Effect of operating regime on the performance of biofilm reactor treating municipal wastewater

Municipal wastewater represents a non-conventional resource of water and should be treated for possible reuse. Effect of operating regime on the performance of biofilm system containing sponge as biofilm carrier was examined using municipal wastewater. The system was run for 17 days to allow biofilm growth. After achieving steady state, the system was operated as single aerobic system for two cycles (cycle 1 at hydraulic loading rate of 3.46 L/L.d and cycle 2 at hydraulic loading rate of 3.77 L/L.d) and combined anaerobic/aerobic for four cycles; cycles 3 and 4 at low hydraulic loading rate (3.73 and 3.46 L/L.d) and cycles 5 and 6 at high hydraulic loading rate (5.12 and 75.34 L/L.d). During cycles 1 and 2, effluent recycle increases residual values of the treatment parameters in the treated effluent except phosphorus. During cycles 3 and 4, the effluent recycle non-significantly improves the percentage removal of turbidity, total suspended solids, chemical oxygen demand, ammonia and total Kjeldahl nitrogen. For total nitrogen and total phosphorous the improvement in the percentage removal was significant. During cycles 5 and 6, effluent recycle non-significantly affects the percentage removal of treatment parameters except total phosphorous which was significantly increased. The rate of excess sludge was 0.13 g solid per g chemical oxygen demand removed. Average sludge volume index of 58.5 ml/g and 54.7 ml/g was obtained during cycles 1 and 2 and cycles 3–6, respectively. The combined anaerobic/aerobic biofilm reactor with effluent recycle has better performance than aerobic biofilm reactor regarding sludge production and effluent quality.