Now, Qimao Gan from The University of Hong Kong and colleagues have interpreted membrane fouling behaviour from an alternative angle to previous studies which involved different membrane chemistries to understand water transport through polyamide rejection layers. By preparing a rough (RO-r) and a smooth (RO-s) polyamide membrane with an identical recipe for interfacial polymerization (IP), they unveiled both the adverse impact of the so-called funnel effect on water transport through smooth membranes and the funnel effect weakened due to the presence of nanovoids for the rough membrane.
They first studied the separation performance and found that RO-r presented higher water permeance with similar NaCl rejection compared with RO-s. They further illustrated the impact of surface roughness structures on water transport pathways by conducting tracer filtration tests using gold nanoparticles. Membrane fouling tests by humic acid were performed under varying conditions, that is, different pH, with and without the presence of calcium, and different initial fluxes. The results exclusively showed that RO-s experienced a faster flux decline and more irreversible flux loss than RO-r, owing to the decreased average localized flux and the improved flux distribution for RO-r.
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