Recovering magnesium hydroxide and sodium chloride from zero discharge desalination concentrate streams

Alemayehu Asfaw Yetayew, University of Texas at El Paso


UTEP and Veolia Water Solutions & Technologies have been demonstrating and commercializing the Zero Discharge Desalination (ZDD) technology as part of a three year project sponsored by the U.S. Bureau of Reclamation. ZDD is able to achieve up to 98% recovery by desalinating brackish groundwater. ZDD is typically comprised of a reverse osmosis (RO) or nanofiltration (NF) system and a unique variation of electrodialysis called electrodialysis metathesis (EDM). The ZDD technology increases the yield of fresh water from water supplies that contain enough CaSO4 to cause precipitation problems when the water is treated with RO or NF alone. The EDM is the heart of the ZDD treatment system and it removes CaSO4 and other troublesome salts. Sodium chloride (NaCl) is the major consumable of the ZDD process and is a cost driver for desalination operations. This thesis describes laboratory experiments to evaluate the potential to recover NaCl and other useful salts from the ZDD process streams. Electrodialysis with monovalent selective anion and cation exchange membranes was explored here to selectively remove sodium chloride from a feed stream with high concentration of calcium sulfate. Experiments with simulated solutions and extended tests with the actual EDM concentrate streams were performed. Very good selectivities were observed for sodium over calcium and chloride over sulfate. The performance of the process with actual EDM concentrate streams shows great promise for rapid transfer to the pilot scale and eventually full scale ZDD process. This work is an example of the usefulness of membrane separations acting as a kidney in brackish groundwater treatment processes.

Subject Area

Civil engineering|Water Resource Management|Environmental engineering

Recommended Citation

Yetayew, Alemayehu Asfaw, "Recovering magnesium hydroxide and sodium chloride from zero discharge desalination concentrate streams" (2013). ETD Collection for University of Texas, El Paso. AAI1540017.