Effect of nitrogen loading rate and alkalinity on partial nitritation in a continuous stirred tank reactor

In order to achieve an appropriate effluent ratio of ammonium and nitrite as an influent of the anaerobic ammonium oxidation process, the optimum conditions for the partial nitritation in a continuous stirred tank reactor (CSTR) were investigated using real reject water. Hydraulic retention time (HRT) and influent alkalinity (HCO3-)/NH4+-N ratio were major factors that greatly influenced the partial nitritation. As a result of continuous operation, ammonium conversion efficiency (ACE) and effluent nitrite to ammonium ratio (NAR) could be achieved at the HRT of 19 h corresponding to 0.71 kg/m3/d of nitrogen loading rate (NLR). Thereafter, the influent HCO3-/NH4+-N ratio was adjusted from 0.5 to 2, and as a result, the optimum partial nitritation efficiency was maintained when the influent HCO3-/NH4+-N ratio was one. The suitability of the determined operating conditions was verified in a CSTR over 30 d of operation time.