A new method for estimating cake height and porosity during crossflow filtration of particulate suspensions

An indirect method was developed to estimate the height and porosity of the cake deposited on the membrane surface during crossflow filtration of a particulate suspension. The method was based on reconstructing the cake recovered from the membrane unit by static filtration on a 0.22 μm filter for the same time and transmembrane pressure (TMP) as used in the crossflow microfiltration (CFMF) run. The accuracy of the porosity measurements was confirmed using uniform sized glass spheres. The developed method was then used to estimate the cake properties during CFMF of lactalbumin suspensions in a tubular membrane. The estimated cake heights (10–81 μm) were in the same order as that measured using techniques like scanning electron micrography and NMR micro-imaging under similar experimental conditions reported in the literature. This study revealed the decrease in cake porosity with time of filtration to a steady-state value of ∼0.2 that demonstrated the marked penetration of smaller particles into cake voids. The steady-state cake height increased with an increase in TMP and with a decrease in crossflow velocity (CFV). However, there was no significant effect of TMP or CFV on the steady-state porosity of the cake. The method is particularly useful for small diameter tubular membranes, for which most direct height measurement techniques are not applicable.