SETTLING OF FLOCCULANT SUSPENSIONS IN SECONDARY CLARIFIERS

The purpose of this paper is to show that a relationship exists between the average settling velocity of floc particles in the upper layers of a secondary clarifier and the concentration of suspended solid within that layer. While it can be theoretically argued that the average settling velocity of particles in the flocculent settling zone is independent of concentration, the practical and operational constraints of secondary clarifiers lead to the conclusion that the average settling velocity of flocculent suspensions is correlated to the suspended solids concentration. Analytical expressions describing the concentration and average settling velocity of a suspension as a function of particle size distribution are presented. Finally, the relationship between particle size distribution and overflow rate is addressed.