Impact of polarity reversal on inorganic scaling on carbon nanotube-based electrically-conducting nanofiltration membranes

Abstract

We demonstrate electrically-conductive nanofiltration (ECNF) membranes that inhibit mineral scaling with an external alternating current (AC) source during the treatment of both synthetic (CaSO4-forming solution) and natural groundwater at certain water recovery. ECNF membranes are synthesized by cross-linking a percolating network of carbon nanotubes within a partially aromatic polyamide coating film, and their surface and transport properties are analyzed. The membranes were evaluated for their ability to desalinate synthetic and real brackish groundwater with high scaling potential. We show that the application of alternating electrical potentials to the membrane surface (4 Vpp, 1 Hz) dramatically inhibits the formation of mineral scale (both CaSO4 and CaCO3), which reduces flux decline and protects the membrane from the destructive impact of sharp crystals forming on the membrane surface. In addition, we show that the use of ECNF membranes enables higher water recovery while minimizing the need for chemical addition during the treatment of brackish groundwater. Our results suggest that mineral scaling on membrane surfaces can be inhibited without the addition of anti-scalant chemical that could potentially pose environmental harm.