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Residues from drinking-water treatment

Description: Residues from drinking-water treatment Residues from certain processes of groundwater treatment for drinking water purposes can exhibit enhanced contents of radionuclides in comparison to the natural background level of soils. In unfavourable circumstances, the handling of these residues can lead to an increased level of radiation exposure for workers (inside the waterworks as well as in the course of recycling or disposal). This article describes the origin of these residues and highlights which exposure pathways can lead to the increased radiation exposure of workers. Naturally occurring radionuclides in groundwater Residue types of water treatment processing Disposal or recycling Legal framework Exposure pathways and exposure scenorios References Naturally occurring radionuclides in groundwater Radionuclides from the natural decay chains of uranium -238, uranium -235 and thorium-232 are present in trace quantities in all rocks. If groundwater comes into contact with these rocks, a small proportion of the radionuclides dissolve from the rock and thus enter the groundwater. The activity concentration is highly dependent on the type of rock and its chemical composition, as confirmed in the study " Radiation exposure from natural radionuclides in drinking water in the Federal Republic of Germany" (in German), which was conducted by the Federal Office for Radiation Protection ( BfS ). The table below shows an extract of the results: Median values (Med) and maximum values (Max) of the activity concentrations of frequently occurring natural radionuclides in untreated groundwater in millibecquerel per litre with respect to the rock type of the aquifer (" Radiation exposure from natural radionuclides in drinking water in the Federal Republic of Germany ") Rock type U -238 Ra -226 Pb -210 Po-210 Ra -228 Med Max Med Max Med Max Med Max Med Max basalt <0.74 5.7 1.0 2.8 1.9 20 0.99 5.6 <0.81 5.4 gneiss <0.74 15 2.2 7.0 7.8 29 1.8 8.3 4.3 7.8 granite 1.2 53 12 98 9.5 70 2.0 19 11 29 limestone 6.0 210 5.9 160 3.2 23 1.3 18 5.4 110 sand 3.6 120 7.1 36 2.1 18 1.3 19 6.7 46 shale 1.1 97 2.6 27 2.1 19 1.8 9.4 3.7 26 sandstone 17 590 12 380 3.6 31 2.9 630 9.3 210 other rock 2.5 620 8.0 300 4.1 270 2.0 410 7.5 130 The activity concentration of radionuclides in untreated groundwater also depends on: the redox potential the pH of the groundwater the solubility of the radionuclides to the top Residue types of water treatment processing In order to comply with the requirements of the Drinking Water Ordinance, groundwater must be treated to drinking-water quality where appropriate. Depending on the chemical composition of the water, different water treatment processes are used to remove undesirable substances. According to a definition [1] issued by the German Technical and Scientific Association for Gas and Water (DVGW), the resulting residues are primarily: iron-containing slurries lime-containing slurries slurries from flocculation activated carbon screenings Further residues can arise during the replacement of filter material ( e.g. filter sand/filter gravel) or special absorbing resins, as well as during plant dismantling ( e.g. precipitates in tubing). Until now, the specific removal of radionuclides during water treatment has not normally been carried out. Nevertheless, radionuclides can accumulate in some of the residues to a level exceeding that naturally found in soils and rocks. Surface water has a lower concentration of natural radionuclides than groundwater, and so residues with enhanced contents of radionuclides are to be expected during the processing of groundwater in particular. Median values (Med) and maximum values (Max) of the activity concentration of frequently occurring natural radionuclides in surface water and groundwater in millibecquerel per litre (" Radiation exposure from natural radionuclides in drinking water in the Federal Republic of Germany ") Type of water U -238 Ra -226 Pb -210 Po-210 Ra -228 Med Max Med Max Med Max Med Max Med Max groundwater 5.4 620 8.4 380 2.7 82 1.6 630 7.8 210 surface water 1.3 39 4.3 32 2.2 29 1.6 19 4.2 42 With regard to residues from the processing of groundwater into drinking water, enhanced contents of radionuclides are known to occur in: iron slurries and lime slurries from neutralisation absorber resins, activated carbon and filter gravel from iron/manganese removal There are also reports of incrustations containing radionuclides in thermal water sources (springs). Enhanced contents of radionuclides are not to be expected either in flocculent slurries, which arise primarily during the treatment of surface water, or in screenings. In its Fact Sheet W256 [2] , the German Technical and Scientific Association for Gas and Water ( Deutscher Verein des Gas- und Wasserfaches , DVGW) offers further information on the occurence, the re-use and the disposal of radionuclide bearing residues from waterworks. to the top Disposal or recycling Pursuant to the German Recycling Act (KrWG), recycling is preferable to disposal. However, recycling does not take precedence in the event of a danger to humans or the environment. Of the above residues, the following can in principle be recycled: iron slurries lime slurries from neutralisation filter gravel In its Fact Sheet W221-3 [1] , the German Technical and Scientific Association for Gas and Water ( Deutscher Verein des Gas- und Wasserfaches , DVGW) recommends various ways of recycling these residues: Iron slurries are used in environmental engineering to reduce the level of phosphate and hydrogen sulfide. In addition, they are used as a secondary raw material in the brick and cement industries as well as in the production of plant granulate. In the past, some 35% of iron slurries were disposed of to landfill; this proportion is predicted to fall in the future as a result of waste legislation. In agriculture and forestry, lime slurries from neutralisation are applied to land to improve (“ameliorate”) the pH in the soil. It is also conceivable to recycle these residues – for example, in the production of lime and cement or the production of artificial soil substrates. As filter gravel from iron and manganese removal remains in use at the waterworks over a period of several years to decades, it only occasionally arises as a residue at the water distribution companies. Therefore, no fixed disposal routes have yet gained general acceptance for these residues. There are examples