Ammonia nitrogen removal in step-feed rotating biological contactors

The effect of step-feed on biological ammonia nitrogen (NH3-N) removal in a rotating biological contactor (RBC) system consisting of two three-stage units (one control and one step-feed) treating synthetic wastewater was examined. The performance of the step-feed RBC was evaluated in comparison to a regularly fed RBC in terms of NH3-N removals and stage-dissolved oxygen (DO) conditions over a range of hydraulic and organic loading rates (HLR = 0.032 to 0.125 m(3) m(-2). d(-1) and OLR = 11.03 to 111.6 g COD m-2.d(-1)). The results indicate that the step-feed unit showed better removal efficiency (%) at high HLR and ORL than the regularly fed control unit. Increasing the HLR and the OLR resulted in a decrease in DO in all the stages of the two units. However, DO values in the step-feed system were higher than those recorded for the control system. In addition, O-2 limiting conditions (DO < 2 mg l(-1)) and heavy growth of Beggiatoa were detected in stage 1 of the control unit at high loading rates.