Methyl tert-butyl ether biodegradation by indigenous aquifer microorganisms under natural and artificial oxic conditions

Microbial communities indigenous to a shallow groundwater system near Beauf ort, SC, degraded milligram-per liter concentrations of methyl tert-butyl e ther (MTBE) under natural and artificial oxic conditions. Significant MTBE biodegradation was observed where anoxic, MTBE-contaminated groundwater dis charged to a concrete-lined ditch. In the anoxic groundwater adjacent to th e ditch, concentrations of MTBE were >1 mg/L. Where groundwater discharge o ccurs, dissolved oxygen (DO) concentrations beneath the ditch exceeded 1.0 mg/L to a depth of 1.5 m, and MTBE concentrations decreased to <1 <mu>g/L p rior to discharge. MTBE mass flux calculations indicate that 96% of MTBE ma ss loss occurs in the relatively small oxic zone prior to discharge. Sample s of a natural microbial biofilm present in the oxic zone-beneath the ditch completely degraded [U-C-14]MTBE to [C-14]CO2 in laboratory liquid culture studies, with no accumulation of intermediate compounds. Upgradient of the ditch in the anoxic, MTBE-and BTEX-contaminated aquifer, addition of a sol uble oxygen release compound resulted in oxic conditions and rapid MTBE bio degradation by indigenous microorganisms. In an observation well located cl osest to the oxygen addition area, D0 concentrations increased from 0.4 to 12 mg/L in <60 days and MTBE concentrations decreased from 20 to 3 mg/L. In the same time period at a downgradient observation well, D0 increased from <0.2 to 2 mg/L and MTBE concentrations decreased from 30 to <5 mg/L. These results indicate that microorganisms indigenous to the groundwater system at this site can degrade milligram per liter concentrations of MTBE under n atural and artificial oxic conditions.