Effects of Environmental Factors on the Sorption of Per- and Polyfluoroalkyl Substances by Biochars

Biochar emerges as a cost-effective sorbent for removing perfluoroalkyl and polyfluoroalkyl substances (PFAS) in water, but our knowledge of how environmental factors affect PFAS sorption by biochar remains unclear. One in-house produced biochar from Douglas Fir feedstock at 900 °C and one commercial biochar were employed to investigate PFAS sorption effectiveness and efficiency, including sorption kinetics, isotherms, and effects of salt and humic acid concentrations. An artificial groundwater solution was also selected to assess biochar’s ability for PFAS removal under a real-world water treatment scenario. PFAS removal efficiency by both Douglas Fir 900 biochar and commercial biochar was negatively affected by humic acid, despite the negative effect being less for commercial biochar compared to Douglas Fir 900 biochar. Conversely, salt (1-10 mM NaCl and 0.5-2 mM CaCl₂) increased PFAS sorption by biochars, likely due to their charge screening effect of biochar surface charge. PFAS removal efficiency by both Douglas Fir 900 biochar and commercial biochar in artificial groundwater solution was largely inhibited (versus that in relatively clean water matrices); however, the commercial biochar can still remove >70% of most PFAS in water. These findings support the feasibility of using cost-effective biochars, especially the commercially produced biochar, for removing PFAS in water.