2013 Volume 30 Pages 3-14
A comprehensive evaluation of flocculation processes is presented with emphasis on physical and engineering aspects. Flocculation by polymer bridging involves three basic sub-processes: mixing of the polymer with the particle suspension, adsorption of the polymer on particle surfaces and the formation and growth of flocs. Each of these is primarily controlled by agitation of the suspension. At the same time, agitation also promotes floc breakage. Since polymer adsorption tends to occur irreversibly, flocculation is a non-equilibrium process and the relative rates of the sub-processes play a critical role. The kinetics of these processes are reviewed and their implications with respect to process design are evaluated. Procedures for controlling the relative rates are shown to provide a basis for the design of efficient flocculation processes in batch systems. Some information on scale-up criteria is presented. Extension of the basic concepts to the design and operation of continuous processes is discussed.
