Physicochemical properties of agricultural biochar for the removal of perfluoroalkyl substances (PFAS) from aqueous solutions

Authors: MAINALI, KALIDAS - Oak Ridge Institute For Science And Education (ORISE); Sharma, Brajendra; Mullen, Charles; Sarker, Majher; ZHENG, WEI - University Of Illinois Urbana-Champaign; Ellison, Candice; Garcia, Rafael

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2026
Publication Date: 5/13/2026
Citation: Mainali, K., Sharma, B.K., Mullen, C.A., Sarker, M.I., Zheng, W., Ellison, C.R., Garcia, R.A. 2026. Physicochemical properties of agricultural biochar for the removal of perfluoroalkyl substances (PFAS) from aqueous solutions. Journal of Environmental Management. https://doi.org/10.1016/j.jenvman.2026.129926.
DOI: https://doi.org/10.1016/j.jenvman.2026.129926

Interpretive Summary: The per- and polyfluoroalkyl substances (PFAS), also known as "forever chemicals", are found in large amounts in waterways and are harmful compounds that persist in the environment for a long time and do not break down easily. Sorption with activated carbon is the most common method to remove PFAS. Biochars are inexpensive and environmentally friendly alternatives to activated carbon, but most biochars are less effective for PFAS removal from water than activated carbon. This research involved creating activated biochars derived from two energy crops (willow and switchgrass) and two agricultural wastes (soybean straw and cocoa shell) by first treating the biochar with a base, then carbonizing, and finally acid washing to produce the activated biochar. These biochars were characterized and evaluated for the sorption of two short-chain and two long-chain PFAS. Activated biochars after base treatment and acid washing demonstrated large pore volumes and high specific surface areas. It was shown that modified biochars from switchgrass, willow, and soystraw were capable of removing almost all of long-chain PFASs through adsorption under optimal conditions. Modifying biochars to change their physicochemical properties could offer long-term solutions to remove PFAS compounds from PFAS-contaminated water systems, and this research will benefit American farmers by protecting crops, livestock, soil health, and food safety.

Technical Abstract: Per- and polyfluoroalkyl substances (PFAS) are becoming increasingly prevalent in aquatic ecosystems worldwide, with their concentration continuing to rise. Carbon-rich sorbents are gaining attention as promising materials for removing PFAS from contaminated aqueous environments. In agricultural settings, PFAS present in irrigated water pose emerging risks to crops and, ultimately, enter the human food supply. This study provides a systematic and comprehensive evaluation of 12 pristine and activated biochars using controlled laboratory batch experiments. The physicochemical properties of these biochars were thoroughly characterized using thermal analysis (TGA, DTG), elemental analysis, FTIR, BET surface area measurements, SEM-EDX imaging, and Zeta potential measurements. The activated biochars exhibited high specific surface areas (817-1372 m²/g) and substantial pore volumes. Notably, the fully activated biochars produced from switchgrass, willow, and soystraw achieved 98.0-99.5% removal of long-chain PFASs through adsorption. PFAS adsorption was improved by materials with high surface area and optimized pore structures, which increase both the number and accessibility of active sites. Hydrophobic interactions between PFAS's fluorinated chains and nonpolar surfaces, together with electrostatic attractions between ionic PFAS and charged adsorbent sites, were identified as the dominant removal mechanisms. Overall, tailoring biochar's physicochemical properties is a promising and sustainable strategy for effectively removing long-chain PFAS compounds from water.