Cations- and anions exchanger for complete desalination
Depending on the composition of raw water respectively on the desired residual salt content in product water, it can be necessary to add to the reverse osmosis a further downstream process step for complete demineralization. For this the ion-exchanger constitutes one of the most common chemical complete demineralization methods. For this strongly acid cations-exchanger respectively strongly alkaline exchanger resins are used.
Both exchanger resins can be used in separated containers or mixed in so-called mixed bed systems. Although by means of mixed bed systems a better product quality can be achieved (low conductivity of water), however, the cleaning respectively regeneration of these systems is more complex and leads to an increased consumption of chemicals.
Ion-exchangers can be used as alternative to reverse osmosis systems, however, due to the regular regeneration cycles no continuous operation is possible. This means that for permanent operation a redundant design of the system is necessary.
Often in case of low demands on product water only a partial desalination is done. Softening respectively water decarbonization are classic application errors. In this case weakly acidic cation-exchangers are used. Disadvantage of the partial desalination is the formation of carbon acid, which has to be removed again in a further procedural step.