Anaerobic Methane Oxidation: Occurrence and Ecology

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Abstract
Anoxic sediments and digested sewage sludge anaerobically oxidized methane to CO2 while producing methane. This strictly anaerobic process showed a temperature optimum between 25 and 37.degree. C, indicating an active microbial participation in this reaction. Methane oxidation in these anaerobic habitats was inhibited by O2. The rate of the oxidation followed the rate of methane production. The observed anoxic methane oxidation in Lake Mendota [Wisconsin, USA] and digested sewage sludge was more sensitive to 2-bromoethanesulfonic acid than the simultaneous methane formation. Sulfate diminished methane formation and methane oxidation. In the presence of Fe and sulfate the ratio of methane oxidized to methane formed increased markedly. MnO2 and higher partial pressures of methane also stimulated the oxidation. The rate of methane oxidation in untreated samples was approximately 2% of the CH4 production rate in Lake Mendota sediments and 8% of that in digested sludge. This percentage could be increased up to 90% in sludge in the presence of 10 mM ferrous sulfate and at a partial pressure of methane of 20 atm (2027 kPa).