Study of Petroleum Hydrocarbons under Chemical-Biological Degradation in Contaminated Soils

Microbial decontamination of petroleum-polluted soils has been recognized to be an efficient, economical and versatile alternative for physical or chemical treatments. In this study, different components of petroleum in contaminated soil were investigated under optimal environmental conditions which were determined by previous experiments. An aerobic bacteria with the ability to utilize both hydrocarbons and benzene as carbon sources was identified as Flavobacterium sp. based on morphological, physiological and biochemical tests. The results demonstrate a 39.88% removal rate for total petroleum hydrocarbons over a period of 27 days. Different fractions of the petroleum were observed to be degraded incongruently. The degradation rate declines with increasing alkane chain length (carbon number). It was found that the total degradation rate can be approximated by the degradation rate of the n-alkane with 23 carbon atoms. N-alkanes with carbon number lower than 23 were removed faster than the total hydrocarbon amount, and the reverse trend was observed for n-alkanes with carbon number higher than 23. Unlike n-alkanes, the degradation rate of total iso-alkanes can be simulated by that of with iso-alkanes with 19 carbon atoms. The benzene utilization studies with the bacteria species showed that it metabolizes benzene when benzene concentration is under 10 mg/L, concentrations over which turn out to be inhibitory. The optimal conditions for effective removal of benzene by this species appear to be 30degC, pH of 6.5-6.7, inoculum concentration of 10% (v/v).