Efficient removal of per-polyfluoroalkyl substances (PFAS) from water by using membrane distillation technology: a review

The toxic characteristics and environmental persistence of per- and polyfluoroalkyl substances (PFAS) have made the removal of such substances from water a critical concern. PFAS have a hydrophobic and oleophobic tendency due to their unique molecular structure, their chemical inertness and structural stability make the traditional methods of degradation and removal almost ineffective in the water environment. This review examines the existing technologies of PFAS removal in water with their advantages and drawbacks, and particularly focus on membrane distillation (MD) as an emerging separation-based approach. In contrast to pressure-driven processes such as nanofiltration and reverse osmosis, MD operates at lower hydraulic pressures and exhibits reduced fouling susceptibility under certain operating conditions, while maintaining high PFAS rejections. Reported studies indicate that direct contact membrane distillation (DCMD) can achieve PFAS rejection rates up to 96%. Current literature suggests that the hydrophobic properties of PFAS molecules promotes the effectiveness of MD, in which hydrophobic membranes are also employed, to achieve notable rejection rates of PFAS. Furthermore, the review covers promising developments that may be made in MD systems which include the use of new membrane materials and optimization of the operating conditions. However, key challenges including membrane fouling, wetting risk, and relatively high thermal energy demand are also critically assessed. Although there have been comprehensive reviews on the PFAS treatment technologies and MD as individual subjects, there has been no dedicated review on PFAS removal using MD. This review identifies current knowledge gaps and outlines future research directions required to enhance performance, scalability, and economic feasibility.