Scale-up of microbubble dispersion generator for aerobic fermentation

摘要

A laboratory-scale microbubble dispersion (MBD) generator was shown to improve oxygen transfer to aerobic microorganisms when coupled to the conventionalair-sparer.However,the process was not demonstrated on a large scale to prove its practical aplication.We investigated the scale-up of a spinning-disk MBD generator for the aerobic fermentation of Saccharomyces cerevisiae(backer'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 invesgigated,the MBD genwerator maintained an adequate supply of surfactant-stabilized air microbubbles to the microorganisms at a relatively low agitation rate (150rpm).There was a signicant improvement in oxygen transfer to the microorgansim relative to the conventional sparger.The volumetric mass transfer coefficient ,k,a,for the MBD ssytem at 150 rpm was 765 h~(-1) compared to 937 h~(-1) for the conventianl sparger at 500 rpm was 765 h~(-1) compared to 937 h~(-1) for the conventaional sparger at 500 rpm.It is plausible to surmise that fermentation using larger working voumes may furter improve the k_La values and the dissolved oxygen (DO)levels because of longer hold-p 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 achievd for the conventional air-sparged system (0.53 g/g) at an agitation rate of 500rpm.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 opeating costs for aerobic fermentation.