A sustainable solution for nitrate pollution in New Zealand's drinking water capacitive deionization (CDI)

Abstract

Abstract This study investigates the performance, feasibility, and practical implications of a small-scale Capacitive Deionization (CDI) system for simultaneous NaCl and Na₂NO₃ removal from water, focusing on rural and agricultural applications in New Zealand. Seven trials were conducted under varying ionic loads, flow rates, and voltages, with operational parameters and removal efficiencies recorded. Conductivity and nitrate concentration trends were closely monitored, revealing high nitrate removal rates (up to 79.8%) and significant conductivity reduction across multiple cycles. The system demonstrated stable adsorption–desorption patterns, with minimal fouling and rapid regeneration. Comparative cost analysis with Reverse Osmosis (RO) and Ion Exchange indicated CDI’s substantial economic advantage, with a cost per litre of 0.61 cents, over five times lower than RO, combined with reduced energy consumption (1.97 NZD/year). Beyond water treatment, the recovered nitrate stream presents an opportunity for agricultural reuse, reducing nitrogen fertilizer costs and contributing to nutrient recycling. The results confirm CDI’s adaptability for low-resource settings, offering a low-maintenance, scalable, and environmentally sustainable alternative for decentralized water treatment. Furthermore, derived performance metrics highlighted consistent removal efficiency even under varying salinity conditions, supporting its resilience for fluctuating feedwater qualities common in rural supplies. Integrating CDI into farm-level water management could enhance water quality and soil nutrient availability, supporting sustainable farming practices. Future research should focus on long-term field trials, optimization of electrode materials for mixed-ion selectivity, and system integration with renewable energy sources to further reduce operating costs and environmental impact.