Bioremediation options for the recalcitrant "bio" oxygenate ETBE

In 2007, production changed from methyl tert-butyl ether (MTBE) to ethyl tert-butyl ether (ETBE) as alternative fuel oxygenate in all refineries in Germany. Additionally, it can be assumed that ETBE will replace MTBE completely in the future, at least in Europe. The reasons for this change originate from two European directives from 2003 which promote the use of biofuels or other renewable fuels. Until 2010 the biofuel fraction in fuels and diesel shall rise to 5.75 %. Additionally, biofuels (ethanol and biodiesel) are actually exempted from taxes in many European countries, and for ETBE containing fuels the bioethanol fraction is exempted from tax. ETBE is synthesized from isobutene (53 %) and ethanol (47 %) and the latter is produced from plants (e.g., sugar beets or wheat). This laboratory study will give an overview about the bioremediation options for ETBE in comparison to MTBE. Additionally, some data are presented from an MTBEcontaminated site. It is known from the literature that biodegradation of ETBE is sometimes possible under certain conditions. Some isolates are capable of growing on these ethers (Fayolle et al., 1998; Ferreira et al., 2006). However, in contrast to MTBE, there is still poor knowledge about the bioremediation of ETBE on contaminated sites. To overcome this problem, the biodegradation of both fuel oxygenates under different conditions was investigated. Particular interesting parameters were the oxygen content of the water, the presence of electron acceptors and the behavior of ETBE and MTBE under occurrence of other fuel components (BTEX). For MTBE laboratory results were verified under field conditions on an MTBE-contaminated site. For the experiments, both isolates and microbial consortia deriving from MTBE contaminated groundwater were used. ETBE degradation was observed with a microbial consortium grown on MTBE for two years. However, a lag phase of four months occurred after the change of the substrate from MTBE to ETBE. Nevertheless, degradation rates for MTBE and ETBE are comparable. Co-contaminants like BTEX hampered both MTBE and ETBE biodegradation. For anaerobic biodegradation experiments different electron acceptors were used (sulfate, nitrate and ferric iron). In contrast to MTBE, ETBE degradation was not observed during 8 months. The most favorable electron acceptor enhancing MTBE biodegradation was nitrate. This was also confirmed under field conditions. In conclusion, it can be noted that ETBE contaminations might be a serious problem in the future because of the intensified use, at least in Europe. ETBE will probably accumulate under anaerobic conditions. Co-contaminants like BTEX will also inhibit ETBE degradation. However, aerobic conditions should enhance biodegradation of ETBE. Therefore, the application of enhanced natural attenuation techniques for the remediation of ETBEcontaminated sites might be an option but detailed field investigations are necessary for a comprehensive assessment.