The present study investigated effect of ammonium utilization on aerobic denitrification by Pseudomonas stutzeri T13. Per nitrogen balance calculation, all consumed ammonium was utilized as nitrogen source for cell propagation by assimilation rather than heterotrophic nitrification. Total organic carbon (TOC) and ammonium were necessary substrates to sustain heterotrophic propagation of P. stutzeri T13 at optimum proportion equal to seven. Under aerobic condition, nitrate was utilized as substitute nitrogen source when ammonium was completely exhausted. Biomass production effectively increased with increasing initial ammonium from 0 mg/L to 100 mg/L. Owing to enlarged biomass, average nitrate reduction rate increased from 7.36 mg L-1 h(1) to 11.95 mg L-1 h(1). Such process also successfully reduced nitrite accumulation from 121.8 mg/L to 66.16 mg/L during aerobic denitrification. As important accessory during aerobic denitrification, ammonium assimilation efficiently doubled total nitrogen (TN) removal from 54.97 mg/L (no ammonium provided) to 113.1 mg/L (100 mg/L ammonium involved). (C) 2017 Elsevier Ltd. All rights reserved.