Biochar selection for removal of perfluoroalkyl substances from reclaimed water for agricultural irrigation

Authors: Ramos, Maria; Ashworth, Daniel; Schmidt, Michael; Xuan, Richeng

Submitted to: Biochar
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2025
Publication Date: 3/14/2025
Citation: Ramos, M.P., Ashworth, D.J., Schmidt, M.P., Xuan, R. 2025. Biochar selection for removal of perfluoroalkyl substances from reclaimed water for agricultural irrigation. Biochar . 7. https://doi.org/10.1007/s42773-025-00436-4.
DOI: https://doi.org/10.1007/s42773-025-00436-4

Interpretive Summary: Per- and polyfluoroalkyl substances (PFAS) are becoming increasingly regulated due to their widespread environmental presence, such as in agricultural compartments (e.g. water, soil, plants). There is therefore a growing interest in developing scalable and economically feasible strategies to remove PFAS from agricultural compartments. Biochar is a carbon-based material derived from organic waste materials (crop waste, etc) and it has been evaluated as a potential adsorbent material for removing PFAS from water. The properties of biochar are known to be directly related to the feedstock and preparation process used. The identification of key biochar properties responsible for successful adsorption of all PFAS compounds as well as the development of predictive models is a crucial step in identifying the potential of using biochar as a scalable approach for remediating PFAS in agricultural contexts. In this study, a comprehensive evaluation of 17 properties of 24 biochars (produced from four feedstocks [wood waste, grasses, manure, crop waste] at six different temperatures [300–800 °C]) was performed to determine the main factors influencing PFAS removal from water by these materials. Batch studies were conducted, and several statistical techniques were used to determine the primary factors influencing the removal of PFAS. Using these 24 biochars as a training dataset, linear models were constructed to predict the removal of selected PFAS based on biochar properties. These models were used in the selection of a commercial biochar, which was seen to perform effectively in removing different PFAS in various waters. The results indicate that careful, evidence-based, selection of biochars with optimal characteristics can provide excellent removal of PFAS compounds from water, which has implications for mitigation strategies to reduce the human health risks of agricultural irrigation with recycled water.

Technical Abstract: Per- and polyfluoroalkyl substances (PFAS) are becoming increasingly regulated due to their widespread environmental presence, such as in agricultural compartments (e.g. water, soil, plants). There is therefore a growing interest in developing scalable and economically feasible strategies to remediate PFAS in agricultural contexts. Biochar is a carbonaceous material derived by pyrolysis of organic waste materials and it has been evaluated as a potential adsorbent material for removing PFAS from water. The physicochemical properties of biochar are known to be directly related to the feedstock and pyrolysis process used. The identification of key biochar properties responsible for successful adsorption of both long- and short-chained PFAS compounds as well as the development of predictive models is a crucial step in identifying the potential of using biochar as a scalable approach for remediating PFAS in agricultural contexts. In this study, a comprehensive evaluation of 17 physicochemical properties of 24 biochars (produced from four feedstocks [wood waste, grasses, manure, crop waste] at six different temperatures [300–800 °C]) was performed to determine the main factors influencing PFAS removal from water by these materials. Batch adsorption studies were conducted, and principal component analysis was used to determine the primary factors influencing the removal of short- and long-chained PFAS. Various parameters were seen to be influential in the removal of long- (C/N, SSA) and short- (N+O)/C, C/N) chained PFAS. Using these 24 biochars as a training dataset, linear models were constructed to predict the removal of selected PFAS based on biochar physiochemical properties. These models were used in the selection of a commercial pine wood biochar (Rogue biochar), which was seen to perform effectively in removing PFOS, PFOA, PFBS, PFHxS, PFNA in different aqueous matrices. Finally, post-pyrolysis thermal treatment was shown to maintain adsorption potential over subsequent cycles, while also providing the additional benefit of increasing the removal efficiency of the short-chained sulfonate PFBS by two- to five times. The results indicate that careful, evidence-based, selection of biochars with optimal physiochemical characteristics can provide excellent removal of PFAS compounds (including short-chained congeners) from water, which has implications for mitigation strategies to reduce the human health risks of agricultural irrigation with recycled water.