in which the gravel is used in road contruction or for the commissioning of new filter units at other waterworks. It could also be reused in landscaping. Information on the quantity of recycled or landfilled residues has not been published and is not available to the DVGW . As yet, there is no known recycling option for incrustations, whereas activated carbon and absorbing resins, in principle, are suitable for thermal recycling due to their high carbon content. to the top Legal framework At the beginning of 2014, the European Atomic Energy Community ( EURATOM ) published the European basic safety standards directive on radiation protection. In this directive, residues from groundwater filtration facilities are classified as an industrial sector involving naturally occurring radioactive materials. Euratom Member States had to implement these regulations into national law. Radiation Protection Act and Radiation Protection Ordinance In Germany, this implementation was achieved in 2017 with the Radiation Protection Act. To supplement this, the Radiation Protection Ordinance was revised in 2018. Both legal regulations have been in force since 31 December 2018. In Annex 1 to the Radiation Protection Act, filter gravel, filter sand and granular activated carbon are included in the list of residues to be considered for the first time and are therefore subject to the regulations of the Radiation Protection Act. Further guidelines Insofar as residues from waterworks are reused in building products, it is also necessary to adhere to the guidelines of the European recommendation on natural radioactivity in building materials, which states that standard building materials should not lead to enhanced radiation exposure of the general public. The Radiation Protection Act also lays down regulations for building products, and these regulations also entered into force on 31 December 2018. Furthermore, it is necessary to check whether the planned mode of recycling or disposal is permissible according to waste legislation. Especially in the case of reuse in landscaping or road building, the requirements for the material recycling of mineral residues/waste, as set out by the Federal/Laender Working Group on Waste (LAGA), must be adhered to in relation to the leaching behaviour of mineral residues. For the transport of materials, the European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR) must be adhered to. to the top Exposure pathways and exposure scenorios Depending on the quantity, the radionuclide content in the residue, and the chosen mode of disposal or recycling, employees – in waterworks or at waste disposal or recycling companies – may obtain an enhanced radiation exposure when handling residues from waterworks. Based on a dose estimation, it is possible to determine whether there is a risk of significantly enhanced radiation exposure for employees (more than 1 millisievert per year in addition to the natural background radioactivity ). A dose estimation should take account of the following situations: time spent by employees in rooms in which residues are stored handling of residues during storage, recycling, transport or disposal maintenance and/or cleaning of operating equipment From a radiation protection perspective, the following exposure pathways must be considered here: external gamma radiation inhalation of dust inhalation of radon and radon decay products Furthermore, if residues are sent to landfill or reused in road building, and especially in landscaping, radionuclides may be dissolved in seepage water and carried into the groundwater. The use of this groundwater can potentially lead to an additional exposure pathway for the general public. Therefore, the use of affected groundwater from a private well for drinking water purposes or for irrigation must be taken into account in dose estimations. Estimation of radiation exposure for employees at waterworks, wasta disposal companies and recyclers In various studies, the radiation exposure of employees at waterworks, disposal companies and recyclers has been estimated in relation to the handling of iron, manganese and lime slurries (Ermittlung von Arbeitsfeldern mit erhöhter Exposition durch natürliche Radionuklide und überwachungsbedürftige Rückstände – Rückstände aus der Trinkwasseraufbereitung, Teil I und Teil II [“Identification of working environments with enhanced exposure to natural radionuclides and residues requiring surveillance – Residues from drinking-water treatment, Part I and Part II”, in German]). The results showed that, even with the least favourable assumptions, the dose reference value for the general population of 1 millisievert per year is unlikely to be exceeded. Likewise, the previously published activity contents for activated carbon and incrustations from waterworks do not point to increased radiation exposure of the general population. Based on current knowledge, the exceedance of the dose reference value cannot be ruled out completely in unfavourable conditions during the disposal or recycling of filter gravel from manganese/iron removal and of heavily loaded absorber resins resulting from the specific removal of uranium . It is advisable to consider such situations on a case-by-case basis. If, following this assessment, the dose reference value is actually exceeded, it is essential to clarify which dose -reduction measures can be introduced with a reasonable amount of effort in these situations. For example, these measures include wearing personal protective equipment or searching for alternative disposal routes. Calculation guidelines The BfS is currently drawing up calculation guidelines that allow an estimation to be made of the effective dose for employees and members of the public due to exposure to naturally occurring radioactive materials (Calculation Guide NORM ). Until such time as this calculation guideline is completed, the BfS offers recommendations for a simplified estimation of the radiation exposure of employees and members of the public. to the top References [1] DVGW (2014): Rückstände und Nebenprodukte aus Wasseraufbereitungsanlagen; Teil 3: Vermeidung, Vermarktung und Verwertung. DVGW-Arbeitsblatt W221-3 (in German) [2] DVGW (2020): Radionuklidhaltige Rückstände aus der Aufbereitung von Grundwasser – Bewertung und Entsorgung“ DVGW-Arbeitsblatt W256 (in German) State of 2026.07.27

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Language: Englisch/English

Last harvest: 30.09.2026 01:00

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