RESUMO
Interfacial interactions involved in reverse osmosis (RO) membrane fouling by humic acid were quantitatively evaluated using the XDLVO (extended Derjaguin-Landau-Verwey-Overbeek) approach. The role of each individual interfacial interaction during membrane fouling was elucidated with special emphasis devoted into the influence of Ca2+ under different solution pHs. The results showed that, regardless of the presence of Ca2+, van der Waals interaction favoring fouling contributed the most to the interfacial interactions at pH 3, whereas the polar interaction inhibiting fouling played a dominant role at pH 7 and pH 10. Electrostatic double layer interaction appeared to be the weakest in all cases, thus contributing the least to membrane fouling. It was the changing of polar interaction that gave rise to the influence of Ca2+ on membrane fouling, which turned out to be more significant at lower pH. Ca2+ would accelerate humic acid RO membrane fouling at most cases. Correlation analysis between interfacial free energy and fouling extent revealed that XDLVO approach could reasonably predict humic acid RO membrane fouling behaviors under different solution conditions.