The aim of the present work was to study the growth of two nitrifying bacteria. For modelling the nitrifying subsystem of the MELiSSA loop, Nitrosomonas europaea ATCC (R) 19718 and Nitrobacter winogradskyi ATCC (R) 25931 were grown separately and in cocultures. The kinetic parameters of a stoichiometric mass balanced Pirt model were identified: mu(max) = 0.054 h(-1), decay rate b = 0.003 h(-1) and maintenance rate m = 0.135 gN-NH4+.gX(-1).h(-1) for Nitrosomonas europaea; mu(max) = 0.024 h(-1), b = 0.001 h(-1) and m = 0.467 gN-NO2.gX(-1).h(-1) for Nitrobacter winogradskyi. A predictive structured model of nitrification in co-culture was developed. The online evolution of the addition of KOH is correlated to the nitritation; the dissolved oxygen concentration is correlated to both nitritation and nitratation. The model suitably represents these two variables so that transient partial nitrification is assessed. This is a clue for avoiding partial nitrification by predictive functional control. (C) 2016 Elsevier Ltd. All rights reserved.