Groundwater remediation by an in situ biobarrier: a bench scale feasibility test for methyl tert-butyl ether and other gasoline compounds

Most gasoline contains high percentages of methyl tert-butyl ether (MTBE) as an additive. The physico-chemical properties of this substance (high water solubility, low sorption in soil) result in high mobility and dissolved concentrations in soil. In situ permeable biological barriers (biobarriers, BBs) can remediate MTBE polluted groundwater by allowing pure cultures or microbial consortia to degrade MTBE when aerobic conditions are present, either by direct metabolism or cometabolism. Lab-scale batch and column tests were carried out to assess a selected microbial consortium in biodegrading MTBE and other gasoline compounds (benzene B, toluene T, ethylbenzene E, xylenes X) and to measure the parameters affecting the efficacy of a BB treatment of polluted groundwater. During the aerobic phase of the batch tests, the simultaneous biodegradation of MTBE, tert-butyl alcohol (TBA), B, T, E and o-X was observed. The rapid biodegradation of BTEXs resulted in decreased oxygen availability, but MTBE degradation was nevertheless measured in the presence of BTEXs. Stationary concentrations of MTBE and TBA were measured when anoxic conditions occurred in the systems. Values for a first order kinetic removal process were obtained for MTBE (0.031 ± 0.001 d-1), B (0.045 ± 0.002 d-1) and T (0.080 ± 0.004 d-1) in the inoculated column tests. The estimate of the BB design parameters suggested that inoculation could significantly modify (double) the longitudinal dispersivity value of the biomass support medium. No effect was observed in the retardation factors for MTBE, B and T.