Efficient containment of PFAS in municipal solid waste landfills using powdered activated carbon-amended GCLs

Abstract

Presented herein is a laboratory investigation on the sorption of four perfluoroalkyl substances (PFAS), namely perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS) and perfluorobutanesulfonic acid (PFBS), in a landfill leachate matrix by two variants of powdered activated carbon (PAC) proposed to be admixed with the bentonite component of geosynthetic clay liners (GCLs). The effectiveness of the sorbents in removing selected PFAS compounds from landfill leachate followed the order PFHxS > PFOA > PFBS > PFBA. PFBA and PFBS reached maximum removal of 85–99.99 % at the highest sorbent dosage (500 mg/10 mL), while PFOA and PFHxS achieved >99.99 % removal at dosages exceeding 200 mg/10 mL and 50 mg/10 mL, respectively. Sorption kinetics data for all PFAS compounds were best described by the pseudo-second-order (PSO) model, thus inferring that both physisorption and chemisorption occurred on the surface of the adsorbents. The experimental sorption isotherms suggest that the interactions between PAC and short-chain PFAS were primarily driven by multilayer adsorption on a heterogeneous adsorbent surface. Notably, none of the isotherm models employed in this study adequately explained the adsorptive behaviour of long-chain compounds on the PAC sorbents. Short-chain PFAS (PFBA and PFBS) exhibited reversible sorption, whereas long-chain compounds (PFHxS and PFOA) demonstrated stronger binding, highlighting the impact of chain length on PFAS retention. Overall, the data presented herein suggest that incorporating PAC into GCLs could effectively mitigate the migration of long-chain PFAS through geosynthetic composite lining systems. While migration of short-chain compounds was retarded, these continue to be significantly more challenging to contain with traditional treatments.