EPA Grant Number: R827015-01-0
Title: Anaerobic Intrinsic Bioremediation of MTBE
Investigators: Joseph M. Sulita
Institution: University of Oklahoma
EPA Project Officer: Bala Krishnan
Project Period: March 1, 2002 to February 28, 2003
Project Amount: $71,796
Research Category: Intrinsic bioremediation/natural attenuation
This report outlines the experimental results that have been collected to date to evaluate the anaerobic biodegradation of radiolabeled MTBE (14C-methyl-tert-butyl ether) and/or TBA (14C-tert-butyl alcohol), a known metabolite of MTBE biodegradation. Surbec-ART Environmental L.L.C., our industrial collaborator, is conducting the extensive screening tests with aquifer materials. Incubations from ten MTBE-impacted sites are currently being monitored for the biodegradation of MTBE and/or TBA. These test bottles have now been incubating for approximately 220 days.
Results to date have shown that the conversion of 14C-MTBE to 14C-CO2 has occurred in numerous test bottles incubated under aerobic conditions. Up to 100% recovery of the radiolabel has been observed in some of the incubations. Similarly, of the four sites tested for TBA biodegradation, all have shown 14C-TBA conversion to 14C-CO2 when oxygen was added.
In contrast, significant anaerobic biodegradation of MTBE has yet to be observed in any incubations containing the ten site materials examined, with one notable exception. The conversion of 14C-MTBE to 14C-CO2 was observed in one subset of incubations from one site. In these MTBE-mineralizing test bottles, which have been incubating primarily under sulfate-reducing conditions, hydrogen was added as a positive control to ensure that an active population of anaerobic microorganisms existed. Indeed, the addition of hydrogen seemed to have a stimulatory effect on anaerobic MTBE biodegradation in these sediments relative to controls. Similarly, slight 14C-TBA mineralization to 14C-CO2 was found in the sediments from this same site. Anaerobic TBA mineralization has yet to be observed under any other condition in any other site incubations.
At this time, geochemical parameters in all of the incubations have been measured, including sulfate or nitrate loss, and iron (II) or methane production. Despite the measurement of several anaerobic terminal electron accepting processes (including iron reduction, sulfate reduction, and methanogenesis) in the experiments, the only positive result for anaerobic MTBE degradation was that mentioned above where hydrogen was amended to aquifer materials from one site. As this is a somewhat unexpected result, we will attempt to reproduce these findings and determine if the amount of radiolabel recovered as mineralized endproduct accounts for more than a simple O-demethylation of the parent substrate. The latter has previously been reported in the literature and reflects a relatively minor alteration of MTBE. The incubations will continue to be monitored for 14C-CO2 and/or 14C-CH4 production until the end of the funding period. A determination will be made later on whether to seek additional funding support for the results obtained.