This study investigated the impact of water pretreatments (i.e. activated carbon, ferric chloride and polyelectrolyte organic polymer) and dynamic chemical ageing by chlorine on performances of PES/PVP hollow fiber membranes. For this, several filtration experiments were carried out on pristine membranes and on 5-year-old membranes sampled from a large drinking water treatment plant (DWTP membranes) exhibiting strong fouling event with no clear explanation. Autopsy performed on the DWTP membranes revealed the presence of a brown fouling layer consisting of organic matters, iron, flocculent polymer and activated carbon. Filtration tests showed the strong fouling sensitivity of the autopsied membranes compared to the pristine membranes. Further autopsy analyses and filtration experiments demonstrated the link between PVP degradation inside the membrane due to frequent chlorine backwashes and the increase in membrane fouling sensitivity. (C) 2015 Elsevier B.V. All rights reserved.