Making waves: Sustainable control of micropollutants via NOM-mediated photosensitized activation of oxidants

Abstract

While photo-based advanced oxidation processes (AOPs) are promising for the abatement of micropollutants in water and wastewater, they are inevitably influenced by the components of the background water matrix. As one of the major water matrix components, natural organic matter (NOM) generates photochemically produced reactive intermediates (PPRIs, e.g., ³NOM* and NOM^•−) upon photolysis. PPRIs have recently been found to activate oxidants (e.g., H₂O₂) and generate reactive species (e.g., HO^•), offering a novel and sustainable approach to degrade micropollutants in water. To facilitate the application of this NOM-mediated process, we summarize the fundamentals from the relevant literature, including PPRI generation, the mechanism of photosensitized activation of oxidants, performance of the processes for micropollutant degradation, and the factors influencing photosensitized activation. NOM^•− is the PPRI activating H₂O₂ whereas the rest of the oxidants are primarily activated by ³NOM*. Resulting from the photosensitized activation, NOM and oxidant can exhibit synergism for micropollutant degradation under solar irradiation. Various factors, such as NOM properties, irradiation wavelength, pH, and other water matrix components (e.g., inorganic carbon and metal ions), affect the efficiency of photosensitized activation. Accordingly, we identify several future research directions: (1) investigating the wavelength dependency of photosensitized activation, (2) manipulating NOM structures in pre-treated processes, and (3) evaluating the formation of undesired byproducts.