In order to assess the variations of nitrogen removal performance and nitrogen concentrations at different frequencies of alternating aerobic/anoxic (FAA) and same ratio of aeration time to anoxic time (2 min∶2 min

4 min∶4 min

10 min∶10 min

30 min∶30 min

and 120 min∶120 min)

mature partial nitrification sludge from laboratory was inoculated to sequencing batch reactor (SBR) at room temperature (18-20 ℃). Results showed that good partial nitrification was maintained at different FAA. The average nitritation rate and ammonia oxidation rate were 89.7% and 87.1%

respectively. When the aeration time: anoxic time was 2 min∶2 min

total nitrogen removal efficiency (TNE) increased to 88.4% and remained stable. With the increase of the aeration time∶anoxic time (decline of FAA)

the TNE tended to decrease

and it reduced to 56.2% when the aeration time∶anoxic time was 120 min∶120 min. Owing that with high FAA (2 min∶2 min)

the nitrite generated during the aeration period could be used by the denitrifying bacteria timely in the next anoxic phase

TNE was increased

and FAA was positively correlated with it. Results of beaker experiment showed that the maximum ammonia utilization rate (RAU) and maximum nitrate production rate (RNP) were 10.387 and 0.42 mg/(g·h) with the aeration time∶anoxic time of 2 min∶2 min. It indicated that the ammonia oxidation rate was faster with higher FAA

which can reduce the relative amount of nitrite oxidizing bacteria (NOB).