A belt filter press is commonly used to dewater sewage sludge but few data concerning this process have been published. A laboratory-scale investigation was carried out to highlight the main process parameters affecting belt filter press efficiency as measured by the dry solid content of the final cake, percentage of solids recovered, and lateral sludge migration on the belt. Belt speed was determined to be the most important parameter: a low belt speed produces drier cakes with lower lateral sludge migration on the belt and also improves filtrate quality. At low belt speed, pressure is gently applied to the initial sludge, enabling a slow structuring of the cake and leading to better water release. (c) 2005 Society of Chemical Industry.