COD, ammonia and dissolved oxygen time profiles in the simultaneous nitrification/denitrification process

Research was undertaken to examine the time courses of COD, NH3N and DO during the simultaneous nitrification/denitrification (SND) process, with particular reference to the question of whether SND is a physical or microbiological phenomena. Two lab-scale sequencing batch reactors were operated under controlled conditions using seed material from a local wastewater treatment plant and a synthetic wastewater. The reactors were operated for a period of 9 months while intensive track studies and online monitoring were used to observe the influence of changes to influent conditions on chemical time profiles. Typically, over 75% of nitrogen removal was achieved through the SND process. Two distinct dissolved oxygen plateaus before ultimate DO breakthrough corresponding to COD and NH3N depletion were observed. However, the time courses of the chemical parameters monitored could reasonably support both physical and microbiological explanations for nitrogen removal via SND.