WORK PLANS - Laserfiche WebLink

Home Browse Search

To be presented at 1999 Petroleum Hydrocarbons Conference, Houston, Texas Laboratory -Scale Evaluation of In Situ Aerobic MTBE Biodegradation Options for Vandenberg Air Force Base, California Ryan D. Wilson, Mario Schirmer , Claudia N. Naas, Amanda Smiths, Christy Smiths, Kate M. Scows, Mike R. Hyman$ and Douglas M. Mackay Department of Earth Sciences, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1 * UFZ Centre for Environmental Research Leipzig -Halle, Department Industrial and Mining Landscapes Permoser Str. 15, 04318 Leipzig, Germany t Dept. of Land, Air and Water Resources, University of California, One Shields Avenue, Davis, CA 95616-8627 $ Department of Microbiology, Campus Box 7615, North Carolina State University, Raleigh NC 27695 Abstract Methyl tert-butyl ether (MTBE) has rapidly become a contaminant of significant concern throughout the US, and is increasingly gaining attention throughout Europe. Dissolved plumes of MTBE travel at the speed of groundwater and resist biodegradation under typical plume conditions, negating natural attenuation as a plume management strategy. Thus some form of in situ treatment is often indicted. As part of ongoing work at Vandenberg AFB (VAFB), we are examining three general approaches to enhancing in situ aerobic degradation of MTBE at the lab scale: 1) enhancement of activity of indigenous microbes capable of metabolizing MTBE, 2) emplacement of non-native MTBE -metabolizing microbes, and 3) stimulation of cometabolism by indigenous microbial consortia. Sediment and water samples were collected from an area that has been highly characterized and where in situ treatment pilot tests are on-going or planned. For the cometabolic evaluations, a series of batch microcosms were set up consisting of sediment and water from the site and combinations of MTBE and either hexane (n -alkane), isopentane (branched alkane), or cyclohexane (cyclic alkane). These alkanes have all been shown by others to result in cometabolic MTBE degradation by various enriched or pure microbial cultures. There is evidence from microcosm studies that there may be indigenous microbes present at VAFB capable of utilizing MTBE as a primary substrate under aerobic conditions. Lab tests have also shown that a gram- negative proteobacteria strain isolated from a compost -filled biofilter treating volatile emissions from a water treatment plant is capable of degrading MTBE when introduced to VAFB soils and water. With regard to prospects for cometabolism, one or more of the tested alkanes were degraded in sediment from upgradient or within the plume, however, MTBE cometabolism was noted in only a subset of these cases. These results may suggest either spatially variable microbial populations, the presence of one or more undetected inhibitory compound(s), and/or the lack of some required nutrient within the plume. Additional work with soils from the plume has shown vigorous microbial growth on propane, modest growth on n -butane, and minor growth on isobutane — three gases we have identified as potential primary substrate candidates for field testing of MTBE cometabolism. Further tests suggests that organisms grown on all three alkanes cometabolize MTBE. Ongoing microcosm work includes examining the effects of various nutrient additions, potential inhibition caused by other alkanes and/or aromatics, and initial MTBE concentration on the rate of MTBE oxidation. The aims of these efforts are to 1) identify the geochemical conditions that can practically be induced in the field to support in situ aerobic degradation of MTBE and 2) identify any potential degradation inhibitors. Page 1