A structured mixing model was built and coupled with an unstructured microbial kinetic model. The integrated mathematical model enables to simulate the concentrations of the reaction components for a fermentation under different operational conditions, with respect to scale-up. The mixing model contains four parameters (V-m/V, N, t(c,rad) and t(c,ax)) which are dependent upon the experimental conditions. In the model the reactor volume is divided into regions with axial exchange flow between them. The number of regions is equivalent to the number of turbines in the fermentor. The most important operational variables are stirrer revolutions, aeration rate, viscosity and reactor volume. As a bioprocess the batch production of glutamic acid by Brevibacterium sp. was chosen. The kinetic of this process is described by unstructured model. The Runge-Kutta-Feldberd method is used to solve the resulting integrated mathematical model. For the scale-up of a batch bioprocess the effect of the feeding components (base for neutralisation of product, oxygen) on the fermentation show the most important influence. This will be shown in this presentation in the case of different mixing conditions as a function of scale-up.