Anaerobic Biodegradation of Alkylbenzenes in Laboratory Microcosms Representing Ambient Conditions

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Abstract
A microcosm study was performed to document the anaerobic biodegradation of benzene, toluene, ethylbenzene, m- xylene, and/or o-xylene in petroleum-contaminated aquifer sediment from sites in Michigan (MI) and North Carolina (NC) and relate the results to previous field investigations of intrinsic bioremediation. Laboratory microcosms, designed to simulate ambient conditions, were constructed under anaerobic conditions with sediment and groundwater from source, mid-plume, and end-plume locations at each site. The general patterns of biodegradation and electron acceptor utilization in the microcosms were consistent with field data. At the MI site, methane was produced after a moderate lag period, followed by toluene degradation in all sets of microcosms. At the NC site, biodegradation of the target compounds was not evident in the source area microcosms. In the mid-plume microcosms, toluene and o-xylene biodegraded first, followed by m-xylene and benzene, a pattern consistent with contaminant decay along the plume length. Chemical extraction of microcosm sediment at the beginning and end of me incubation indicated that iron-reducing conditions were dominant and iron reduction occurred on a sediment fraction not extracted by 0.5N HC1. In the end-plume microcosms, degradation of benzene, toluene, and xylene isomers occurred but was variable between replicates. Consistent with field data, dissolved concentrations of the target contaminant(s) persisted at low but detectable levels (0.05 to 0.25 μM) in microcosms from both sites where biodegradation was measured.