Cake Resistance in Rotational Dynamic Filtration: Determination and Modeling

Dynamic microfiltration, which has proved quite efficient in treating highly concentrated solid streams, suffers from accumulation of particles on the membrane surface. Such accumulation leads to the formation of a cake layer on the membrane surface, which causes rapid and severe resistance to filtration. In order to predict the extent of cake formation at different operational conditions in a rotational dynamic filtration unit, an understanding of the cake formation was needed. The resistance was investigated in two sequential experimental steps, which enabled the formulation of an increasingly complex model. First, the operational conditions were evaluated in a system, which included only solvent (no solutes). Such system permitted the quantification of the basic system parameters, i.e. Rm and kp, by varying rotation speed and flux. Second, particles of CaCO3 were added to the solvent and the filtration performance, at increasing particle concentration, was measured. By comparing the system with and without particles, the cake resistance was derived. Across multiple experiments, the cake resistance was evaluated under different experimental conditions, i.e. feed concentration, rotational speed, and permeate flux. By following this procedure, a good correlation between particle concentration and particle resistance was established. The correlation could be expressed in the form of a mathematical model, which describes resistance in a dynamic filtration unit, as a function of particle concentration. The resulting model was generalized, by incorporating rotation speed, such that it describes all experiments from a single parameter set. Finally, the model was evaluated with the fermentation broth of an industrial yeast process. Here it was shown, that the model is suitable for describing cake resistance during filtration of biological material.