Removal of radioactive cesium from an aqueous solution via bioaccumulation by microalgae and magnetic separation.

We evaluated the potential sequestration of cesium (Cs) by microalgae under heterotrophic growth conditions in an attempt to ultimately develop a system for treatment of radioactive wastewater. Thus, we examined the effects of initial Cs concentration (100-500 μM), pH (5-9), K and Na concentrations (0-20 mg/L), and different organic carbon sources (acetate, glycerol, glucose) on Cs removal. Our initial comparison of nine microalgae indicated that Desmodesmus armatus SCK had removed the most Cs under various environmental conditions. Addition of organic substrates significantly enhanced Cs uptake by D. armatus, even in the presence of a competitive cation (K). We also applied magnetic nanoparticles coated with a cationic polymer (polyethylenimine) to separate Cs-containing microalgal biomass under a magnetic field. Our technique of combining bioaccumulation and magnetic separation successfully removed more than 90% of the radioactive Cs from an aqueous medium. These results clearly demonstrate that the method described here is a promising bioremediation technique for treatment of radioactive liquid waste.