Nitrate-Mediated Photooxidation of Steroid Estrogens: Efficacy and Prospects for Wastewater Treatment

UV light-based advanced oxidation processes have shown considerable promise for mitigation of trace organic contaminants (TrOCs). Recent work has garnered interest in ambient NO₃ ^- as a photooxidant within UV treatment processes. This work provides a systematic investigation on the efficacy of NO₃ ^- as a photooxidant for removal of aqueous 17β-estradiol (17β-E2) and its metabolites, estrone (E1) and estriol (E3). Results demonstrate that even low (1 mg L^-1) concentrations of NO₃ ^- enhance degradation of 17β-E2 by >48% during medium-pressure UV (MP UV) treatment in comparison to control conditions, and NO₃ ^- concentrations ≥5 mg L^-1 resulted in >90% removal of 17β-E2 at fluences ≥1000 mJ cm^-2. Three photoproducts consistent with known nitrogenous byproducts of 17β-E2 were also observed throughout treatment and found to persist even under high (2000 mJ cm^-2) fluence conditions. In a municipal wastewater matrix, estrogen removal was improved under high (25 mg L^-1) NO₃ ^- conditions as compared to ambient (∼3 mg L^-1) levels. This work demonstrates the utility of NO₃ ^- as an <i>in situ</i> photooxidant for removal of TrOCs such as steroid estrogens in real waters and provides an impact to stakeholders interested in leveraging these processes in complex matrices such as municipal wastewater.