Biosorption of Al(+3) and Cd(+2) by an exopolysaccharide from Lactobacillus rhamnosus.

The aim of this study was to assess the removal of Cd(2+) and Al(3+) from aqueous solutions by an exopolysaccharide (EPS) from Lactobacillus rhamnosus E/N. The biosorption kinetics of EPS for Cd(2+) and Al(3+) were studied by equilibrium dialysis after incubation from 0 h to 58 h. The actual concentrations of Cd(2+) and Al(3+) in external solutions were measured by a fluorescence method after complexation with 8-hydroxyquinoline. Binding of metal ions by EPS was observed, with maximum adsorption after 0 to 24 and 48 to 58 h for Cd(2+) , and after 24 h for Al(3+) . The existing analytical method, involving the binding of metal ions was measured using a dialysis membrane was significantly improved in our study. This new method could be applied in future studies of this type. The results of this study demonstrate that EPS from Lb. rhamnosus E/N has a Cd(2+) and Al(3+) biosorption capacity. Surface adsorption of the metal ions at surface of EPS was confirmed through scanning electron microscopy. Fourier transform-infrared spectroscopy analysis suggests a role of the functional groups ─OH, C═O, and COO(-) from EPS in the binding of Cd(2+) and Al(3+) ions.