Organic fouling inhibition on electrically conducting carbon nanotube-polyvinyl alcohol composite ultrafiltration membranes

Robust and electrically conductive thin films (2500 S/m) made of cross-linked poly(vinyl alcohol) and carboxylated multi-walled carbon nanotubes (PVA-CNT-COOH) were synthesized via a sequential deposition and cross-linking method. The PVA-CNT-COOH modified membranes were then used in an electrofiltration cell in which the effects of applied potentials on fouling of high concentrations (3-5 g/L) of alginic acid (AA) were studied. It was demonstrated that after 100 min of operation while applying −3 V and −5 V, the change in operating pressure was reduced by 33% and 51%, respectively, compared to application of no voltage. Increase in ionic strength resulted in overall higher fouling rates, where the application of −5 V resulted in a pressure change reduction of 43% compared to no application of potential. A modified Poisson-Boltzmann equation used in a DLVO-type theory demonstrated that at the applied potentials, electrostatic interactions produced significant repulsive forces between the membrane surface and the charged organic foulant. Calculations at experimental conditions demonstrated the pure AA aggregates would be strongly repulsed away from membrane surface. In synthetic wastewater the repulsion force is greatly reduced, resulting in overall reduced fouling inhibition.