Cost Comparison of Capacitive Deionization and Reverse Osmosis for Brackish Water Desalination

Abstract

Although the energy efficiency of brackish water capacitive deionization (CDI) and reverse osmosis (RO) have been extensively compared, their relative costs remain poorly defined. We develop a parametric model to estimate the levelized cost of water (LCOW) of three CDI configurations (CDI, membrane CDI, and flow electrode CDI) and compare it with the LCOW of brackish water RO calculated using a process-based optimization model. We find significant deviations between cost-optimal and energy-optimal RO design and operation, highlighting the importance of LCOW in comparative evaluations of desalination technologies. Our results suggest that material (including electrode and ion exchange membrane) costs are the largest cost component for CDI processes. As such, the economic viability of CDI critically depends on the component lifespan, with lifespans longer than 1 year (105 cycles for 5 min cycle duration) required to reduce brackish water desalination costs relative to RO. Finally, sensitivity analyses indicate that CDI processes are unlikely to be cost-competitive against RO for feedwater concentrations greater than 2 g/L. Future research to enhance the economic feasibility of CDI processes should focus on developing more durable electrodes, increasing cost-normalized electrode capacitance, and developing low-cost ion exchange membranes and coatings.