Microbial cell recovery enhancement through flocculation

Abstract

The removal of cellular material from fermentation broths is of importance in many fermentation processes. The present work compares the performance of recently developed polyelectrolyte flocculating additives with traditionally available additives. Objectives are to establish criteria for the choice of a flocculating additive and establish optimum conditions for the formation of stable, fast settling floc, and for quantitative separation of cellular material from the medium. Fermentation broths of actively growing Candida intermedia were used to evaluate the effectiveness of fifty commercial flocculating additives at different dosages and pH values. Certain strong anionic and strong cationic polyelectrolytes and mineral hydrocolloids were found to be most effective in their enhancement of settling rates. Some differences in behavior exist between glucose grown cells, hydrocarbon grown cells, and washed cells in buffer suspension. Flocculation of cells from fermentation broths is concluded to be highly dependent upon adsorbed material. A high charge density to interact or compete with adsorbed material and a solubility in the adsorbed material are important facton in choosing an additive for a given application. The fluid mechanics of a flocculating suspension is an important variable since low shear does not provide adequate contacting between cells for floc formation and high shear leads to floc breakup. An apparatus was constructed to grow floc under constant fluid mechanical conditions both in laminar and turbulent flow regimes. Turbulent shear was found to be very important in forming large, compact floc in cases where irreversible ionic bridging is the mechanism as for the strong anionic polyelectrolyte, polystyrene sulfonate. Adequate mixing is required to disperse the flocculating additive, but the level of turbulence is relatively unimportant in cases where reversible colloidal bridging is the mechanism as for the mineral hydrocolloid, bentonite.

The effect of complex growth media on microbial flocculation by the cationic polyelectrolyte chitosan

“…The one flocculant which produced a clear supernatant on centrifugaticm was anionic in nature, even though these cells have a negatively charged surface. This surprising result is in accordance with the conch&ns of Gamer and Wang (1970), who claimed an excess of multivalent cations and cationic macromolecules present in a normal broth form an adsorbed layer on the cell surface changing its flocculation properties. It has been consistently demonstrated that cationic polymers are far better flocculants than non-ionic or anionic polymers and Hughes et al, ( 1990) have shown that the natural cationic polyelectrolyte chitosan, is particularly effective.…”

Mass‐transfer effects on the rate of isomerization of D‐glucose into D‐fructose, catalyzed by whole‐cell immobilized glucose isomerase

“…The precipitation is brought about by: a) electrostatic interaction between the negative charge of the surface of the cells and the positive charge of Primafloc C-7, b) the electrostatic interaction between the conglomerates formed under (a) and the Primafloc A-10 added later. 2 The precipitated material is successively extruded, dried at 56°C for 24 hr, and granulated. The heat treatment probably immobilizes the intracellular enzyme glucose isomerase inside the microorganism.3 After granulation cylinders are obtained of roughly m in diam and 4 x m in length (K.S.H.…”

Treatment and clarification of fermented broth in bacterial enzyme production

“…A classical study on the use of various types of flocculating agents for the yeast cell recovery was reported by Gasner and Wang (1970).…”