Evaluation of volumetric mass transfer coefficient in a stirred tank bioreactor using response surface methodology

Stirred tank reactors are most commonly used both in the laboratory and industry. Particularly for bioreactors, the volumetric mass transfer coefficient (k _L a) of oxygen is used as one of the important parameters for determining efficiencies of reactors and for successful scale-up. A number of correlation methods have been previously developed to predict the k _L a in stirred tank bioreactors. In the present work, we propose a new correlation for k _L a based on a mathematical and statistical approach using Response Surface Methodology (RSM) based on Box-Behnken design of experiments. This correlation includes the effect of various parameters such as impeller agitation rate (50–800 rpm), air flow rate (0.5–3.5 L/min), and temperature (10−40°C) for different impeller configurations (single and dual Rushton, pitched blade, and mixed turbines). It was observed that the k _L a increases with increasing the parameters for all the impeller configurations studied. Among the operating parameters, the most significant variable impacting k _L a was found to be agitation rate, followed by air flow rate, and temperature. The models developed using RSM successfully interpreted the experimental k _L a and were further validated under other operating conditions. It was also found that, compared with conventional power-law models, the RSM approach enables a more efficient correlation procedure and formulates simplified models with comparably high accuracy, suggesting that the RSM is promising for evaluation of oxygen mass transfer in stirred tank bioreactors.