Study of permeate flux behavior during photo-filtration using photocatalytic composite membranes

Abstract

Photocatalytic PVDF-TiO2 composite membranes were prepared by phase separation method. It was found that the membrane surface became more hydrophilic under UV irradiation, as characterized by a decrease in water contact angle after the membranes were exposed to UV. The photo-induced superhydrophilicity phenomenon of TiO2 was attributed to such increase in membrane hydrophilicity. As a result, when filtration of pure water was performed under UV irradiation (photo-filtration), a gradual increase of permeate flux could be obtained over time. The role of UV irradiation mode on flux behavior during photo-filtration was investigated. Effective flux recovery could only be achieved under UV irradiances equal or higher than a threshold value. A flux “memory” effect was observed, in which the flux remained higher than its initial value for a certain duration even after irradiation was stopped, suggesting that the photo-filtration process could be more efficient if UV irradiation was operated in a on/off basis instead of a full-time one. In the scope of this study, five irradiation modes were selected, and based on the experimental data obtained from our lab-scale photo-filtration system, results of the cost/efficiency balance for a large-scale photo-filtration system were extrapolated. It was found that photo-filtration can be performed efficiently yet still economically.