Removal of radioactive iodine and cesium in water purification processes after an explosion at a nuclear power plant due to the Great East Japan Earthquake

The presence of radionuclides at five water purification plants was investigated after an explosion at a nuclear power plant hit by the Great East Japan Earthquake on 11 March 2011. Radioactive iodine (I-131) and cesium (Cs-134 and Cs-137) were detected in raw water in Fukushima and neighboring prefectures. I-131 was not removed by coagulation-flocculation-sedimentation. I-131 was removed by granular activated carbon (GAC) and powdered activated carbon (PAC) at a level of about 30%-40%, although I-131 was not removed in some cases. This was also confirmed by laboratory-scale experiments using PAC. The removal percentages of I-131 in river and pond waters by 25 mg dry/L of PAC increased from 36% to 59% and from 41% to 48%, respectively, with chlorine dosing before PAC. Cs-134 and Cs-137 were effectively removed by coagulation at both a water purification plant and in laboratory-scale experiments when turbidity was relatively high. In contrast, Cs-134 and Cs-137 in pond water with low turbidity were not removed by coagulation. This was because Cs-134 and Cs-137 in river water were present mainly in particulate form, while in pond water they were present mainly as cesium ions (Cs-134(+) and Cs-137(+)). However, the removal of 'Cs and Cs-137 in pond water by coagulation increased markedly when Cs-134 and Cs-137 were mixed with sediment 24 h before coagulation. (C) 2012 Elsevier Ltd. All rights reserved.