Details of Transport Rates in Stirred Fermenters

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This project provides for the purchase of a large (200 liter) fermenter to complement smaller fermenters already available at the University of Arizona, as well as support for an initial exploratory study of oxygen transport. The fermenter allows studies of scale effects in fermenter operation under various conditions. In particular, research is underway to study the spatial distribution of mixing and transport in fermenters leading to a sound foundation for fermenter design. Several studies have shown that poor distribution of oxygen and nutrient substrates can reduce cell growth rate and yield of desired product, particularly proteins. In order to achieve optimum mixing rates which do not rupture the cells, it is necessary to know how transport rates (ka), mixing and shear are distributed in the vessel at various impeller rotation rates and for various impeller designs. This will be achieved by measuring local values of dissolved oxygen and oxygen content of gas bubbles at the same locations to obtain a spatial distribution of each. Detailed determinations of flow distributions of liquid and gas will then be used to compute local ka distributions under various operating conditions and designs. As a result of this research, scale-up will become more accurate, since distributions of ka values and how they vary with scale will be available.