Towards improved understanding of the hydrodynamics of a semi-partition bioreactor (SPB): A numerical investigation

Abstract

Extractive fermentation is a technology used to combat product inhibition. However, there has been comparatively low adoption of this technique in industry and this can be attributed to, among other reasons, a need for novel and optimised bioreactor configurations to facilitate this unit operation. Recent research has proposed a novel Semi-Partition Bioreactor (SPB) which combines the fermentation (mixer section) and extraction (settler section) steps in one reactor thus simplifying the operation of extractive fermentation. However, while the bioreactor was shown to be feasible, an improved understanding of the reactor’s hydrodynamics is required to allow for optimised designs. This study thus focuses on the use of validated Computational Fluid Dynamics (CFD) simulations to investigate the hydrodynamics of the SPB. Key findings illustrate that, unsurprisingly, normal stirred tank reactors’ hydrodynamics are significantly changed by the introduction of a settler. Consequently, the modified hydrodynamics influence the volumetric flux between the fermentation and extraction sections. Accurate modelling of this flux gives insights into various operational choices and physical systems (for instance modifying the settler insert). Key then is accurately matching the CFD model with experimental work. For example, it has been shown that mixing time (in the settler) can be predicted to within 14.8% accuracy if the transient nature of the volumetric flux is considered as opposed to a 57% accuracy if a constant flux is assumed. Finally, a design approach for the in silico prediction of possible volumetric removal rates of top phase from the settler has been proposed. This approach would be of interest to a bioreactor engineer seeking to, for example, estimate an optimal removal rate that prevents over-accumulation of a toxic species and subsequent product inhibition.