Assessment on the Stability of Radiocesium in Sludge from a Water Purification Plant by a Leachate Test and a Sequential Extraction Test

Radiocesium released by the Fukushima Daiichi nuclear power plant accident fell in mountainous areas located in northern and western regions of Gunma Prefecture. Therefore, several research groups measured the radiocesium in the sediments in lakes and rivers, as well as soils around rivers, lakes and mountains. In this study, we investigated not only the concentration of radiocesium contained in wasted-sludge samples from a water purification plant, but also the leachate behaviors from the sludge to water. As results, the concentrations of radiocesium in wasted-sludge samples collected from a water purification plant at Kiryu Bureau of Waterworks on 2013 were obviously lower than that on 2011. Additionally, the degrees of radiocesium concentrations were related to those of turbidities in raw water of the water supply. Through leachate tests of radiocesium using aqueous solutions adjusted from pH 2 to pH 10, the risk leaching from wasted-sludge to water was considered to be low without any regard to the pH values of the solutions. Furthermore, the chemical forms of radiocesium in the sludge by a sequential extraction method were expected to mainly exist as residue and oxide forms, which are classified as fractions hardly eluted in nature.