Water Recovery Rate in Short-Circuited Closed-Cycle Operation of Flow-Electrode Capacitive Deionization (FCDI)

Abstract

While flow-electrode CDI is a promising desalination technology that has major advantages when the electrodes are operated in the short-circuited closed-cycle (SCC) mode, little attention has been paid to the water recovery rate, which, in the SCC mode, is determined by the need for partial replacement of the saline electrolyte of the flow electrodes. Results of this study show that an extremely high water recovery rate of ∼95% can be achieved when desalting a 1000 mg NaCl L–1 brackish influent to a potable level of 150 mg L–1. The improved performance with regard to the electrical cost is related, at least in part, to the alleviated concentration polarization at the membrane/electrolyte interface during electrosorption. In effect, the current efficiency decreases with an increase in the water recovery rate. This finding is ascribed to inevitable co-ion leakage since the flow electrodes reject ions with the same charge. In addition, water transport across the ion exchange membranes also influences the water recovery rate. The effect of partial replacement of the saline electrolyte during (semi-)­continuous operation requires particular consideration because the associated dilution of the carbon content in the flow electrodes results in a decrease in process performance.

Recent progress in materials and architectures for capacitive deionization: A comprehensive review

“…Different modes of flow electrode CDI. (a) Short‐circuited closed loop (SCC); (b) isolated closed loop (IC) or within chamber (WC)—reprinted from Ma, Ma, Zhang, et al (2019), copyright (2019), with permission from American Chemical Society; (c) cross‐chamber (CC). Reprinted from Liu, Coronell, and Call (2020), copyright (2020), with permission from Elsevier…”

“…In another study, electrosorption performance was evaluated by two different approaches for HCDI (Zornitta et al, 2018). The first approach comprised of experiments Ma, Ma, Zhang, et al (2019), copyright (2019), with permission from American Chemical Society; (c) cross-chamber (CC). Reprinted from Liu, Coronell, and Call (2020), copyright (2020), with permission from Elsevier having electrodes of various thickness, while other approach was using different electrode materials.…”

Brackish water desalination using reverse osmosis and capacitive deionization at the water-energy nexus

“…This would produce a significant less volume of brine solution, compared to conventional constant flowrate operation. For flow-electrode CDI, Ma et al (2019) achieved an extreme water recovery of 95-99% with the brine concentration of 20-50 g/L, though the charge efficiency is compromised.…”

Flow Electrode Capacitive Deionization (FCDI): Recent Developments, Environmental Applications, and Future Perspectives

“…Of the many exciting CDI variants, there is particular interest in flow-electrode capacitive deionization (FCDI) . While the underpinning mechanism relating to salt removal in FCDI can be partially attributed to capacitive adsorption (i.e., ion migration in an electrical field followed by storage in oppositely charged electrodes), electrodialysis effects also play an important role due to the use of flowable electrodes (composed of active materials, conductive additives, and aqueous/organic electrolyte) in FCDI systems. , By continuously replenishing the electrode chamber with new or regenerated particle electrodes, FCDI exhibits high desalting efficiency and the possibility of continuous operation. − An extremely high flow efficiency of ∼100% can also be attained since the desalinated stream and the brine stream are generated in different chambers . The ease of management of the flow-electrodes in an ex-situ apparatus provides opportunities for broadening FCDI applications (e.g., to resource concentration and recovery). − In addition, FCDI cells could, potentially, be integrated with renewable energy sources (e.g., solar, wind, tides, and geothermal heat) and used in remote off-grid power areas.…”

“…(a) Brief timeline highlighting the historical developments of FCDI technology based on selected papers, − ,− ,,,,,,,, [Adapted with permission from refs (Copyright 2013 Royal Society of Chemistry), (Copyright 2018 Elsevier), (Copyright 2015 Royal Society of Chemistry), (Copyright 2014 Elsevier), (Copyright 2015 American Chemical Society), (Copyright 2017 Royal Society of Chemistry), (Copyright 2018 American Chemical Society), and (Copyright 2019 Elsevier)] and (b) number of publications in the FCDI area since 2013. Publications are categorized based on their main research topics.…”