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 ¹³⁷Cs-containing microalgal biomass under a magnetic field. Our technique of combining bioaccumulation and magnetic separation successfully removed more than 90% of the radioactive ¹³⁷Cs from an aqueous medium. These results clearly demonstrate that the method described here is a promising bioremediation technique for treatment of radioactive liquid waste.