Improving design guidelines for class-I circular sedimentation tanks

Abstract

Circular sedimentation tanks are preferred for removal of inorganic solids by class-I sedimentation during water and wastewater treatment processes. The present design practice for obtaining the exit diameter of circular settling tanks is based on using an arbitrarily fixed overflow rate. Such practice does not consider the non-uniformity of sediment particles and the mechanics of suspension and settlement. Although the equations which describe sedimentation are available, design equations have not been attempted as yet. In this paper the design equations for a circular sedimentation tank have been formulated taking into account the non-uniformity of suspended particles. These equations are based on the desired removal efficiency and ensure that the deposited material is not resuspended. The design equations are dependent upon the fluid, flow and sediment characteristics, and enable the exit diameter and the flow depth of the settling tank to be calculated.

Keywords:

• Circular tank
• Design
• Particle size distribution
• Removal efficiency
• Scour
• Sedimentation
• Water treatment