Anaerobic biotransformation of fuel oxygenates under sulfate-reducing conditions

Abstract

The anaerobic biotransformation of methyl tert‐butyl ether (MTBE), ethyl tert‐butyl ether (ETBE), and methyl tert‐amyl ether (TAME) was evaluated under different anoxic electron‐accepting conditions. Enrichments were established with a polluted estuarine sediment inoculum under conditions promoting denitrification, sulfate reduction, Fe(III) reduction, or methanogenesis. Complete loss of MTBE and TAME was observed under sulfate‐reducing conditions, concomitant with the reduction of sulfate. A stoichiometric amount of tert‐butyl alcohol and tert‐amyl alcohol accumulated indicating that O‐demethylation was the initial step in MTBE and TAME biodegradation under sulfate‐reducing conditions. No transformation of MTBE or TAME was observed under the other electron‐accepting conditions over 3 years. Under all conditions tested, there was no biotic loss of ETBE observed. MTBE and TAME were depleted upon refeeding the sulfate‐reducing cultures. This study definitely demonstrates the anaerobic biodegradability of MTBE and TAME under sulfate‐reducing conditions.

Microbial community analyses of three distinct, liquid cultures that degrade methyl tert-butyl ether using anaerobic metabolism

“…One previous study by Somsamak et al (2001) reported complete loss of MTBE in sulfate enrichment incubations with fuel contaminated estuary sediment. In their study, 1.1 mM MTBE was transformed to a stoichiometric amount of TBA with the concomitant reduction of sulfate after 1,160 days of incubation.…”

“…Methane has not been detected at any point with this enrichment; therefore clone analysis with Archaeal primers was not performed. Sulfate has been widely reported as a significant electron acceptor for in situ, anaerobic MTBE and TBA transformation (Bradley et al 2001a(Bradley et al , b, 2002Somsamak et al 2001). Therefore, culture NW2 will be critical to understanding …”

“…In a microcosm study with bed sediment of the Ohio River, stoichiometric transformation of MTBE to TBA was reported and TBA accumulated as a dead-end product under methanogenic conditions (Mormile et al 1994). In sulfate-reducing enrichments reported by Somsamak et al (2001), MTBE degradation also ended with TBA.…”

“…What was missing from all anoxic studies were model cultures that could be manipulated in the same manner as the aerobic microorganisms so that single variables could be tested while other conditions remained constant in reasonable time frames (days or weeks rather than months or years). The only reported ''culture'' has been a sulfate-reducing culture that was maintained as a solids-containing aquifer enrichment rather than a liquid enrichment (Somsamak et al 2001). The number of studies that can be performed with cultures in sediment is limited, and to date the dominant organisms have not been identified.…”

“…Although anaerobic MTBE biodegradation has been reported in sediment incubations (microcosms) (Schmidt et al 2004;Wilson et al 2005), and one enrichment that was maintained in sediment (Somsamak et al 2001), to date stable liquid cultures have not been characterized in terms of activity or microbial community composition. Three such cultures and the accompanying phylogenetic data are presented below.…”