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EFFECT OF ETHANOL ON THE NATURAL ANAEROBIC BIODEGRADATION OF BENZENE
Citation:
Adair*, C J. AND J T. Wilson*. EFFECT OF ETHANOL ON THE NATURAL ANAEROBIC BIODEGRADATION OF BENZENE. Presented at 16th Annual UST/LUST Nat'l. Conf, New Orleans, LA, March 01 - 03, 2004.
Impact/Purpose:
To inform the public.
Description:
Ethanol is commonly used as a fuel oxygenate. A concern has been raised that the presence 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 may also inhibit natural anaerobic fermentation of BTEX compounds, including benzene. Most work in this area has been done on the effect of ethanol on the supply of electron acceptors. These experiments investigate the effect of ethanol on the natural fermentation of benzene.
Sediment was acquired from aquifers impacted by gasoline spills at five locations in the United States. Ground water at these sites was methanogenic. The sediment was used to construct laboratory microcosms containing approximately 2 mg/liter of benzene, 20 mg/liter of BTEX, and 2,000 mg/liter of ethanol in the pore water. The microcosms were incubated in an anaerobic glove box at room temperature.
The biodegradation of ethanol and benzene followed almost every conceivable pattern in the sediment from the five locations. In microcosms from Vandenberg AFB, California and from Petaluma, California ethanol was completely degraded within 2 months. When ethanol was added to the microcosms, benzene persisted without degradation for the entire period of incubation (20 months in sediment from Vandenberg AFB and 15 months in sediment from Petaluma). In microcosms without ethanol, from both locations, benzene was entirely degraded in 3 months. In sediment from Deer Park, New York ethanol was degraded rapidly; 90% of ethanol was degraded within 2 months and it was completely degraded within 9 months. The presence of ethanol stimulated benzene degradation. In microcosms with ethanol, 80% of benzene was degraded in 6 months, and ethanol was entirely degraded in 13 months. Without ethanol, benzene failed to biologically degrade within 24 months in some of the microcosms. In sediment from Parsippany, New Jersey the ethanol was completely degraded in one month. The rate of benzene degradation was slow. When ethanol was not added to the microcosms, benzene was entirely degraded within 20 months. When ethanol was initially present in the sediment, benzene had not degraded after 25 months of incubation. In sediment from Boca Raton, Florida ethanol was not degraded in 24 months. There was no biodegradation of benzene in microcosms with or without ethanol in 24 months.
If ethanol stops the natural fermentation of benzene in a gasoline spill, the plume of benzene may expand. The University of California at Davis, the California Department of Health, and Research and Development at U.S. EPA are conducting a controlled release study at Vandenberg AFB, California to determine if this possibility is a real concern.