Investigation of the structure of two-phase flows in bubble column bioreactors

Abstract

Spacial, mean and Sauter bubble diameters, local mean gas holdups and specific interfacial area profiles were evaluated in bench scale bubble column reactors with a model medium and during the cultivation of a yeast,Hansenula polymorpha, on ethanol and glucose substrates. The results indicate that the spacial variation of these properties in most of the column (with the exception of the aerator zone) is slight. These two-phase system can therefore be characterized by local values measured in the column. The variation in the mean and Sauter bubble diameters, the specific interfacial area, the volumetric mass transfer coefficient, the oxygen transfer rate and the biomass concentration were determined during cultivation as functions of time and substrate concentration. There is a close relationship between system properties measured in both model and cultivation media. However, during cultivation, small bubbles are formed which gradually accumulate in the medium. This causes a significant increase in the specific geometric interfacial area. A comparison of this area with the corresponding volumetric mass transfer coefficient indicates that only part of this area is active with regard to oxygen transfer. The active mass transfer area can be evaluated by disregarding small bubbles with diameters of less than 0.8 mm.