Application of Advanced Oxidation Processes for the Removal of Tire-Derived 6PPD-Quinone, and Reviews on Recent Research Trends

6PPD-quinone (6PPD-Q) is a highly toxic ozonation transformation product of 6PPD (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine), a widely used tire antioxidant and antiozonant. 6PPD-Q can easily enter aquatic systems through urban runoff and has been detected in diverse aquatic environments. It can generate transformation products with different structural characteristics and toxicity through natural, biological, and oxidative processes. Even though different studies of the occurrence, fate, and toxicity of 6PPD-Q and its transformation products have been extensively performed, research on developing water treatment technologies for their removal remains very limited. This review provides an overview of advanced oxidation processes (AOPs) for 6PPD-Q removal, focusing on degradation performance and major reaction mechanisms. Currently applied processes, including UV-based homogeneous AOPs and heterogeneous AOPs such as photocatalytic, Fenton-like, and electrochemical processes are evaluated based on their reaction mechanisms and treatment characteristics. AOPs with limited applications to 6PPD-Q are also discussed in terms of their fundamental principles and potential applicability. The limitations of current approaches and future research needs for effective 6PPD-Q treatment are identified.