Modeling and scale-up of the unsterile scleroglucan production process with Sclerotium rolfsii ATCC 15205

An empirical model was applied to describe the growth related formation of scleroglucan in batchwise cultivation of Sclerotium rolfsii. In this case, the level of oxygen supply controls the carbon flux into glucan, biomass, a nd CO2 evolution and therefore determines the yield coefficients Y-Glucan/B DM and Y-BDM/O2, It was observed that scleroglucan formation is enhanced un der microaerobic conditions. However, as the empirical model and data of ac tual batch cultivations show, different maxima exist for product end concen tration [g/l] and volumetric productivity [g/ld] depending on the total oxy gen uptake during cultivation. A sufficient bulk mixing of the highly visco us culture suspension becomes particularly important during large-scale cul tivations. addition, the scleroglucan production process proved to be shear sensitive. A correlation between the attainable molecular weight of the gl ucan and the stirrer tip velocity in bioreactors of different sizes is pres ented. For all these reasons, a scale-up of this process is very complex. L arge-scale cultivations under microaerobic conditions, aiming for maximum p roduct end concentration, were slowed down by poor bulk mixing leading to a lower carbon flux into glucan formation. On the other hand, a scale-up des igned for maximum volumetric productivity using high oxygen supply was succ essfully conducted up to a reactor volume of 1.500 l. To minimize the loss in product quality (molecular weight of the glucan) due to high stirrer tip velocities, a mixing concept was developed employing reduced agitation com bined with maximum aeration to secure a sufficient axial bulk mixing in the reactor.