SOME ENGINEERING PARAMETERS FOR PROPIONIC-ACID FERMENTATION COUPLED WITH ULTRAFILTRATION

The effect of circulation rate on permeate flux, the energy requirements for heating or cooling, the reactor homogeneity, and cell activity are discussed for a continuous culture system with cell recycle. The fermentation system was a continuous stirred-tank reactor with an ultrafiltration membrane unit for cell recycle. The membranes have a tubular configuration and are composed of a carbon support coated with zirconium oxide. The permeate flux obtained for a long-run fermentation with Propionibacterium acidi-propionici was higher when the circulation rate was increased: 5.13 L/m2-h for a circulation rate of 0.810 m3/h and 7.09 L/m2-h for 1.104 m3/h. The temperature rise inside the fermenter for different circulation rates was studied, allowing determination of the need of input or output of energy for temperature control. Residence time distribution studies showed that, with a circulation rate of 0.606 m3/h, the dead volume was 9.2%, whereas at 1.104 m3/h the reactor behavior was almost ideal. The influence of the circulation rate on loss of cell activity is also discussed, and rheological studies are suggested as an indirect indicator of cell viability. © 1990 Humana Press Inc.