The combined effects of dissolved oxygen (DO) and pH on nitrogen removal were investigated in a laboratory-scale sequencing batch reactor (SBR) with anammox-enriched granular sludge obtained from a nitritation/anammox system. The highest specific nitrogen removal rate (SNRR) (1.1 gN gVSS(-1) d(-1)) was observed under non-aerated conditions, resulting in the nitrogen removal efficiency of 81.6%. Although nitrogen removal was readily inhibited under aerated conditions, an increased SNRR occurred at the DO concentration of 0.5 mg O-2 L-1. This is in contrast with the directional DO suppression on nitrogen removal in the anammox process, indicating that other nitrogen conversion pathways, such as nitrification and endogenous denitrification, were also active in the studied reactor. The highest SNRRs were obtained within a pH range of 6.5-8.5, characterized by low concentrations of free ammonia (FA) and free nitrous, acid (FNA). Oxygen-consuming bacteria (nitrifiers) were implicitly inhibited by the low pH so that less oxygen was utilized. In tests carried out using the optimum pH physiological range (6.5-8.5) for microorganisms, an explicit DO elbow was observed when the ammonium and nitrite were almost completely removed. This finding confirms the occurrence of nitrogen removal by the oxygen-consuming bacteria in the system studied. (C) 2016 Elsevier Ltd. All rights reserved.