Micro- and nanobubble-enhanced Fenton-like processes: Performance, mechanisms and perspectives

The widespread deployment of Fenton-like advanced oxidation processes (AOPs) in water remediation remains severely constrained by low oxidant utilization efficiency and a narrow operating pH window. Micro- and nanobubbles (MNBs) possess large specific interfacial areas, prolonged aqueous residence, charged gas-liquid interfaces, and pronounced interfacial enrichment capacity, offering a promising strategy to enhance Fenton-like reaction efficiency through interfacial regulation. This review systematically examines the physicochemical properties of MNBs and their synergistic coupling with Fenton-like systems, and categorizes integrated reactor configurations into bubbling reactors, hydrodynamic cavitation/Venturi reactors, and electrically driven MNB reactors. Currently, most MNB-Fenton systems are confined to bench-scale batch operations, with limited continuous-flow validation to support engineering scale-up. Across nine within-study comparisons, seven k_obs enhancement factors were 1.2-6.7, whereas two larger values were partly attributable to slow PMS-alone controls. Paired studies further showed approximately 10-18 percentage-point increases in TOC removal. One NB/Cl^-/PMS study also reported a 25%-33% reduction in PMS dosage. The observed enhancement is associated with recurring interfacial enrichment and intensified transport, whereas changes in oxidant activation, electron-transfer processes, and pollutant speciation are system dependent. This review delineates the advantages and current bottlenecks of existing MNB-Fenton platforms, providing guidance for the scalable design of advanced water treatment technologies tailored to complex water matrices.