Isotherms and kinetics studies of biosorption nickel (II) and chromium (VI) from aqueous solution by dried activated sludge

Aims: The aim of this study is the recovery of municipal refuse and using it as a biosorbent for Nickel (II) and Chromium (VI) (Ni ^{2+ an} d Cr ⁶⁺ )removal from aqueous solutions. Materials and Methods: Activated sludge was obtained from the wastewater treatment plant in a dairy industry. All experiments were performed in the batch system and effective parameters such as the pH, adsorbent dosage, and the initial concentration and contact time of Ni ²⁺ and Cr ⁶⁺ were investigated. The adsorption isotherms and kinetics were evaluated to describe the metal uptake and dynamic reactions. Results: The results of this study showed that with an increasing adsorbent dose and contact time, Ni ²⁺ and Cr ⁶⁺ removal efficiency increased. The maximum adsorption of Ni ²⁺ and Cr ⁶⁺ was obtained in pH 6 and 2, respectively. Meanwhile, with increasing Ni ²⁺ and Cr ⁶⁺ concentration, the removal efficiency decreased. The results best fitted the Langmuir isotherm and the maximum absorption capacity of Ni ²⁺ and Cr ⁶⁺ onto dry activated sludge (DAS) were 2.17 and 2.23 mg/g, respectively. Analysis of the adsorption kinetics showed that the intraparticle diffusion kinetic had been good and presented Ni ²⁺ and Cr ⁶⁺ uptake onto DAS, and the intraparticle diffusion rate constant of Ni ²⁺ and Cr ⁶⁺ were 0.044 and 0.042 (mg/g min ^0.5 ), respectively. Conclusions: According to the results, dry activated sludge is suggested as a low cost and available adsorbent for removing Ni ²⁺ and Cr ⁶⁺ from aqueous solutions.