Sorption of perfluoroalkylated substances (PFASs) onto granular activated carbon and biochar

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have attracted increasing concerns owing to their potential ecotoxicological effects. The sorption of PFASs, i.e. perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorobutanoic acid (PFBA) and perfluorobutansulfonic acid (PFBS), by granular activated carbon (GAC) and softwood-derived biochar was studied. The sorption equilibrium of PFASs on GAC was obtained within 3-24 h, while the time required to reach equilibrium for biochar was 12-48 h. PFASs sorption on both GAC and biochar were well represented by the pseudo-second-order model. In the case of sorption isotherms, the PFAS sorption capacity was chain-length dependent with following order: PFOS > PFOA > PFBS > PFBA. GAC exhibited high maximum Langmuir sorption capacity for both PFOS (123.5 µmol g^-1) and PFOA (86.2 µmol g^-1), which were 43% and 39.6% greater than biochar. The maximum sorption capacity for PFBS on GAC (48.3 µmol g^-1) was higher than that for PFBA (31.4 µmol g^-1), while the opposite sorption trend was observed for biochar. The sorption mechanisms involved both electrostatic attraction and hydrophobic interaction. The sorption of PFASs increased with the decrease in pH. The competitive sorption of PFASs occurred during the sorption process, resulting in decreased PFASs removal efficiencies. The Fourier transform infrared (FTIR) analyses indicated the presence of a variety of functional groups on the surfaces of adsorbents. Some FTIR responses shifted after sorption, indicating electronic interactions during sorption. All the results indicate that adsorption technology is a feasible method to control the contamination of PFASs, and both GAC and biochar are effective adsorbents for PFASs removal from wastewater.