Molecular mechanism of inorganic colloids fouling in forward osmosis membrane: Role of organic matter

Although forward osmosis (FO) membrane has shown great potential for treating industrial wastewater containing large inorganic colloids, the effect of inevitable organics on membrane fouling behavior has yet been elucidated. This study focused on investigating and quantifying the impact of minute concentrations of sodium alginate (SA) on the membrane fouling behavior of hematite solution from the perspective of energy changes. Two noteworthy phenomena were identified through a combination of experimental and computational methods: (1) The pure hematite solution resulted in a limited decrease in water flux (29 %), while decreased by 45 % when added 1 % SA, showing more severe membrane fouling. (2) However, increasing SA to 2 %, water flux decrease returned comparable to hematite solution (31 %). Density functional theory (DFT) calculations combined with experimental characterizations showed that the morphology of the hematite-SA fouling layer changed from a cross-linked to aggregated state due to increased SA content. Moreover, extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory calculations demonstrated that more SA increased the repulsion force between the fouling layer and the membrane by 5.7 times. This finding reveals the influence of minute organic matter on the membrane fouling induced by inorganic colloids, providing valuable insight for developing membrane fouling mitigation strategies.