The mechanism of silica and transparent exopolymer particles (TEP) on reverse osmosis membranes fouling

Dissolved silica and transparent exopolymer particles (TEP) are the primary foulants in reverse osmosis (RO) desalinated brackish water and wastewater. In this study, we investigated the fouling properties of varying silica concentrations with TEP on the membrane surface and discovered a synergistic fouling effect between the silanol group (Si-OH) and the TEP carboxyl group (-COOH). The membrane fouling experiments showed that silica fouling approached saturation at 6 mM, with little variation in membrane flux as the silica concentration increased. Furthermore, the -OH functional group of the monosilicate molecule can chemically react with the -COO- functional group on the membrane surface to create hydrogen bonds, allowing monosilicate deposition directly on the membrane. Silica-silica interactions reacted with aggregates at high silica concentrations and joined with TEP to create a more substantial, more complex cross-linked network, resulting in severe membrane fouling. At pH 9, silica fouling was most severe due to the dramatic increase in the solubility of monosilicic acid dissolution in solution and the decreased polymerization rate. This work reveals the essential process of membrane fouling induced by silica and TEP, significantly increasing knowledge on silica-TEP fouling.