Combined photochemical-biological processes for treatment of unleaded gasoline oxygenates : MTBE, ETBE and TAME

A study was conducted to determine the feasibility and the opportunity of photochemical pretreatment on the biodegradation and detoxification of Methyl Tert Butyl Ether (MTBE), Ethyl Tert Butyl Ether (ETBE) and Tert Amyl Methyl Ether (TAME), the most common oxygenates used as octane enhancers in unleaded gasoline. The production, storage, uses and disposal of oxygenates result in an unknown amount of groundwater pollution. Because of their high solubility, MTBE, ETBE and TAME are detected in large portions in saturated zones of aquifers. The biodegradation of these oxygenates is difficult and slow, and information regarding their biodegradability is scarce. Photo-decomposition of oxidants under appropriate UV radiation has been shown to be very effective because the hydroxyl radicals produced possess high oxidation potential. In this study, the H2O2/UV process was used to generate hydroxyl radicals. Maximal oxygenates transformation was obtained in a few minutes. The experiment succeeded in choosing two very active bacterial communities (isolated from polluted soil) which can use ETBE and the mixture of MTBE, TAME and ETBE as a sole source of carbon and energy in aerobic conditions. The mixed cultures were tested in aerobic fixed-bed reactors where continuous biodegradation activity was maintained for 86 retention times. Results showed that the presence of MTBE and TAME caused a reduction in ETBE biodegradation rate. The biodegradation rates of MTBE and TAME were much lower, suggesting that such compounds may be treated either by photooxidation or by biological oxidation methods