IN SITU AND EX SITU APPROACHES FOR MTBE BIOREMEDIATION

MTBE is widely used as a gasoline additive, and it has become a common and persistent groundwater contaminant. We have developed both in situ and ex situ bioremediation technologies for treating MTBE-contaminated groundwater. The in situ approach relies on stimulating the growth and activity of propane-oxidizing bacteria that co-metabolically degrade MTBE, and the ex situ technologies rely on the use of engineered bioreactors and a novel bacterium that grows on MTBE as a sole carbon source.In earlier work, we demonstrated that propane-oxidizing bacteria can mineralize MTBE to CO2 after growth on propane (Steffan et al., 1997). Consequently, propane injection can be used to promote MTBE biodegradation by indigenous microorganisms in MTBE-contaminated aquifers, or to maintain the activity of exogenous propane-oxidizers used as seed cultures. To evaluate in situ propane biostimulation, laboratory treatability studies were conducted using aquifer material collected at sites in New Jersey and California. In microcosms from the California site, MTBE was degraded in samples amended with propane or propane and nutrients (nitrogen and phosphorous). Degradation (initial MTBE concentration ∼ 8 mg/L) was observed after a limited lag period of 10 to 20 days. In the samples from New Jersey, MTBE was not degraded in response to propane addition alone, but the oxygenate was degraded in samples inoculated with a culture of the propane-oxidizing bacterium ENV425.For ex situ treatment of MTBE, two 85-L membrane bioreactors (MBRs) were seeded with a bacterial strain recently isolated at Envirogen. This strain, designated Hydrogenophaga flava ENV735 (ENV735) grows on MTBE as a carbon source. The reactors were operated for several months with influent feeds of MTBE (1000 mg/L) in water, or MTBE (2000 mg/L) and BTEX (30 ppm) in water. For each reactor, the average effluent MTBE concentration was ∼100 μg/L during normal operation, and BTEX was below detection limits in the effluent.