Impact of an anoxic desulfurization process on methane content of the purified biogas

•H2S removal efficiencies of 92–97% were achieved in the anoxic bioscrubber.•Absorption mediated decreases in CO2 content of up to 3.0% in the purified biogas.•Increase in CH4 content of the purified biogas was proportional to the CO2 decrease.•Methanotrophs and methanol-oxidizing denitrifiers were consistently identified.