Desalination of brackish water using capacitive deionization (CDI) technology

摘要

Capacitive deionization (CDI) is a desalination technology utilizing electrosorption and desorption of ionic salts. Carbon materials are the main components of electrodes in CDI, while addition of organic and inorganic materials with carbon materials enhances the desalination performance. In this study, powdered activated carbon (PAC) as well as PAC combined with titanium dioxide (TiO2) electrodes was prepared. The deionization performance was evaluated using three CDI systems. Feed solution having concentration of 2,000 mg/L was used in smalland lab-scale CDI systems. PAC + TiO2 electrodes showed 28% more salt removal as compared to PAC electrodes in the small-scale CDI system using one pair of electrodes. Laboratory-scale CDI system using six pairs of PAC + TiO2 electrodes showed adsorption capacities of 2.64, 4.30, and 6.67 mg NaCl/g-adsorbent at 1.3, 1.6, and 1.8 volts, respectively. Pilot scale CDI system using 20 pairs of PAC + TiO2 electrodes at 1.8 volts showed maximum salt removal of 84, 82, and 71% for the feed NaCl concentrations of 2,000, 2,500, and 3,000 mg/L with adsorption capacities of 7.7, 10.4, and 11.2 mg NaCl/g-adsorbent, respectively. As the amount of salt ions to adsorbent increases, the exchangeable sites on the adsorbent structure become saturated, which results in decrease of salt removal efficiency, while the adsorption capacities increased with increase in concentration due to elevated mass transfer rate of salt ions inside the pores.