MS2 bacteriophage inactivation using a N-doped TiO2-coated photocatalytic membrane reactor: Influence of water-quality parameters

Alternative water-disinfection processes are needed due to the formation of harmful disinfection byproducts during traditional chlorination. Depth filtration using microfiltration membranes has the advantage of applying low transmembrane pressure. However, removal of small nanoparticles such as viruses cannot be based on size-exclusion or sieving due to the large pore sizes. Combining membrane filtration and advanced oxidation processes such as photocatalysis may provide high water quality in a single step by combined filtration and photocatalytic inactivation. This hybrid process, where a photocatalyst immobilized onto a membrane substrate is termed photocatalytic membrane reactors (PMRs). The efficiency of a N-doped TiO2-coated Al2O3 PMR for removal of MS2 bacteriophage was investigated with different water qualities. MS2 inactivation was determined by individual addition of cations, anions and natural organic matter. The combined effect of water content on the disinfection potential of the suggested PMR was examined using a natural surface water source. Virus removal by the PMR under irradiation was 4.9 +/- 0.1 log (> 99.99%) in natural surface water. However, results revealed complex virus-PMR interactions even before exposure to the light source. Removal of MS2 by the PMR in a complex water matrix was driven by electrostatic forces in addition to photocatalytic inactivation. While alkaline pH of water resulted in poor interaction and low removal of MS2 by PMR, Ca2+ addition led to increased MS2 removal. High affinity to interaction with Ca2+ was observed for both MS2 and PMR, whose zeta potential moved towards more positive values. Therefore, salt bridge effect is the most likely route to reduced virus-membrane electrostatic repulsion.