As I mentioned in the post you're reply to, the 25
Post# of 148278
For example, I have worked on a lot of processes that use 18kL bioreactors. The final working volume could range from 11kL to 16kL and could be 15435 L for instance.
They are operated like this for a WIDE range of reasons some include mixing and gassing capabilities of the tank system in relations to the cell culture's rate of consumption and metabolic profile.