salinity removal

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Remember that excessive salinity (seawater or brackish water) can only be reduced by using the reverse osmosis or electro dialysis membrane techniques (see chapter separation by membranes) or by distillation (see chapter degasification, odour control, evaporation).

If the aim is to use membranes to resolve a divalent ion problem (or ions having a higher valency), then nanofiltration should be used. E.g.:

  • softening : NF has been used for many years in some regions of the USA (especially Florida) in order to lower Ca2+ et Mg2+ contents;
  • sulphates (e.g. water contaminated by gypsum discharges, some mine drainage water); MF membranes will usually eliminate from 90 to 98% of SO42– ions.