[Partial nitrification in SBR under normal temperature and limited oxygen condition].

Partial nitrification was researched in a SBR reactor under the limited oxygen condition (DO 0.3-0.4 mg/L) and the normal temperature of 14.1-24.2 degrees C to produce the correct influent for ANAMMOX process from secondary wastewater (NH4+ -N 30-100 mg/L). The influent for the ANAMMOX process must be composed of NH4+ and NO2- in a ratio of 1/1.31 and therefore only a partial nitrification of ammonium into nitrite was required. The control of alkalinity and the indication of monitoring profile of DO allowed to achieve this partial nitrification with a final effluent only composed of NH4+ -N and NO2(-) -N at the right stoichiometric ratio. The equal consumption of HCO3- /NH4+ in secondary wastewater resulted in a natural pH decrease when approximately 57% of NH4+ -N was oxidized. When the pH dropped to a certain level, the lowering of the metabolic rate of the ammonium oxidizer would lead to rapid decline of the oxygen uptake rate (OUR) in reactor, and the jump characteristic point (it was distinguished by the jump over 1.0 mg/L of DO value) in the DO profile would emerge, which signalled the end-point of the partial nitrifying. The optimum alkalinity of partial nitrification was studied under 4 concentrations in the range of NH4+ -N 30-100 mg/L of secondary wastewater. The result indicated that the bicarbonate/ammonium ratio was the key factor influencing the nitrification ratio (NO2-/NH4+), and it was absolutely possible to successfully achieve partial nitrification that provided right substrate for ANAMMOX reactor through the control of the alkalinity.