Fouling in Capacitive Deionization: A Critical Review

Capacitive deionization (CDI) is a promising alternative technology for efficient removal of aqueous charged species from brackish or contaminated feed streams. Over the past decade, CDI has transitioned from a laboratory curiosity to a viable technology for desalination and resource recovery. However, rapid advancements in this field have raised concerns regarding various operational issues, including energy efficiency and fouling tendencies. Electrosorption of metal ions and hydroxides on CDI electrodes and membranes, alongside the hydrophobic interactions with organic compounds, can cause pore clogging and reduce sorption capacities, ultimately compromising cycle longevity. A comprehensive understanding of CDI (and membrane CDI) fouling is crucial for developing effective mitigation strategies for full-scale applications. In this review, we summarize the principles of inorganic, organic, and composite fouling in CDI, evaluate the strengths and limitations of current fouling characterization techniques, and assess how feed/electrode properties and operating parameters influence fouling occurrence and development. Additionally, we outline existing CDI cleaning protocols and highlight research needs herein, aiming to identify new insights that will enhance the cost-effective application of this innovative technology.