Pros and cons of airlift and bubble column bioreactors: How internals improve performance

Gas fermentation is a promising technology of high commercial interest, particularly for capturing CO 2 and CO from industrial off-gases to reduce greenhouse gas emissions and replace fossil fuels for bulk chemical production. Therefore, evaluating promising bioreactor settings ab initio is a crucial step. Whereas alternate configurations may be tested in laborious scale up studies, the procedure may be accelerated by in silico studies that accompany or even partially replace wet-lab work once the models are validated. In this context, the current study compares various pneumatically agitated reactor types – bubble column reactor (BCR), annulus- and center-rising internal-loop airlift reactor (AR-IL-ALR and CR-IL-ALR), and external-loop airlift reactor (EL-ALR) – to identify advantages and disadvantages for the given application based on computational fluid dynamics (CFD) models. Process performance is optimized by introducing internal structures to guide the flow. Despite a significant increase in the mass transfer coefficient ( k L a ) through internal modifications, the CR-IL-ALR still exhibited the poorest performance. The optimized AR-IL-ALR demonstrated good mixing and, after introducing an open-cone shaped internal in the head part and a conical bottom, superior mass transfer, achieving an enhancement over 10 % in the mass transfer coefficient to 315 1/h. This study thereby outlines the potential of internal structures for process improvement, as well as the value of a priori in silico design of reactor configurations. • Computational tools can reveal process improvements by internal structures. • BCRs have high mass transfer but poorer mixing than ALRs. • The AR-IL-ALR performed superior compared to other reactors after optimization.