Influence of membrane surface properties on initial rate of colloidal fouling of reverse osmosis and nanofiltration membranes

Recent studies have shown that membrane surface morphology and structure in fluence permeability, rejection, and colloidal fouling behavior of reverse osmosis (RO) and nanofiltration (NF) membranes. This investigation attempts to identify the most influential membrane properties governing colloidal f ouling rate of RO/NF membranes. Four aromatic polyamide thin-film composite membranes were characterized for physical surface morphology, surface chem ical properties, surface zeta potential, and specific surface chemical stru cture, Membrane fouling data obtained in a laboratory-scale crossflow filtr ation unit were correlated to the measured membrane surface properties, Res ults show that colloidal fouling of RO and NF membranes is nearly perfectly correlated with membrane surface roughness, regardless of physical and che mical operating conditions. it is further demonstrated that atomic force mi croscope (AFM) images of fouled membranes yield valuable: insights into the mechanisms governing colloidal fouling, At the initial stages of fouling, AFM images clearly show that more particles are deposited on rough membrane s than on smooth membranes. Particles preferentially accumulate in the "val leys" of rough membranes, resulting in "valley clogging" which causes more severe Aux decline than in smooth membranes. (C) 2001 Elsevier Science B.V, All rights reserved.