Bubble Column Bioreactors: Comparison with Stirred Fermenters Based on Local Gas Hold-up Distribution

Local gas hold-up in viscous aerated batches in bubble column and impeller gas dispersion devices was studied. Unlike the former analyses valid for water, the emphasis of this study was on gas hold-up in relatively viscous and shear-thinning liquids mimicking physically nutrient solutions from industrial fermentation practice. Gas hold-up is correlated with viscosity, plasticity and shear-inducing velocities. Vessels with ID 0.2-0.4 m were studied. The prevailing parabolic type of radial profile specific for water was shown to change to a flat saddle type one with incidental peaks. Comparison with stirred vessels with two different impeller designs showed opposite effects. Possible control of gas dispersion efficiency by appropriate selection of gas dispersion devices is discussed.