Cadmium (II) distribution in complex aquatic systems containing ferrihydrite, bacteria and an organic ligand: The effect of bioactivity

The distribution of Cd(2+) in the presence of phthalic acid (H(2)L(p)), ferrihydrite and bacteria (Comamonas spp.) was investigated in biologically active systems involving H(2)L(p) biodegradation. Tests showed that Cd(2+) sorption onto bacteria, ferrihydrite and bacteria-ferrihydrite mixture increased with pH in all systems, irrespective of H(2)L(p) degradation or not. The use of bacterial growth medium, Bushnell Hass Broth modified for low phosphate, had negligible effect on Cd sorption. In the presence of ferrihydrite, no difference was observed between Cd(2+) sorption in the ferrihydrite-live bacteria and in the ferrihydrite-dead bacteria systems as ferrihydrite proved to be the dominant sorption phase. Cadmium sorption to ferrihydrite and to bacterial cells was described using the diffuse layer model and a nonelectrostatic 4-site model, respectively, which were developed for systems lacking H(2)L(p) degradation. For systems experiencing H(2)L(p) degradation this modeling approach predicted the general trend of Cd(2+) sorption-edge shift and gave good fits to the observed sorption data. The results obtained demonstrate that Cd(2+) sorption in the biologically active system was reasonably estimated by a model developed for biologically inactive systems, although uncertainty exists due to processes involving H(2)L(p) biodegradation products and changes in the bacterial population. (C) 2011 Published by Elsevier Ltd.