Stirred-tank bioreactors have been designed for:
(a) purification of product
(b) addition of preservatives to the product
(c) availability of oxygen throughout the process
(d) ensuring anaerobic conditions in the culture vessel
(c) A stirred tank bioreactor is usually cylindrical, possessing a stirrer which facilitates even mixing of the reactor contents and oxygen availability through out the bioreactor.
The bioreactor has an agitator system, an oxygen delivery system, foam control. pH and temperature control systems. Hence, option (c) is correct.