Analysis of Structural Features on Performance of Secondary Clarifiers

Abstract

The objective of this study is to evaluate the significance of four structural design features (inlet configuration, weir location, intermediate baffle existence, and sludge draw-off location) and their interactions on the control of density currents in activated-sludge secondary clarifiers. A 1:25-scale model of a prototype rectangular clarifier was used, and experiments were conducted in the field with activated-sludge mixed liquor. A factorial design procedure was used to estimate quantitatively the significance of each structural design feature and their interrelationships. The effect of the structural design features on the performance of an activated sludge secondary clarifier depended on the predominant flow pattern (bottom or surface density current) through the clarifier. Because of the strong interactions among the structural design features, the effectiveness of each structural-design-feature level (i.e., the particular configuration of a structural design feature) on the performance of the clarifier was strongly related to the condition of the other structural features. A regression equation for the effluent suspended-solids concentration was developed from the experimental data.