HOW MUCH WORKING VOLUME DO YOU NEED FOR YOUR FERMENTATION RUN?

(PICTURE TAKEN FROM http://www.geocities.com/lesjudith/AlcoholChart/fermenter.gif

In any industrial fermentation, the broth represents the substate that is going to be transformed into the fermentation products. A simple formula is that, more fermentation broth means more fermentation products.

However, in reality the picture is far from the simple truth. Even though most of the fermentation broth will be converted to form the fermentation products, a percentage of the broth or carbon will be converted to form biomass or new microbial cells. As fermentation progresses, you will see the concentration of the substrate will decrease followed with increasing amount of biomass.

In laboratory research using small volume fermentors this rule does not apply directly. The objective of fermentation research differ from production fermentors. Production scale fermentors are large and can take high volume of fermentation broth. There is very minimum impact of withdrawing sample broth from the industrial fermentors for monitoring.

In the case of research or laboratory fermentors, the fermentor capacity is very small sometimes in the range of one litre or a bit more.

In planning how much volume of fermentation broth should be needed to be used by the research fermentor depends on many factors

The total amount of fermentation broth should:

1 At least give a head space volume of 20% of fermentor volume ( not working volume)
2 It should be enough to cover for all sampling requirements needed for analyses throughout the completed fermentation run
3 The minimal volume remaining in the fermentor should at least cover the impeller section for mixing. We cannot have a volume that is less than the height of the impeller
4 After removal of samples for analyses there still should be a residual volume about 40 to 50% volume to ensure the fermentation process is not affected