A critical issue for water treatment by membrane process is membrane fouling, which could result in rising hydraulic resistance, decreasing water permeability, and increasing energy consumption and maintenance cost. Among a variety of foulants, transparent exopolymer particles (TEPs) plays an important role in biofilm formation and membrane fouling, however it has been largely overlooked for many years due to the transparent nature of TEPs.
In this study, we separated TEPs from Chlorella Vulgaris culture broth, determined its concentration via Alcian Blue staining method, and characterized its particle size distribution and zeta potential. Fouling characteristics of TEPs towards ultrafiltration membranes were furhter evaluared using three types of hollow fiber membranes fabriacated in our laboratory: 1) conventional polyvinylidene fluoride membrane (PVDF), 2) mixed matrix membranes with titanium dioxide (PVDF/P25), and 3) mixed matrix nanocomposite membranes with nitrogen-doped titanium dioxide (PVDF/N-TiO2). Membranes were characterized by scanning electron microscopy (SEM) and surface contact angle measurement, and their fouling characteristics evalauted under both dark and visible light irradiation conditions. The results demonstrated that rejections of TEPs by PVDF, PVDF/P25 and PVDF/N-TiO2 membranes were all above 85%. A significant enhancement of fouling resistance was observed for PVDF/N-TiO2 membrane under visible light irradiation. The addition of TiO2 nanoparticles into the PVDF matrix improved the membraen surface hydrophilicity and performance. Photo-activation of TiO2 nanoparticles under light irrididation was believed to have contributed to the enhanced anti-fouling properties of the membrane.