V Transfer Models and/or Parameters
Evaluating Removal of Radionuclides from Landfill Leachate Using Generally Practiced Wastewater Treatment Processes
Nao Kamei-Ishikawa, Ayumi Ito, and Teruyuki Umita
Abstract Some amounts of the radionuclides released in the nuclear accident at the Fukushima Daiichi Nuclear Power Plant are transferred to wastes such as sewage sludge ash and municipal waste ash. Among these wastes, those that contain less than 8,000 Bq/kg radiocesium are being disposed in controlled landfill sites that have been in use since before the accident. At the landfill sites, a leachate treatment system is generally used, and there are no specific treatment steps for removal of radionuclides. In this study, the stable element concentrations of the relevant radionuclides in the leachate and treated water at each treatment step were determined to evaluate the radionuclide removal at each step. Target elements in this study were Cs, Co, Mn, Ni, and Sr. More than 93.9 % of the Co, Mn, Ni, and Sr present in the leachate could be removed at the alkali removal step by precipitation; however, Cs could not be removed by any of the treatment processes.
Keywords Cesium • Cobalt • Fractionation • Landfill leachate • Leachate treatment
• Manganese • Nickel • Stable isotopes • Strontium
Radionuclides such as 134Cs, 137Cs, 90Sr, and 239+240Pu, which were released to the environment in the nuclear accident at the Fukushima Daiichi Nuclear Power Plant, have been found in bottom ash and fly ash of incinerated wastes produced in Fukushima Prefecture, Japan . 134Cs and 137Cs have been found in sewage sludge produced in a wide area of northern and eastern Japan . The Japanese government divides wastes into three types, depending on radiocesium concentration in the waste, and each type has its own disposal methods . For the waste with the lowest level of radiocesium concentrations (<8,000 Bq/kg), controlled landfill sites can be used as the disposal place. The radiocesium concentrations in sewage sludge ash produced in Iwate Prefecture have been lower than 8,000 Bq/kg; therefore, these ashes have been disposed in a controlled landfill site that has been used since before the nuclear accident.
Controlled landfill sites have leachate treatment systems. Although leachate characteristics depend on the individual sites, generally leachate has high alkalinity and contains a high organic matter content and a large amount of suspended solids . To remove these contaminants, several types of treatment steps are used: coagulation-flocculation, chemical precipitation, membrane filtration, activated carbon adsorption, biological treatment, and ion-exchange treatment . However, the extent of removal of any radionuclides present in the leachate by existing treatment steps is not clear.
The objective of this study was to evaluate radionuclide removal from the leachate sampled at a controlled landfi site. Stable elements were analyzed as analogues of the radionuclides. The main elements studied were Co, Cs, Mn, Ni, and Sr; their radionuclides (58Co, 60Co, 134Cs, 137Cs, 54Mn, 59Ni, and 63Ni) were actually detected or expected to be found in environmental samples collected after the nuclear accident .