UV-Advanced Reduction Processes (UV-ARP) have garnered significant attention for the degradation of contaminants such as PFAS via photochemically generated hydrated electrons. However, the parameters typically reported in the aquatic photochemistry literature for reactive species are not well-characterized for UV-ARP. These parameters, such as steady-state concentrations and scavenging capacities, are important for evaluating treatment conditions on UV-ARP efficiency. To address this need, we used chloroacetate to probe the hydrated electron concentration and scavenging capacity during UV/sulfite treatment of perfluorooctane sulfonate (PFOS) in four source waters. Chloroacetate degradation kinetics measured at multiple spikes throughout the 24 h treatment cycle revealed the temporal variation in hydrated electron concentration and scavenging capacity. The results show that the long-term treatability of PFOS by UV-ARP is not significantly impacted by the initial scavenging conditions but rather is influenced by the presence of scavengers like dissolved organic matter and bicarbonate. Lastly, using the measured photochemical parameters, the degradation of nitrate and PFOS was modeled in the source waters. Collectively, this study demonstrates both the utility of probe compounds for probing hydrated electron-based treatment processes and initial water quality is not a long-term predictor of ultimate hydrated electron exposure for a target contaminant.

Using chloroacetate to quantify hydrated electron concentrations and scavenging in the UV/sulfite advanced reduction processes

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