REMOVAL OF TOXIC METALS BY BIOSORPTION ONTO NONLIVING SEWAGE-SLUDGE

Toxic metals, such as zinc, nickel, and cadmium, can be removed from d ilute aqueous solutions by sorption onto nonliving sewage sludge appli ed as finely dispersed biosorbent particles after sterilization and dr ying. A comparison between the suggested method and precipitation, the most common method used for metals removal, was conducted in parallel . The main parameters examined in single component systems include ini tial metal concentration, temperature, and inhibition of the removal p rocess by the existence of soluble constituents. Adsorption isotherms were employed to describe the metals uptake; the Langmuir types were f ound to fit the experimental data better than the Freundlich ones. Mor eover, the desorption of metals from metal-loaded biomass was investig ated. The possible selective separation of metals from binary and tern ary mixtures by biosorption, which could lead to the recovery and recy cling of the removed metals, was also examined by introducing an illus trative selectivity factor.