In Situ MTBE Biodegradation Supported by Diffusive Oxygen Release

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Abstract
Microcosm studies with sediments from Vandenberg Air Force Base, CA, suggest that native aerobic methyl tert-butyl ether (MTBE)-degrading microorganisms can be stimulated to degrade MTBE. In a series of field experiments, dissolved oxygen has been released into the anaerobic MTBE plume by diffusion through the walls of oxygen-pressurized polymeric tubing placed in contact with the flowing groundwater. MTBE concentrations were decreased from several hundred to less than 10 μg/L during passage through the induced aerobic zone, due apparently to in situ biodegradation: abiotic MTBE loss mechanisms were insignificant. Lag time for initiation of degradation was less than 2 months, and the apparent pseudo-first-order degradation rate was 5.3 day-1. Additional MTBE was added in steps to raise the influent concentration to a maximum of 2.1 mg/L. With each step, MTBE was degraded within the preestablished aerobic treatment zone at rates ranging from 4.4 to 8.6 day-1. Excess dissolved oxygen suggested that even higher MTBE concentrations could have been treated. Continued flow through the treatment zone was repeatedly confirmed through tracer and other tests. These and others' results suggest that it is possible to create permeable in situ treatment zones solely by releasing oxygen to support native microbial degradation of MTBE.