Mechanisms of Cd 2+, Cu 2+ and Ni 2+ biosorption by aerobic granules

Abstract

The mechanisms of biosorption of Cd 2+, Cu 2+ and Ni 2+ by aerobic granules were examined based on a series of batch experiments as well as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. Results showed that soluble Cd 2+, Cu 2+ and Ni 2+ ions could be removed by aerobic granules through three mechanisms, i.e., ion exchange, binding to extracellualr polymers and chemical precipitation. It was found that the equivalent ratio of the released light metals, such as Ca 2+, Mg 2+ and K +, to the adsorbed heavy metals was in the range of 0.71–0.82, which indicated that the ion exchange would be the main mechanism involved in biosorption of Cd 2+, Cu 2+and Ni 2+ by aerobic granules. The analyses by FTIR and XPS further revealed that chemical functional groups (e.g., alcoholic, carboxylate and ether) on aerobic granules would be the active binding sites for biosorption of Cd 2+, Cu 2+ and Ni 2+ by aerobic granules.