Biosorption of zinc(II) from aqueous solution by dried activated sludge

The biosorption potential of dried activated sludge as a biosorbent for zinc(II) removal from aqueous solution was investigated. The effects of initial pH, contact time, initial zinc ion concentration, and adsorbent dosage on the biosorption processes were determined, and the equilibrium data were modeled by the Langmuir and Freundlich isotherms. The Langmuir isotherm model (R2 = 0.999) was proved to fit the equilibrium data much better than the Freundlich isotherm model (R2 = 0.918). The monolayer adsorption capacity of dried activated sludge for zinc(II) was found to be 17.86 mg/g at pH of 5 and 25 degrees C. The kinetic data were tested using pseudo first- and second-order models. The results suggested that the pseudo second-order model (R2 > 0.999) was better for the description of the adsorption behavior of zinc(II) onto the dried activated sludge. Fourier transform infrared spectral analysis showed that the dominant mechanism of zinc(II) biosorption onto the dried activated sludge was the binding between amide groups and zinc ions.