Effect of physical, chemical, and biological aging on activated carbon and biochar properties and PFAS immobilisation in soils

An increasingly common technique for managing per- and polyfluoroalkyl substances (PFAS)-contaminated vadose soils is immobilisation using sorbents. However, uncertainty remains regarding the long-term stability of PFAS immobilisation. This study investigated the effects of different environmental aging processes, physical (wetting-drying cycles), chemical, and biological, on the performance of widely used sorbents for PFAS immobilisation in soil using accelerated aging to simulate long-term environmental conditions. Six sorbents were evaluated, including two granular activated carbons (GAC), two powdered activated carbons (PAC), colloidal activated carbon (CAC), and biochar. Simulated physical and biological aging caused the greatest reductions in sorption efficiency, likely due to pore blockage, as confirmed by material characterisation, including surface area measurement and scanning electron microscopic images. Sorbent type significantly influenced performance, with PAC being the least affected by aging and biochar the most susceptible. When soils and sorbents were aged together, sorbent responses differed between soil types, with sorption efficiency decreasing after chemical aging in sandy soil and after physical aging in high-clay soil compared with other aging treatments. Despite these deliberately harsh simulated conditions, activated carbon-based sorbents remained highly effective, maintaining over 85% PFAS immobilisation in most scenarios, including highly contaminated soils (∑PFAS > 20 mg/kg). Overall, these findings demonstrate that although aging alters sorbent properties, activated carbon-based sorbents remain durable and effective for sustainable PFAS management under diverse environmental conditions.