Abstract
The sufficient provision of oxygen is mandatory for enzymatic oxidations in aqueous solution, however, in process optimization this still is a bottleneck that 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 with macrobubble aeration. Comparing the aerators at identical kL a of 160 and 60 1/h, the microbubble aeration is resulting in 25 and 44 times enhanced gas utility compared with aeration with macrobubbles. To prove the feasibility of microbubbles in biocatalysis, the productivity of a glucose oxidase catalyzed biotransformation is compared with macrobubble aeration as well as the gas-saving potential. In contrast to the expectation that the same productivities are achieved at identically applied kL a, microbubble aeration increased the gluconic acid productivity by 32% and resulted in 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.
Highlights
To compare a novel fine bubble with classic macrobubble aeration techniques and prove the feasibility for application in biocatalysis, this contribution is focusing on oxygen as a gaseous substrate
This study focuses on the comparative investigation of microbubble and macrobubble aeration applied in oxygen‐consuming glucose oxidase (GOx) catalyzed biotransformation towards the product gluconic acid
The investigation shows that the microbubble aerators, Shirasu Porous Glass (SPG) and sintered frit, achieve significantly higher mass transport performance in the vvm range of 0.017–16.67 compared with open pipe macrobubble aeration in a BSA containing solution
Summary
To compare a novel fine bubble with classic macrobubble aeration techniques and prove the feasibility for application in biocatalysis, this contribution is focusing on oxygen as a gaseous substrate. There is a need for highly efficient aeration techniques in the industry Requirements for these aeration systems are a high mass transfer performance, efficient gas utilization, low‐pressure drop, low shear stress, and reduced foaming tendency (Terasaka, Hirabayashi, Nishino, Fujioka, & Kobayashi, 2011). Microbubble aeration offers several advantages due to its simple generation and promising high dissolution rates in aqueous media (Iwakiri et al, 2017; Jia et al, 2019) This enhanced mass transfer performance results first from the high volume‐specific interfacial area and second from the prolonged residence time by low rising velocity as shown in Figure 1 (Duval et al, 2012; Struthwolf & Blanchard, 1984; Terasaka et al, 2011). To get a deeper understanding and interpretation of the effects influencing the productivity after 3.5 h, a detailed characterization of the model enzyme GOx Type VII from A. niger is carried out
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