Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in sewage treatment plants.

In this study, the concentrations of PFOS and PFOA in the biological units of various full-scale municipal sewage treatment plants were measured. Samples of influent, primary effluent, aeration tank effluent, final effluent and grab samples of primary, activated, secondary and anaerobically digested sludge were collected by 5 sampling events over one year. The two sewage treatment plants (STPs) selected for this study include plant A receiving 95% domestic wastewater and plant B receiving 60% industrial wastewater and 40% domestic wastewater. PFOS and PFOA were observed at higher concentration in aqueous and sludge samples in plant B than that of plant A. Mass flow of PFOS increased significantly (mean 94.6%) in conventional activated sludge process (CAS) of plant B, while it remained consistent after the secondary treatment in plant A. Mass flow of PFOA increased 41.6% (mean) in CAS of plants A and B and 76.6% in membrane biological reactor (MBR), while it remained unchanged after the treatment of liquid treatment module (LTM). Our results suggest that mass flow of these two compounds remains consistent after treatment of activated sludge process operating at short sludge retention time (SRT). Seasonal variations of PFOS in concentrations of raw sewage were found in plant A, while PFOA did not have significant seasonal variation in both plants A and B.