(Invited) Development and Scale-up of Membrane Capacitive Deionization (MCDI) for Desalination and Water Reuse

Abstract

Desalination and water reuse are the key solutions to address global water scarcity. It is important to recognize the water-energy interactions and develop energy-efficient technologies to separate ions from brackish water, seawater and reclaimed wastewater. Most recently, membrane capacitive deionization (MCDI), inspired by energy storage devices (e.g., supercapacitors), is a promising desalination technology with several advantages of energy efficiency (TDS < 4000 ppm), high water recovery, less chemical additive, and environmental friendliness. In MCDI, ions are electrostatically captured within highly porous carbon electrodes through the formation of electrical double layer during the charging step, and then released into the solution by discharging the electrodes. By incorporating ion-exchange membranes (IEMs) in front of each electrode, the desalination performance can be significantly improved, achieving high salt adsorption capacity and charge efficiency. Over the past few years, we have made efforts to scale up the MCDI stacks for commercialization purposes, which are composed of 32 pairs of 400 mm × 200 mm activated carbon electrodes. Note that a stop-flow operation is applied in the discharge process to increase the water recovery (> 75%). A pilot-scale study of an MCDI system was performed to reclaim the secondary effluents from a municipal wastewater treatment plant. In addition, MCDI prototypes offer promising engineering opportunities for water recycling in high-tech industries, including reverse osmosis reject and wet scrubbing. Furthermore, we will discuss the challenges and perspectives for the future of MCDI as a cost-efficient, low-energy approach for desalination and resource recovery.