Phosphorus Removal Capacity, Arsenic Leaching, and PFAS Content of Drinking Water Treatment Residuals with Potential to Enhance Stormwater Infrastructure in New England

Stormwater runoff is a significant contributor of phosphorus (P) loading to waterbodies around the world. Green stormwater infrastructure (GSI) that uses filtration media, such as bioretention, can effectively retain suspended solids and associated particulate P, but is commonly less effective for soluble P retention. The addition of aluminum-based drinking water treatment residuals (DWTRs) may increase P-sorbing capacity of GSI media, though guidance is needed for material selection and to reduce risk of potential contamination. This study examined the P removal capacities of DWTRs (n=11) from drinking water treatment plants in the New England region (northeastern USA). DWTRs were compared for P-sorption potential using batch isotherm and column experiments and characterized for several material properties as well as arsenic leaching and per and polyfluoroalkyl substances (PFAS) content. Results indicate that P retention capacity of DWTRs is generally high (>1,000 mg P kg−1) but varies by approximately one order of magnitude. Lower DWTR bulk density and greater oxalate-extractable Al + Fe were correlated with greater P retention in column experiments. Our findings also indicate that the potential for significant arsenic leaching is low. PFAS were detected in 36% of DWTRs, often at low levels near the method detection limit, with three DWTRs having higher levels of certain PFAS. The addition of DWTRs to GSI is promising for enhanced soluble P removal on a decadal scale (10–90 years), but additional research on As, PFAS, and other contaminants should be pursued prior to use, especially in areas with known or suspected source water contamination. Achieving effective long-term P removal requires selecting DWTRs with favorable material properties (e.g., drier, lower bulk density, greater oxalate-extractable Al + Fe), and mixture with sand at up to 10% DWTR by volume and potentially higher if proven to not impede hydraulic conductivity. Field monitoring of DWTR-enhanced infrastructure at multiple time points postinstallation (e.g., years 1, 5, 10, 20, and 30) is needed to confirm P removal longevity over expected infrastructure lifespans.