Intrinsic and enhanced biodegradation of benzene in strongly reduced aquifers

Laboratory microcosm studies were performed to examine intrinsic and enhanced benzene bioremediation using five different sediment and groundwater samples from three deeply anaerobic aquifers sited in northern Netherlands. The influence of addition of nitrate, sulfate, limited amounts of oxygen, and combinations of these electron acceptors was also analyzed. In one of these samples, nitrate addition initiated benzene biodegradation after lag-times of > 70 days. Benzene degradation was initiated in all samples using small amounts of oxygen (25% of the reduction capacity of the aquifer materials). The oxygen required to initiate degradation increased with increasing reduction capacity of the aquifer materials. Under these conditions, initial aerobic benzene oxidation was followed by anaerobic processes that further degrade the formed oxidized intermediates using sulfate and/or iron as electron acceptors. Anaerobic bioremediation of strongly reduced BTEX-contaminated aquifers is often limited by the absence of a microbial community adapted to anoxic benzene degradation. Bioaugmentation with natural benzene degrading microbial consortia, and aerated bioactivated zones are viable remediation methods.