A model for submerged outside-in hollow-fiber MF/UF filtration for wastewater treatment is presented. The model aims at integrating the major influence factors on medium scale of granularity. In particular, the model covers the geometry of the system, the hydrodynamics of the feed and of the permeate flow, and the filtration resistance. The filtration resistance model considers membrane resistance, pore blocking, cake layer formation, polydispersed particles, biofilm formation, and concentration polarization on high levels of detail. The model is thoroughly analyzed in simulation and sensitivity studies. The role of uncertain parameters is discussed. The influence of important operational parameters of the biological system and of the membrane aeration rate on the filtration performance is investigated. The model provides insight into the MF/UF filtration process in membrane bioreactors and the interplay of the related physical, chemical, and biological phenomena. (c) 2006 Elsevier B.V. All rights reserved.