Designing biochars for improved sorptive removal of per- and polyfluoroalkyl substances

Authors: ZHENG, WEI - University Of Illinois Urbana-Champaign; HUGGETT, ERIN - University Of Illinois Urbana-Champaign; CIRCENIS, SOPHIE - University Of Illinois Urbana-Champaign; MAINALI, KALIDAS - Oak Ridge Institute For Science And Education (ORISE); Sharma, Brajendra

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2026
Publication Date: 5/13/2026
Citation: Zheng, W., Huggett, E., Circenis, S., Mainali, K., Sharma, B.K. 2026. Designing biochars for improved sorptive removal of per- and polyfluoroalkyl substances. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.70195.
DOI: https://doi.org/10.1002/jeq2.70195

Interpretive Summary: The fact that per- and polyfluoroalkyl substances (PFAS) are found in large amounts in waterways and have negative health effects on people is becoming increasingly concerning. Sorption with activated carbon is the most common method to remove PFAS. Biochars are less expensive alternatives to activated carbon, but most biochars are less effective for PFAS removal from water than activated carbon. This research involved creating a custom biochar by first treating woody biomass with lime sludge and then pyrolyzing it to produce biochar. After optimization of the biochar production conditions, it was shown that lime sludge treatment improved the absorptive properties of biochar. The engineered biochar was capable of removing nearly all of the perfluorooctanoic acid (PFOA) and both linear and branched perfluorooctane sulfonate (PFOS) under optimal conditions. This study demonstrates that lime sludge pretreatment is a durable and cost-effective method to produce high-performance sorbents for treating PFAS-contaminated water systems. This information will be useful to those firms interested in removal of PFAS from water for applications including drinking water and irritation of food producing farm land. It will also be of interest to those producing and marketing biochar as a novel agriculturally derived product.

Technical Abstract: The widespread occurrence of per- and polyfluoroalkyl substances (PFAS) in aquatic environments, along with their adverse impacts on human health, has been recognized as an emerging issue. Sorption using carbon-based sorbents is the most common approach for PFAS removal; however, conventional biochars typically underperform compared to activated carbon. In this study, a designer biochar was developed by pretreating woody biomass with lime sludge, followed by systematic optimization of lime-sludge loading, pyrolysis temperature, and residence time. The results showed that the pretreatment process enhanced pore development and modified the surface chemistry of the designer biochar. Under optimal conditions (1:4 lime sludge-to-biomass, 850 °C, 5 h), the designer biochar achieved near-quantitative removal (>99%) of perfluorooctanoic acid (PFOA) and both linear and branched perfluorooctane sulfonate (PFOS), outperforming unmodified biochar and comparable to a commercial activated carbon. Sorption kinetics and isothermal studies confirmed the superior performance of the designer biochar, exhibiting rapid equilibration (<1 h) and increased sorption capacity. Mechanistic analysis revealed that improved PFAS removal by the designer biochar was driven by multiple adsorption mechanisms, including hydrophobic interactions, electrostatic attraction, and cation bridging facilitated by Ca²' and Mg²' species derived from lime sludge. This study highlights lime sludge pretreatment as a sustainable and cost-effective strategy for producing high-performance carbon-based sorbents for PFAS remediation in contaminated water systems.