Investigating the fouling layer of polyamide nanofiltration membranes treating two different natural waters: internal heterogeneity yet converging surface properties

摘要

This study investigated the fouling of four polyamide nanofiltration membranes by two surfacenwaters that differed substantially in major properties. The emphasis was on determining thencharacteristics of the fouling layer on the membranes. The rates of fouling for the two watersndiffered considerably, with a more rapid flux decline being observed for the water having highernbiopolymer and major ion concentrations. Measurements of membrane roughness, contact anglenand zeta potential in general showed considerable differences for each of these properties amongnthe virgin membranes. However, values of each of these parameters tended to converge for allnmembranes after fouling, regardless of which water had been used. This result is very significantn(for example for the removal of trace contaminants, which in many cases may depend onnmembrane properties) because in practice a membrane spends virtually all of its operating lifenfouled to some degree. Several techniques including transmission electron microscopy (TEM)nwere used to conduct detailed investigations of the fouling layer. These results demonstrated thengreat heterogeneity within that layer, despite the similar overall properties mentioned above. Thisnheterogeneity is significant for quantitative understanding of the relationship between fouling andnflux and for strategies to reduce or remove fouling.