The influence of hydraulic retention time (HRT) in a submerged hollow fibre membrane bioreactor was studied by conducting experiments at four different HRTs (4, 2, 1.3 and 1 h) at room temperature of 25 degrees C. It was found that a shorter HRT led to a higher development of trans-membrane pressure. The highest sludge cake and pore-blocking resistances of 4.02 x 10(11) m(-1) and 0.77 x 10(11) m(-1) respectively were noted for the shortest HRT (of 1 h) application. UV and fluorescence spectroscopy analyses showed that the nature of organics in the biomass and sludge cakes were different. The organic fraction analysis by liquid chromatography with organic carbon detector (LC-OCD) showed a significant amount of biopolymers and a lower amount of humics for longer HRT. (C) 2011 Elsevier B.V. All rights reserved.