Oxic settling anaerobic (OSA) process for excess sludge reduction: 16 months of management of a pilot plant fed with real wastewater

•An OSA pilot plant, fed with real wastewater, was managed for 16 months.•Batch tests were performed to study the processes concerning the sludge holding tank.•The excess sludge production was evaluated calculating the observed yield Yobs.•Denitrification and phosphorus release were detected inside the sludge holding tank.•OSA sludge production was low compared to conventional activated sludge system.