Author:

Abstract:

The car fuel octane enhancer and oxygenate methyl tertiary-butyl ether (MTBE) has become a common pollutant of shallow aquifers worldwide, most frequently detected in urban areas. Concentrations in ground water are generally low (0.17 μg/l), but at contaminated sites resulting from point sources suc1i as leaking underground storage tank sites, detected concentrations are up to 830 mg/l. Because of controversy regarding toxicity and lacking European and national legislations, MTBE has long remained untreated in Europe. Unfortunately, low sorption and slow or negligent biodegradation result in relatively fast distribution in ground water, resulting in detection in public drinking water supply wells, where low taste and odor thresholds (2-40 μg/l) make the water unfit for consumption. Belgium has adopted a ground water standard for MTBE (300 μg/l), which renders remediation of MTBE contaminated sites compulsory when this concentration threshold is crossed. To meet the need for an efficient treatment for MTBE- and TBA contaminations in ground water, the scope of the presented work is to develop an inoculated bioreactor to remediate MTBE and TBA on site. At the Flemish Institute for Technological Research (VITO) a bacterial consortium has been enriched out of a Belgian MTBE contaminated soil sample (Moreels et al., 2004 -FEMS Microb. Ecol. 49: 121-128). This consortium, which has been shown to be suitable as an inoculum to induce MTBE/TBA-degradation in aquifer, is currently being characterized for optimal MTBE- and TBA degradation in a bioreactor. The prior aim is to determine MTBE- and TBA degradation rates in function of important parameters as MTBE- and TBA concentration, dissolved oxygen, pH, temperature and presence of other contaminants as BTEX and ETBE. Results will be modeled in order to predict and optimize MTBE- and TBA degradation at field conditions during a pump-and-treat application. Present results show that the VITO-consortium quickly mineralizes MTBE and TBA in batch suspensions. TBA was only transiently detected. Preliminary modeling of these results shows a good correlation between average MTBE concentration in solution and the MTBE-degradation rate in mg MTBE g dry weigh -1 hour -1. The model indicates a logarithmic increase of the degradation rate up to 46.63 (±11.57) mg MTBE g dw -1h -1 at 15 (± 0.31) mg MTBE/1. Furthermore, the average MTBE degradation rate is 60.75 (± 8.34) mg MTBE g dw -1 h -1 at an initial concentration of 100 mg/i MTBE. TBA, BTEX and ETBE degradation studies, including modeling, are planned in the near future, as are tests to determine the relation between MTBE/TBA degradation rates and pH, temperature and dissolved oxygen concentration. The results of these tests will be discussed as well.