Optical Approach for Measuring Oxygen Mass Transfer in Stirred Tank Bioreactors

Bioreactor engineering allows modeling the conditions of real life biological processes. Particularly, oxygen represents one of the most important factors for life, and the understanding and control of its mass transfer in bioreactors is one of the most challenging problems in the industry. The aim of this study was to develop an optical approach for measuring the oxygen mass transfer coefficient (k _La). An assembly was constructed for this purpose, consisting of a stirred tank bioreactor, a high-intensity light source, a luminometer and a digital camera. Air flux supply and stirring velocity of the bioreactor were tested over a range of thirty-five values. The air bubbles generated were counted and their diameters were measured from photographs. The luminometer measured light obstruction due to bubbles. A polarography electrode sensor measured the dissolved oxygen in water to correlate it with the optical approach. The results showed a close correlation between k _La and light obstructed due to bubbles of air. The bubble diameter and holdup results suggest that the size of the bubbles decreases and becomes more homogeneous as stirring speed increases. A multivariable linear model for k _La as a function of the measured light obstruction and air flux injection was constructed. A strong correlation between this model and results was obtained. This approach avoids the need for chemical sensors for sensing systems, with a noninvasive and nondestructive methodology to determine the k _La for dilute solutions. This technique could be developed to evaluate a scaled-up bioreactor before running a bioprocess.