ABSTRACT
Using a model system, a concept for the immobilization of microbial cultures within alginate beads directly in a 1500-L fermentor with a height to diameter ratio of 1.85 is described. The system is comprised of a 60-cm diameter bowl fixed to the top of an agitation shaft, where calcium-ion-rich media is continuously recirculated from the bulk solution to the bowl. The rotation of the shaft and bowl creates a climbing film (vortex) of solution. An atomizing disk centrally recessed within the bowl sprays an alginate solution into the climbing film where the droplets harden into beads. The effect of heat treatment on the alginate solution on resulting bead properties was examined. The sterilization operation did not appear to have a major effect on the alginate bead mechanical properties of firmness and elasticity which was much more a function of alginate concentration. Beads of various sizes were produced by the unit. The system was characterized by the dimensionless numbers Reomega = (omega x rho x D(2))/mu and ReQ = (Q x rho)/(mu x D). At Reomega and ReQ values less than 500 and 0.15, respectively, the mechanism was direct drop. Parent droplets followed by satellite droplets were observed. When either the flow rate or speed was increased, filaments formed predominantly, which was unwanted in this system because filament breakdown into smaller droplets does not occur due to the proximity of the disk to the climbing film in the bowl. This system could be applied to the immobilization of microorganisms, as well as plant or animal cell cultures, and for other sizes or fermentors. The overflow from the bowl carries the gellified beads into the bulk solution where immobilized cells could act upon the fermentation media.
