A semi-industrial scale AnMBR for municipal wastewater treatment at ambient temperature: performance of the biological process

•The AnMBR plant was operated for more than 600 days at ambient temperature.•Effluent COD remained below effluent standards with average COD removal above 87 %.•Waste sludge reduced by between 9 and 43 % less than CAS.•Methane yield ranged from 70 to 169 STP L CH4·kg−1 CODinf during the selected periods.·T, SRT, HRT and influent COD/SO42−-S are crucial parameters of AnMBR performance.