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Optimized methods for simultaneous removal of nitrate, nitrite and ammonium are important features of nutrient removal. Nitrogen removal efficiency in an intermittently aerated sequencing batch reactor (IA-SBR) with multiple filling events was studied. No external carbon source was added and three filling events were considered. Oxidationreduction potential (ORP) and pH curve at solids retention time (SRT) of 20 d were analyzed. Effects of three organic loading rates (OLR), 0.67, 1.0 and 1.5 kgCOD/m3d, and three nitrogen loading rates (NLR), 0.054, 0.1 and 0.15 kgN/m3d, on nitrogen removal were studied. Nitrate Apex in pH curve and Nitrate Knee in ORP profile indicated that the end of denitrification would be achieved sooner. The kinetic coefficients of endogenous decay (kd) and yield (Y) were identified to evaluate heterotrophic specific denitrification rate (SDNRb). In period 2 at NLR of 0.054 kgN/m3d and considering 2 anoxic and 3 aerobic phases, nitrogen removal efficiency was 91.43%.