(546a) Mass Transfer in a Von Kármán Bioreactor to Improve Fermentation

Heterogeneity in bioreactors poses a challenge for commercialization of many biochemical processes as it can significantly impact product quality and process scaleup. To tackle these challenges, novel approaches are needed to better manage environmental trajectories experienced by microorganisms. In this work we discuss the usage of von Kármán swirling flow to both reduce reactor heterogeneity and mass transport limitations. Here, we describe the development of a benchtop von Kármán reactor (vKR) and compare its performance with an analogous stirred tank bioreactor in a case study for producing citramalate in a yeast strain. Citramalate is the precursor of poly methyl methacrylate, a transparent material known as acrylic glass or plexiglass.

Experiments were performed in a 3-L vKR to characterize the volumetric gas-liquid mass transport coefficient (k_La) as well as gas holdup as a function of impeller speed and gas flow rate, from which dimensionless correlations were developed. Compared with stirred tank reactors of similar volume, the values of k_La and gas holdup produced in the vKR are significantly larger. When compared with analogous fermentation experiments performed in a conventional stirred bioreactor, it is evident that even small volume (2-L) stirred bioreactors can be susceptible to mass transfer limitations, which in turn limits their use to quickly grow biomass and in characterizing biokinetics. In such situations, a von Kármán bioreactor may provide an alternative to overcome this problem. Lastly, we examine the possibility of further improving the von Kármán bioreactor efficiency by optimizing oxygen feed rate to manipulate metabolic flux distributed between organism growth and production of the target product.