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

Abstract

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 (131I) and cesium (134Cs and 137Cs) were detected in raw water in Fukushima and neighboring prefectures. 131I was not removed by coagulation–flocculation–sedimentation. 131I was removed by granular activated carbon (GAC) and powdered activated carbon (PAC) at a level of about 30%–40%, although 131I was not removed in some cases. This was also confirmed by laboratory-scale experiments using PAC. The removal percentages of 131I 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. 134Cs and 137Cs were effectively removed by coagulation at both a water purification plant and in laboratory-scale experiments when turbidity was relatively high. In contrast, 134Cs and 137Cs in pond water with low turbidity were not removed by coagulation. This was because 134Cs and 137Cs in river water were present mainly in particulate form, while in pond water they were present mainly as cesium ions (134Cs+ and 137Cs+). However, the removal of 134Cs and 137Cs in pond water by coagulation increased markedly when 134Cs and 137Cs were mixed with sediment 24 h before coagulation.