Performance Improvement of Capacitive Deionization for Water Desalination Using a Multistep Buffered Approach

Due to the increasing demand for clean and potable water stemming from population growth and exacerbated by the scarcity of fresh water resources, more attention has been drawn to innovative methods for water desalination. Capacitive deionization (CDI) is a low maintenance and energy efficient technique for desalinating brackish water, which employs an electrical field to adsorb ions into a high-porous media. After the saturation of the porous electrodes, their adsorption capacity can be restored through a regeneration process. Herein, based on a physical model previously developed, we conjecture that for a given amount of time and volume of water, multiple desalination cycles in a high flow rate regime will outperform desalinating in a single cycle at a low flow rate. Moreover, splitting a CDI unit into two subunits, with the same total length, will lead to higher desalination. Based on these premises, we introduce a new approach aimed at enhancing the overall performance of CDI. An array of CDI cells are sequentially connected to each other with intermediate solutions placed in between them. Desalination tests were conducted to compare the performance of the proposed system, consisting of two CDI units and one intermediate solution buffer, with a two-cascaded-CDI unit system with no intermediate solution. Experimental data demonstrated the improved performance of the buffered system over the nonbuffered system, in terms of desalination percentage and energy consumption. The new proposed method can lead to lower amount of energy consumed per unit volume of the desalinated water.