Estimation of Hydrocarbon Biodegradation Rates in Gasoline-Contaminated Sediments from Measured Respiration Rates

An open-microcosm method, which is described, was used to determine respiration rates and hydrocarbon biodegradation rates in unsaturated sediments. Bioreactors were filled with sediments known to contain hydrocarbon-degrading microbes; hydrocarbons and oxygen were added periodically; and the reaction rates of hydrocarbons, O sub(2), and carbon dioxide were monitored. Experiments were then conducted to relate hydrocarbon biodegradation rates with O sub(2) and CO sub(2) reaction rates, and the bioreactors were used subsequently to determine CO sub(2) and O sub(2) reaction rates in subsurface sediment samples from a gasoline spill site. The hydrocarbon degradation rates were estimated from the reaction rates and compared to rates determined in the field. Results from the analyses of respiration rates and estimated hydrocarbon biodegradation rates were similar.