Characterization of denitrification and nitrification in a step-feed alternating anoxic-oxic sequencing batch reactor

This study was conducted to. characterize the denitrification and nitrifica tion in a bench-scale sequencing batch reactor operating with a three-stage , alternating anoxic-oxic sequence and step feed (SAOSBR) for treating synt hetic wastewater. The results of long-term operation and dynamic studies sh owed that the SAOSBR increased the availability of organic matter in wastew ater for exogenous denitrification in anoxic periods, and subsequently allo wed nitrification to occur under a lower organic loading in oxic periods. C omparatively high kinetic rates of 1.2 to 6.6 mg nitrate/g mixed liquor sus pended solids (M.SS) . h for denitrification and 1.0 to 2.8 mg nitrogen/g M LSS . h for nitrification were found in dynamic studies. With sufficient in fluent organics and alkalinity, complete denitrification and full nitrifica tion could be achieved sequentially in the alternating anoxic and oxic peri ods, resulting in an average total nitrogen removal efficiency up to approx imately 90%. Alkalinity recovery because of exogenous denitrification was e xperienced, and a minimum influent alkalinity to total Kjeldahl nitrogen (T iffs) ratio of 2.4 was required to reach complete TKN removal. The pH value would be a better parameter other than oxidation-reduction potential or di ssolved oxgyen to determine the completeness of nitrification. and denitrif ication in the SAOSBR.