Mixing in Bioreactor Vessels

Microorganisms and cells perform, in general, optimally at homogeneous conditions in a vessel. In fed systems, the substrates are added locally and concentration differences are the inevitable result. Mixing through the vessel should make these differences small enough to get optimal conditions for the organisms. Mixing time data are inventoried for bubble column, stirred tank, and airlift reactors, for different scales and operation conditions. Scale and slenderness, the height versus diameter value, are the main determining factors. In most cases, the bubble column has a mixing time that is smaller than that of the other reactor types at the same power input. Scale-up makes the mixing time inevitably larger. To find out when this becomes problematic, a critical time concept is used.