Flow Dynamic Effect in Cake Shape and Resistance in Membrane Filtration

Abstract

Membrane filtration is one of the methods for separating targeted material from a fluid stream. Membrane based filtration is applied in many areas of processing to separate and concentrate fluids. However, fouling and film growth at the filter surface is a major problem that causes loss in efficiency. The cake buildup during the filtration process is investigated experimentally to understand the affect of flow dynamics on the cake characteristics, shape and associated resistance. The experiments were conducted without and with shear generated using an impeller operated at various rotational speeds. The results illustrate that indeed the cake shape and character are affected by the flow dynamics that eventually influence filtration resistance. Likewise the filtrate rate and the cake shape significantly affect the flow dynamics. Furthermore, the filtration resistance is not only affected by the thickness of the cake, but also by how the cake is formed. After similar volumes of filtrate, the flux rate of 120 Lm−2hr−1 for 4.4 mm thick and 1.8 g cake is observed for dead-end filtration, while the flux rate of 600 Lm−2hr−1 for 1.1 mm thick and 0.35 g cake where observed with a shearing rate of 630 s−1. Understanding the size and characters of cake buildup is very important to designing a system to overcome the drawbacks associated with membrane fouling. Moreover, developing a technology with the cleaning process that removes or eliminates cake and maintains a reasonable flux for an extended period requires a thorough understanding of the filtration system geometry and flow dynamics.