At the end of 2007, the production of the fuel additive methyl tert-butyl ether (MTBE) was stopped in all German refineries and ethyl tert-butyl ether (ETBE) was produced instead of. The reasons for this change originate from two European directives from 2003 which promote the use of biofuels or other renewable fuels. 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. In contrary 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. Degradation rates for MTBE and ETBE were comparable. Co-contaminants like BTEX hampered both MTBE and ETBE biodegradation. In the course of these promising results a new project (NANOKAT) was approved in 2006 with the topic: „Biodegradation of MTBE and ETBE with immobilized microorganisms“. Aim of this project was the use of immobilized microorganisms within a „funnel and gate“ system. The combination: inorganic matrices/biological material should lead to a better handling of the used microorganisms. The biodegradation of MTBE with immobilized microorganisms and by various techniques could be demonstrated and the following conclusions can be made: - Some (not all) MTBE degrading microorganisms are able to degrade also ETBE
- Degradation of MTBE/ETBE alone is obviously not profitable for microorganisms
- Biodegradation experiments with immobilized microorganisms showed encouraging results.
- Especially silica-gel coatings on porous clay were robust and showed no reduction in MTBE degrading activity over a storage time of 10 weeks.