Integrated\nFlow-Electrode Capacitive Deionization\nand Microfiltration System for Continuous and Energy-Efficient Brackish\nWater Desalination

Abstract

Flow-electrode\ncapacitive deionization (FCDI) is an emerging electrochemically\ndriven technology for brackish and/or sea water desalination with\nmerits of large salt adsorption capacity, high flow efficiency, and\neasy electrode management. While FCDI holds promise for continuous\noperation, there are very few investigations with regard to the regeneration/reuse\nof flowable electrodes and the separation of brine from electrodes\nwith these operation prerequisites for real nonintermittent water\ndesalination. In this study, we propose a novel module design to achieve\nthese critical steps involving integration of an FCDI cell and a ceramic\nmicrofiltration (MF) contactor. Our investigations reveal that the\nbrine discharge rate is the dominant factor for stable and efficient\noperation of the integrated module. Results obtained show that the\nintegrated FCDI/MF system can be used to successfully separate brackish\nwater (of salinities 1, 2 and 5 g L^–1) into both\na potable stream (<0.5 g L^–1) and a brine stream\n(concentrated by 2–20 times) in a continuous manner with extremely\nhigh water recovery rates (up to 97%) and reasonable energy consumption.\nAnother notable characteristic of the integrated system is the high\nthermodynamic energy efficiency (∼30%) with such efficiencies\n4–5 times larger than those of conventional capacitive deionization\nunits and comparable to reverse osmosis and electrodialysis systems\nachieving similar separation efficiencies. In brief, the results of\nstudies described here indicate that continuous and efficient operation\nof FCDI is a real possibility and pave the way for scale-up of this\nemerging technology.