The influence of high salinity on the characteristics of the activated sludge and performance of a pilot-scale immersed membrane bioreactor (iMBR) has been studied. The bioreactor was subjected to salinity shocks of up to 5 g/L, and the response with respect to membrane permeability monitored. Key physical and chemical parameters were measured included mixed liquor suspended solids (MLSS), viscosity, capillary suction time (CST), turbidity, and the soluble microbial product (SMP) and extracted extracellular polymeric substances (EPS) of the mixed liquor. The interrelationships between these parameters and the membrane permeability were then assessed. Results indicate that high salinity greatly affects the physical and biochemical properties of activated sludge, increasing SMP and EPS concentrations, as well as decreasing membrane permeability. Both SMP and EPS were correlated with physical parameters of the activated sludge such as particle size, CST and turbidity. Furthermore, permeability was found to be negatively correlated with SMP carbohydrate at the two different flux rate imposed, corroborating previous reports linking SNIP carbohydrate to iMBR membrane fouling. (c) 2006 Elsevier B.V. All rights reserved.