Formaldehyde-Free Lignin-Based Composite for Rapid, High-Capacity PFAS Removal from Groundwater at a Former Firefighting Training Site

Here, we report a formaldehyde-free, biobased sorbent prepared by glyoxal-mediated cross-linking of kraft lignin with polyethylenimine (LBGPEI), designed for the treatment of heavily PFAS-contaminated water matrices. Ionic-dye screening-guided formulation selection toward the optimal composite, which exhibited an interpenetrated, cation-rich network with a high titratable amine density (2.31 mmol g–1). Using PFNA (C9, PFCA) and PFOS (C8, PFSA) as complementary probes, LBGPEI delivered rapid adsorption with substantial capacity accessible within minutes. Equilibrium data were well described by the Langmuir model, yielding maximum capacities of 3.0 mmol g–1 for PFNA (1392 mg g–1) and 4.5 mmol g–1 for PFOS (2250 mg g–1), among the highest reported for biobased materials. In both short-term batch experiments (15 min) and flow-through studies using heavily contaminated groundwater from Örnsköldsvik Airport in Sweden (former firefighting training site) and spiked water samples with a PFAA mixture, LBGPEI achieved 60–95% removal of long-chain PFAS. Investigation of the PFAS binding mechanism revealed that electrostatic interactions with protonated amines and hydrophobic stabilization within lignin domains collectively enabled the rapid capture of PFAS at high concentrations. These results support LBGPEI as a promising biobased sorbent for the selective removal of mid- to long-chain PFAS from heavily contaminated water sources.