A vortex-bowl disk atomizer system for the production of alginate beads ina 1500-liter fermentor

Using a model system, a concept for the immobilization of microbial culture s within alginate beads directly in a 1500-L fermenter with a height to dia meter ratio of 1.85 is described. The system is comprised of a 60-cm diamet er bowl fixed to the top of an agitation shaft, where calcium-ion-rich medi a is continuously recirculated from the bulk solution to the bowl. The rota tion of the shaft and bowl creates a climbing film (vortex) of solution. An atomizing disk centrally recessed within the bowl sprays an alginate solut ion into the climbing film where the droplets harden into beads. The effect of heat treatment on the alginate solution on resulting bead pro perties was examined. The sterilization operation did not appear to have a major effect on the alginate bead mechanical properties of firmness and ela sticity which was much more a function of alginate concentration. Beads of various sizes were produced by the unit. The system was characterized by th e dimensionless numbers Re omega = (omega . rho . D-2)/mu and ReQ = (Q . rh o)/(mu . D). At Re omega and ReQ values less than 500 and 0.15, respectivel y, the mechanism was direct drop. Parent droplets followed by satellite dro plets were observed. When either the flow rate or speed was increased, fila ments formed predominantly, which was unwanted in this system because filam ent 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 we ll as plant or animal cell cultures, and for other sizes or fermenters. The overflow from the bowl carries the gellified beads into the bulk solution where immobilized cells could act upon the fermentation media. (C) 2000 Joh n Wiley & Sons, Inc.