Reactive species in peracetic acid-based AOPs: A critical review of their formation mechanisms, identification methods and oxidation performances

The efficient removal of emerging micropollutants poses significant challenges in wastewater treatments. Advanced oxidation processes (AOPs) are extensively studied in the field, and peracetic acid (PAA) has attracted great attention as an alternative oxidant in recent years. Various reactive species yield in PAA-based AOPs, which are regarded as the promising approaches for pollutants elimination. This review systematically investigates the formation pathways, identification methods and oxidation performances of the reactive species in PAA-based AOPs, putting focus on the organic radicals such as CH₃C(O)O•, CH₃C(O)OO•, CH₃OO• and •CH₃. Firstly, the formation pathways of reactive species induced by PAA activation are outlined. Then the specific probes and quenchers used for the identification of reactive species are summarized, and the commonly used methods are described and discussed. The reaction kinetics and mechanisms of reactive species and compounds are compared, indicating that the oxidation performances of organic radicals are mainly depended on the properties of radicals and the structure of compounds. Finally, the prospects on further research of PAA-based AOPs are proposed. This article provides a comprehensive overview of organic radicals for the first time, which can serve useful reference for ongoing studies in PAA-based AOPs.