Over 90% of the water supplied in the coastal region in Israel in 2013 (600 Mm3 y−1) will be from desalination plants. The wastewater generated from this water (>400 Mm3 y−1) is planned, after proper treatment, to be reused for agricultural irrigation, making this low-salinity water the main agricultural-sector future water source. In this respect both the Mg2 + concentration and the Sodium Adsorption Ratio value of the water are of concern. We show that the typical Na+ concentration addition to wastewater (between ∼100 and ∼165 mg L−1) is much higher than the combined addition of Ca2 + and Mg2 + (between 0 and several mg L−1). Since desalinated water is typically supplied with low Ca2 + and Mg2 + concentrations (∼35 and 0 mg L−1 respectively), the treated wastewater is characterized by very low Mg2 + concentrations, low salinity and very high SAR values, typically >6 and up to 10 (meq L−1)0.5. SAR values can be lowered by adding either Ca2 + or Mg2 + to desalinated water. Adding Mg2 + is preferable from both health (minimizing cardiovascular disease hazards) and agriculture (inexpensive Mg fertilization) aspects. The low cost of Mg2 + addition at the post-treatment stage of desalination plants corroborates the request for Mg2 + addition in regions where treated wastewater from desalinated water origin is planned to be reused for irrigation.
Keywords: desalinated water, irrigated soils, Mg2 + deficiency, sodium adsorption ratio, treated wastewater