Mixing Estimation of a Laboratory-Scale External-loop Air-lift Bioreactor for Fungal Culture Using pH Tracer Method

Mixing has been one of the important parameters in characterizing and designing external air-lift bioreactors for the biological processes that require intensive mixing for mass transfer. In this study, pH tracer method was employed to characterize the mixing quality of a three-phase laboratory-scale external-loop air-lift bioreactor (EALR) used for cultivation of a pelletized filamentous fungal culture. By labeling fluid elements using pH tracer, the response curves can be obtained, which were then used to estimate the mixing characteristics in the individual bioreactor sections expressed by the Bodenstein numbers (Bo). When applied to a 1.25-L EALR with culture medium solution only, the technique yielded reasonable results. Results showed that the riser behaved as a CSTR and the downcomer as a plug-flow reactor. When applied to fungal pellet culture, however, the technique virtually failed to provide quality results due to the presence of heterogeneous phase.