Control of partial nitritation of centrate in a sequencing batch reactor

This research identified suitable conditions for long-term inhibition of nitrite-oxidizer bacteria (NOB) in a sequencing batch reactor for the treatment of centrate by over-nitrite pathways. The NOB were inhibited by free ammonia concentrations greater than 20 mg NH3-N/L combined with a dissolved oxygen concentration less than 0.3 mg O2/L and a temperature of 30 degrees C. The experiments were performed in a laboratory-scale 2.5-L reactor fed with synthetic and actual centrate from a full-scale wastewater treatment plant (800 to 1500 mg NH4+ -N/L). The influence of influent-alkalinity-to-ammonium ratio (AAR) on the effluent-nitrite-to-ammonium ratio (NAR) also was investigated. The control of the effluent NAR was possible by adjusting the influent AAR when NOB inhibition was maintained and when total alkalinity depletion took place before the end of the cycle. The maximum nitritation rate of 860 mg NO2- -N oxidized/L x d was obtained when the influent NH4+ -N concentration was 800 mg NH4+ -N/L and the hydraulic retention time was 1.7 days.