Electrochemical advanced oxidation processes for wastewater treatment: Advances in formation and detection of reactive species and mechanisms

Over the past three decades, the knowledge of the mechanisms of electrochemical advanced oxidation processes (EAOPs) has progressively evolved with the advances in analytical and spectrometric techniques. A comprehensive understanding of the types and mechanisms of production of reactive species in EAOPs is a prerequisite to the understanding of their reactivities and elucidation of intermediate products generated during the oxidation process and degradation pathways. The type, nature, and quantity of reactive species generated in electrochemical treatment processes are controlled by many factors, including the type of the treatment technique, electrode/electrocatalyst materials, water/wastewater composition, water pH conditions, and operating parameters. Depending on the technique and operating parameters, single or multiple oxidants can be produced alone or combined electrochemical processes. However, the potency and reactivity of each oxidant are quite similar regardless of the technique, except in the case of heterogeneous and homogeneous hydroxyl radicals. This minireview presents the current state of mechanisms and models of reactive species generated in different EAOPs, highlighting different methods for their identification and reactivity.