Deptartment of Environmental and Biomolecular Systems
Oregon Health & Science University
The realization that methyl tert-butyl ether (MTBE) has become a widespread contaminant has fueled the need for an understanding of processes that control its environmental fate. The studies presented here provide a means for analyzing for MTBE and its degradation products and refine the understanding of MTBE fate in groundwater by providing a detailed assessment of the major pathways and kinetics of MTBE degradation under controlled laboratory conditions designed to simulate environmental conditions. The findings show that MTBE and its degradation byproducts are subject to both biotic and abiotic degradation and measure the kinetics of the degradation observed. The column studies (Chapter 5) show that MTBE is subject to microbial degradation, with a rate corresponding to a 2-3 year half-life in uncontaminated soils and in the presence of oxygen. However, most of the MTBE that occurs in association with gasoline spills will not be degraded by this mechanism, since these plumes are typically anaerobic and more readily degradable compounds are usually present. Studies with PM-1 (Chapter 4), an MTBE degrading isolate, showed that PM-1 is capable of mineralizing MTBE. They further showed that MTBE and other fuel oxygenates are degraded by similar pathways and at similar rates. Engineered treatment systems using PM-1 have since been shown to be an efficient means of treating water contaminated by MTBE. The tert-butyl formate hydrolysis study (Chapter 3) shows that TBF is subject to neutral as well as acid and base catalyzed hydrolysis. The rates of this degradation at 22Â°C correspond to half-lives of five days, 6 hours, and 11 minutes at pH values of 7, 2, and 11, respectively. It examines why, though TBF is the primary degradation product of many MTBE degradation pathways, it is rarely seen in field samples. The Fenton reagent studies (Chapter 6) show that MTBE is subject to a previously undescribed environmental degradation mechanism. This mechanism involves delivery of the reactants (H2O2 and MTBE, in a raindrop) to a catalytic surface (iron oxyhydroxides in sediments). The subsequent degradation arises from the production of hydroxyl radical via a Fenton-like reaction, and the reaction of the hydroxyl radical thus formed with MTBE. Evidence show that this mechanism may account for as much as 8% of atmospherically deposited MTBE under ideal conditions. All of these studies relied on the simultaneous analysis of MTBE disappearance and product appearance, analyses that could not be accomplished at environmentally relevant concentrations using conventional purge and trap techniques. Because of this analytical objective, the first task of the project was to design an analytical protocol to make the rest of the project possible. This protocol is the direct aqueous injection with detection by mass spectrometry technique discussed in Chapter 2.
OGI School of Science and Engineering
Church, Clinton Dean, "Pathways and Kinetics of MTBE Degradation" (2007). Scholar Archive. 271.