A numerical investigation of the hydrodynamics and mass transfer in a three-phase gas-liquid-liquid stirred tank reactor

Industrially relevant bioprocesses such as paraffin activation present a complex multiphase system consisting of an aqueous growth medium and an immiscible alkane phase that is aerobically metabolized by active micro-organisms. Thus, the oxygen transfer rate from sparged gas is a key design parameter for which empirical correlations have been proposed to inform bioreactor design. However, a fundamental predictive approach is needed to enable the evaluation of novel multiphase bioreactor designs in silico. This study reports on the development of a fundamental predictive model of oxygen transfer based on computational fluid dynamics. Key findings suggest that the alkane phase impacts the hydrodynamics by turbulence modulation rather than a change in fluid properties. The model-predicted oxygen transfer rate is compared to experimental measurements and shown to have an accuracy similar to empirical correlations. However, only the fundamental model captures complex interactions arising due to the alkane phase and can thus be more readily extrapolated to novel multiphase bioreactor designs. The insights gained in this study will guide future investigations into the simulation of hydrodynamics and oxygen transfer in the presence of micro-organisms, thereby providing a fundamental approach to bioreactor scale-up.