Hydrodynamic characterization of substrate gradients in a pilot scale fermenter using CFD and spatially distributed sensors

The hydrodynamic conditions in stirred fermenters govern the physical behavior in the system, which dictates the mixing of liquid and gas phase, air dispersion capability and oxygen transfer rate [1]. The characterization of the hydrodynamics in pilot scale reactors is crucial in order to ensure sufficient substrate and nutrient supply for the microorganisms. The characterization of the hydrodynamics in an 700 L reactor was carried out empirically by measuring conductivity at different spatial positions in the reactor. The tracer response is utilized to determine the mixing time and compare this with Computational Fluid Dynamics (CFD) simulations. Based on the hydrodynamic characterization, the homogeneity of the substrate concentrations in the tank was analyzed using the enzymatically catalyzed decomposition of hydrogen peroxide to oxygen. The reaction was monitored by measuring the resulting steady state oxygen concentration at several positions in the reactor using optical fiber based sensors. The gradients were characterized for different agitation levels. The spatial measurements depict gradients in the pilot scale reactor, but also serve as a tool to validate the CFD simulations. The validation of the CFD simulations enables the test of different feeding strategies without having to conduct additional experiments. The methodology employed in this characterization can be applied to different fermentation technologies and to cultures which exhibit a high productivity.

References:

[1] Nienow AW (1998), Hydrodynamics of stirred bioreactors, Appl Mech Rev, vol 51, no 1.