The aim of this work is to evaluate, through experimental monitoring and modelling, to what extension is possible to affect the kinetic parameters of Ammonia Oxidizing Bacteria (AOB) through the continuous inoculum (bioaugmentation) with AOB selected in a different reactor and characterized by different kinetics. Two membrane bioreactors (MBR) pilot plants were used to simulate the continuous inoculum of nitrifying sludge from a side-stream reactor treating synthetic wastewater, similar to anaerobic digester supernatant, to a main-stream reactor operated with low solids retention time (SRT = 2.5 d) treating real domestic wastewater. An activated sludge model (ASM), with two step nitrification denitrification (ASMN) was applied to carry out the evaluation in both MBRs, while conventional batch kinetic tests were performed to estimate AOB kinetic parameters. Through modelling it was possible to clearly demonstrate that effectiveness of bioaugmentation, especially within a certain range of temperature in the seeded reactor. The nitrification process, prior to bioaugmentation, was well described using two different sets of kinetic parameters, that is the half-saturation constant for ammonia (KNH) and the maximum specific growth rate (μmax,AOB), estimated in the side-stream (KNH = 0.8±0.15 mg N-NH4 L-1; μmax,AOB = 0.95±0.02 d-1) and main-stream (KNH = 0.39±0.17 mg N-NH4 L-1; μmax,AOB = 0.84±0.019 d-1) MBRs. Despite the significant difference between the KNH in the reactors, the continuous inoculum of biomass from the side stream, was not followed by the expected change (increase) in the half saturation constant in the seeded reactor where the parameters remained practically unchaged (KNH = 0.4±0.14 mg N-NH4 L-1; μmax,AOB = 0.85±0.015 d-1).