Determination of Oxygen-Absorption Rate

To estimate the design parameters for oxygen uptake in a fermenter, you can use the correlations presented in the previous sections, which can be applicable to a wide range of gas-liquid systems in addition to the air-water system. However, the calculation procedure is lengthy and the predicted value from those correlations can vary widely. Sometimes, you may be unable to find suitable correlations which will be applicable to your type and size of ferment ers. In such cases, you can measure the oxygen-transfer rate yourself or use correlations based on those experiments. 

The oxygen absorption rate per unit volume qj v can be estimated by 

Since the oxygen is sparingly soluble gas, the overall mass-transfer coefficient KL is equal to the individual mass-transfer coefficient KL. Our objective in fermenter design is to maximize the oxygen transfer rate with the minimum power consumption necessary to agitate the fluid, and also minimum air flow rate. To maximize the oxygen absorption rate, we have to maximize KL, a, C - CL. However, the concentration difference is quite limited for us to control because the value of C L is limited by its very low maximum solubility. Therefore, the main parameters of interest in design are the mass-transfer coefficient and the mterfacial area. 

Normally, we use air to supply the oxygen demand of fermenters. The maximum concentration of oxygen in water which is in equilibrium with air C L at atmospheric pressure is about one fifth of the solubility listed, according to the Henry s law, 

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