Heavy metal removal by caustic-treated yeast immobilized in alginate

Saccharomyces cerevisiae yeast biomass was heated in 0.75 M NaOH at 70-90 degrees C for 10-15 min to increase its biosorption for heavy metals, and then immobilized in alginate gel. Biosorption for Cu2+, Cd2+ and Zn2+ on alginate gel, native yeast, native yeast immobilized in alginate gel, and caustic-treated yeast immobilized in alginate gel, were all compared. Immobilized yeasts (native yeast and caustic-treated yeast) could be reactivated and reused in a manner similar to ion-exchange resins. Immobilized caustic-treated yeast has high heavy metal biosorption capacity and high metal removal efficiency over a rather wide pH region. The biosorption isotherm of immobilized caustic-treated yeast was studied and empirical equations were obtained. The initial pH of polluted water affected the metal removal efficiency in extreme pH regions, and the biosorption capacity almost remained constant over a wide pH range. The equilibrium biosorption appeared to be temperature independent in the range from 7 degrees C to 45 degrees C at low initial metal concentration.