With only 0.03% of the world's water is suitable potable water for human use, the need for clean water is a current concern that can only become more urgent in the future. While much of the attention has been on desalination of seawater into potable water, the ability to desalinate brackish/briny water (~0.5 to 30 ppt salt) efficiently would be a significant option for water reclamation. If successful, there should be positive economic and water-resource impact of desalination of brackish water, which affects most the in-land water desalination efforts in agricultural, municipal water, and wastewater treatment, where the high recovery rates of capacitive desalination processes are particularly attractive and where post-treatment, or brine disposal, makes low-recovery membrane-based systems expensive. In terms of educational impact, the PI and co-PI will develop an introductory course that focuses on water and energy, integrating engineering and social sociopolitical perspectives (both PI and co-PI hold joint appointments in the Department of Engineering and Public Policy). In addition, the PI and co-PI will incorporate the proposed research into teaching and outreach through participating in the Pittsburgh Water Economy Network and the NAS/NAE Science and Engineering Ambassador Program.
Capacitive de-ionization (CDI), whereby charged species are captured by porous electrodes and then released into a waste stream, is a promising approach for desalination of brackish water; but the technology is limited by the low efficiency of the cation/anion removal cycle and by the tendency of the electrodes to foul. This proposal seeks to replace existing carbon electrode structures with new composite electrode structures that exhibit pseudo-capacitive and/or fast intercalation properties, where the materials quickly capture and release ions from weak faradic reactions. These electrodes will be able to access electrochemical reactions that are significantly denser, from a charge accumulation perspective, thereby allowing for thinner, more efficient electrode structures that are also less susceptible to diminished performance under fouled conditions. The PIs will first select viable candidate materials and evaluate their interfacial charge and ion transfer mechanisms in a relevant pseudocapacitive deionization (PDI) environment. They will then characterize the impact of PDI particle and electrode macro/meso-structures on the performance observed for PDI reactions, followed by evaluations of the performance of PDI surfaces in the presence of model colloidal foul ants, since electrode fouling by colloids and bacteria severely diminishes the ion adsorption capacity of conventional CDI electrodes.
