The optimal automation of the acclimation process of a biorreactor, for treating toxicant wastewaters, may be possible if a sound mathematical model is developed in order to cope with the instrumentation limitations that exist nowadays. This work presents a first step in creating such a model. Experimental data was used to identify the changing kinetic parameters of the model as acclimation progresses. It was found that only one key parameter changed during the acclimation process. Then an acclimation model, i.e. a model of such a parameter progression in time, as a function of the total substrate treated, is proposed.