Application of Dry Activated Sludge for Lead and Cadmium Adsorption: Isotherm and Kinetic Modeling

Heavy metals have an important role on organism life and their high concentration may be a great threat for humans and other organisms’ lives. Up to now, various methods have been used for the removal of these metals, which include the adsorption process. The aim of this study was the recovery of municipal disposals, and using as absorbent for lead & cadmium removal from aqueous solutions. Adsorption of lead & cadmium on dry activated sludge was investigated. Activated sludge was obtained from diary industry (Tehran). All experiments were performed in batch system on 202 synthetic samples to investigate the effects of pH, contact time initial concentration lead & cadmium and adsorbent dose. The most conventional adsorption and kinetic models were applied to describe metal adsorption and dynamic reaction. The results showed that with increasing of adsorbent doses, contact time and pH solution, lead & cadmium removal efficiency increased. The maximum lead & cadmium adsorption was obtained at pH: 6 and an equivalent time of 180 min. With increasing initial concentration of lead & cadmium, removal efficiency decreased. The obtained results in this study were matched with langmuir 2 isotherm (R2>0.99) and interparticle diffusion kinetic (R2>0.94). Maximum adsorption capacity of lead & cadmium on dry activated sludge was obtained to be 2.66 and 1.66mg/g, respectively. Maximum constant rate of lead & cadmium was 0.045 and 0.041mg/g.min0.5, respectively. According to the results, dry activated sludge is recommended as a low cost and available adsorbent to remove lead & cadmium from aqueous solutions.