Assessment of activated carbon as a sorbent amendment for immobilizing perfluoroalkyl acids for surface sediment remediation

Abstract

The detection of elevated levels of perfluoroalkyl acids (PFAAs) in sediments has become a significant concern, urgently requiring management and remediation efforts. In this study, we investigated the effectiveness of industrially cost-effective activated carbon (AC) in remediating PFAA-contaminated sediments at different disturbance intensities and explored the sorption capacity of AC under broad environmentally relevant conditions and in response to environmental variations. AC exhibited high sorption effectiveness for PFAAs (excluding perfluorobutanoic acid < 40 %) across different pH, ionic strengths (IS), and dissolved organic matter (DOM). However, the increase in pH or reduction in IS might reactivate partially immobilized PFAAs. DOM outcompeted longer-chain PFAAs for sorption sites, resulting in their reactivation on AC, while it showed a stronger sorption than a competitive effect on shorter-chain PFAAs. The 192-day remediation experiment showed that AC significantly deactivated mobile PFAAs and decreased PFAA release by 45.5 %–99.2 % and 61.0 %–98.8 % under weak and intense disturbances, respectively, when compared with untreated sediment. Although intense disturbance led to an increase in PFAA release, the PFAA levels in the water column of the AC group after intense disturbance were comparable or even lower than those before intense disturbance, primarily owing to the secondary sorption of suspended AC. These findings are crucial for the appropriate and safe use of AC for PFAA sequestration, the management of PFAA-contaminated sediments, and the development of effective sediment remediation strategies.