Selective separation of naphthalene sulfonic acids and salts from wastewater by electric field-assisted nanofiltration membranes

Sulfonated organic pollutants are prevalent in textile dyeing and pharmaceutical wastewaters and typically coexist with high concentrations of NaCl. Current nanofiltration (NF) processes, however, are often bottlenecked by the intrinsic permeability-selectivity trade-off, making the fractionation of these highly soluble organics from saline streams inefficient. In this study, an electric field-assisted (EFA) cross-flow NF system was constructed to enhance the separation of 1,5-naphthalenedisulfonic acid (NDSA) from NaCl solutions. The application of a low external voltage (0–2.5 V) triggered a pronounced leap in dianionic NDSA rejection. At the optimal voltage of 2.0 V, the NDSA rejection rate reached 95% (62% for the original NF process), with a seven-fold improvement in the selectivity coefficient from 2.2 to 15.8. Mechanistic quantification via the DSPM-DE model attributed this enhancement to the field-induced charging effect. The external voltage induced additional negative charges into the membrane pores, increasing the effective volumetric charge density from 1.44 to 19.59 mol·m -3 . Energy consumption analysis revealed that the electrical input accounted for only 0.6% of the total energy expenditure, enabling a 50% energy saving compared to conventional multi-stage NF configurations required for an equivalent selective separation performance. These findings position the electric field-assisted nanofiltration (EFA-NF) strategy as a technically viable and energy-efficient route for industrial wastewater fractionation.