Potential drawbacks associated with agricultural irrigation with treated wastewaters from desalinated water origin and possible remedies

Abstract

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.