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

In agricultural contexts, the presence of per- and polyfluoroalkyl substances (PFASs) in recycled water may pose a threat to irrigated crops and the human food chain. Biochar potentially represents a low-cost and environmentally friendly approach to removing PFAS from recycled water via adsorption. Identifying key biochar properties responsible for successful adsorption of long- and short-chained PFAS as well as developing predictive models are crucial in identifying the potential of biochar as a scalable approach for remediating PFAS in agriculture. Here, a systematic and comprehensive evaluation of 17 physicochemical properties of 24 biochars was performed to determine the main factors influencing PFAS removal from water. Batch studies were conducted, and principal component analysis as well as correlation studies were used to determine factors influencing PFAS removal. Various parameters were influential in the removal of long- (carbon/nitrogen ratio, specific surface area) and short- ([nitrogen + oxygen]/carbon ratio, carbon/nitrogen ratio) chained 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 to select a commercial pine wood biochar (Rogue biochar), which performed effectively in removing PFOS, PFOA, PFBS, PFHxS, PFNA in different matrices. Post-pyrolysis thermal treatment facilitated maintenance of adsorption potential over subsequent cycles, while providing the additional benefit of increasing the removal of the short-chained sulfonate PFBS by two- to five times. Careful, evidence-based selection of biochars with optimal physiochemical characteristics can provide excellent removal of both long- and short-chained PFAS compounds from water.