Optimal loading of iron nanoparticles on reverse osmosis membrane surface to reduce biofouling

Biofouling is one of the major challenges for reverse osmosis (RO) membranes. Commercial RO membranes coated with different loadings (0.1, 0.3, 0.5, 0.7 and 0.9 wt% in solution) of iron nanoparticles (nZVI or FeNPs) were submitted to accelerated biofouling under high-pressure crossflow, using pretreated, sterilized seawater from the Sea of Cortez (Mexico) inoculated with Bacillus halotolerans MCC1 (109 CFU mL−1) as feed. FeNPs were synthesized and characterized (zeta potential, XRD, and SEM) via a reduction method. Coated and uncoated membranes were characterized for roughness, contact angle, surface free energy, XPS, FESEM, water and salt permeance, membrane resistance, fouled flux and fouling resistance. The coated membranes showed a slight increase in roughness and contact angle and a reduction in surface free energy. After accelerated biofouling, the coated membranes showed lower hydraulic resistance and higher permeate flux than the uncoated membrane, albeit with slightly lower salt rejection. Moreover, membrane autopsies revealed a highly significant reduction in biofilm thickness, total cells, TOC, and live and dead cells for the coated membranes relative to the uncoated membrane. The FeNP loading using a 0.3 wt% solution was found to be the most suitable tradeoff between biofilm prevention and flux decline for desalination processes.