Photochemical generation of reactive intermediates from urban-waste bio-organic substances under UV and solar irradiation

Singlet oxygen (¹O₂), hydroxyl radicals (^•OH), and excited triplet states of organic matter (³OM^*) play a key role in the degradation of pollutants in aquatic environments. The formation rates and quantum yields (Φ) of these reactive intermediates (RI) through photosensitized reactions of dissolved organic matter (DOM) have been reported in the literature for decades. Urban biowaste-derived substances (UW-BOS), a form of organic matter derived from vegetative and urban waste, have recently been shown to be efficient sensitizers in the photo-degradation of different contaminants. Nevertheless, no quantitative measurements of photo-oxidant generation by UW-BOS have been reported. In this study, the formation quantum yields of ¹O₂ and ^•OH, as well as quantum yield coefficients of TMP degradation (indicative of ³OM^* formation), were quantified for two UW-BOS samples, under 254-nm UV radiation or simulated sunlight and compared to a DOM standard from the Suwanee River (SRNOM). Values of Φ for UW-BOS samples ranged from Φ(+¹O₂) = 8.0 to 8.8 × 10⁻³, Φ(+^•OH) = 4.1 to 4.3 × 10⁻⁶, and f _TMP = 1.22 to 1.23 × 10² L Einstein⁻¹ under simulated sunlight and from Φ(+¹O₂) = 1.4 to 2.3 × 10⁻², Φ(+^•OH) = 1.3 to 3.5 × 10⁻³, and f _TMP = 3.3 to 3.9 × 10² L Einstein⁻¹ under UV. Although UW-BOS are not necessarily better than natural DOM regarding photosensitizing properties, they do sensitize the production of RI and could potentially be used in engineered treatment systems.