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

This study was conducted to characterize the denitrification and nitrification in a bench-scale sequencing batch reactor operating with a three-stage, alternating anoxic-oxic sequence and step feed (SAOSBR) for treating synthetic wastewater. The results of long-term operation and dynamic studies showed that the SAOSBR increased the availability of organic matter in wastewater for exogenous denitrification in anoxic periods, and subsequently allowed nitrification to occur under a lower organic loading in oxic periods. Comparatively high kinetic rates of 1.2 to 6.6 mg nitrate/g mixed liquor suspended solids (MLSS) x h for denitrification and 1.0 to 2.8 mg nitrogen/g MLSS x h for nitrification were found in dynamic studies. With sufficient influent organics and alkalinity, complete denitrification and full nitrification could be achieved sequentially in the alternating anoxic and oxic periods, resulting in an average total nitrogen removal efficiency up to approximately 90%. Alkalinity recovery because of exogenous denitrification was experienced, and a minimum influent alkalinity to total Kjeldahl nitrogen (TKN) 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 dissolved oxgyen to determine the completeness of nitrification and denitrification in the SAOSBR.