Removal of toxic metals by biosorption onto nonliving sewage sludge

Toxic metals, such as zinc, nickel, and cadmium, can be removed from dilute aqueous solutions by sorption onto nonliving sewage sludge applied as finely dispersed biosorbent particles after sterilization and drying. 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 initial metal concentration, temperature, and inhibition of the removal process by the existence of soluble constituents. Adsorption isotherms were employed to describe the metals uptake; the Langmuir types were found to fit the experimental data better than the Freundlich ones. Moreover, the desorption of metals from metal-loaded biomass was investigated. The possible selective separation of metals from binary and ternary mixtures by biosorption, which could lead to the recovery and recycling of the removed metals, was also examined by introducing an illustrative selectivity factor.