Evaluating the process performance and potential of a high-rate single airlift bioreactor for simultaneous carbon and nitrogen removal through coupling different pathways from a nitrogen-rich wastewater.

The feasibility of a continuous feed and intermittent discharge airlift bioreactor for simultaneous carbon and nitrogen removal from a low COD/N wastewater was evaluated. The effect of two independent variables, HRT (10-20 h) and NH4+/(NH4++NO3-) ratio (0.25-0.75), on the bioreactor performance was studied. The relatively high anaerobic to aerobic time ratio made an effective contribution to NH4+, NO3-, and TN removal. TN removal was enhanced with increase in HRT and decrease in NH4+/NH4++NO3- and at the optimum condition, 616 mg/L (88%) and 213 mg/L (76%) of sCOD and TN were removed, respectively. The results suggested that the nitrogen removal process was based on a combination of anaerobic ammonium oxidation (Anammox), simultaneous nitrification-denitrification (SND), and presumable dissimilatory nitrate reduction to ammonium (DNRA) mechanisms.