Easy Case for Measuring Kla
When there are few microorganisms or when there is little nutrient, not much oxygen is needed. It may be possible to maintain a relatively high percentage of the saturation concentration. There will be big excursions when the air valve is opened and closed, and it is easy to draw a tangent to the rising curve.
More Difficult Case
Much more typical for industrial fermentations is low oxygen concentration because there are many organisms and high substrate concentration. This is the time when aeration is critical and when a good measure of Kla is needed. The D.O. may already be only slightly above its critical concentration, and excursions caused by turning off the air valve will be small. This sketch is not nearly bad enough; sometimes the rising curve is very poorly defined.
