Assessment of aluminum-based drinking water treatment residuals from multiple utilities in the United States as green sorbents for PFAS

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants causing human health concerns. In this study, five aluminum-based drinking water treatment residuals (Al-WTRs) were evaluated as green adsorbents for the removal of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) from water. Al-WTRs are nonhazardous solid wastes generated during the coagulation process of water treatment using aluminum salts or polymers. Although high PFAS adsorption capacity of Al-WTRs generated in one facility in the US has been reported, no study exists assessing PFAS adsorption capabilities of WTRs generated in multiple facilities using various types of aluminum coagulants. Batch adsorption experiments of PFOA and PFOS on Al-WTRs showed removal efficiencies exceeding 70 % for PFOA (1–20 µg/L) and 94 % for PFOS (10–500 µg/L) across all Al-WTRs. Maximum adsorption capacities for PFOS (up to 46.30 µg/g) were significantly higher than those for PFOA (up to 2.019 µg/g), indicating the stronger affinity of the Al-WTRs for PFOS. Low desorption rates for both PFOA and PFOS suggested irreversible adsorption. Correlation analysis revealed that oxalate-extractable Al, Fe, and organic matter primarily contributed to PFOA adsorption, while pore size, oxalate-extractable Al, Fe, and total calcium primarily contributed to PFOS adsorption. These easily measurable parameters could be used as predictors when utilizing Al-WTRs as sustainable sorbents for PFAS removal. This study not only establishes the comparative and predictive performance of Al-WTRs from multiple utilities for PFAS sorption but also demonstrates their recycling potential within a circular-economy framework.