Abbreviations: TAN: total ammonia nitrogen TOC: total organic carbon VSS: volatile suspended solidsReported models of denitrification rates integrate in an unique parameter the pH-dependent inhibition by HNO 2 and the pH effect on the bacterial metabolic activity; furthermore, they do not quantify separately the pH effect on the nitrate and on the nitrite reduction *Corresponding author rates. The goal of this work was to quantify both effects on the kinetics of nitrate and nitrite reduction to improve the models' predictive value. Assays were performed at a pH range of 6.5-9.0 in batch reactors at 37ºC with an activated sludge. At the studied pH range