Q-194. Anaerobic Methyl tert-Butyl Ether (MTBE) and tert-Butyl Alcohol (TBA) Biodegradation under Shifting Geochemical Conditions both in Situ and with Novel, Anaerobic Liquid Enrichment Cultures

N. Wei, K. T. Finneran;
Univ. of Illinois, Urbana, IL.

Methyl tert-butyl ether (MTBE) is a prevalent groundwater contaminant, and its metabolite tert-butyl alcohol (TBA) often accumulates in subsurface environments. In situ conditions within source areas are typically anaerobic, and oxygen introduced can be consumed quickly by chemical oxidation of Fe (II) and sulfides. The purpose of our research was to investigate the kinetics and mechanisms of MTBE and TBA biodegradation under shifting anoxic conditions and the effect of extracellular electron shuttling (EES) compounds. Experiments were conducted using petroleum contaminated aquifer sediments, river sediment, and anaerobic digester sludge; liquid enrichment cultures were also set up using the above materials. Radiolabeled (14C) and non-radiolabeled MTBE and TBA were amended to different incubations to quantify MTBE/TBA biodegradation. Different electron acceptors and electron shuttling compounds were added to identify the MTBE/TBA degradation dynamics as conditions shifted from one electron accepting process to another (e.g. Fe(III) reduction to sulfate reduction). Aquifer sediment had intrinsic potential for anaerobic oxidization of TBA. Fe (III) +electron shuttle incubations had the shortest lag period (110d) and up to 65% [14C]-TBA was oxidized to CO2, which is comparable to those reported under aerobic conditions. Fe (III) without EES had a longer lag period but mineralization was similar. Sulfate reduction mineralized 55% of the TBA after 380 days. Nitrate actually inhibited TBA degradation relative to unamended controls. Molecular analysis (16S rDNA) is being conducted to determine the microbial community associated with each process. Three separate liquid enrichment cultures that degrade MTBE as the sole carbon and energy source have been developed. The electron acceptors used are AQDS, sulfate or fumarate. 2mM MTBE is continuously degraded within 20 days. TBA initially accumulated in all cultures, but recent data suggest TBA degradation as well. These are the first stable, anaerobic enrichment cultures that degrade MTBE, and are critical to understanding the ecology, physiology, and biochemistry of anaerobic MTBE biodegradation.