Degradation of weathered diesel fuel by microorganisms from a contaminated aquifer in aerobic and anaerobic microcosms

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AbstractA diesel fuel‐contaminated aquifer in Menziken, Canton of Aargau, Switzerland, was in situ bioremediated from 1989 to 1994 by adding O2, NO−3 PO3−4, and NH+4 through an infiltration well. After a remediation time of 3.5 years, aquifer material from the contaminated zone was excavated and found to contain >106 hydrocarbon‐degrading microorganisms/g and 1.15 ± 0.15 mg/g weathered diesel fuel comprizing mainly isoprenoid alkanes and an unresolved complex mixture (UCM) of unknown components. Samples of this material were incubated for up to 470 days in aerobic and anaerobic microcosms. The microbial activity was determined by measuring the production of inorganic carbon and the consumption of O2 and NO−3. The degradation of the weathered diesel fuel was quantified by infrared spectroscopy and by capillary gas chromatography. In aerobic microcosms, all isoprenoid alkanes and most of the UCM were biodegraded as long as a nitrogen source was present. The O2 consumption could be stimulated by adding KH2PO4 and by elevating the temperature to 22° C. In anaerobic microcosms with KNO3, NO−3 was consumed, inorganic carbon was produced, and the isoprenoid alkanes and the UCM were partially metabolized. In some selected microcosms, the NO−3 consumption rate was stimulated by adding external substrates such as toluene, o‐xylene, m‐xylene, p‐xylene, n‐alkanes, or fatty acids. Mineralization of toluene, naphthalene, and hexadecane to CO2 under denitrifying conditions was confirmed by using [14C]‐labelled substrates.