Biotransformation and mineralization of alkylbenzenes under denitrifying conditions

Abstract

Batch microcosm tests were performed with nonacclimated and acclimated aquifer material from Traverse City (MI) to assess the extent of biodegradation of radiolabeled benzene, toluene, ethylbenzene, and xylenes (BTEX), either as single substrates or in a mixture, by indigenous microorganisms under denitrifying conditions. For single substrate studies, the rates and extent of biodegradation of toluene and m-xylene in the acclimated aquifer material were generally similar to those observed in the nonacclimated material. Benzene was recalcitrant in both cases o-Xylene was recalcitrant in the nonacclimated aquifer material, but degradation occurred after toluene addition. In the acclimated aquifer material, o-xylene degradation commenced without addition of toluene. Mineralization accounted for 36 to 54% of the total alkylbenzene removal Under mixed substrate conditions, solution concentrations of radiolabeled benzene decreased when nitrate was present, but not in the absence of an added electron acceptor. Mineralization did not occur, and no degradation products could be identified. Benzene removal was linked to alkylbenzene degradation, however, solution concentrations of benzene increased with subsequent toluene additions. It appears that benzene is not being degraded in these denitrifying microcosms, but merely sorbed or sequestered with the potential for subsequent release. Microbial activity, in this case the biodegradation of alkylbenzenes, enhanced this sorption beyond that observed for the initial aquifer material.