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 (137)Cs-containing microalgal biomass under a magnetic field. Our technique of combining bioaccumulation and magnetic separation successfully removed more than 90% of the radioactive (137)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.