Quantification of spatial heterogeneity in large bioreactors

Substrate gradients are known to exist in production scale stirred tank bioreactors due to imperfect mixing and differences in the mass transfer rate of oxygen [1,2]. Access to experimental mixing and mass transfer data from large scale is limited, and the results are dependent on the geometry of the vessels and impellers in use. A method for measuring oxygen gradients in situ in a production scale bioreactor with minimal alteration of the vessel is proposed. The flexibility of the sensors makes the method applicable in the industry and facilitates the collection of experimental data at large scale without disturbing the workflow at the production plant. The setup has been tested in a 1 m³pilot scale mixing vessel with a model oxygen transfer experiment. Furthermore it has been tested in a pilot scale bioreactor during yeast fermentation in order to investigate the durability of the sensors during heat sterilization cycles as well as fouling from biological growth. The setup is able to quantify differences in the oxygen driving force in the model system, indicating the existence of mass transfer gradients.

[1]        Larsson, G., Törnkvist, M., Ståhl Wernersson, E., Trägårdh, C., Noorman, H., & Enfors, S. O. (1996). Substrate gradients in bioreactors: Origin and consequences. Bioprocess Engineering, 14(6), 281–289.

[2]        Oosterhuis, N. M., & Kossen, N. W. (1984). Dissolved oxygen concentration profiles in a production-scale bioreactor. Biotechnology and Bioengineering, 26, 546–550.