Competitive biosorption of zinc(II) and cobalt(II) in single- and binary-metal systems by aerobic granules.

The biosorption process for removal of cobalt(II) and zinc(II) by aerobic granules was characterized. Single component and binary equimolar systems were studied at different pH values. The equilibrium was well described by Redlich-Peterson adsorption isotherm. The maximal adsorption capacity of the granules, in single systems (55.25 mg g(-1) Co; 62.50 mg g(-1) Zn) compared with binary systems (54.05 mg g(-1) Co; 56.50 mg g(-1) Zn) showed reduction in the accumulation of these metals onto aerobic granules. The kinetic modelling of metal sorption by granules has been carried out using Lagergren equations. The regression analysis of pseudo second-order equation gave a higher R(2) value, indicating that chemisorption involving valent forces through the sharing or exchange of electrons between sorbent and sorbate may be the rate limiting step. The initial biosorption rate indicated that aerobic granules can adsorb Co(II) more rapidly than Zn(II) from aqueous solutions. Meanwhile, FTIR and XPS analyses revealed that chemical functional groups (e.g., alcoholic and carboxylate) on aerobic granules would be the active binding sites for biosorption of Co(II) and Zn(II).