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Improving Permeate Flux in the Microfiltration of a Bacterial Cell Suspension by Flocculation with Cationic Polyelectrolytes

Matthew T. Aspelund1, Charles E. Glatz2, Kevin M. Graves2, Glenn Rozeboom3, and Meng Heng3. (1) Chemical and Biological Engineering, Iowa State Univeristy, 2114 Sweeney Hall, Ames, IA 50011, (2) Chemical and Biological Engineering, Iowa State University, 2114 Sweeney, Ames, IA 50011, (3) Process Science, Danisco Genencor, 1000 41st Avenue Dr SW, Cedar Rapids, IA 52404

The effect of cationic polyelectrolyte flocculation on permeate flux was studied for dead-end, stirred cell, and crossflow microfiltration of fermentation broth containing subtilisin produced by Bacillus subtilis. Several cationic flocculants were screened for permeate flux and irreversible membrane fouling.

Flocculant addition caused an increase in the permeate flux and a decrease in the specific cake resistance in dead-end microfiltration. Structural differences in the cakes that may have accounted for the flux differences were examined by light microscopy. Flux improvements did not fully carry over to stirred-cell and crossflow experiments and measurement of floc size distributions showed that floc breakup may have been one cause for this. Additional experiments were conducted to determine the effect of flocculant dose on floc stability under shear.