ABSTRACT
Over 90% of the water supplied in the coastal region in Israel in 2013 (600 Mm(3) y(-1)) will be from desalination plants. The wastewater generated from this water (>400 Mm(3) 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 Mg(2 + ) concentration and the Sodium Adsorption Ratio value of the water are of concern. We show that the typical Na(+) concentration addition to wastewater (between approximately 100 and approximately 165 mg L(-1)) is much higher than the combined addition of Ca(2 + ) and Mg(2 + ) (between 0 and several mg L(-1)). Since desalinated water is typically supplied with low Ca(2 + ) and Mg(2 + ) concentrations ( approximately 35 and 0 mg L(-1) respectively), the treated wastewater is characterized by very low Mg(2 + ) 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 Ca(2 + ) or Mg(2 + ) to desalinated water. Adding Mg(2 + ) is preferable from both health (minimizing cardiovascular disease hazards) and agriculture (inexpensive Mg fertilization) aspects. The low cost of Mg(2 + ) addition at the post-treatment stage of desalination plants corroborates the request for Mg(2 + ) addition in regions where treated wastewater from desalinated water origin is planned to be reused for irrigation.
