You are here:
Production of Methane During Anaerobic Degradation of Ethanol in Gasoline
Citation:
WILSON, J. T. AND C. J. ADAIR. Production of Methane During Anaerobic Degradation of Ethanol in Gasoline. Presented at National Tanks Conference, Atlanta, GA, March 18 - 20, 2008.
Impact/Purpose:
Present information at National Tanks Conference.
Description:
Field and laboratory studies show that the natural biodegradation of benzene may be inhibited by the presence of ethanol. Preferential biodegradation of ethanol can consume electron acceptors such as sulfate, nitrate, or oxygen that are needed for BTEX biodegradation. An additional concern has emerged over the anaerobic biodegradation of ethanol in ground water. Methane is the dominant degradation product for ethanol at many sites. At these sites, methane concentrations would be expected to exceed their solubility in water. Attendees will learn how to estimate the quantity of methane that might escape to the vadose zone and present an explosion hazard. Field and laboratory experiments have been conducted to evaluate the effect of ethanol on the natural attenuation of benzene in ground water. The results of a full-scale field study at a site on Vandenberg AFB in California were recently published in Environmental Science & Technology. The study was conducted on groundwater that had been impacted by a spill of motor gasoline. “The University of California at Davis supplemented two flow paths in the aquifer with benzene and benzene plus ethanol. The progression of each plume was recorded. As the ethanol degraded, sulfate was also depleted. Consequently, methanogenic conditions developed in situ. A clearly defined plume of methane was generated and migrated downgradient from the active methanogenic zone.” Numerous laboratory microcosm experiments have been conducted using soil collected from the Vandenberg site as well as others. Microcosms were constructed in an anaerobic glove box and dosed with know concentrations of BTEX and ethanol. Autoclaved control microcosms were also prepared. Microcosms were sampled quarterly and the rates of ethanol removal and the rates of methane production were compared over time. In sediment samples from most of the sites, ethanol was readily degraded to form methane. The results of these experiments will be presented to illustrate the risk imposed by methane production during the anaerobic degradation of ethanol in gasoline at UST sites.