Micro-nano bubbles-enhanced foam fractionation with octanoyl-modified chitosan (OTCS) for high-efficiency removal of PFAS from the source of drinking water lake and reservoir

Effective removal of typical compounds like perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) is crucial for drinking water safety. Foam fractionation shows promise for PFAS removal, but its efficacy is limited by the low PFAS concentrations in natural waters, which hinder interfacial adsorption and foam stability. This study synthesized a novel green surfactant, octanoyl chloride-modified chitosan (OTCS), and developed an enhanced foam fractionation system coupled with micro-nano bubbles technology (OTCS-MNBs) for the efficient removal of PFOA and PFOS. Compared to the OTCS-conventional air bubbles foam fractionation system OTCS (OTCS-CABs), the OTCS-MNBs system achieved removal efficiencies of 98.73% and 99.21% for PFOA and PFOS, respectively, representing improvements of 1.47-fold for PFOA and 1.29-fold for PFOS. The system demonstrated pH adaptability (pH 3–9) and excellent foam stability, with moderate ionic strength enhancing reaction kinetics through salting-out effects. Analysis revealed that micro-nanobubbles exhibited higher specific surface area, longer residence time, and superior resistance to coalescence compared to conventional bubbles, thereby providing more adsorption sites and sufficient contact time for PFAS. In practical water experiments conducted with four typical Chinese lakes and reservoir sources, the system achieved removal efficiencies exceeding 80% for PFOA/PFOS, demonstrating its potential for practical application in complex water conditions. This highly efficient and environmentally friendly foam fractionation process effectively mitigates the environmental and health risks associated with PFAS and provides valuable technical guidance for water treatment plants addressing emerging contaminant challenges.