(155c) Flocculation of Yeast Suspension by a Cationic Polymer: Characterization of Flocculent-Cell Interaction

Addition of a cationic polymer can lead to the flocculation of yeast cells thus forming macroscopic flocs [1]. Flocculation occurs by two main mechanisms (a) formation of macromolecular bridges between the particles, and (b) surface potential and charge reduction due to the adsorption of highly charged polyelectrolytes on oppositely charged particles. The efficiency of flocculation is determined by the structure of polymer layers formed on the surface, i.e., the spacial distribution of adsorbed segments near the interface, the adsorption layer thickness, number and length of loops and tails protruding from the surface into the solution per unit area [2]. In studying the flocculation behavior of microbial cells, many interaction forces need to be considered, such as, gravitational force, van der Waals attractive force, electrostatic repulsive force and specific short-range force [3]. In this study, we have investigated the flocculation of yeast cell suspensions by a cationic polymeric flocculent. The flocculation behavior of yeast cell suspensions at different times during the flocculation process is explained in terms of floc size, physicochemical surface characteristics of yeast and cell surface electric potentials (zeta potentials), dynamic mobility and Kappa value measurements. The flocculent particle size was visualized by a video camera, SILICON VIDEO® 2112 CCD. The initial rate of flocculation and growth of floc particles were dependant on the flocculent dosage. Particle size increased with increasing flocculent dosage up to certain point and then decreased. The magnitude of negative value of the zeta potential decreased and finally reached a positive plateau with increasing flocculent dose. However, during the flocculation process zeta potential was negative and magnitude decreased with the increasing flocculent dose. Our results indicate that homoflocculation occurs at the beginning of flocculation process. However, aggregation occurs at higher flocculent doses as the flocculation proceeds.

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