Wetland Treatment of MTBE Contaminated Groundwater at a Local Refinery

The purpose of this study was to explore the potential of wetlands for bioremediation of a methyl tert-butyl ether (MTBE) spill at a Colorado refinery where other contaminants present at the site have potential to inhibit MTBE biodegradation. MTBE biodegradation has been observed to be inhibited by the presence of other contaminants that are common at refineries, such as Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX). MTBE biodegradation is also typically limited by availability of oxygen, and only rarely has been observed to degrade under anaerobic conditions. To test the feasibility of MTBE bioremediation, a bench-scale study followed by a pilot-scale study in the field were conducted. The bench-scale studies were performed as batch tests in which two enrichment cultures were compared for their ability to degrade MTBE in the presence of BTEX. It was observed that culture MO (originally enriched only on MTBE) was superior to culture MB (originally enriched on MTBE and BTEX) in terms of its ability to degrade MTBE. However, both cultures showed inhibited degradation of MTBE in the presence of BTEX. Interestingly, when the MO culture was placed in a semi-batch reactor, simultaneous MTBE and BTEX biodegradation was observed. This suggests that metabolic by-products accumulated in the batch tests may inhibit the ability to degrade MTBE in the presence of BTEX. It was thus hypothesized that in a continuous-flow system, such as a wetland, MTBE and BTEX will degrade simultaneously. In the second part of the study, pilot wetlands are now being tested at the refinery. The wetlands consist of 30-gallon aquaria filled with sediments from the Sand Creek near Denver, CO. The feed water to the systems is taken directly from the pre-treated water from an air-stripper that is currently in operation at the refinery. Six different conditions are being tested in which the inoculum, Fe(III) availability are being tested. Molecular analysis will be used to gain insight into the effect of the microbial community and to assess bioremediation potential at the site. The results of the pilot-scale study will thus serve to guide the design of the full-scale wetland study. It is expected that the complex environment and flow-through conditions of a wetland will promote simultaneous biodegradation of MTBE in the presence of multiple co-contaminants.