Reaggregation of Flocs in Coagulation-Cross-Flow Microfiltration
Publication: Journal of Environmental Engineering
Volume 133, Issue 5
Abstract
Cake layer in cross-flow microfiltration can be reduced by coagulation of particles. This is because enlarging particle size by coagulation increases shear induced diffusivity and the back transport of rejected particles. In addition, it is known that flocs can be broken when they are passing through a pump. In light of these facts, this study aims to experimentally look at the floc-breaking phenomenon being related to cake layer reduction. Kaolin is used as particles and aluminum sulfate as a coagulant for the experiment. The results of particle size analyses show that the aggregated particles in feed are completely disaggregated by the pump but reaggregated in the membrane module. This suggests that the reaggregation of particles is critical to cake reduction and flux enhancement. This study proves that most of it occurs around the movable cake layer on membrane where value is small. Charge neutralization of particles is also proven a dominant coagulation mechanism for reaggregation around the movable cake layer over sweep flocculation. These results suggest that rapid mixing and charge neutralization of particles are more important in reducing cake layer than flocculation. In this reason, in-line mixer is expected to work better with coagulation-cross-flow microfiltration than conventional coagulation tank and this study proved it.
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Acknowledgments
This work was supported by the Brain Korea 21 project and Grant No. KOSEF2000-2-30900-004-3 from the Basic Research Program of the Korea Science and Engineering Foundation. It was done in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the first writer in the Department of Civil and Environmental Engineering at KAIST.
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Information & Authors
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Published In
Journal of Environmental Engineering
Volume 133 • Issue 5 • May 2007
Pages: 507 - 514
Copyright
© 2007 ASCE.
History
Received: Jun 21, 2006
Accepted: Oct 16, 2006
Published online: May 1, 2007
Published in print: May 2007
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