Temporal Analysis of Radiocesium Concentration in Sewage Sludge after Fukushima Daichi Nuclear Power Plant Accident

Abstract Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in April 2011 had released radioactive substances to the environment. Radiocesium transported from the urban area to the sewerage system by transfer wash-off mechanism. Eventually, radiocesium accumulated in the sludge produced by the wastewater treatment plant. This study was aimed to evaluate the possibility of using the time-series of Radiocesium concentrations in sewage sludge to quantify the wash off rate of the radionuclide on the surface of an urban area. This study used monitoring data from four WWTPs in Fukushima Prefecture and daily concentrations of Radiocesium in their sewer sludge over 8 years were collected. The results show time-dependent of Radiocesium concentration in sludge fitted with double exponential regression which means there are two rates: rapid rate (22 – 36 months) and slow rate (123 – 213 months). Values of the model parameters based on temporal analysis of radiocesium concentrations in sewage sludge are consistent with radiocesium wash off after the Chernobyl accident indicating that the decreasing rate of radiocesium concentrations in sewage sludge reflect the wash off rates on the surface of the corresponding urban area.