Biosorption of cadmium ions using a photosynthetic bacterium, Rhodobacter sphaeroides S and a marine photosynthetic bacterium, Rhodovulum sp. and their biosorption kinetics.

We examined the biosorption characteristics of cadmium ions onto a photosynthetic bacterium, Rhodobacter sphaeroides S and a marine photosynthetic bacterium Rhodovulum sp. PS88 in a batch culture system. Both photosynthetic bacteria are capable of cadmium removal with 30 g/l sodium chloride and divalent cations (Mg2+ and Ca2+) in the culture medium. In particular, the strain PS88 shows a high removal ratio and high specific removal rate of cadmium ions from the culture medium under aerobic-dark (heterotrophic) and anaerobic-light (photoheterotrophic) conditions. The adsorption of cadmium onto strains PS88 and S is dependent on the cadmium concentration, and follows the Freundlich adsorption isotherm. In addition, biosorption isotherms for cadmium show that the strain PS88 exhibits higher values of the empirical constant for the cadmium adsorption capacity, Kr, than that of the strain S under both aerobic-dark (K(f)=17.44) and anaerobic-light (K(f)=1.270) conditions.