The physicochemical distribution of 131I in a municipal wastewater treatment plant

Publication date: November 2017
Source:Journal of Environmental Radioactivity, Volumes 178–179
Author(s): Volker Hormann, Helmut W. Fischer
As a consequence of therapeutic and diagnostic treatment of patients with thyroid diseases, ¹³¹I is introduced into the sewage system on a regular basis. This presents an opportunity to use the ¹³¹I as a tracer to study its partitioning and transport within a wastewater treatment plant (WWTP). In the case of nuclear accidents where ¹³¹I is one of the most prominent nuclides, an understanding of iodine partitioning and transport will be valuable for developing models that may prognosticate the activity concentrations in sludge and outflow, especially after an accidental input. In this study, samples from various locations inside a municipal WWTP were taken and for each sample, three different fractions were separated by a chemical extraction process. These fractions were analysed for their ¹³¹I activity concentrations by gamma-ray spectroscopy. While about 30% of the radioiodine activity in the inflow is associated with organic molecules, this amounts to about 90% after biological treatment. This is caused by the accumulation of ¹³¹I bound to organic matter in the return sludge and by a transfer of ¹³¹I from the inorganic to the organic fractions, most likely mediated by microbial action. In the outflow, inorganic and low-molecular ¹³¹I is dominant, but the overall activity concentration is reduced to about 50–75%.



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