Filtration Model for Suspensions that Form Filter Cakes with Creep Behavior

摘要

Waste-activated sludge was filtered and the formed filter cake studied.It was shown that average specific filter-cake resistance increases during filtration.A stress-relaxa- tion experiment was performed and the two relaxation times found were of the same order of magnitude as the duration of the filtration stage.It was therefore concluded that the local solid volume fraction of sludge filter cakes changes not only with effec- tive pressure but also with time.In contrast,it is usually assumed in filtration model- ing that solid volume fraction is a unique function of effective pressure.A new filtra- tion model was thus developed by adopting the concept of filter-cake creep and applying it in conventional models.It was shown that the model developed,unlike conventional filtration models,satisfactorily describes the experimental data in the case of waste-activated sludge.Furthermore,the model is capable of being scaled with respect to feed concentration and volume.