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.

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