Practical Removal of Radioactivity from Sediment Mud in a Swimming Pool in Fukushima, Japan by Immobilized Photosynthetic Bacteria

About 90% of the radioactive Cs in the sediment mud of a school’s swimming pool in Fukushima, Japan was removed by treatment for 3 d using the alginate immobilized photosynthetic bacterium Rhodobcater sphaeroides SSI. Even though batch treatment was carried out 3 times repeatedly, the activity of immobilized cells in removing Cs was maintained at levels of about 84% (second batch) and 78% (third batch). Cs was strongly attached to the sediment mud because, even with HNO3 treatment at pH of 2.00–1.60 for 24 h, it was not eluted into the water. Furthermore, more than 75% of the Cs could be removed without solubilization with HNO3. This suggests that the Cs attached to the sediment mud was transformed into immobilized cells via the Cs+ ion by the negative charge of the immobilized cell surface and/or the potassium transport system of the photosynthetic bacterium.