New Operational Modes to Increase Energy Efficiency in Capacitive Deionization Systems

In order for capacitive deionization (CDI) as a water treatment technology to achieve commercial success, substantial improvements in the operational aspects of the system should be improved in order to efficiently recover the energy stored during the deionization step. In the present work, to increase the energy efficiency of the adsorption–desorption processes, we propose a new operational procedure that utilizes a concentrated brine stream as a washing solution during regeneration. Using this approach, we demonstrate that by replacing the electrolyte during regeneration for a solution with higher conductivity, it is possible to substantially increase round-trip energy efficiency. This procedure was experimentally verified in a flow cell reactor using a pair of carbon electrodes (102 cm geometric area) and NaCl solutions having concentrations between 50 and 350 mmol·L–1. According to experimental data, this new operational mode allows for a better utilization of the three-dimensional structure of the porous material. This increases the energetic efficiency of the global CDI process to above 80% when deionization/regeneration currents ratio are optimized for brackish water treatment.