A Passive Convergence-Permeable Reactive Barrier Coupling Adsorption and Peroxydisulfate-Driven Degradation for Sustainable Groundwater Remediation of PFOA

Abstract Perfluorooctanoic acid (PFOA), which is a persistent and mobile per- and polyfluoroalkyl substance (PFAS), challenges conventional in situ groundwater remediation. This study applied a passive convergence-permeable reactive barrier (PC–PRB) for long-term PFOA treatment by integrating adsorption enrichment, peroxydisulfate (PDS)-driven degradation, and in situ regeneration of the reactive medium. Commercial granular Fe-modified biochar (GFBC) was used as the reactive medium and exhibited a maximum adsorption capacity of 2.0 mg g–1. Batch experiments achieved 91.6% PFOA removal with 69.4% defluorination. In one-dimensional (1D) column tests, the highest retardation factor (R = 87.0) occurred during initial adsorption at pH 7, whereas for cyclic operation under alkaline conditions maintained R = 37.5 and 46.4% defluorination were maintained after two cycles. Three-dimensional (3D) box experiments confirmed adaptive PDS redistribution under convergent flow, with a notably increased PRB remediation capacity (>4.5-fold by day 64) without permeability loss, and a >84% removal maintained for 70 days at 100 μg L–1 PFOA. Furthermore, a reduced reactive-transport model implemented in FEFLOW reproduced PFOA adsorption-degradation dynamics in 1D columns (R2 = 0.555–0.896; NRMSE = 0.106–0.218) and enabled conservative prediction in 3D systems. The PC–PRB system provides a predictable, self-regulating, and scalable solution for in situ PFAS remediation.