The mechanism of cake filtration of soft colloids is studied.Dextran-MnO/sub 2/ particles are prepared and used in "dead-end" cakefiltration. The deformation of particles and the compression of cakedue to solid compressive pressure result in the suddenly decrease ofporosities of cake and particles, which result in an abrupt increaseof specific filtration resistance of cake. The dynamic analysis methodproposed by Lu and Hwang (1993) is modified and used to estimate thevariations of local cake properties during filtration. From the trendof a filtration curve of soft colloids, the whole filtration operationcan be divided into three stages according to the curvature of thecurve. At the beginning of filtration, the deposition and therearrangement of colloidal particles on the membrane surface cause theoverall filtration resistance to increase. The linear filtration curveimplies a constant average specific filtration resistance of cakeduring this period of filtration. The second stage begins when thefiltration time exceeds 60 seconds. The deformation and compression ofcolloids result in a formation of skin layer with a compact structurenext to the membrane surface. Therefore, the slope of the tangent offiltration curve increases sharply in this stage due to a suddendecrease in cake porosity and an increase in filtration resistance.When filtration time exceeds 720 seconds, the new-formed cake has aloose structure because most of solid compressive pressures areexerted on the skin layer formed at the second stage. As a result, thefiltration curve changes back to be linear which similar to that inthe first stage. All of these phenomena are demonstrated using thescanning electronic microscopy (SEM).
第二十三屆輸送現象及其應用研討會暨膜分離論壇第四屆台灣-新加坡環境保護技術研討會論文集=Proceedings of The 23st Symposium of Transport Phenomena and 1ts Applications/Membrance Seperation Forum/The 4st Taiwan-Singapore Jiont Symposium on Environmental Technology