Biochemical Engineering Fundamentals, Part 1 - Bailey J., Ollis D. 1989

Transport phenomena in biotechnological systems
Determination of the oxygen transfer rate

Ideally, The rate of oxygen transfer should be measured directly within a bioreactor containing both the nutrient medium and The Cell population (or populations) under study. Such an experiment, however, is feasible only when all requirements for handling the medium and inoculum are met, along with all necessary precautions to prevent accidental contamination and fouling of the medium and culture; therefore, this approach is too complex and labor-intensive for studying mass transfer effects. Consequently, the oxygen transfer rate is typically investigated using synthetic, cell-free systems whose properties roughly approximate those of the bioreactor system. The primary objective of these experiments is to elucidate the dependence of kla' on system hydrodynamics.

To ensure that the synthetic medium adequately mirrors the cell culture under investigation, they must share identical:

1. Viscosity and other rheological characteristics (see Section 8.8).

2. Resistance to mass transfer at the gas–liquid interface.

3. Bubble coalescence.

4. Oxygen solubility and diffusion coefficient.

In general, the suitability of a synthetic (cell-free) system for studying and approximating a biological process depends on the degree to which these conditions are met. Experiments examining oxygen uptake in pure Water, for instance, satisfy virtually none of these criteria. Below, we briefly review the effects of liquid medium viscosity, Surfactants, and mixing characteristics on the rate of oxygen transfer.