Abstract: BACKGROUND: The presence of dissolved methane is an important environmental problem related to greenhouse gas emissions from wastewater treated in methanogenic bioreactors. Methane has a global warming potential of 28. For low-strength wastewaters, such as sewage,dissolved methane could account forupto50%of the total methaneproduced.Dissolved methane is easily desorbed fromeffluentswhen released into the environment or post-treated in aerobic bioreactors. The use of dissolved methane as a carbon source for biological denitrification has been proposed as an alternative for reducing both greenhouse gas emissions and nitrogen concentrations in treated wastewater. RESULTS: The effluent of a methanogenic reactor operating at ambient temperature was post-treated in a two-compartment biological membrane bioreactor (MBR). The first compartment consisted of an anoxic denitrification reactor in which dissolved methane was oxidized. The second compartment was an aerobic membrane filtration reactor. Up to 60% nitrogen removal and 95% methane consumption were observed. Batch experiments indicated the presence of microorganisms that were capable of denitrification using dissolved methane. CONCLUSIONS: Denitrification using dissolved methane as a carbon source was feasible in an anoxic–aerobic MBR system. Denitrification resulted from a mixture of aerobic and anaerobic methane oxidizing bacteria, anammox and heterotrophic bacteria activity.

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