Dynamic analysis of cake properties in microfiltration of soft colloids

The properties of cakes formed using soft colloids in “dead-end” microfiltration were studied. The empirical power functions were used to relate the local cake properties. However, the cake compressibility factors are functions of time due to the retardation effect of cake compression. A dynamic analysis method is proposed to estimate the cake properties during soft colloid microfiltration. The results show that the entire filtration course can be divided into three stages. At the beginning of filtration, the deposition and rearrangement of the colloidal particles on the membrane surface cause the overall filtration resistance to increase. The average porosity and average specific filtration resistance of the cake vary slightly during this period of filtration. In the second stage, a rapid increase in filtration resistance and a decrease in cake porosity due to cake compression and colloid deformation can be found. A compact skin layer begins to be formed next to the filter membrane in this stage. The skin thickness is about 10–20% of the entire cake but this layer exhibits about 90% of the overall filtration resistance. The average cake porosity increases gradually in the third stage due to the loose packing in the newly formed cake. This trend can be reflected in the dt/dv versus v filtration curves and is demonstrated by the experimental data. The structure of the cake formed in each stage was observed using scanning electronic microscopy (SEM).