RESIDENCE TIME DISTRIBUTION IN A PACKED-BED BIOREACTOR CONTAINING POROUS-GLASS PARTICLES - INFLUENCE OF THE PRESENCE OF IMMOBILIZED CELLS

An experimental investigation of the liquid phase residence time distr ibution (RTD) in a packed bed bioreactor containing porous glass parti cles is presented. For Re < 1, intraparticle forced convection is negl igible and only diffusion. characterized by an effective diffusion coe fficient, must be considered to describe the mass transfer process bet ween the extraparticle and the intraparticle fluid phase. For Re > 1, the mass transfer rate becomes dependent on the liquid flow rate. indi cating the existence of intraparticle convection. A model including ax ially dispersed flow for the external fluid phase and an 'apparent' ef fective diffusivity that combines diffusion and convection, predicts e xperimental RTD data satisfactorily. Yeast cells immobilized inside th e porous glass beads did not affect the mass transfer rate at low biom ass loading. At high biomass loading (0.02 g yeast cells g-1 carrier), the mass transfer rate between the extraparticle and intraparticle fl uid phase was significantly decreased. Comparison of the RTD data from experiments performed in the presence and absence of cells in the ext ernal fluid phase revealed that the mass transfer rate is influenced b y the cells immobilized inside the porous particles and not by the cel ls present in the external fluid phase.