Influence of Extracellular Polymeric Substances on the Adsorption of Cadmium onto Three Bacterial Species

AbstractIn this study, we measured the effect of EPS on Cd and proton adsorption behaviors by measuring the extent of adsorption onto biomass with and without the EPS removed via a cation exchange resin. We conducted both Cd adsorption experiments and potentiometric titrations of biomass using three common bacterial species: one Gram-positive (Bacillus subtilis) and two Gram-negative (Shewanella oneidensis, Pseudomonas putida) species. The Cd adsorption experiments were conducted as a function of metal loading in order to probe whether environmentally-low metal loadings lead to different adsorption mechanisms and roles for EPS than the higher metal loadings of most previous adsorption studies. We suspended each biomass sample in a solution of dissolved Cd in 0.01 M NaClO4 at metal loadings of 1, 2, 5, and 74 μmol/g. Surface complexation modeling (SCM) was used to determine stability constants for the important Cd-bacteria complexes, and the effect of metal loading on the resulting calculated stability con...