Electrochemical CDI integration with PRO process for water desalination and energy production: Concept, simulation, and performance evaluation

Abstract

Capacitive deionization (CDI), an electrochemical desalination technology, was numerically coupled with pressure-retarded osmosis (PRO), a salinity gradient power generation technology, for water and energy production. A novel multi-pass desorption process was employed for CDI, result in a high freshwater recovery and highly concentrated desorption effluent. The high and low concentrated streams produced by the electrochemical CDI system were used in PRO as continuous draw and feed solutions, respectively. The integrated CDIPRO system performance was mathematically assessed in terms of water recovery (WR), concentrated gain ratio (CGR), PRO power generation, and overall power consumption for different desorption flow rates, applied currents, and number of desorption passes. The WR and CGR values in the electrochemical desalination system (CDI) increased to 98% and 59, respectively, as the number of desorption passes were increased to six in addition to a decrease of the desorption flow rate to 0.4 mL/s. Almost 96.7% of the fresh water was recovered and a desorption effluent concentration of 1.2 M was obtained from the six-pass desorption method with a 0.8 mL/s flow rate using the CDI-PRO integrated system. Treated water with concentration of 0.016 M from the adsorption process and concentrated water with the concentration of 1.2 M from the desorption processes of CDI system were used as the feed and draw streams, respectively. PRO system produced a power density of 8 W m(-2) in this integrated system. Furthermore, 2.2 kJ/L of energy consumption for water production without process integration is reduced to 0.67 kJ/L through the implementation of the proposed system.