VIR-CDI: Novel Voltage-Incremented Ramping Capacitive Deionization for Scalable and Selective Nitrate Removal from Water

Overview

Nitrate contamination of freshwater is one of the most pressing environmental challenges. Nitrates from fertilizer runoff enter freshwater and drive eutrophication, triggering harmful algal blooms and oxygen depletion. Nitrate exposure has also been linked to methemoglobinemia and gastrointestinal cancers. Meeting regulatory limits (10 mg/L nitrate–N in U.S.) remains difficult due to the energy intensity and limited selectivity of conventional technologies such as reverse osmosis (RO). Capacitive deionization (CDI) is a water treatment method in which an electric field drives ions into porous carbon electrodes via electric double layer adsorption, it is also operational at standard pressures/temperatures and requires less infrastructure than RO. However, traditional CDI suffers from high competitor ion adsorption/energy consumption. While nonpotentiostatic strategies have been explored for desalination, voltage stepping for nitrate removal has never been investigated. This study developed and evaluated a novel voltage incrementation methodology in batch-mode CDI. Using synthetic wastewater (300 mg/L KNO₃/NaCl), voltage profiles were tested from constant 1.2 V to 0.4 V-1.2 V stepping. Ramped systems achieved up to 92.6% nitrate removal, with selectivity coefficients reaching 2.3 and molar ratio reductions as high as 9.6×. Specific energy consumption was as low as 0.12 kWh·m⁻³, with productivity up to 12.8 mg·g⁻¹·min⁻¹. Performance improvements are attributed to gradual electric double layer development, which delays chloride saturation and promotes preferential nitrate adsorption under dynamically increasing electrostatic driving forces. All ramped samples met the World Health Organization’s limit (50 mg/L). These results show voltage optimization alone enhances nitrate selectivity and reduces energy intensity in CDI systems without chemical functionalization, advancing scalable, energy-efficient solutions for nutrient-contaminated water remediation. By integrating capacitor physics principles with electrochemical ion transport dynamics, this work demonstrates a novel, scalable methodology with applications in municipal wastewater treatment, agricultural runoff remediation, and low-energy water purification in resource-constrained regions. More broadly, this research advances mechanistic understanding of electric double layer behavior under non-potentiostatic conditions, offering interdisciplinary contributions to environmental engineering, electrochemistry, ion transport physics, and materials science.

Competition history

• CSEF 2026 Environmental Engineering (Senior Division) · Entry S-11-10

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