Dissect the role of particle size through collision-attachment simulations for colloidal fouling of RO/NF membranes

Abstract

Colloidal size affects the whole process of particle transport and membrane filtration. However, its compound effect on fouling remains controversial. In the present study, we adopt a collision-attachment approach to systematically investigate the role of colloidal size on fouling. Our study highlights the critical importance of four competing mechanisms: reduced specific cake resistance and enhanced foulant-membrane interaction of larger particles tend to mitigate flux decline, while the simultaneously increased hydrodynamic drag and reduced particle back-transport tend to promote fouling. The net effect of particle size on fouling is governed by the competition among these mechanisms. When strong foulant-membrane repulsion prevails, we show enhanced flux stability for larger particles as a result of a greatly increased energy barrier to resist particle deposition. Nevertheless, this trend could be reversed for weak foulant-membrane interaction. Our study reconciles the contradictory experimental observations of the effect of particle size on colloidal fouling and provide important insights for effective fouling mitigation.