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 in situ 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.