Advanced Oxidation Processes for PFAS and Micropollutants: Mechanisms, Reactors, and By-Product Risk

Abstract

This review aims to synthesize current knowledge on advanced oxidation processes (AOPs) for the treatment of per- and polyfluoroalkyl substances (PFAS) and micropollutants, emphasizing mechanistic pathways, reactor engineering, degradation performance, and by-product risk to inform future research and practical applications. A qualitative systematic review was conducted using 15 peer-reviewed articles selected from Scopus, Web of Science, ScienceDirect, and SpringerLink, focusing on AOP applications for PFAS and micropollutant remediation. Data were extracted on reaction mechanisms, reactor designs, degradation efficiency, and by-product formation. Textual content was analyzed using NVivo 14 software, applying open, axial, and selective coding to identify recurring themes until theoretical saturation was reached. The analysis synthesized findings across four main themes: mechanistic pathways of AOPs, reactor design and process engineering, degradation performance, and by-product formation and risk assessment. The review revealed that AOPs, including photocatalysis, electrochemical oxidation, plasma-based systems, and hybrid methods, generate reactive species such as hydroxyl radicals and sulfate radicals that effectively degrade PFAS and micropollutants. Reactor configuration, energy input, catalyst material, and flow dynamics critically influence process efficiency. While high pollutant removal is achievable under controlled conditions, complete PFAS mineralization remains challenging, and shorter-chain intermediates frequently persist. By-product formation, including partially fluorinated compounds and other transformation products, poses potential toxicity risks that necessitate additional polishing and risk assessment strategies. Hybrid and coupled AOPs often outperform single-mode systems, highlighting the importance of integrating mechanistic understanding with reactor engineering. Advanced oxidation processes offer a promising approach for PFAS and micropollutant remediation; however, successful application requires a holistic integration of chemical mechanisms, reactor design, performance optimization, and by-product risk management. Future research should focus on pilot-scale validation, real water matrices, and comprehensive toxicological assessment to ensure safe and effective water treatment solutions.