Nitrogen and phosphorus removal paths in a sequencing batch reactor - dependence on a dissolved oxygen profile in aerobic phases

This paper presents results of wastewater treatment in a sequencing batch reactor operating at a dissolved oxygen (DO) setpoint of 1 mg O-2 l(-1) in the aerobic phase. It has been demonstrated that depending on the DO concentration profile (in time) in aerobic phases, paths of N and P removal in the reactor are different. Simultaneous denitrification depends on the amount of time when DO concentration is below 1 mg O-2 l(-1). A relatively large uptake of easily biodegradable organic substrates in the first anoxic/anaerobic phase (I A/A) results in the reduction of nitrates in aerobic phases with internally stored organics as a carbon source. This may promote the growth of denitrifying phosphorus-accumulating organisms in the process. In the second A/A phase, synergic N and P removal was observed. The process was limited by nitrite and nitrate concentrations.