Cosolvency effect in subsurface systems contaminated with petroleum hydrocarbons and ethanol

In Brazil, most gas stations and terminals store tanks containing hydrated ethanol, gasohol and diesel. In case of spills, it is possible that a high aqueous ethanol concentration can facilitate the transfer of hydrocarbons into the aqueous phase, enhancing contaminant concentrations in groundwater, a process called cosolvency. This study investigates the cosolvency effect of ethanol on the aqueous solubility of mono- and polycyclic aromatic hydrocarbons, and presents a simple log-linear model to predict this effect under equilibrium conditions. Cosolvency experiments were carried out in batch reactors under equilibrium conditions for pure mono- and polycyclic aromatic hydrocarbons, gasohol and diesel. A linear relationship between cosolvency power and Kow was determined, which allows predictions of the increase of aromatic hydrocarbon solubility due to the presence of ethanol. Results indicate that cosolvency would be significant only for high aqueous ethanol concentrations (higher than 10%). Under these conditions, cosolvency may be critical only in cases of large gasohol spills or in simultaneous releases of neat ethanol and other fuels. In this way, the hydrophobic and toxic polycyclic aromatic hydrocarbons (PAHs), that are usually present in minor aqueous concentrations in fuel spills without ethanol, may be dissolved in larger amounts in groundwater.