Impact of oxygen nanobubble treatment on the behavior of oxidizable surfactants (linear alkylbenzene sulfonates) and persistent surfactants (perfluorooctane sulfonate and perfluorooctanoic acid)

Schematic diagram showing oxygen nanobubble (ONB) treatment of two surfactant types: oxidizable LAS (removed via foam fractionation and oxidative degradation) and persistent PFOS/PFOA (removed via foam fractionation only). Surfactants, including conventional oxidizable compounds such as linear alkylbenzene sulfonates (LAS) and highly persistent surfactants such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), are ubiquitous in aquatic environments across a wide range of concentrations. Understanding how surfactant structure influences removal mechanisms is essential for optimizing nanobubble-based treatment processes. The partitioning and degradation behavior of LAS were compared with those of PFOS and PFOA during oxygen nanobubble (ONB) treatment. Results showed that, at elevated concentrations (13,000 μg/L), surfactants were efficiently transferred into the foam phase via ONB-induced foam fractionation, achieving removal efficiencies of 81.3% for LAS, 94.4% for PFOS, and 89.7% for PFOA. Under non-foaming conditions (1,000 μg/L LAS; 100 μg/L each of PFOS and PFOA), oxidative degradation of LAS was induced by ONBs, following second-order kinetics, whereas no measurable oxidative transformation of PFOS and PFOA was observed. These results indicate that surfactant oxidizability plays a key role in determining removal mechanisms: LAS undergoes both interfacial partitioning and chemical degradation, while PFOS and PFOA removal occurs primarily through physical partitioning. This study establishes a mechanistic link between molecular structure and treatment performance, providing guidance for the design and optimization of nanobubble-based processes in complex wastewater systems containing mixed surfactants.