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Partial desalination

Process description

A combination of high water hardness and considerable nitrate, chloride or sulphate content can be successfully treated with the Carix process*. The process is based on the combination of a hardness-absorbing weak acid cation exchanger and an anion exchanger which absorbs nitrate, chloride and sulphate. If the two ion exchangers are fully loaded, they are regenerated together and simultaneously by introducing carbonic acid. This saves operating costs and protects the environment.

Gas application

To regenerate the ion exchangers, CO2-saturated water is prepared and pumped through the filter beds. CO2 dissolved in water partially reacts to bicarbonate (HCO3-) and protons (H+). The free protons regenerate the cation exchanger, the hydrogen carbonate the anion exchanger. The residual CO2 is degassed from the rinse water process and used again for preparation of CO2-saturated water.   


  • Simultaneous lowering of hardness, sulphate, chloride and nitrate content in one step to result in favourable drinking water values
  • The regeneration only requires carbon dioxide and no additional salts
  • Favourable for the corrosion index (Larson index), since not only bicarbonates but also sulphates and chlorides are reduced.
  • Low CO2-consumption and operating costs

Messer solution

Messer offers cost-saving and reliable technologies for injection of gaseous or liquid CO2.


*  CARIX® is a registered trademark of  Veolia Water Technologies