Scale-up of microbubble dispersion generator for aerobic fermentation |
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Authors: | Hensirisak P Parasukulsatid P Agblevor F A Cundiff J S Velander W H |
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Institution: | (1) Biological Systems Engineering Department, Virginia Polytechnic Institute and State University, 24061 Blacksburg, VA;(2) Department of Chemical Engineering, Virginia Polytechnic Institute and State University, 24061 Blacksburg, VA |
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Abstract: | A laboratory-scale microbubble dispersion (MBD) generator was shown to improve oxygen transfer to aerobic microorganisms when
coupled to the conventional air-sparger. However, the process was not demonstrated on a large scale to prove its practical
application. We investigated the scale-up of a spinning-disk MBD generator for the aerobic fermentation of Saccharomyces cerevisiae (baker’s yeast). A 1-L spinning-disk MBD generator was used to supply air for 1- and 50-L working volume fermentation of
baker’s yeast. For the two levels investigated, the MBD generator maintained an adequate supply of surfactant-stabilized air
microbubbles to the microorganisms at a relatively low agitation rate (150 rpm). There was a significant improvement in oxygen
transfer to the microorganism relative to the conventional sparger. The volumetric mass transfer coefficient, k
L
a, for the MBD system at 150 rpm was 765 h−1 compared to 937 h−1 for the conventional sparger at 500 rpm. It is plausible to surmise that fermentation using larger working volumes may further
improve the k
L
a values and the dissolved oxygen (DO) levels because of longer hold-up times and, consequently, improve cell growth. There
was no statistically significant difference between the cell mass yield on substrate (0.43 g/g) under the MBD regime at an
agitation rate of 150 rpm and that achieved for the conventional air-sparged system (0.53 g/g) at an agitation rate of 500
rpm. The total power consumption per unit volume of broth in the 50-L conventional air-sparged system was threefold that for
the MBD unit for a similar product yield. Practical application of the MBD technology can be expected to reduce power consumption
and therefore operating costs for aerobic fermentation. |
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Keywords: | Microbubble fermentation aeration Saccharomyces cerevisiae power consumption |
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