Gasoline and Diesel Oil Biodegradation

Abstract : Fuels are major organic pollutants of soils and ground waters. Persistency of pollutants in the environment depends on the intrinsic biodegradability of constituting hydrocarbons of fuels, on the presence of active microflorae at the polluted areas and on local environmental factors. The intrinsic biodegradability of fuels such as gasoline or diesel oil was determined by using a reference aerobic microflora taken from an urban waste water treatment plant. Gasoline exhibited a high intrinsic biodegradability (96%) but that of a commercial diesel oil was significantly lower (between 60 and 73%). The recalcitrant hydrocarbons of fuels were cycloalkanes and branched alkanes, in particular those having quaternary carbon atoms or consecutive substituting groups on the main carbon chain. In the case of various types of diesel oil, the composition in terms of hydrocarbon structural classes accounted for the diverse biodegradation rates observed. In particular, the biodegradation rate was close to 100% when linear alkanes were most abundant (Fischer-Tropsch diesel oil). The fuel degradation capability was widespread among the environment microflorae tested. Microflorae from polluted soils displayed in general a slightly higher degradation capacity than that of nonpolluted soils. Several mechanisms are involved in the efficiency of microflorae taken from polluted environments: - the presence of microorganisms with specialised metabolic capacities; - the occurrence of cometabolism; - some positive interactions between strains (cooperation). The mechanisms involved in the degradation of recalcitrant hydrocarbons were illustrated in the case of cyclohexane degradation by pure strains.