ENHANCING OXYGEN-TRANSFER IN BIOREACTORS BY PERFLUOROCARBON EMULSIONS

This work aims to investigate the capability of perfluorocarbon (PFC) emulsions in enhancing oxygen transfer in bioreactors. Based on the penetration theory, a model has been derived for evaluating the potential oxygen transfer enhancement effects of PFC emulsions with very fine PFC particles. Defined as the ratio between the maximum oxygen transfer rates in systems with and without the emulsions, the enhancement factor achievable with dilute PFC emulsions can be estimated as the square root of the product of ratios of oxygen permeability and solubility in media with and without the emulsions. The effect of PFC emulsions on oxygen transfer in low-shear cultivation systems was further studied experimentally with direct measurements of volumetric oxygen transfer coefficients, kappa-L(a), in bioreactors and with microbial fermentations conducted under low-shear conditions. It was found that significantly higher cell populations could be maintained at an aerobic state by using systems supplemented with the investigated emulsions. The experimentally determined values of oxygen transfer enhancement factor compare well with the theoretical values for emulsions with up to 15% (v/v) PFC. The feasibility of enhancing oxygen transfer in bioreactors by introduction of adequate amounts of PFC emulsions was clearly demonstrated.