Measurement and modelling of sorbent-amendment impacts on seasonal and long-term PFAS transport through unsaturated soil lysimeters
Michel Hubert, Björn Bonnet, Sarah E. Hale, Erlend Sørmo, Gerard Cornelissen, Lutz Ahrens, Hans Peter H. Arp
Abstract
This study investigated the effectiveness of waste-derived biochar amendments and commercial sorbents in stabilizing PFAS-spiked soils in field-scale in situ lysimeters over nearly one year under seasonal changes in Sweden. All tested sorbent amendments reduced average PFAS leachate concentrations by over 99 % for long-chain and 83-96 % for short-chain PFCAs and PFSAs, even under fluctuating water levels. Sewage sludge-derived biochar performed comparably to tested commercial sorbents. Long-chain PFAS remained evenly distributed in the soil, while short-chain PFAS accumulated in lower sections due to higher mobility. Higher PFAS leaching occurred in the spring due to snowmelt events and during summer months due to heavy rainfall. A 1D-transport model was developed to derive retardation factors and identify the fraction sorbed at the air-water interface before and after treatment, as well as PFAS leaching over 100 years. In no-sorbent lysimeters, 30-65 % of perfluorooctane sulfonate (PFOS) was retained at the air-water interface, with seasonal variations of up to 20 %. Inclusion of the sorbent reduced air-water interface effects, as solid-phase sorption became dominant. Over 100 years, nearly all PFOS are predicted to leach from no-sorbent lysimeters, while less than 1 % will leach from soil treated with sewage sludge- derived biochar. Such sorbent amendments can be integrated into ongoing remediation projects.