Operating Principles Design and Selection Factors

Sedimentation equipment can be divided into batch-operated settling tanks and continuously operated thickeners or clarifiers. The operation of the former is very simple and their use has recently diminished. They are still used, however, when small quantities of liquids are to be treated. Most sedimentation processes operate in continuous units. 

Alternative designs for gravity thickeners (a) circular-basin continuous thickener, (b) deep-cone thickener, and (c) lamella thickener. 

Design curves for thickeners (a) total flux versus concentration, and (b) settling flux versus concentration. 

The Coe and Clevenger test overestimates the critical flux leading to underdesign of thickener area, while the Talmage and Fitch procedure underestimates it leading to overdesign. The latter procedure is less laborious because it only requires one settling test. 

The mass balances of liquid and solids in the process can be represented by 

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