Performance of aerated submerged biofilm reactor packed with local scoria for carbon and nitrogen removal from municipal wastewater

•A single anaerobic/aerobic biofilm reactor is better than the aerobic reactor.•Effluent recycling in single anaerobic/aerobic reactor enhances TN removal.•Effluent recycle in the aerobic submerged biofilm reactor enhances ammonification.•The system produces sludge with good settling properties.•An average sludge production in the reactor was 0.145g TSS/g COD removed. An up-flow submerged biofilm reactor packed with scoria was evaluated for municipal wastewater treatment. The reactor was operated two cycles (with and without effluent recycle) as single aerobic reactor at hydraulic loading rate (HLR) of 3.5–4.0L/L/day and four cycles (with and without effluent recycle) as anaerobic/aerobic reactor at two HLR (3.5 and 5.2L/L/day). Results indicated better removal efficiency in case of anaerobic/aerobic cycles especially for ammonia and total nitrogen. Effluent recycling in the aerobic reactor enhanced ammonification with significant reduction in ammonia and nitrogen removal, while in case of single anaerobic/aerobic reactor the effluent recycling improved ammonia and nitrogen removal and kept nitrate concentration in the final effluent below 10mgN/L. The reactor produced good settled sludge with sludge volume index (SVI) of 46–74ml/g for aerobic cycles and 18–50ml/g for anaerobic/aerobic cycles. The average sludge production was 0.145g TSS/g COD removed.