Quantifying Hydrated Electron Transformation Kinetics in UV-Advanced Reduction Processes Using the R e-,UV Method.

Ultraviolet advanced reduction processes (UV-ARP) have garnered significant attention recently for the degradation of several hard to treat contaminants, including recalcitrant per- and polyfluoroalkyl substances (PFAS). The rate of contaminant degradation in UV-ARP is directly related to the available hydrated electron concentration ([e aq - ]). However, reports of [e aq - ] and other parameters typically used to characterize photochemical systems are not widely reported in the UV-ARP literature. Deploying monochloroacetate as a probe compound, we developed a method ( R e-,UV ) to quantify the time-based hydrated electron concentration ([e aq ] t ) available for contaminant degradation relative to inputted UV fluence. Measured [e aq ] t was then used to understand the impact of e aq - rate of formation and scavenging capacity on the degradation of two contaminants─nitrate and perfluorooctane sulfonate (PFOS)─in four source waters with varying background water quality. The results show that the long-term treatability of PFOS by UV-ARP is not significantly impacted by the initial e aq - scavenging conditions but rather is influenced by the presence of e aq - scavengers like dissolved organic carbon and bicarbonate. Lastly, using [e aq ] t , degradation of nitrate and PFOS was modeled in the source waters. We demonstrate that the R e-,UV method provides an effective tool to assess UV-ARP treatment performance in a variety of source waters.