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KINETICS OF ETHANOL BIODEGRADATION UNDER METHANOGENIC CONDITIONS IN GASOLINE SPILLS
Citation:
Adair*, C J., R. Kolhatkar, AND J T. Wilson*. KINETICS OF ETHANOL BIODEGRADATION UNDER METHANOGENIC CONDITIONS IN GASOLINE SPILLS. Presented at 2003 NGWA Conf. on MTBE, Baltimore, MD, 06/4-6/2003.
Description:
Ethanol is commonly used as a fuel oxygenate. A concern has been raised that biodegradation of ethanol from a spill of gasoline may inhibit the natural biodegradation of fuel hydrocarbons, including benzene. Ethanol is miscible in water, and ethanol is readily metabolized by microorganisms that use a variety of electron acceptors. When gasoline that contains ethanol is spilled, the ethanol may partition to ground water and consume electron acceptors that would otherwise be available for metabolism of benzene and fuel hydrocarbons.
Ethanol can also degrade under methanogenic conditions. If degradation of ethanol to methane is rapid, the ethanol will be degraded in the ground water immediately proximate to the spill, and will have little effect on the supply of soluble electron acceptors in the aquifer surrounding the spill.
Sediment was acquired from aquifers impacted by gasoline spills at six locations in the United States. Ground water at these sites was methanogenic. The sediment was used to construct laboratory microcosms containing 2,000 mg/liter of ethanol in the pore water. The sediments were incubated in an anaerobic glove box. In sediment from Parsippany New Jersey, from Vandenberg AFB California, and from Petaluma California, the first order rate constant for natural biodegradation of ethanol was greater than 0.1 per day, resulting in depletion of ethanol below the detection limit of 10 mg/liter in less than two months. In sediment for Port Hueneme California, the rate of ethanol biodegradation was 0.02 per day, resulting in depletion in ethanol within a year. In sediment form Boca Raton Florida, the rate of ethanol degradation was 0.0001 per year, and ethanol was not depleted during the laboratory study.
When the ethanol degraded, it degraded to completely to methane and carbon dioxide. The fermentation of ethanol to methane and carbon dioxide would be the dominant mechanism of natural ethanol biodegradation at five of the six sites investigated. Electron acceptors would not be consumed. At five of the six sites investigated, a spill of ethanol in gasoline would have had minimal impact on the supply of electron acceptors in the aquifer.