Partial nitrification using aerobic granules in continuous-flow reactor: Rapid startup

•Nitritation granules were cultivated in this study.•Cultivation period of nitritation granules noted was 52days.•The Pseudoxanthomonas mexicana strain were enriched enhance granule stability.•Nitrosomonas europaea was enriched in granules to achieve 85–90% nitritation. This study applied a novel strategy to rapid startup of partial nitrification in continuous-flow reactor using aerobic granules. Mature aerobic granules were first cultivated in a sequencing batch reactor at high chemical oxygen demand in 16days. The strains including the Pseudoxanthomonas mexicana strain were enriched in cultivated granules to enhance their structural stability. Then the cultivated granules were incubated in a continuous-flow reactor with influent chemical oxygen deamnad being stepped decreased from 1500±100 (0–19days) to 750±50 (20–30days), and then to 350±50mgl−1 (31–50days); while in the final stage 350mgl−1 bicarbonate was also supplied. Using this strategy the ammonia-oxidizing bacterium, Nitrosomonas europaea, was enriched in the incubated granules to achieve partial nitrification efficiency of 85–90% since 36days and onwards. The partial nitrification granules were successfully harvested after 52days, a period much shorter than those reported in literature.