As pointed out by various experts from academia and industry the current data do not allow discriminating the influence of the
impeller choice on kLa as long as they are not flooded.
Importantly, the value of kLa is critically dependent of the broth
composition, particularly from its surface active components. Every
practically working biotechnologist knows that from the application
of antifoam agents.
kLa measurements in model media are difficult to extrapolate
to fermentation broths thus measurements during the original cultures
are desirable. Moreover, as the fermentation media change
their properties significantly across cultivations, online measurements
become necessary. Thus the aim in the work reported here
was to improve kLa measurement during real high cell density culture
without notably disturbing the culture.
We will show that exploiting the oxygen balance around the
culture in tightly controlled fermentation runs allows sufficiently
accurate and reproducible kLa measurements. These measurements
are precise enough to investigate details of the reactor design
elements. As a practically interesting example of the application
of the online balancing technique, the influence of the number
of hollow blade impellers in a standard bioreactor was considered.