Contribution of air-water interface in removing PFAS from drinking water: Adsorption, stability, interaction and machine learning studies

As a class of synthetic persistent organic pollutants, contamination of Per-and poly-fluoroalkyl substances (PFAS) in drinking water has attracted widespread concern. Aeration has been confirmed to enhance the removal of PFAS in drinking water by activated carbon (AC). However, the contribution of the air-water interface in removing PFAS is not yet to be fully understood at the molecular level. In this work, molecular dynamics (MD) simulations were employed to investigate the role of nanobubble in removing PFAS in the aqueous environment. The result suggests that the free energies of the air-water interface are about 3-7 kcal mol-1 lower than that of the bulk water region, indicating that the transformation of PFAS from the water phase into the air-water interface is favorable from the viewpoint of thermodynamics. The interface-water partition coefficients (Psur/wat) of PFAS are in the order of PFOS > PFOA > PFHxS > PFBS. On the air-water-AC three-phase interface, PFBS can not only move along the interface region but also leave the interface region into water phase, while PFOS tended to move along the interface region until it was captured by AC. Finally, the Delta Gwater_ interface quan-titative structure-activity relationships (QSAR) models were developed to predict the removal efficiencies of PFAS enhanced by aeration in aquatic systems. The proposed mechanism promotes the understanding of the contribution of air-water interface in removing PFAS from drinking water by activated carbon.

Automated summary

This study used molecular dynamics simulations to investigate the role of nanobubbles in removing PFAS in aqueous environments. The results showed that the free energies of the air-water interface were lower than that of the bulk water region, indicating that the transformation of PFAS into the air-water interface is thermodynamically favorable. On the three-phase interface, PFBS can both move along the interface region and leave the interface region into the water phase, while PFOS tends to move along the interface region until it is captured by activated carbon.