Characterization of biodegradation rates of separated diesel components

Abstract

In situ bioremediation has been successfully applied to a limited number of hydrocarbon contaminated sites (Bragg et al., 1994, Madsen 1991), however, the expanded application of in situ bioremediation has been limited by an inability to accurately predict the time required for remediation (NCR, 1993). Development of predictive models requires data addressing the rates of biodegradation of hydrocarbon compounds and how these rates are influenced by the composition of the hydrocarbon assemblage. Studies with complex mixtures, like whole fuels, have shown that hydrocarbons in petroleum do not follow a simple degradation sequence and the biodegradation rates of specific compounds vary among fuels (Elmendorf, 1994, Mulikins-Phillips and Stewart 1974, Walker et al., 1975). These studies indicate that the interactions between hydrocarbons of different classes influence the rates of biodegradation of specific compounds as well as entire classes. However, without data on the rates of biodegradation of the compounds and classes independent from the complex mixture it is difficult to extrapolate this data to use as a predictive tool for other fuels or as fuel-composition changes due to weathering. The biodegradation of specific compound classes isolated from complex mixtures versus composite hydrocarbon mixtures have not been reported. Three hydrocarbon classes (n-alkanes, branched & cyclic alkanes, and aromatics) were separated from a diesel fuel. The biodegradation rates of each class and specific compounds within each class were quantified over a 35 day period in microcosms that contained one of the three classes as the sole carbon source and in micorcosms that contained an assemblage of the three classes that resembled the original diesel fuel (composite solution). Triplicate microcosms were sampled on experimental days 0, 3, 7, 15, and 35. Microbial populations were quantified by total hetrotrophic plate counts. Hydrocarbon concentrations were quantified by GC/FID and specific compound identification were confirmed by GC/MS. After 35 days, the relative biodegradation for each hydrocarbon class was n-alkanes> aliphatic fraction of composite solution> aromatics> branched & cyclic alkanes> aromatic fraction of composite solution. The biodegradation rates ranged from 200 @g/day to 4,500 @g/day.