High rate partial nitrification treatment of reject wastewater.

Partial nitrification (PN) treatments on reject wastewater were carried out. Dissolved oxygen concentration was limited by controlling air flowrate, which was the main operational strategy in this study. Stable PN performance was obtained during continuous operation for 80 days, with a maximum nitrogen loading rate (NLR) of 4.2 kg-N m(-3) day(-1) and ammonium conversion rate of 2.1 kg-Nm(-3) day(-1). The production of nitrite oxidizers was assumed to be responsible for the nitrogen loss in the reactor. The ratios of NO2--N/ (NO2--N+NO3--N) were always above 99.9%, and BOD removal efficiencies were also stable at around 70% even if a sharp increase in NLR was applied during the stable period. Additionally, bacterial consortia analysis showed ammonium-oxidizing bacteria were the dominant microorganisms, which provided evidence for the long-term stable performance of this PN reactor. During the experiment, sludge setting properties deteriorated due to the absence of a biomass carrier. The stable performance of partial nitrification from reject wastewater demonstrated the feasibility of the operation strategy in this study.