Development of a strategy to control the dissolved concentrations of oxygen and carbon dioxide at constant shear in a plant cell bioreactor.

To examine the effects of volatile components on plant cell growth, a bioreactor control system was developed to simultaneously control the dissolved concentrations of both oxygen and carbon dioxide. The first step in this work was to develop a mathematical model to account for gas-liquid mass transfer; biological utilization and production of O(2) and CO(2); and the series of chemical reactions of CO(2) in water. Using this model and dynamic measurements for dissolved O(2) and CO(2), it was observed that (1) both absorption and desorption of a volatile component could be described by a single mass transfer coefficient, K(l)a, and (2) K(l)a values for oxygen and carbon dioxide transfer were directly proportional. The second step of this work was to employ the mathematical model in an adaptive feed-forward strategy to control the dissolved O(2) and CO(2) concentrations by manipulating the inlet gas composition to the bioreactor. This strategy allowed dissolved concentrations to be controlled without the need for changing either the total gas flow rate or agitator speed. Adaptive control was required because the volumetric rates of O(2) and CO(2) consumption and production vary with time during long term operation and therefore these rates must be continually updated. As the final step, we demonstrated that this control strategy was capable of controlling the dissolved gas concentrations in both short- and long-term studies involving the cultivation of Catharanthus roseus plant cells.