Technological and economic perspectives of membrane capacitive deionization (MCDI) systems in high-tech industries: From tap water purification to wastewater reclamation for water sustainability

Abstract

Water sustainability is at the core of high-tech industries and reflects their efforts in terms of both economic and environmental benefits. In this study, a membrane capacitive deionization (MCDI)-based water treatment system was proposed for the production of ultrapure water and wastewater reclamation by deionization. The system achieved good deionization performance in single-pass mode for treating soft tap water (T1), hard tap water (T2), cooling tower blowdown (W1) and wastewater discharge from high-tech industries. Overall, the removal efficiencies for hardness and conductivity in the tested scenarios were at least 70.8% and 51.9%, respectively, and selectivity in ion removal was the highest in Na+ for T1, W1 and W2 and in Ca2+ for T2, as it was mainly affected by the initial molar concentration of major ions. The system also showed favorable characteristics of high charge efficiency and relatively low energy consumption. At an applied voltage of 1.6 V, the energy requirements vary from 0.014 to 0.68 kWh/m3 with a charge efficiency higher than 70%, while the optimal deionization time was estimated to be between 12 and 60 min considering the increase in both the mean deionization rate and mean deionization capacity for various feedwater scenarios. The levelized cost of water for the studied MCDI scenarios ranges from 0.35 to 0.53 $USD/m3, in which the capital and material costs generally outweigh the energy and other operational costs. The results of this study are expected to provide essential techno-economic recommendations for the practical adoption of the on-site MCDI process in industries.