The synthetic hormone 17 alpha-ethinylestradiol (EE2) is an endocrine disrupter of great concern with insufficient removal in wastewater treatment plants (WWTP) and subsequent Impacts on the aquatic environment. In this paper, membrane bioreactor (MBR) technology was compared with conventional activated sludge (CAS) systems Contrary to previous studies on MBRs, continuous purification was combined with the determination of sorption and biodegradation parameters In addition, EE2 removal was studied in two different MBR configurations Continuous purification with AS acclimated in the MBR (MLVSS of 9g L(-1) and a 50-d SRT) resulted in the stabilization of the EE2 removal at a plateau of 65% (initial load of 1.8 mg(EE2) g(MLVSS)(-1) d(-1)) In contrast, CAS resulted in EE2 accumulation in the permeate. During batch kinetics, CAS was shown to remove EE2 only through sorption (87% removal of EE2) whereas AS acclimated to the MBR process developed biodegradation abilities towards the synthetic hormone (7% removal of EE2) Therefore, the membrane process combined with AS was shown to be essential to improve EE2 removal (with the autotrophic activity as the key factor). In addition, either the external or the external-immersed configuration can be applied, due to similar performance with respect to EE2 removal (C) 2010 Elsevier B.V All rights reserved