A novel A2N2 system was developed to deal with low C/N domestic wastewater. The operating performance under different nitrification duration distribution ratio in N-SBR unit was investigated. The experiment was conducted as follows: under the condition of A2/O-SBR unit anaerobic was set as 1.5 h

anoxic 2 h

aerobic 0.5 h and the aeration flow rate of A2/O-SBR and N-SBR units was 100 and 120 L·h-1

respectively

and then the nitrification time distribution ratios were set as 5:1

4:1

3.5:1

3:1

7:1 and 8:1 to determine the optimal operation parameter. The results indicated that the efficient utilization of carbon sources was achieved in the A2/O-SBR unit

while the nitrification duration distribution ratio had little impact on the removal of organic substances. In order to ensure a better nitrification and denitrification and phosphorus removal performance

the first nitrification duration time must be≥3.5 h. Under the condition of total nitrification time was unchanged

an appropriate increase in the first nitrification time would greatly improve the system TN removal. An appropriate increase in the secondary nitrification time can reduce the effluent NH4+-N concentration to meet the first A discharge standard in China(GB 18918-2002). When nitrification time allocation ratio was 4:1

the system achieved the optimal nitrogen and phosphorus removal performance with average effluent concentrations of TN and PO43--P of 11.5 and 0 mg·L-1

respectively

and the corresponding average removal efficiency was 75% and 100%

respectively.