Foam Characterization and Disruption in a Gas Sparged Pilot Stirred Tank

Foaming in bioreactors can lead to severe operational problems and it is often controlled by chemical antifoam agents which cause additional downstream separation requirement and, in some cases, the decrease of gas-liquid mass transfer. For this reason, mechanical foam disruption is a very attractive alternative to chemical agents, but it is rarely adopted in industrial practice. In this work, the applicability of an agitation method for foam disruption in a gas-liquid stirred tank is considered. The stirred tank is a pilot scale version of typical industrial fermenters used in fed batch mode, with a large free volume between the upper impeller and the vessel top. The experimental characterization consists in the measurements of the local gas volume fraction, the power consumption, and the bubble size distribution in an aerated liquid with typical physical properties of fermentation broths, in different air flow rates and impeller speeds. The discussion of the results leads to a novel methodology for the foaming systems monitoring and to a strategy to control the foam by using mechanical agitation, widening the applicability of stirring as foam disruption in industrial bioreactors.