Saline Brine Separation: Thermodynamic and Techno-Economic Comparison of Counterflow Reverse Osmosis with Electrodialysis

Separation into a more concentrated and a diluted stream is an energy-efficient alternative to thermal distillation for saline brine management. Here, we compare counterflow reverse osmosis (CFRO) with electrodialysis (ED) for brine separation in terms of energy consumption and overall treatment cost. Conditions for energy-optimal thermodynamically equipartitioned operation are derived for both technologies. The brine-reflux CFRO configuration requires more energy/module area than does the split-feed design but can be operated at practical pressure levels for high-salinity applications. After identification of the cost-optimal voltage in ED and pressure in CFRO, realistic single-stage systems, including losses, are compared. CFRO consumes significantly lower energy and is less expensive than ED for intermediate-salinity brine separation, such as textile dyeing effluent recycling. Therefore, this is an ideal beachhead application for CFRO compared to seawater brine concentration up to near saturation, where its cost is comparable to that of ED.