Fate of radiocesium in sewage treatment process released by the nuclear accident at Fukushima

• Ten percent of the Cs entering the sewage treatment plant would be transferred to the sludge.
• Cs behaves more similarly to Rb than K in the sewage treatment process.
• Only a small amount of Cs would be released to the air by the sludge incineration.

The nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) which occurred after the Great East Japan Earthquake on March 11, 2011 resulted in releases of radionuclides such as 134Cs (half-life:T1/2 = 2.06 yr), 137Cs (T1/2 = 30.04 yr) and 131I (T1/2 = 8.05 d) to the environment. For this paper, we observed the monthly variations of radiocesium (134Cs and 137Cs) and stable Cs concentrations in influent, effluent, sewage sludge, and sludge ash collected from a sewage treatment plant 280 km north of the FDNPP from July to December, 2011. Using the stable Cs results, we concluded the mass balance of Cs in the sewage treatment plant showed that about 10% of the Cs entering the sewage treatment plant would be transferred to the sewage sludge, and then Cs in the sewage sludge was totally recovered in the sludge ash. The behavior of Cs was similar to that of Rb, but it was not similar to that of K in the sewage treatment process.