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Polyelectrolyte-Based Sacrificial Protective Layer for Fouling Control in Reverse Osmosis Desalination

Son, Moon, Yang, Wulin, Bucs, Szilard S., Nava-Ocampo, Maria F., Vrouwenvelder, Johannes S., Logan, Bruce E.
Environmental science & technology letters 2018 v.5 no.9 pp. 584-590
alginates, brackish water, brine solutions, coatings, desalination, electrolytes, filtration, fouling, models, reverse osmosis, sodium chloride
Reverse osmosis (RO) membranes inevitably foul because of the accumulation of material on the membrane surface. Instead of trying to reduce membrane fouling by chemically modifying the membrane, we took a different approach based on adding a sacrificial coating of two polyelectrolytes to the membrane. After membrane fouling, this coating was removed by flushing with a highly saline brine solution, and a new coating was regenerated in situ to provide a fresh protective layer (PL) on the membrane surface. The utility of this approach was demonstrated by conducting four consecutive dead-end filtration experiments using a model foulant (alginate, 200 ppm) in a synthetic brackish water (2000 ppm of NaCl). Brine removal and regeneration of the PL coating restored the water flux to an average of 97 ± 3% of its initial flux, compared to only 83 ± 3% for the pristine membrane. The average water flux for the PL-coated membranes was 15.5 ± 0.6 L m–² h–¹ until the flux was decreased by 10% versus its initial flux, compared to 13.4 ± 0.5 L m–² h–¹ for the nontreated control. The use of a sacrificial PL coating could therefore provide a more sustainable approach for addressing RO membrane fouling.