The influence of complex biological feedstock on the fluidization and bed stability in expanded bed adsorption

The stability of expanded bed adsorption systems (EBA) was studied in bioma ss containing culture broth by residence time distribution (RTD) experiment s, using pulse inputs of fluorescent molecules as tracers. Different commer cial adsorbents (Streamline DEAF, SP, Phenyl, Chelating, and AC) were teste d at various biomass concentrations (2.5-12 %, wet weight) of whole (Saccha romyces cerevisiae) yeast, yeast cell homogenate, and Escherichia coil homo genate. Analyzing the RTD according to the PDE model (PDE: axially disperse d plug-flow exchanging mass with stagnant zones) allowed the calculation of three parameters: the number of transfer units for mass exchange between m obile and stagnant fraction (N), the Peclet number for overall axial disper sion (P), and the mobile fraction of the liquid in axially dispersed plug f low (phi). When fluidization was performed in particle-free buffer the norm alized response signal (after perfect input pulse) was symmetric (N:0; P: 5 0-100; phi: 1), thus, demonstrating the formation of a homogeneous fluidize d (expanded) bed. Upon application of suspended biomass the RTD was skewed, depending on the adsorbent used and the type and level of biomass present in the sample. This situation leads to three different characteristic pictu res: the well-fluidized system (N: greater than or equal to 7-10; P:less th an or equal to 40; (phi: 0.80-0.90)), the system exhibiting bottom channeli ng (N: < 1-2; P: greater than or equal to 40; phi: 0.5-0.7) and, the system where extensive agglomeration develops (N: 4-7; P: 20-40; phi: < 0.5). The se results demonstrate that changes in the hydrodynamics of EBA a I ready t ake place in the presence of moderate concentrations of biomass. Furthermor e, those changes can be quantitatively described mainly in terms of the fra ction of stagnant zones in the system, which are formed due to the interact ion of biomass and adsorbent. The technique described here can be used to e valuate a certain combination of adsorbent and biomass with regard to its s uitability for expanded bed adsorption from whole broth. (C) 1999 John Wile y & Sons, Inc.