Mitigation of fouling and wetting in membrane distillation by electrical repulsion using a multi-layered single-wall carbon nanotube/polyvinylidene fluoride membrane

Abstract

Membrane distillation (MD) demonstrates enormous potential to treat high salinity water due to its unique rejection mechanism; however, fouling and wetting continue to be major technical challenges in high recovery conditions due to the concentration of contaminants. Electrical repulsion with electrically conductive membranes shows promise to address fouling and wetting, as it prevents contaminants from accessing the membrane surface. Improvements to electrical conductivity and hydrophobicity occurred using a multi-layered single-wall carbon nanotube (SWCNT) coating on a polyvinylidene fluoride (PVDF) membrane without MD performance degradation. These results were identified by analyzing cyclic voltammetry, electrochemical impedance spectroscopy, and direct contact angle. An experimental and theoretical evaluation on the feasibility of using electrical repulsion with the SWCNT/PVDF membrane to address the fouling and wetting of the MD was carried out. This evaluation was undertaken using a series of fouling/wetting experiments and repulsive force calculations. The results confirmed that fouling and wetting in the MD process were effectively mitigated by electrical repulsion with the SWCNT/PVDF membrane, allowing more than twice the operation time without any performance degradation; this was despite the low applied voltage and long-term operational conditions. The experimental observations demonstrated that electrical repulsion with the SWCNT/PVDF membrane potentially facilitates sustainable MD operations with high recovery conditions.