Selection, design, and procurement of a demineralization system for a surface water treatment plant

Abstract

Reverse osmosis (RO) and electrodialysis reversal (EDR) were pilot tested in conjunction with the design of a surface water treatment plant for the City of Sherman, Texas. The supply was water from Lake Texoma, a brackish source having a high scaling potential for calcium and barium sulfate. Test results showed both to be suitable for demineralizing the lake water; however, RO was found to be more susceptible to scaling by sulfate salts. Design and contract documents were prepared around the use of either technology to provide a cost-competitive procurement. Twenty-year present worth cost was used as the basis of contract award. The demineralization system equipment specifications incorporated requirements that reflected the inherent process advantage of EDR for this application, based on EDR's ability to operate at greater recovery without the need for continuous chemical addition for scale control (based on side-by-side pilot testing with RO). The initial 7.5-mgd plant capacity, currently under construction, will include three 1.5-mgd EDR trains, for a total EDR capacity of 4.5 mgd. Each train will contain two hydraulic stages for approximately 75 percent TDS removal.