New desalinated drinking water regulations are met by an innovative post-treatment process for improved public health

The recent supply of large volumes of seawater desalinated water in Israel prompted both the development of new water quality standards and the development of a novel post treatment process, designed to comply with the new standards at a cost effective price. The new process is designed to supply water with alkalinity, Ca²⁺ and calcium carbonate precipitation potential values as required in the new criteria, along with the addition of a threshold Mg ²⁺ concentration recently recommended by the WHO. The current paper describes the process in general, and focuses in particular on attaining these criteria while maintaining a low total hardness concentration (120 mg/L as CaCO³). The process is based on dissolving calcite using H ₂SO₄ and replacing the excess calcium ions generated in this process by Mg²⁺ ions (using a specific cation exchange resin - Amberlite) and by Na⁺ (using a second cation exchange resin - chabazite, from the zeolite group). Once exhausted the resins are re-loaded with Mg²⁺ and Na⁺ by the brine generated in the RO process, thus no unwanted brines are generated. A case study is presented for which operational costs were approximated at 0.034 $US/m³ product water.