Regenerable antimicrobial activity in polyamide thin film nanocomposite membranes

Abstract

Control of microbial growth at the membrane surface on a continuous basis is needed to mitigate biofouling in long term membrane applications. In this study, a regenerable antimicrobial nanocomposite membrane was developed for sustainable membrane biofouling control via slow release of silver. Nanozeolites attached to the surface of a commercial polyamide nanofiltration membrane by covalent binding served as carriers for Ag+ or Ag(0). At a silver loading of 7.18±0.62mg/m2, the nanocomposite membranes effectively inhibited growth of P. aeruginosa for up to seven 24 h exposure cycles, and the antimicrobial efficacy correlated well with silver release kinetics data. The release of silver strongly depended on the Cl- concentration in the solution. At low Cl- concentrations, the low aqueous solubility of silver controlled silver release; the Ag+ and Ag(0) loaded membranes showed similar release rate. At high Cl- concentration, silver release from the Ag(0) loaded membrane was notably more stable and longer lasting as Ag(0) oxidation became the rate-limiting step. After depletion, reloading silver via a simple physisoprtion protocol resumed the antimicrobial activity. The regenerated membranes had similar silver loading and antimicrobial activity as the freshly prepared membranes, demonstrating the potential of this approach in long-term control of membrane biofouling.