Development of advanced image analysis techniques for the in situ characterization of multiphase dispersions occurring in bioreactors

Fermentation bioprocesses typically involve two liquid phases (i.e. water and organic compounds) and one gas phase (air), together with suspended solids (i.e. biomass), which are the components to be dispersed. Characterization of multiphase dispersions is required as it determines mass transfer efficiency and bioreactor homogeneity. It is also needed for the appropriate design of contacting equipment, helping in establishing optimum operational conditions. This work describes the development of image analysis based techniques with advantages (in terms of data acquisition and processing), for the characterization of oil drops and bubble diameters in complex simulated fermentation broths. The system consists of fully digital acquisition of in situ images obtained from the inside of a mixing tank using a CCD camera synchronized with a stroboscopic light source, which are processed with a versatile commercial software. To improve the automation of particle recognition and counting, the Hough transform (HT) was used, so bubbles and oil drops were automatically detected and the processing time was reduced by 55% without losing accuracy with respect to a fully manual analysis. The system has been used for the detailed characterization of a number of operational conditions, including oil content, biomass morphology, presence of surfactants (such as proteins) and viscosity of the aqueous phase.