(L n ·g) and 98.2% (from 0.13 to 0.002 μg n+1 /(L n ·g)), respectively, as ethanol content increased from 0 to 50%. In addition, the desorption rate of benzene and toluene from bentonite decreased by about one order of magnitude as the ethanol increased from 0 to 25% and 0 to 50%, respectively. It can be inferred that ethanol could affect the effectiveness of natural attenuation processes that rely on adsorption to soils as a containment technique for benzene and toluene by retarding the adsorption to soils and remobilizing compounds that had already been adsorbed to soils. Key words: benzene; toluene; ethanol; soil; adsorption; desorption DOI: 10.1016/S1001-0742(10)60653-5 Citation: Garoma T, Skidmore L, 2011. Modeling the influence of ethanol on the adsorption and desorption of selected BTEX compounds on bentonite and kaolin. Journal of Environmental Sciences, 23(11): 1865–1872 Introduction Petroleum products are a major source of groundwater contamination (USEPA, 2010). The main source of this contamination is from leaking underground storage tanks (USTs) (USEPA, 2010; Nadim et al., 2001), which are commonly used to store petroleum products. There are about 607,000 confirmed leaking UST sites in the U.S. (USEPA, 2010). Other causes for groundwater contami- nation by petroleum products are from improper disposal, pipe breaks, and spills at extractions wells, refineries, distribution terminals and during transportation (Nadim et al., 2001). Gasoline, a major petroleum product, consists of a mixture of hydrocarbons that are toxic to humans. Benzene, toluene, ethylbenzene and xylene (BTEX) are monocyclic aromatic hydrocarbons that are found in gaso- line and are highly toxic (USGS, 2010). Human exposure to these compounds can cause kidney and liver dam- age, nervous disorders, and reproductive harm (USDHHS, 2004; Caprino and Togna, 1998). Benzene is also classified as a human carcinogen (Caprino and Togna, 1998; Smith, 1996). Research has shown that benzene is known to cause leukemia and can alter blood cell counts in people below 1 * Corresponding author. E-mail: tgaroma@mail.sdsu.edu part per million exposures (Lan et al., 2004). To protect the public, these compounds must be removed from groundwater before it can be used as a drinking water source. At many contaminated sites, natural attenuation processes which rely on adsorption of the contaminants to soils and biodegradation of the contaminants by mi- croorganisms are employed as containment and treatment techniques. Research has shown that the migration of hydrophobic gasoline components in the subsurface is re- tarded by their adsorption to organic matter in soils (Brown and Burris, 1996; Zhu et al., 2004). The effectiveness of ad- sorption as a natural attenuation processes depends, among other things, on gasoline composition or formulation, soil organic matter, and presence of organic solvents (Chen et al., 2000; Delle, 2001). It is very important to accurately estimate the extent of contaminant removal or containment by natural attenuation processes to make site decisions that are protective of the public and the environment. In particular, this is critical in light of the projected sharp increase in the use of ethanol over the coming years due to its use as fuel and/or fuel oxygenate, replacing methyl tert-butyl ether (MTBE). Ethanol, an organic solvent, is completely miscible in water and could affect the physicochemical properties