Degradation of natural organic matter using Ag-P25 photocatalyst under continuous and periodic irradiation of 405 and 365 nm UV-LEDs

Removal of natural organic matter (NOM) in drinking water is an important objective imposed by water utilities due to plant operational problems, taste and odor issues. Photocatalysis using titanium dioxide (TiO2) has been increasingly explored in water treatment studies as a potential technology to remove NOM, with most studies employing 365 nm UV light. However, photocatalysis under this wavelength limits the application of UV/TiO2 to larger scales as it is not cost-effective and energy-efficient. We approached this limitation by exploring the impact of switching between periodic and continuous irradiation when removing NOM under both non-visible and visible light exposure (365 and 405 nm). In addition, we used silver (Ag) to increase the photocatalytic efficiency of TiO2 in the visible region. The optimum concentration of Ag was first investigated by comparing the surface area, and hydroxyl radical (˙OH) formation rate of Ag-P25 with different Ag:P25 ratios. Of the Ag:P25 ratios explored, 1.29% Ag-P25 was found to be the optimal based on high surface area and ˙OH formation rate. The effect of periodic irradiation on Suwanee River NOM removal using two wavelengths was then investigated. Dissolved organic carbon (DOC) concentrations and UV absorbance at 254 nm (UV254) indicated that the 1.29% Ag-P25 was more efficient than P25 at a higher irradiation cycle of 365 nm. The electrical energy per order (EEO) values calculated for each treatment further indicated that using 1.29% Ag-P25 resulted in a lower energy requirement for removing DOC and UV254 than P25.