Fluid Mixing Variables in the Optimisation of Fermentation Production

Authors:

J.Y. Oldshue

C.K. Coyle

H. Zemke

K. Bruegger

This paper examines the impact of fluid mixing variables on the optimization of aerobic fermentation, focusing on gas-liquid oxygen transfer and its effect on microbial growth and productivity. It highlights how mixer design, shear rates, impeller geometry, and cell concentration influence fermentation yield, oxygen uptake, and overall process efficiency. The study also considers cost factors, demonstrating that strategic investment in mixer power and equipment can significantly enhance fermentation performance while maintaining economical production.

Key Learnings

• Fluid mixing is critical in aerobic fermentation, primarily affecting gas-liquid oxygen transfer and microbial growth.
• Shear rates, impeller geometry, and mixer power significantly influence fermentation yield and cell viability.
• Higher oxygen transfer rates do not always increase productivity; over-stimulation can reduce total yield.
• Cell concentration and broth viscosity directly affect mass transfer efficiency and production costs.
• Mixer cost, including capital and power, is relatively low compared to its potential impact on productivity.
• Scale-up experiments must carefully consider differences between small- and large-scale fermenters to maintain accuracy.
• Gas-liquid mass transfer and fluid shear effects must be evaluated independently to optimize fermentation outcomes.
• Tank design, including D/T ratio and height-to-diameter proportions, influences oxygen transfer efficiency and CO₂ desorption.
• Pilot studies are essential for determining optimal mixer variables and assessing the overall performance of the fermentation process.
• Small differences in process conditions, such as water quality and local equipment, can significantly alter fermentation results.