An investigation has been undertaken to determine the removal of heavy metals (Cd 2+ , Cu 2+ , Ni 2+ and Zn 2+ ) of high environmental priority due to their toxicity from dilute aqueous solutions by biosorption using inexpensive biomaterials like activated sludge. Activated sludge is used widely in water treatment plants and is easily available. Each experiment was performed over a period of time to determine the biosorption of heavy metals from the aqueous phase to the solid phase. The maximum sorption uptake of the studied metal ions by activated sludge showed the following order: Cd 2+ > Cu 2+ > Ni 2+ > Zn 2+ . The pseudo first-and second-order kinetic models were used to describe the kinetic data. The experimental data fit with the second-order kinetic model very well. The type of mechanism involved is analyzed in terms of the intraparticle diffusion model. Other models are also reviewed. Quantification of metal-biomass interactions, nature of adsorption, kinetics, ion-exchange as well as models used to characterize activated sludge biosorption are reviewed. All solutions are analyzed using inductively coupled plasma (ICP).

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