The comparative study was conducted to investigate the performance and removal efficiencies of PFOS and PFOA in MBR and PAC-MBR. Solid phase extraction (SPE) followed by HPLC coupled with tandem MS (HPLC/MS/MS) was applied to quantitatively identify PFOS and PFOA in aqueous and sludge samples. Removal efficiencies of these two compounds were less than 7% in MBR, which suggest that MBR could not effectively remove PFCs due to their persistent in the activated sludge process. In contrast, removal efficiencies of 77.4% for PFOS and 67.7% for PFOA were observed in PAC-MBR with PAC dosage of 30 mg/L, indicating that adsorption of PFCs onto PAC plays an important role in their removal. Moreover, with the increase of PAC dosage from 30 mg/L to 100 mg/L in PAC-MBR, removal efficiency for PFOS or PFOA both increased to more than 90%. Mass balance of PFOS and PFOA was established to explore their removal mechanisms in MBR and PAC-MBR. Results show that PAC-MBR can effectively remove these two compounds in the wastewater by PAC adsorption, which was identified as the major removal mechanism. In MBR, adsorption onto activated sludge was the only mechanism for removal of PFCs. (C) 2013 Elsevier B.V. All rights reserved.