SUMMARY

• Sewage sludge is known to contain a wide range of per- and polyfluoroalkyl substances (PFAS). To evaluate the feasibility of stabilising PFAS in sludge, two concentrations of six perfluorinated carboxylic acids (PFCAs, C6–C11), three perfluoroalkane sulfonic acids (PFSAs, C4–C8), and GenX were spiked into sludge samples and amended with biochar, granular activated carbon (GAC), or RemBind® 100 or 100X at varying doses.
• RemBind® 100X demonstrated the best stabilisation performance, followed by GAC and RemBind® 100. Biochar had minimal effect on reducing PFAS leaching. At an initial PFAS concentration of 30 µg/kg, treatment with RemBind® 100X at 2 wt.% after 35 days reduced total PFAS (∑PFAS) leaching by 89% in water leachates and 85% in SPLP leachates compared to untreated control sludge. A similar trend was observed at 300 µg/kg.
• RemBind® 100X, GAC, and RemBind® 100 at a dose of 1 wt.% all achieved significantly lower leachable ∑PFAS than at 0.1 wt.%, confirming a clear dose-response relationship for PFAS stabilisation in sludge.
• Over the 115-day experimental period, leachable PFAS levels gradually increased over time in GAC-treated samples, while fluctuating in the water leachate of RemBind® 100X-treated sludge. This suggests a dynamic adsorption/desorption process and potential degradation of PFAS precursors during incubation.
• Overall, this study demonstrates the effectiveness of sorbent addition in reducing PFAS leaching in both water and acidic water conditions. However, the observation that stabilised PFAS can be effectively extracted using basic methanol raises important questions regarding remediation endpoints, warranting further investigation.