Abstract
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 3.5-4.0 L/L/day and four cycles (with and without effluent recycle) as anaerobic/aerobic reactor at two HLR (3.5 and 5.2 L/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 10 mg N/L. The reactor produced good settled sludge with sludge volume index (SVI) of 46-74 ml/g for aerobic cycles and 18-50 ml/g for anaerobic/aerobic cycles. The average sludge production was 0.145 g TSS/g COD removed.