A bioreactor is often pretty much similar or identical in structure with modern fermentors. However, since you do not necessarily _ferment_ anything in a bioreactor, the term fermentor is a bit of a misnominer, albeit often both ‘fermentor’ and ‘bioreactor’ are used synonymously. And what comes to the size of bioreactors – they are not always small scale at all: some industrial bioreactors can have capacities of thousands of litres, and therefore the term ‘bioreactor’ has nothing to do with size.
A bioreactor may refer to any manufactured or engineered device or system that supports a biologically active environment.  In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. This process can either be aerobic or anaerobic. These directors are commonly cylindrical, ranging in size from liters to cubic meters, and are often made of stainless steel.