Water resources in dry regions are stressed by drought and population growth. Wastewater reclamation can provide an additional source of water for these areas. However, trace contaminants such as pharmaceuticals that are not removed during wastewater treatment may pose ecological and/or human health concerns. This project will provide new information on the role of sunlight in destroying potentially toxic trace contaminants, addressing the national need for sustainable, low cost and energy efficient technologies for water treatment. Results will inform design of wastewater reclamation treatment systems in water-stressed areas. The project will take advantage of programs at the University of Arizona to augment educational activities among disadvantaged students in STEM areas. If successful, this project will provide valuable information on how to remove potentially harmful pharmaceutical and other contaminants from wastewater to allow its safe re-use in areas where water security is threatened. <br/><br/>Solar-driven processes involving effluent organic matter (EfOM) generate reactive oxygen species (ROS) that contribute to transformations of trace organic contaminants (TOrCs). For an important subset of TOrCs, a reaction with singlet oxygen is the dominant natural reaction pathway in treated wastewater. It is not yet possible to provide a physically accurate representation of that pathway or the kinetics of indirect photolytic transformations of TOrCs by singlet oxygen. Areas of uncertainty include (i) the dependence of quantum efficiency for singlet oxygen generation on light wavelength, (ii) the identities and concentrations of sensitizers in EfOM that participate in generating singlet oxygen, (iii) reaction rate constants for many TOrCs with singlet oxygen, and (iv) the toxicities of ROS-generated transformation products. The primary objective of proposed work is to support the development of a robust and physically accurate kinetic model for the light-driven degradation of TORCs via reaction with singlet oxygen in treated wastewater. The proposed research will use mathematically-supported methods to eliminate or minimize uncertainties in the photochemistry of singlet-oxygen-dependent mechanisms for TOrC transformations in treated wastewater. More specifically, the work is designed to expose (i) the concentrations and characters of EfOM fractions that serve as sensitizers in the singlet oxygen pathway, and (ii) the dependence of quantum efficiency for singlet oxygen on light wavelength. Results will support development of improved kinetic models that are potentially useful for reactor design in advanced wastewater treatment systems. Next generation models based on bulk organic characteristics in EfOM and quantum efficiencies normalized to dissolved organic concentration are necessary to overcome deficiencies in state-of-the-art kinetic representations that are necessarily conditional in character.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.