Rheological property of self-flocculating yeast suspension

Using the online monitoring technique established for yeast flocs with the focused beam reflectance measurement system, the rheological property of the simulation system with self-flocculating yeast and water was examined. By controlling yeast flocs size relatively stable at the range from 350 to 470 μm, the impact of biomass concentration on the rheological property was first studied. Compared with regular yeast suspension, which is a Newtonian fluid in general, the suspension of yeast flocs exhibited non-Newtonian fluid behavior, from a pseudoplastic fluid with biomass concentration lower than 40 g/L to a yield pseudoplastic fluid as biomass concentration increased, since the higher the biomass concentration, the more resistant the suspension to shear force. On the other hand, it was found that, when yeast flocs size decreased to about 200 μm, a linear correlation between shear rate and shear stress was established, and the rheological property of the suspension was close to a Newton fluid, but non-Newtonian flow behavior developed when the size of yeast flocs increased to above that criterion, indicating its main contribution to the non-Newtonian flow behavior of the suspension. Based on these results and rheological model established with the simulation system, the rheological property of the ethanol fermentation system with the self-flocculating yeast was predicted.