Revisiting Basics of kLa Dependency on Aeration in Bubble Columns: a Is Surprisingly Stable

Abstract

A comprehensive experimental characterization of a small-scale bubble column bioreactor (60 mL) is presented. Bubble size distribution (BSD), gas holdup, and kLa were determined for different types of liquids, relevant fermentation conditions and superficial gas velocities uG. The specific interfacial area a and liquid mass transfer coefficient kL have been identified independent of each other to unravel their individual impact on kLa. Results show that increasing uG leads to larger bubbles and higher gas holdup. As both parameters influence a in opposite ways, no increase of a with uG is found. Furthermore, kL increases with increasing bubble size outlining that improved oxygen transfer is not the result of higher a but of risen kL instead. The results build the foundation for further simulative investigations.