Removal of dissolved methane from digested effluent by anaerobic methane oxidation linked to ferric oxides and sulfate reduction

Bioreactors supplied with sulfate and Fe(III) oxides (hematite and goethite), as electron acceptors, were tested for their capacity to remove dissolved methane from a digestate from a methanogenic reactor treating synthetic wastewater. Negligible removal of dissolved methane occurred when no electron acceptor was provided. However, when hematite and goethite were supplied, methane removal rates of 6.7 and 3.7 g CH₄/m³-day, respectively, were achieved coupled to the reduction of both minerals. Simultaneous supply of sulfate and hematite supported the highest removal rate observed (9.1 g CH₄/m³-day) coupled to the reduction of both electron acceptors. Taxonomic characterization based on 16S rRNA gene sequencing revealed Methanobacterium and Methanolinea as the microorganisms potentially involved in the removal of dissolved methane. This treatment concept could contribute to prevent the emission of dissolved methane from digested effluents, which ultimately may attenuate global warming associated with greenhouse gases emissions from wastewater treatment plants.