High-rate partial nitrification treatment of reject water as a pretreatment for anaerobic ammonium oxidation (anammox)

In this study, a lab-scale swim-bed partial nitrification reactor was developed to treat ammonium-rich reject water to achieve an appropriate NO2--N/NH4+-N mixture that could serve as a pretreatment for anaerobic ammonium oxidation (anammox). Strictly controlling the DO concentration was adopted as the main operational strategy. In addition, the influent concentrations of inorganic carbon/ammonium (IC/NH4+) and alkalinity/ammonium (Alk/NH4+) that were approximately 0.8 and 4.8, respectively, were regarded as the suitable ratios for the steady and high-rate operation of the reactor in this study. When reject water that was not diluted was introduced to this system, the maximum nitrogen loading rate was 5.9 kg-N/m3/day, the ammonium conversion rate was 3.1 kg-N/m3/day, and the effluent NO2-N/(NO2-N + NO3-N) percentage ratio was over 99.9%. Furthermore, DNA analysis confirmed the existence of AOB, which was responsible for the stable performance that was achieved in the PN reactor.