Question

In sedimentation design, depth is not used for performance (removal) calculations. However, a minimum clarifier depth (side water depth) is often specified. Why?

Answer 1

The factor which governs the side water or clarifier depth is the desired distance between the sludge blanket and the effluent weirs. A minimum clarifier depth is essential so as to prevent the entering of sludge blanket solids to the effluent launder. The typical ranges for clarifier depth are 12 to 14 ft for primary clarifiers and 14 to 16 ft for secondary clarifiers. For circular clarifiers, the clarifier depth should be evaluated by considering both the center depth and the clarifier slope. An additional volume for solid accumulation is available fin a sloping-bottom clarifier and therefore it can typically be designed with shallow clarifier depth when compared to that of a flat-bottom clarifier.