Which parameter quantifies the rate of oxygen transfer from gas to liquid per unit volume in bioprocessing?

Which parameter quantifies the rate of oxygen transfer from gas to liquid per unit volume in bioprocessing?

• A. Flux
• B. Diffusivity
• C. KLa
• D. Oxygen Solubility

Answer: (C)

Understanding how oxygen moves from gas to liquid in a bioreactor is about the rate at which transfer occurs per unit liquid volume. That rate is captured by the volumetric mass transfer coefficient, KLa. It combines how easily oxygen transfers across the liquid film (the liquid-side mass transfer coefficient, kL) with how much interfacial area is available per volume (a), including bubble surface area created by agitation. The key relation is OTR = KLa (C* − C_L), where C* is the dissolved oxygen concentration at equilibrium with the gas, and C_L is the current dissolved concentration. Because KLa directly multiplies the driving force to yield a rate per unit volume, it’s the measure that quantifies how quickly oxygen can be transferred into the liquid in a given volume. Flux describes transfer per unit area, not per volume, so it doesn’t answer the rate per reactor volume. Diffusivity is a property of the species in the medium that affects how fast molecules move by diffusion, but it doesn’t by itself set the volumetric transfer rate. Oxygen solubility (C*) is the maximum amount that can dissolve at equilibrium, not the rate at which dissolution occurs.

Understanding how oxygen moves from gas to liquid in a bioreactor is about the rate at which transfer occurs per unit liquid volume. That rate is captured by the volumetric mass transfer coefficient, KLa. It combines how easily oxygen transfers across the liquid film (the liquid-side mass transfer coefficient, kL) with how much interfacial area is available per volume (a), including bubble surface area created by agitation. The key relation is OTR = KLa (C* − C_L), where C* is the dissolved oxygen concentration at equilibrium with the gas, and C_L is the current dissolved concentration. Because KLa directly multiplies the driving force to yield a rate per unit volume, it’s the measure that quantifies how quickly oxygen can be transferred into the liquid in a given volume.

Flux describes transfer per unit area, not per volume, so it doesn’t answer the rate per reactor volume. Diffusivity is a property of the species in the medium that affects how fast molecules move by diffusion, but it doesn’t by itself set the volumetric transfer rate. Oxygen solubility (C*) is the maximum amount that can dissolve at equilibrium, not the rate at which dissolution occurs.