Long-term monitoring of water treatment technology designed for radium removal—removal efficiencies and NORM formation

Abstract

A drinking water treatment plant in Viimsi, Estonia was monitored over three years for iron, manganese, radium-226, radium-228, and their daughter nuclides in order to determine the efficiency of the treatment process, get an insight of the removal mechanisms and interactions between radium, iron, and manganese, and assess the overall longevity and performance of the technology and possible build-up of NORM from the treatment process. During the study, samples were collected from raw water, first and second stage filtrate, consumer water, backwash water, and filter materials. The results show a consistent removal efficiency for iron and manganese, as well as an average of over 85% removal for radium with a slight decline with time. Backwash process has been optimized for maximum radium removal from the filters, while keeping the radium concentrations in the backwash water below exemption levels. However, accumulation of radium and thorium occurs in the filter material, exceeding exemption levels in the top layer of the filter columns in less than a year. By the end of the observation period, activity concentrations in the top layer of the columns were above 30 000 Bq/kg for Ra-226 and Ra-228, and around 15 000 Bq/kg for Th-228. Radionuclides are not homogenously distributed in the filter columns. In order to estimate the average activity concentrations in the filter media, the height distribution of radionuclides has to be accounted for. Two years and two months after commissioning of the treatment plant average activity concentrations of Ra isotopes in the filter columns were in a range of 10 000 Bq/kg while Th-228 activity concentration was roughly 3500 Bq/kg.

Formation of radioactive waste in Estonian water treatment plants

“…The role of dissolved oxygen (DO) is also important as it is needed for complete oxidation of iron and manganese. In order for the complete oxidation of iron and manganese to occur, at least 5.0 mg * l −1 is needed in a given circumstance (Hill et al 2017). In the same study, it was shown that due to restriction of air flow to the aeration system, manganese-a known radium absorbent as MnO 2 -was not oxidised, but instead was competing with radium for adsorption sites on the filter material.…”

Naturally-Occurring Radioactive Materials at water treatment plant on the Poços de Caldas Plateau Region, Brazil

“…Another important factor to be mentioned regarding NORM in water treatment is the type of treatment applied during the whole process (e.g., coagulation, flocculation, decantation, and filtration) (FONOLLOSA et al, 2015;LYTLE et al, 2014). Hill et al (2017) monitored the concentrations of iron, manganese, 226 Ra, and 228 Ra at different stages of the treatment process for later comparison in terms of removal efficiency and interaction between these elements. Leier et al (2019) studied 18 treatment plants in Estonia and found high concentrations of 226 Ra and 228 Ra, of which they accumulate in the filter material, at a level where the material can be classified as radioactive material.…”