Selective electrodialysis: Targeting nitrate over chloride using PVDF-based AEMs

The depletion of natural resources and the escalating environmental concerns associated with pollution necessitate innovative approaches for sustainable resource management. In this study, we investigated the selective separation of nitrate from chloride in electrodialysis (ED) using a recently introduced PVDF-based anion-exchange membrane (PVDF-50) and two commercially available membranes (ACS and AMX from Neosepta). Experimental ED data show that the membrane PVDF-50 presents a higher value of nitrate over chloride selectivity compared with the two commercial membranes, the highest reported in literature. However, recognizing that completely preventing the permeation of chloride ions into the concentrate stream was not feasible, we explored the potential of a system in which anion-exchange membranes presenting different monovalent selectivity were alternated. In this approach, referred to as nitrate-selectrodialysis (NO₃-SED), the different selectivity of PVDF-50 and AMX membranes was leveraged to demonstrate the possibility of increasing nitrate concentration, while simultaneously reducing chloride levels in a stream. This approach proves highly advantageous in applications where mitigating chloride contamination is a significant concern while recovering nitrate.