Modeling the Kinetics of UV/Peracetic Acid Advanced Oxidation Process

Peracetic acid combined with UV (i.e., UV/PAA) has emerged as a novel advanced oxidation process (AOP) for water disinfection and micropollutant degradation, but kinetic modeling for this AOP was lacking. In this study, a comprehensive model was developed to elucidate the reaction mechanisms and simulate reaction kinetics of UV/PAA process. By combining radical scavenging experiments and kinetic modeling, accurate quantum yield of PAA under UV₂₅₄ (Φ = 0.88 ± 0.04 mol-Einstein^-1) was determined via simultaneously quenching ^•OH and CH₃C(O)O^• with 2,4-hexadiene. The comparison between experimental observations and model predictions over a wide range of conditions allowed estimation of the rate constants of PAA with ^•OH (k = 1.3 ± 0.2 × 10⁹ M^-1 s^-1) and HO₂^• (k_HO ≤ 5 × 10² M^-1 s^-1) with good accuracy. With derived Φ, k and k_HO, the kinetic model accurately predicts PAA decay under UV₂₅₄ photolysis across varying PAA and H₂O₂ concentrations and water pH (5.8-7.2). Meanwhile, the model reveals that UV/PAA generates a lower ^•OH concentration than UV/H₂O₂ at equivalent oxidant concentrations, with CH₃C(O)OO^• as the most abundant carbon-centered radical. This study significantly improves the knowledge of reactive species generation and reaction kinetics and mechanisms under UV/PAA, and provides a useful kinetic model for this AOP in water treatment.