Anti-fouling property of alumina-doped polyvinylidene fluoride (PVDF) membranes

Abstract

Ultra- and micro-filtration (UF/MF) membranes have been increasingly used in a number of water separation processes. However, the popular nascent polyvinylidene fluoride (PVDF) membranes are susceptible to organic fouling and/or biofouling, which still remain as the main problem that reduces the cost-effectiveness of the processes. Recently, an innovative surface modification approach was developed which involves the doping of anhydrous and hydrated aluminum oxides (γ-alumina, boehmite and gibbsite) onto the PVDF membrane surface in an attempt to improve the membrane anti-fouling property. In this study, the anti-fouling performance of the aluminum oxide-doped membranes was evaluated, in comparison to the nascent PVDF membranes. Filtration of sodium alginate solution found that the nascent PVDF UF membrane was quite susceptible to organic fouling due to its hydrophobic nature. In contrast, organic fouling to either the γ-alumina-embedded or gibbsite-grown UF membranes was insignificant. However, during the filtration of calcium alginate dispersion, gel layer was formed on the surface of all tested UF membranes. Nevertheless, the extent of gel layer formation on the γ-alumina-embedded membrane was significantly lower than that on the nascent membrane. It appears that the growth of gibbsite particles did not help to reduce the extent of gel layer formation, which possibly resulted from the increased membrane surface roughness. With regard to biofouling, it showed that the attached bacteria per unit area were reduced with increased coverage ratio of the aluminum oxides on the UF/MF membrane surface. Although γ-alumina embedment could not completely eliminate bacterial attachment, the biofilm growth on it was largely prohibited. It seems that in situ embedment of nanoparticles on the membrane surface is sufficient to reduce common organic fouling, retard gel layer deposition and prohibit biofilm formation.