Development of a ventilated structure spacer for salinity mitigation in brackish water using flow electrode capacitive deionization.

Abstract

In flow-electrode capacitive deionization (FCDI) systems, the spacer serves as the core structural element governing ion migration pathways. Concentration polarization emerges as a critical factor determining system performance, with spacer architecture directly influencing ion transport dynamics. This study introduces a novel ventilated spacer (V-FCDI) featuring a cage-like design surrounded by a thin nylon fabric layer, positioned exclusively near the membrane interfaces, in contrast to thick woven mesh spacers (W-FCDI). This ventilated architecture strategically mitigates concentration polarization through localized flow disruption at the membrane surfaces, while simultaneously lowering hydraulic and ohmic resistance in the bulk region and extending feed residence time. A computational fluid dynamics (CFD) simulation of a periodic unit cell validated the hydrodynamic behavior within the spacer, revealing enhanced near-surface flow in the ventilated configuration. The experimental investigation systematically assessed the efficacy of the V-FCDI against W-FCDI by varying flow rates and applied voltage. The V-FCDI design demonstrates a marked improvement, with a 9.0% increase in average salt removal rate, a 9.5% higher voltage-driven desalination capability, an 11.2% reduction in specific electrical energy consumption, and an 18.8% reduction in specific pumping energy consumption compared to the W-FCDI. The findings establish new design principles for high-performance FCDI systems, offering a pathway toward energy-efficient brackish water desalination.