Comparative evaluation of activated sludge and biofilm processes for per- and polyfluoroalkyl substances (PFASs) removal in a full-scale wastewater treatment plant

The increasing use of short-chain per- and polyfluoroalkyl substances (PFASs) and PFASs alternatives has led the widespread environmental distribution and new pollution profiles, posing new challenges for the efficient removal of PFASs. This study systematically compared the occurrence, removal, and sludge enrichment characteristics of PFASs in two parallel wastewater treatment processes (activated sludge and biofilm). A total of 21 PFASs were detected in the influent, with short-chain PFASs accounting for 60.8%. The total PFASs removal efficiency of biofilm process (58.9%) was higher than that of activated sludge process (53.6%), especially under the high proportion of short-chain PFASs in the influent. Among the 15 PFASs detected in sludge, biofilm process sludge exhibited significantly higher total PFASs concentration and a more complex composition, with notably increased proportion of short-chain PFASs (particularly PFBS). In contrast, the sludge of activated sludge process was dominated by long-chain PFASs with negligible short-chain components. Biofilm processes exhibit superior removal performance for wastewater containing a high proportion of short-chain PFASs and their alternatives. The study provides comprehensive insights into the effective removal of PFASs in different wastewater treatment configurations, offering valuable guidance for PFASs control in wastewater treatment plants.