VISCOSITY OF FERMENTATION BROTH AND THE CHOICE OF THE RIGHT IMPELLER

It is sad to observe that most students or even researchers in fermentation technology, downplay the importance of viscosity of the fermentation broth and the choice of the right impeller. They seem to have the opinion that viscosity characterization and impeller design and configuration is not crucial to the optimization of the fermentation process. They are led in the blind belief that that the Rushton impeller is the best for all situations. Perhaps they are not aware there are many critical designs of impellers which is not only making mixing efficient but even optimizing in terms of energy saving and costs. This is especially crucial now where the cost of energy in increasing all the time which could make or break the economics of the fermentation industries
Every impeller has its own unique characteristics in terms of its mixing, flow. One impeller does not suit all! We have to determine the choice of proper impeller by carrying laboratory experimental studies.

There is usually a change in impeller design as the viscosity increases. Usually under low viscosity fermentation broth the common choice of impellers are propellers and flat blade impellers. But as the viscosity increases the choice of impellers are more towards gte anchors and helical screws or ribbons

The analyses of the viscosity of the fermentation broth are crucial at this stage of determination. We have to determine its rheological pattern and the changes of viscosity with time in coming with the right impeller. But most often this is not done…. It is a known fact viscosity changes with time in any fermentation process. A good fermenter which is energy efficint should hav a stirrer which is adaptable to changes in viscosity

The obsession is more on scaling up studies without fully understanding the scaling up process, and to rely on rules of the thumb.


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