No abstract

MTBE degradation was investigated using a continuously stirred tank reactor (CSTR) with biomass retention (porous pot reactor) operated under aerobic conditions. MTBE was fed to the reactor at an influent concentration of 150 mg/l (1.70 mmol/l). A second identical reactor was operated as a control under the same conditions with the addition of 2.66 g/l of sodium azide, to kill any biological activity. Results from these experiments suggest that biomass retention is critical to the degradation of MTBE. The rate of MTBE removal was shown to be related to the VSS concentration. MTBE removal exceeded 99.99% when the VSS concentration in the reactor was over 600 mg/l. Results obtained from batch experiments conducted on mixed liquor samples from the porous pot reactor indicate that the individual rates of biodegradation of MTBE and TBA were higher for initial concentrations of 15 mg/l than for concentrations of 5 mg/l. The presence of TBA at lower concentrations did not effect the rate of MTBE degradation, however higher concentrations of TBA did reduce the rate of biodegradation of MTBE. Denaturing Gradient Gel Electrophoresis (DGGE) analysis reveals that the culture consisted of a community of bacterial organisms of about 6 species.

Five aerobic cultures capable of degrading MTBE under different substrate conditions were developed using porous pot chemostat reactors. The five substrate conditions were: MTBE alone, MTBE and DEE, MTBE and DIPE, MTBE and EtOH, and MTBE and BTEX. All five cultures demonstrated greater than 99.9% removal of MTBE, with an influent concentration of 150 mg/L for the MTBE only reactor, 75 mg/L for the DEE, DIPE, and EtOH reactors, and 85 mg/L for the BTEX reactor. The bacterial communities of the reactors were monitored periodically by DGGE analysis in order to determine when a biological steady state was achieved. At this time, complete phylogenectic analysis was done in order to determine the identity of the bacteria. All cultures were found to be mixed cultures. Members of the order Cytophagales, within the Phylum Flexibacter-Bacterioides-Cytophaga inhabited all reactors. Members of the α-Proteobacteria were also found, but only in reactors which had an alternative substrate (MTBE and DIPE and MTBE and EtOH). One member of Nitrospina, a little-known uncultured Division, was found in the MTBE only reactor. Though the same groups of organisms prevailed in the reactors, the individual species were shown to be different. This means that a diversity of MTBE degraders exists, and that each thrives under different substrate conditions. This also suggests that Cytophagales may play a key role in the degradation of MTBE in water.