| This study investigates the potential for biodegradation of methyl tert-butyl ether (MTBE), a prevalent gasoline additive and groundwater contaminant, under various substrate and oxidation-reduction (redox) conditions. Porous pot reactors designed for biomass retention were operated aerobically under the following conditions: MTBE only, MTBE and ethanol, MTBE and di-isopropyl ether, MTBE and diethyl ether, and MTBE with benzene, toluene, ethylbenzene, and p-xylene (BTEX). In all reactors, optimal performance was achieved when operated without biomass wasting. Mineralization of MTBE and the alternative substrates was observed in all reactors, with an average stable effluent concentration of all compounds being at or below 1 ppb (0.001 mg/1). Anaerobically, MTBE degradation was investigated in porous pot reactors and in batch systems. After a 180 day acclimation period, conversion of MTBE to its intermediate, tert-butyl alcohol (TBA), was observed in both batch and continuous-flow iron-reducing systems, and one instance of degradation was observed in the denitrifying porous pot reactor. No degradation of MTBE under methanogenic or sulfate-reducing conditions was observed after over 1 year of incubation. A molecular tool, denaturing gradient gel electrophoresis (DGGE) was used to monitor and profile the bacterial community structure of all reactors. Members of the Flexibacter-Bacterioides-Cytophaga (F-B-C) group of bacteria were most represented among all aerobic reactors, while delta-Proteobactena were found to be prevalent in the iron-reducing system. Beta-Proteobacteria with high similarity to the known MTBE degrader, PM1, were detected by DGGE late in operation of the MTBE only and the MTBE and BTEX reactors. Two pure MTBE-degrading cultures with high similarity to PM1 were also isolated from the MTBE only reactor. Studies in pure culture also indicated no significant effect of alternative substrate (BTEX) on MTBE degradation. Results indicate that aerobic degradation of MTBE is reliable under various substrate conditions, and that a porous pot reactor designed for biomass retention is highly effective for attaining low effluent concentrations of MTBE and its intermediates. |
