SUMMARY

Capacitive deionization (CDI) is a desalination technology that electrochemically separates ions from a feed water stream. State of the art technologies such as reverse osmosis and distillation operate in processes at elevated pressure and/or temperature, increasing energy demands. CDI, which operates at near ambient conditions, can provide advantages associated with system footprint, cost, and safety. Despite these advantages, CDI has been slow to the marketplace, due to two limitations: (1) the electrodes have a limited surface area available for ion removal, confining effective use of CDI to treating brackish water (C<5 g/l), and (2) Thermodynamic energy efficiency for brackish water treatment is only around 5%, well below the capabilities of most seawater (C=35 g/l) treatment technology.

To address these limitations, emphasis will focus on increasing the effective electrode surface area through evaluating a new approach termed flow electrodes. While flowable slurry electrodes can increase surface area, several questions regarding effective transport (ion and electron) within the electrode and feed solution remain. Here, we aim to elucidate though electrochemical characterization, imaging, and transport based modeling a comprehensive view of effective transport in this desalination system. To address low efficiencies, a theoretical investigation will explore the entropic nature of electrochemical desalination. Traditional desalination and nontraditional theoretical cycles will be explored, with analogies drawn between common refrigeration based cycles. In addition to theoretical explanations, experiments conducted on a bench scale system will set out to verify the potential for alternative desalination cycles.