Micro/nanoscale interface morphology between bio-foulants and surface of reverse osmosis membrane indicates degree of fouling

The interaction of bio-foulants at the interface of reverse osmosis (RO) membranes is highly correlated with the degree of fouling during wastewater treatment. However, there are few observations showing the micro/nanoscale bio-foulant morphology at the interface and its relationship with the degree of fouling. In this study, two typical bacterial strains (Escherichia coli CGMCC1.3373 and Bacillus cereus CR19) present in reclaimed water were used to test their fouling potential and reveal their interactions with RO membranes. B. cereus, a typical chlorine-resistant bacterium, exhibits significantly higher extracellular polymeric substance (EPS) content and higher interaction energy with membranes. The rate of decrease in membrane flux in the B. cereus group was 1.5 times higher than that in the E. coli group. By rapidly freezing the bio-foulants and examining the micro/nanoscale morphology around their interface with RO membranes, it was revealed that the membrane was fouled by stacked bacterial cells with EPS adhering to each other and to the RO membrane surface. B. cereus secreted more EPS, stacked more compactly, and adhered to the RO membranes more firmly than E. coli, resulting in more severe fouling. To our knowledge, this is the first study to demonstrate that the micro/nanoscale morphology of the interface between bio-foulants and RO membranes indicates the degree of fouling.