Roles of membrane–foulant and inter/intrafoulant species interaction forces in combined fouling of an ultrafiltration membrane

Abstract

To explore better the combined organic–inorganic fouling mechanisms of ultrafiltration (UF) membranes, SiO2 and bovine serum albumin (BSA), humic acid (HA) were chosen as model inorganic and organic foulants, respectively. Fouling experiments with single and combined foulants, corresponding fouling layer structure, and the membrane–foulant and inter/intrafoulant species interaction forces were investigated. The results showed that the addition of SiO2 particles led to opposite fouling phenomena for BSA and HA, which could be explained by the membrane–foulant and interfoulant species interaction forces. In the initial filtration stage, the combined fouling behavior was related to the relative strength of the interaction forces of membrane with both inorganic and organic foulant. Specifically, when the SiO2–membrane interaction force>organic–membrane interaction force, the combined fouling would be enhanced with the addition of SiO2 particles; otherwise, it would be mitigated. In the later filtration stage, the combined fouling was related to the inorganic–organic interaction forces. Thus, the stronger SiO2–BSA interaction force led to the formation of large SiO2–BSA aggregates, which resulted in a more porous fouling layer and higher hydraulic permeability. In contrast, the negligible SiO2–HA interaction forces caused the SiO2 particles to fill uniformly in or between the HA molecules, which resulted in a more compact fouling layer and more serious membrane fouling.