The Fate, Transport and Remediation of the Gasoline Additive Ethanol

摘要

Over the last two decades, methyl tertiary butyl ether (MTBE) and ethanol have been the two most common oxygenate gasoline additives. Due to various environmental issues and socio-political decisions, MTBE use is being reduced in the United States, while ethanol addition to gasoline will soon increase dramatically. This paper reviews the subsurface fate, transport and remediation of the gasoline additive ethanol. Since ethanol is infinitely soluble in water, very high ethanol concentrations may occur locally in groundwater, especially where neat (pure) ethanol is made, or blended with gasoline. Dissolved-phase ethanol has the potential to be quite mobile due to its very low adsorption to soil organic matter, and its very low Henry's Constant. However, ethanol transport with groundwater may be greatly limited by its tendency to readily biodegrade, both aerobically and anaerobically. While ethanol's rapid biodegradation will limit the spread of ethanol plumes, the resulting dissolved oxygen consumption may cause the expansion of associated hydrocarbon plumes (ex: BTEX compounds). Several modeling efforts have predicted that BTEX plumes may increase 10-150% in length, though there is little field data for verification. Such BTEX plume length increases may impact the sites intending to use monitored natural attenuation as a remedial technology. Neat ethanol spills may produce ethanol concentrations in ground water that are high enough to cause increased levels of aromatic hydrocarbons. Also, neat ethanol spills may greatly increase the mobility of previously residual petroleum compounds, which may affect the outcome of risk based corrective action analyses. Therefore, the increased use of ethanol may complicate the transport and remediation of gasoline spills. Unfortunately, field data on ethanol plumes is very limited with only a few sites reporting any dissolved-phase concentration data. The existing literature on the remediation and treatment of ethanol is reviewed. Generally, the biological treatment methods should work very well for ethanol, while the physically-based technologies (air stripping or adsorption) are expected to perform poorly. At the present time, far less field data is available regarding the subsurface fate, transport and remediation of ethanol, than is available for other gasoline compounds (ex: benzene or MTBE).