(762a) Desalination of the Colorado River Water: A Hybrid Approach

Reverse Osmosis (RO) is the most important technology for water desalination. The 96 million US gallons per day (gpd) Yuma desalination plant for desalination of irrigation return flows (3200 mg/L total dissolved salts (TDS)) in Colorado River (CR) is designed to operate at about 70% water recovery.  Gabelich et al [1], studied RO desalination of CR water (887-1184 mg/L) in a pilot plant and demonstrated high recovery (≈95%).  In this paper we design a hybrid system for desalination of CR water at the same capacity as the Yuma plant, for a feed with TDS = 941 mg/L.

The hybrid process comprised of Ion exchange (IEX) water softening and pH adjustment, integrated in between two RO steps. IEX treatment and pH adjustment of the concentrate from the Primary RO (PRO) is done before it is sent to the Secondary RO (SRO). IEX treatment of PRO concentrate helped remove Ca²⁺, Mg²⁺ and Ba²⁺ which are the principal scale forming precursors and pH adjustment increased the solubility of Mg²⁺ salts. Use of concentrated retentate from SRO for regeneration of the IEX column eliminates the need for regeneration chemicals [2,3]. The hybrid process was evaluated for achieving high water recovery (≥95%).

The PRO and the SRO were modeled as cascades and optimal configurations were developed. Recovery in the PRO without the addition of antiscalants was 75%.  The IEX was simulated with multiple columns feeding simultaneously and a single column regenerating. IEX treatment and pH adjustment of PRO concentrate allowed operation of SRO at 70% recovery and if antiscalants are added to control silica scaling SRO can be operated at recoveries as high as 95%. The overall recoveries were 92% without antiscalant addition and 98% with antiscalant addition in SRO. IEX/RO operation at higher recoveries reduces the amount of brine to be disposed. Economic analysis is done to study the impact of reduced brine on the cost of product water.

1. C. J. Gabelich et al., Journal of Membrane Science 301 (2007) 131-141
2. T. Vermeulen et al., Desalination, 47 (1983) 149-159
3. A. Venkatesan and P. C. Wankat, Desalination, 271 (2011) 122-131