SEDIMENTATION OF FLOCCULENT SUSPENSIONS - STATE OF THE ART

Three modes or types of sedimentation are recognized in flocculent suspensions: Clarification, in which floccules are separated and settle independently; zone settling, in which floccules are incorporated into some solids structure so that all are constrained to subside at more or less the same rate; and compression or compaction, in which the solids structure is strong enough to exhibit a compressive yield value. Current models for sedimentation in the three modes are reviewed, with particular emphasis on their use and reliability (or lack of it) for sedimentation basin design. Most models of thickening presented in the literature derive from a basic partial differential equation for force balance. Models differ in which terms of the equation are disregarded. Several of the theories of compaction are essentially equivalent solutions for the same model, but with different sets of independent variables. Copyright © 1979 American Institute of Chemical Engineers