Effect of UV disinfection on the photoformation of reactive species from effluent organic matter of wastewater treatment plant.

UV is one of the main disinfection methods used in wastewater treatment plants (WWTPs) for the inactivation of pathogens in the effluents before being discharged into the receiving waters. The effluent organic matters (EfOM) are well-known photosensitizers for the generation of reactive species, mainly including the triplet states of EfOM (EfOM*), singlet oxygen (O) and hydroxyl radical (OH), which contribute to the removal of trace pollutants in water. However, the effect of UV disinfection on the photoreactivity of EfOM remains unclear. Here we investigated the photophysical and photochemical properties variation of EfOM after UV disinfection, along with humic substances (HS) as comparison. The UV disinfection caused a decrease of aromaticity, fluorescence intensity and molecular weight for all samples, while a reduction formation of triplet state of these dissolved organic matters (DOM*), O, hydrogen peroxide (HO), and superoxide anions (O) under simulated sunlight was observed. In contrast, the generation of OH was increased after UV disinfection. The quantum yield of O was positively correlated with triplet quantum yield coefficient (f) in all cases. However, the quantum yield of OH exhibited positive and negative correlations with f for EfOM and HS, respectively. The quantum yields showed positive correlations with E2/E3 (ratio of the absorbance at 254 to 365 nm) for untreated DOM samples, while for the first time we found the trends differ distinctly after UV disinfection. These findings indicate that UV disinfection in WWTPs significantly increases the potential of OH photoproduction from effluents and the cost-effective solar irradiation after UV disinfection is expected to be a novel technique for further removal of pathogen and trace organic pollutants in wastewater effluents and receiving waters.