Assessment of calculation methods for calcium carbonate saturation in drinking water for DIN 38404-10 compliance
- 1Omnisys, Eiberlaan 23, 3871 TG, Hoevelaken, the Netherlands
- 2Delft University of Technology, Faculty of Civil Engineering and Geosciences, Department of Water Management, P.O. Box 5048, 2600 GA, Delft, the Netherlands
- 3Waternet, P.O. Box 94370, 1090 GJ, Amsterdam, the Netherlands
- 4Vitens, P.O. Box 1205, 8001 BE Zwolle, the Netherlands
- 5VanDijkConsulting, Rossenberglaan 9, 3833 BN, Leusden, the Netherlands
- 6Oasen, P.O. Box 122, 2800 AC, Gouda, the Netherlands
Abstract. The new German standard on the calculation of calcite saturation in drinking water, DIN 38404-10, 2012 (DIN), marks a change in drinking water standardization from using simplified equations applicable for nomographs and simple calculators to using extensive chemical modeling requiring computer programs. The standard outlines the chemical modeling and presents a dataset with 10 water samples for validating used computer programs. The DIN standard, as well as the Standard Methods 2330 (SM) and NEN 6533 (NEN) for calculation of calcium carbonate saturation in drinking water were translated into chemical databases for use in PHREEQC (USGS, 2013). This novel approach gave the possibility to compare the calculations as defined in the standards with calculations using widely used chemical databases provided with PHREEQC. From this research it is concluded that the computer program PHREEQC with the developed chemical database din38404-10_2012.dat complies with the DIN standard for calculating Saturation Index (SI) and Calcite Dissolution Capacity (Calcitlösekapazität) or Calcium Carbonate Precipitation Potential (CCPP). This compliance is achieved by assuming equal values for molarity as used in DIN (obsolete) and molality as used in PHREEQC. From comparison with widely used chemical databases it is concluded that the use of molarity limits the use of DIN to a maximum temperature of 45 °C. For current practical applications in water treatment and drinking water applications, the PHREEQC database stimela.dat was developed within the Stimela platform of Delft University of Technology. This database is an extension of the chemical database phreeqc.dat and thus in compliance with SM. The database stimela.dat is also applicable for hot and boiling water, which is important in drinking water supply with regard to scaling of calcium carbonate in in-house drinking water practices. SM and NEN proved to be not accurate enough to comply with DIN, because of their simplifications. The differences in calculation results for DIN, SM and NEN illustrate the need for international unification of the standard for calcium carbonate saturation in drinking water.