Effect of UV254 disinfection on the photoformation of reactive species from effluent organic matter of wastewater treatment plant

Abstract

UV254 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 (3EfOM*), singlet oxygen (1O2) and hydroxyl radical (•OH), which contribute to the removal of trace pollutants in water. However, the effect of UV254 disinfection on the photoreactivity of EfOM remains unclear. Here we investigated the photophysical and photochemical properties variation of EfOM after UV254 disinfection, along with humic substances (HS) as comparison. The UV254 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 (3DOM*), 1O2, hydrogen peroxide (H2O2), and superoxide anions (O2•−) under simulated sunlight was observed. In contrast, the generation of •OH was increased after UV254 disinfection. The quantum yield of 1O2 was positively correlated with triplet quantum yield coefficient (fTMP) in all cases. However, the quantum yield of •OH exhibited positive and negative correlations with fTMP 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 UV254 disinfection. These findings indicate that UV254 disinfection in WWTPs significantly increases the potential of •OH photoproduction from effluents and the cost-effective solar irradiation after UV254 disinfection is expected to be a novel technique for further removal of pathogen and trace organic pollutants in wastewater effluents and receiving waters.