Phototransformation of Trace Organic Compounds in Effluent-Receiving Waters: Exploring the Significance of Singlet Oxygen

Abstract

With ongoing climate change, economic growth and urbanization, a water crisis arises from both decreasing water resources and increasing water demands. Municipal wastewater effluent is now considered a potential potable water resource, particularly in semi-arid and arid regions. Indirect potable reuse employs an environmental buffer to polish the quality of treated wastewater. Natural attenuation processes may mitigate wastewater-derived pollutants, including recalcitrant trace organic compounds (TOrCs), in effluent-receiving environmental buffers. Photolysis is amongst natural processes that may contribute to attenuating the presence of such organic contaminants. In photolysis reactions, singlet oxygen (1O2) production can be an important mechanism leading to TOrC attenuation.Here, the significance of photolysis in the attenuation of TOrCs is evaluated in effluent-receiving waters, with particular attention to the role of 1O2. Quantitative kinetic parameters of 1O2, depicting its formation and reaction with TOrCs, are determined. Properties of effluent organic matter (EfOM) responsible for 1O2 formation are suggested, and the contribution of photolysis to the in-stream attenuation of TOrCs is examined in an effluent-dependent river. Primary findings include apparent quantum yields for 1O2 formation in effluent-receiving waters and second-order rate constants for the reaction of 1O2 with TOrCs. A subset of measured optical parameters and molecular-level components from EfOM is correlated with 1O2 formation. Photolysis plays a significant role in attenuating a range of TOrCs in a sunlit stream. Results provide essentials for incorporating the 1O2-involving light-driven natural process into engineered multi-process treatments for water reuse systems.