Effects of step-feed on long-term performances and N2O emissions of partial nitrifying granules.

This study used two anoxic/oxic sequencing batch reactors (A/O SBRs) respectively with pulse-feed (PF-SBR) and step-feed (SF-SBR) to investigate the effects of step-feed on partial nitrifying granules. The stable partial nitrification lasted 111 and 139 days in PF-SBR and SF-SBR, and then gradually switched to full nitrification. Granules in both reactors showed similar physical properties and excellent ammonia removal performances throughout 253 days operations. The SF-SBR had significantly higher total nitrogen (TN) removal efficiency than the PF-SBR. Based on long-term monitoring, the N2O emissions in SF-SBR decreased 53.8% and 61.6% during partial and full nitrification as compared with that in PF-SBR. Although the removed TN was very limited, most of the N2O was emitted during oxic phases. The percentage of N2O emission to TN removed during oxic phases was 90.75% and 47.21% for PF-SBR, 55.09% and 29.55% for SF-SBR, respectively under partial and full nitrification modes.