Nitritation and denitrifying P removal under mode of nitritation and nitrification was investigated in continuous MUCT process treating domestic wastewater. Nitritation was established through short hydraulic retention time to 6 h and low dissolved oxygen concentration of 0.3-0.5 mg/L. Nitritation was stabilized for 95 days with average nitrite accumulation ratio over 90%. Ammonia and total nitrogen removal under nitritation reached 99% and 83%, respectively, much better than complete nitrification. Real-time quantitative PCR assays presented that cell numbers and percentages of ammonia oxidizing bacteria (AOB) population had a clear correlation with nitrite accumulation ratios. The highest percentage of AOB was 13% of total bacterial population. P removal was mainly completed by denitrifying P removal of about 90% occurring in anoxic zone. The P removal efficiency under nitritation was 30% higher than that under complete nitrification. Denitrifying P removal under nitritation was highly beneficial to the treatment of wastewater with limiting carbon source. (C) 2013 Elsevier Ltd. All rights reserved.