Native Nitrate in Wastewater Enhances 222 nm UV Advanced Oxidation of Micropollutants

222 nm irradiation, emitted from krypton chloride excimer (KrCl*) lamps, of waters containing nitrate has previously been demonstrated to lead to <i>de facto</i> advanced oxidation, due to the high absorbance and hydroxyl radical quantum yield of nitrate at 222 nm. Because nitrate is widespread in environmental waters, including nitrified wastewaters and wastewater-impacted surface water, this raises the possibility of UV advanced oxidation, which harnesses <i>in situ</i> nitrate for radical generation when KrCl* lamps are used as the UV source. In turn, this process is effective directly in wastewater effluent without the addition of chemicals. In this study, we compare UV222 treatment, without the addition of an external radical promoter, to UV254 with 10 mg/L hydrogen peroxide (H₂O₂) for the removal of 1,4-dioxane in three effluent waters containing nitrate at 2.1-8.9 mg-N/L. UV222 leads to 2.8-3.9 faster 1,4-dioxane degradation, on an incident fluence basis, resulting in an electrical consumption that is within 0.89-1.3 times that of UV254/H₂O₂, despite low-pressure mercury vapor lamps having at least 3.5× higher electrical efficiency than KrCl* lamps. When the cost of hydrogen peroxide dosing and quenching is considered, UV222 treatment leads to a projected cost savings of 12.4-21.8% compared to UV254/H₂O₂. Furthermore, despite the low UV transmittance (UVT) of these effluent waters at 222 nm (<30% UVT), UV222 treatment still leads to 1.5-3.2 times faster removal of NDMA compared to UV254, on an incident fluence basis, due to the enhanced photolysis of NDMA at 222 nm. Lastly, modeling results indicate that other reactive species generated by UV222 photolysis, such as CO₃^•- and NO₂^•, can contribute significantly to the degradation of micropollutants such as pharmaceuticals and consumer products.