Biodegradation of Fuel Ethers

Abstract

Fuel oxygenates, including ethers such as methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME), as well as alcohols such as tert-butyl alcohol (TBA), tert-amyl alcohol, and ethanol, have been added to gasoline since the mid 1970s, especially to improve air quality. The major part of the contamination appeared to be related to leaking underground storage tanks used for gasoline storage; the detection of MTBE in water occurred four to six times more frequently in areas using reformulated gasolines (RFGs) than in areas not using RFGs, with 20% of the samples containing MTBE. Fuel ethers are not easily biodegradable compared with less-water-soluble compounds in gasoline, such as monoaromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes). Although difficult to carry out, microbial degradation was found to be possible. Apart from the few microorganisms that are able to use fuel ethers as sole carbon and energy sources, other strains need a cosubstrate to degrade them by cometabolism. The possible pathways for the cometabolic biodegradation of MTBE are summarized in this chapter. Natural attenuation of MTBE in groundwater is mainly caused by dispersion, dissolution, and biodegradation. Fuel ethers constitute a good example of xenobiotics recently released in diverse environments: air, soils, surface waters, and groundwater. Their persistence in the environment deserves extensive microbiological investigation to better understand the reasons for their poor natural biodegradation. The results presented in the chapter suggest that the MTBE catabolic pathway would be the result of randomly associated enzymatic activities.