Design of Class-I Sedimentation Tanks

Abstract

The present practice for the design of primary settling tanks is based on the overflow rate corresponding to the percentage removal using isoremoval plots. The design procedure would be more rational if it were based on the removal efficiency and the scour criterion of the deposited particles. This technical note presents closed-form equations for the removal efficiency and scour velocity of particles. The removal efficiency equation considers the size distribution of particles, and the scour velocity equation is based on the Rouse equation. The removal efficiency equation yields the minimum particle size completely removed by the sedimentation tank. Using these equations the design equations have been obtained for the length and width of the settling tank. Besides other parameters, the design equations involve the completely removed minimum particle size, the specific gravity of the sediment particles, and the kinematic viscosity of water. These equations will be useful for the design of grit chambers and settling basins undergoing class-I settling.