Seasonal and annual variations in removal efficiency of perfluoroalkyl substances by different wastewater treatment processes

Abstract

Municipal wastewater treatment plants (WWTPs) are important in the migration and transformation of perfluoroalkyl substances (PFASs) in water bodies. Six municipal WWTPs located in the upper reaches of the Guanting reservoir, along the Yanghe River, were sampled from November 2016 to July 2017. Influents, effluents, and activated sludge solutions were sampled and the concentrations of 17 PFASs were analyzed. Perfluorobutanoic acid (PFBA), Perfluorooctanoic acid (PFOA), Perfluorohexanoic acid (PFHxA), Perfluoropentanoic acid (PFPeA), Perfluorobutane sulfonat (PFBS) and Perfluorooctane sulfonate (PFOS) accounted for more than 90% of these. Seasonal variations in PFASs in influent directly influenced concentrations in supernatant and effluent. The annual average PFAS concentrations were 46.4, 45.1, and 38.5 ng L−1 in influent, supernatant, and effluent, respectively, indicating that WWTPs do not efficiently remove PFASs from wastewater. Annual average PFAS removal efficiencies differed among WWTPs, were influenced primarily by the treatment process used at each, and followed the order Cyclic Activated Sludge System (CASS, 32.2%) > Orbal Oxidation Ditch (OD, 17.5%) > Anaeroxic–Anoxic–Oxic (A2/O, −1.49%). Short-chain PFASs were removed significantly more efficiently in the CASS compared to the other systems. These results can show how traditional wastewater treatment plants can help remove PFASs from the environment.