The aim of this work was to evaluate the effect of temperature on the performance of industrial hollow-fibre (HF) membranes treating urban wastewater in a submerged anaerobic MBR system (SAnMBR). To this end, a demonstration plant with two commercial HF ultrafiltration membrane modules (PURON (R), Koch Membrane Systems, PUR-PSH31) was operated at 20, 25 and 33 degrees C. The mixed liquor total solid (MLTS) level was a key factor affecting membrane permeability (K). K was higher under psychrophilic than mesophilic conditions when operating at similar transmembrane fluxes and MLTS, because the biomass activity of the psychrophilic mixed liquor was lower than the mesophilic mixed liquor. Thus, lower extracellular polymeric substances (EPSs) and soluble microbial products (SMPs) levels were observed at psychrophilic conditions, which affected not only the three-dimensional floc matrix, but also the fouling propensity. However, no chemical cleaning was needed during the experimental period (almost 1 year) because no irreversible fouling problems were detected. (C) 2012 Elsevier B.V. All rights reserved.