Scaling-up Aerobic Fermentation which Produce Non-Newtonian, Viscoelastic Broths

Abstract

Gas liquid mass transport usually controls the rate of an aerobic fermentation. The effect of mass transport must be included when scaling-up this kind of fermentation. One method for scaling-up gas/liquid contacting systems is to keep the mass transfer coefficient constant. Both impeller speed, N, and gas flow rate, Q, must be determined for a successful scale-up. Equating mass transfer coefficients for similar systems of different volumes gives one relationship between unknown values of N and Q, but another relationship is needed so that both can be calculated. We measured mass transfer coefficients using a simulated fermentation broth. Carbon dioxide was reacted with sodium hydroxide in a dilute aqueous polysaccharide solution in a stirred tank. Mass transfer coefficients corrected for the effect of chemical reaction were calculated from measured reaction times. The work includes independent measurements of rheological and elastic properties and surface tension. Data from geometrically similar tanks of up to 2000 l were used to test the usefulness of mass transfer coefficient correlations for scale-up.