Salt rejection and scaling on non-conductive membranes in direct- and alternating-current electric fields

Abstract

This study provides a comprehensive study about the salt rejection and fouling on non-conductive membranes in the electric fields of direct current (DC) and alternating current (AC). A simple membrane cell design that facilitates the application of electric field on traditional non-conductive membrane was built. Then different salts and foulants were applied as the feeds in the electric fields with varying voltage, frequency, waveform and bias. The impact of AC and DC within 1V on ion rejection and organic fouling is insignificant due to the low current flow and membrane conductivity. However, scaling can be effectively mitigated by both DC and AC at tuned conditions. Current direction, frequency, waveform and bias are found to substantially influence the scaling tendency. The anti-scaling performance in AC field is attributed to the continuous motion of ions that disturbs nucleation and crystal growth. Compared to DC, AC may operate at lower power consumption, thus offering an energy-effective strategy for scaling reduction.