Anaerobic Biodegradation Of Benzene Under Environmental Conditions Of Sub -Arctic Groundwaters

Abstract

This research was conducted to detect and understand the potential for anaerobic degradation of benzene in a sub-arctic aquifer environment. The major hypothesis tested in this dissertation is that indigenous microorganisms from anaerobic groundwater wells contaminated with BTEX (benzene, toluene, ethylbenzene, xylenes) can use benzene as a carbon or energy source under conditions favoring iron- and sulfate-reduction and methanogenesis. To test this hypothesis microcosms were prepared and incubated under anaerobic conditions, with either hematite (Fe2O3) or sodium sulfate (Na2SO4) added to permit growth of iron and sulfate reducing bacteria. Several concentrations of benzene were used as a substrate, and the microcosms were incubated at temperatures of 21�C and 4�C. Cell counts were done and some characteristics of the bacteria, such as shape, gram staining, and spore formation were determined. The aromatic hydrocarbon benzene, was anaerobically transformed under both psychrophilic (4�C) and mesophilic (21�C) conditions. The temperature and substrate concentration played a role in determining the rate at which benzene was biodegraded under conditions favorable to iron-reducing, sulfate-reducing, or methanogenic bacteria. The rate of degradation under conditions favoring methanogenesis was faster than that under iron and sulfate-reducing conditions at 4�C, but not at 21�C. In general, at 21�C the biodegradation of benzene was faster in the presence of an exogenous electron acceptor. Benzene degraded completely under iron and sulfate-reducing conditions but did not degrade completely in most of the microcosms under methanogenic conditions. Phenol and was detected as intermediates for this transformation under all conditions. Benzene degradation rates were independent of the electron acceptor. This suggests that removal of benzene was initiated via fermentation reactions occurring under all conditions. Addition of a small concentration of sulfate or ferric as electron acceptors made degradation more complete. The in vitro research conducted on the anaerobic biodegradation of benzene provided new insight into the anaerobic degradation processes that occur at cold temperatures associated with sub-arctic environments. It also provided insights of the roles different types of microorganisms may play in the natural attenuation of contaminants.