Intercalation-Based Battery Deionization of Natural Brackish Water: Humic Acid Fouling Mechanisms and Mitigation via Activated Carbon Pretreatment

Abstract Battery electrode deionization (BDI) based on intercalation electrodes represents a promising approach for brackish water desalination, yet its performance under organic fouling when treating complex environmental waters remains mechanistically unclear. In this study, we evaluated the desalination behaviors of intercalation electrode materials in brackish water collected from the Chesapeake Bay using a flow cell with a symmetric BDI architecture, focusing on the impact of organic fouling and mitigation via powdered activated carbon (PAC) pretreatment. Nickel hexacyanoferrate (NiHCF) exhibited superior cycling stability (40–45 mAh g–1 within 50 cycles) and higher desalination capacity (∼90 mg g–1), whereas copper hexacyanoferrate (CuHCF) demonstrated lower energy consumption (∼0.08 Wh g–1). Leaching analysis confirmed the differential stability of these materials: CuHCF released substantially higher levels of dissolved Cu than the Ni leached from NiHCF, consistent with its greater susceptibility to structural degradation during cycling. The presence of 9.3 mg TOC/L humic acid (HA) reduced desalination rates by ∼10%. Pretreatment of the brackish water with PAC removed ∼80% of dissolved organics, restoring the desalination rate by ∼10% and lowering energy consumption by up to ∼50%. Through surface characterization using electrochemical impedance spectroscopy, zeta potential measurements, and H-cell resistance measurements, we found that organic foulants significantly increased the charge transfer and mass transfer resistances of the electrodes, and elevated the ionic resistance of the anion exchange membrane. Our results reveal how organic fouling and pretreatment influence intercalation electrode performance in environmental waters, thus providing insights for improving desalination system durability in practical applications.