In a steady-state bioreactor, which parameter can be determined from the oxygen transfer equation?

• A. Heat Transfer Coefficient
• B. Oxygen Solubility
• C. Dilution Rate
• D. KLa

Answer: (D)

The oxygen transfer equation describes how quickly oxygen moves from gas to liquid, driven by the difference between the saturation concentration of oxygen (C*) and the actual dissolved oxygen (C_L). The rate of transfer is proportional to this driving force with the proportionality constant k_L a, so OTR = k_L a (C* − C_L). In steady state, the oxygen transfer rate must balance what the cells consume, so the OTR is tied to the oxygen uptake rate. By measuring the driving force (C* and C_L) and the transfer rate (or uptake rate) you can solve for k_L a. That’s why the parameter determined from the oxygen transfer equation is the overall gas–liquid mass transfer coefficient, k_L a. The heat transfer coefficient, oxygen solubility, and dilution rate are governed by different balances or properties and do not come from the oxygen transfer equation.