Emerging investigator series: photocatalytic treatment of PFAS in a single-step ultrafiltration membrane reactor†

Amidst the discovery of widespread per- and polyfluoroalkyl substances (PFAS) contamination and growing concerns of prolonged exposure even at low levels, many water treatment facilities are adopting reversed osmosis and nanofiltration processes to address these pollutants. Yet, these technologies are not sustainable, generating highly concentrated brines and requiring high operational pressures and energy inputs. Meanwhile, ultrafiltration (UF) membranes operate at less than 1 bar of transmembrane pressure (TMP) but are considered ineffective at removing organic pollutants. However, surface modifications make it possible to remove PFAS via UF. This study investigated the use of an adsorptive, photocatalytic, iron-enhanced titanium nanotube activated carbon composite coating on UF membranes to simultaneously remove and degrade PFAS in situ. In a photo-membrane reactor (PMR) under UV irradiation, the membranes removed up to 80% of the initial PFOA within 2 hours and the average removal over two 8-hour operation cycles was 69%. Although PFOA removal decreased to 35% when tested on a mixed PFAS solution, 46% of PFOS was still removed and 95% of the adsorbed PFOA was destroyed, while short-chain PFAS were removed to a lesser degree. This work provides a proof-of-concept of the PMR technology, which with further development could provide a single-step treatment for aqueous PFAS contamination in groundwater and pretreated surface and wastewaters.