Reclaiming produced water for beneficial use: salt removal by electrodialysis

This paper addresses the use of electrodialysis (ED) to remove salts from produced water (PW) to meet drinking water, irrigation water, and/or livestock watering standards. Specifically, ED treatment of five simulated PWs with low (CO, TX, and WY) and high (UT and OK) total dissolved solids (TDS) concentrations and varying cations and anions distributions was evaluated at three voltage settings. Both the absolute and percent TDS removal were found to increase linearly with voltage for all five waters. With Neosepta® CMX-SB/AMX-SB membranes, the cations/anions were generally found to be removed in the following order (from fastest to slowest): Ca2+ ≈ Mg2+ > K+ > Na+ and SO42− > HCO3− > Cl−. Also, the feed concentrations of the individual anions appeared to affect their removal rates at low applied voltage settings. Finally, CO, TX, and WY waters were treatable to drinking water and livestock watering standards after 1 h at 6.5 V. Although UT water was treatable to the same standards after 2 h at 9.8 V, the stack power needed to treat the UT water was approximately 23 times higher than that required to treat each of the three low TDS waters. OK water was deemed untreatable to those standards under the laboratory operating conditions.