Comparative Investigation of Fine Bubble and Macrobubble Aeration on Gas Utility and Biotransformation Productivity.

The sufficient provision of oxygen is mandatory for enzymatic oxidations in aqueous solution, however in process optimization this is still a bottleneck which cannot be overcome with the established methods of macrobubble aeration. Providing higher mass transfer performance through microbubble aerators, inefficient aeration can be overcome or improved. Investigating the mass transport performance in a model protein solution, the microbubble aeration results in higher kL a values related to the applied airstream in comparison to macrobubble aeration. Comparing the aerators at identical kL a of 160 1/h and 60 1/h, the microbubble aeration is resulting in 25 and 44 times enhanced gas utility compared to aeration with macrobubbles. In order to prove the feasibility of microbubbles in biocatalysis, the productivity of a glucose oxidase catalyzed biotransformation is compared to macrobubble aeration as well as the gas-saving potential. In contrast to the expectation that the same productivities are achieved at identical applied kL a, microbubble aeration increased the gluconic acid productivity by 32 % and resulted in a 41.6 times higher oxygen utilization. The observed advantages of microbubble aeration are based on the large volume-specific interfacial area combined with a prolonged residence time, which results in a high mass transfer performance, less enzyme deactivation by foam formation and reduced gas consumption. This makes microbubble aerators favorable for application in biocatalysis. This article is protected by copyright. All rights reserved.