Peracetic acid-driven advanced oxidation processes for wastewater treatment: Demystifying organic radicals and non-radical species

Peracetic acid (PAA) based advanced oxidation processes (AOPs) have received increasing attention in wastewater treatment. However, it is challenging to identify the radical and/or non-radical species and elucidate the intrinsic interaction mechanisms involved in PAA-based AOPs. This work presents a systematic review of the selective generation mechanisms of radicals (hydroxyl and organic radicals), with a focus on organic radicals, and non-radical species (reactive complexes (RC), high-valent metals (HVM), singlet oxygen (¹O₂), and electron transfer process (ETP)). Furthermore, we examine various strategies for the precise identification and characterization of radical and/or non-radical species (e.g., quenching, chemical probes, spectroscopy, mass spectrometry, and electrochemical testing), and emphasize existing controversies. Subsequently, we provide an in-depth discussion of the reaction mechanisms between the reactive species and the contaminants/water matrices, as well as the potential for generating halogenated byproducts. Finally, we highlight the challenges and opportunities of the PAA-based AOPs in wastewater treatment, aiming to inspire future research endeavors that promote the practical application of PAA-based AOPs in wastewater treatment.