CFD-kinetic Modelling for the Scale-up of P. putida Fed-batch Fermentations

Bioprocess industry has always struggled with the generation of oxygen and substrate gradients in large-scale bioreactors due to the non-ideal mixing. In microbial processes, scale-down simulators are a practical tool for assessing the microorganism response to the heterogeneous condition of largescale systems. Scale-down simulators use local gradients of various compartments formed in the large-scale system and recreate the condition on a smaller scale. However, experimental monitoring of local concentrations is a demanding task. It is not possible to record experimentally the conditions each cell experiences during its residence time in a fermenter. For this reason, Computational Fluid Dynamics modelling and in particular, coupling the Eulerian model with Lagrangian particle tracking can be of assistance [1]. CFD modelling of large-scale bioreactors enables the prediction of biomass trajectories in a detailed manner in the form of the microorganism’s lifelines and it provides a platform for developing scale-down simulators [2].In this study, an Euler-Lagrange CFD model was developed and was coupled to a kinetic model of Pseudomonas putida in fed-batch mode [3]. The numerical model comprises an Eulerian multiphase system representing the aeration and the liquid phase in combination with a Lagrangian phase representing the biomass. The simulations were performed at three different stages of the fermentation to account for the increase in the broth’s height with continuous feeding and its effect on the mixing and gradient formation. The effect of operating conditions, such as number of impellers and their speed, was also studied on the generation of gradients inside the system.