(358b) Evolution of Particle Size Distribution for Yeast Flocculation by Polymer Bridging: Experiment and Modeling

Yeast suspensions have been flocculated using eight different cationic polyelectrolytes. The particle size distribution was measured every twenty seconds. The effects of flocculant characteristics, flocculant concentration and stirring speed on the evolution of the particle size distribution have been determined. The volume average floc diameter increased sharply in the first one hundred seconds. However after this it increased very slowly for high flocculant doses. However, the average floc diameter increased almost linearly at low flocculant doses. The largest average floc diameter is obtained at the optimal stirring speed.

The flocculation process has been divided into two stages for more precisely simulating the experimental results. Initially the flocculant adsorbs to the initial yeast particles. Once sufficient yeast cells with adsorbed flocculant are present, collisions between these particles leads to the formation of floc particles. The growth of the floc particles may be described by a population balance model. The collision efficiency factor and fragmentation rate are predicted to be functions of time since the polyelectrolyte molecular continues to adsorb onto the yeast particles surface. The model developed agrees well with the experimentally observed evolution for the floc size distribution for flocculation of yeast cells.