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Abstract Introduction: Methyl tert-butyl ether (MTBE) has been incorporated in reformulated gasoline at concentrations up to 15% (vol) to replace lead tetraethyl in order to comply with the octane index and to reduce the polluting emissions in exhaust gases.This compound is water soluble (48,000 mg/L) and one of the most common pollutants of ground water and surface water. Because of its undesirable effects on drinking water and ecologically harmful effects, MTBE removal has become a public health and environmental concern. Objective: Evaluatin of biodegradability of MTBE by isolated microorganisms from activated sludge. Materials and Methods: In this study a microbial consortium that efficiently degraded methyl tert-butyl ether was obtained by Isolated microorganisms of Activated Sludges in the Aqueous Solutions. Microorganisms were isolated from a variety of sources, generally from petroleum or chemical and urban wastewater treatment plants. All experiments were conducted at a constant temperature of 25ºC. Vials of 50 ml and 125 ml volume sealed with Teflon-lined Mini-Nert caps were used for microcosm experiments. In all experiments 1% sodium azide were used as controls. Cultures were incubated at 25°C in the dark on an orbital shaker (rotation speed of 150 rpm). The mineral medium was used for batch cultures. Samples of bacterial cultures that metabolize MTBE have been analysed for both MTBE and its metabolite TBA by direct GC analysis using FID. Cultures able to metabolize MTBE have been found in activated sludge and soils. Microbial consortium were plated on agar with MTBE vapor as the carbon source. After three weeks growth to saturation, independent clones were diluted into fresh mineral medium. This microorganisms, was a gram-positive bacterium. An aerobic microbial consortium able to biodegrade methyl tert-butyl ether (MTBE) was enriched in laboratory for four months. Results: MTBE has been shown to biodegrade under aerobic conditions and cometabolic conditions. Clearly, aerobic biodegradation of MTBE is demonstrable. In our laboratory, a microbial consortium was isolated from activated sludges based on its ability to grow on MTBE and was identified as cocobacillus. The capacity of this microbial consortium to degrade and grow on MTBE as a sole carbon and energy source is described in this paper. No biomass aggregates were observed during all the batch cultures, but the attached biomass was observed (the concentration of the initial attached biomass was about 0.11 g/ L of dry weight). 500 mg of yeast extract per liter and 20 mg of Peat humic support growth of microbial consortium, it clearly had a stimulatory effect on consumption upper than 20%. Consortium was capable of degrading concentration as great as 1000 mg/l MTBE, whereas concentrations of 1000 mg/l MTBE and higher was not degraded. Conclusion: MTBE in low concenteration is biodegradable and biodegradability of MTBE enhanced by stimulator substances.

Keywords: Methyl Tert-Butyl Ether (MTBE), Biodegradation, Sewage

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