Stabilization of per- and polyfluoroalkyl substances (PFAS) in sewage sludge using different sorbents

Abstract

Sewage sludge is known to contain a wide range of per- and polyfluoroalkyl substances (PFAS). To test the feasibility of stabilizing PFAS in sludge, we spiked two known amounts of six perfluorinated carboxylic acids (PFCAs, C6 – C11), three perfluoroalkane sulfonic acids (PFSAs, C4 – C8), and GenX to the sludge and amended it with biochar, granular activated carbon (GAC), or one RemBind® product (100 or 100X) at different doses. Our results showed that RemBind® 100X had the best stabilization performance, followed by GAC and RemBind® 100. Biochar had little effect on decreasing leaching of PFAS. Compared to control sludge without any sorbents at an initial PFAS concentration of 30 µg/kg, the treatment by RemBind® 100X at 2 wt.% after 35 days led to decrease of a ∑PFAS leaching by 89% in the water and 85% in the SPLP leachates. At 300 µg/kg, a similar trend was observed as well. RemBind® 100X, GAC, and RemBind® 100 at a dose of 1 wt.% stabilized PFAS and resulted in significantly lower leachable ∑PFAS than that at a dose of 0.1 wt.%, indicating the dose-effect of sorbents on PFAS stabilization in sludge. During the experimental duration of 115 days, the leachable PFAS gradually increased with time for those with GAC but fluctuated in the water leachate of the sludge with RemBind® 100X, implying a dynamic adsorption/desorption process and potential degradation of PFAS precursors occurring during the incubation. Overall, this study demonstrated the positive effect of sorbent addition toward decreasing PFAS leaching by water and acidic water. The fact that the stabilized PFAS can be extracted well by basic methanol, although this may happen rarely in reality, raises the question of remediation end point, which deserves to be further investigated.