DESIGN OF CLASS-I SEDIMENTATION TANKS

The present practice for the design of primary settling tanks is based on the overflow rate corresponding to the percentage removal using is oremoval plots. The design procedure would be more rational if it were based on the removal efficiency and the scour criterion of the deposi ted particles. This technical note presents closed-form equations for the removal efficiency and scour velocity of particles. The removal ef ficiency equation considers the size distribution of particles, and th e scour velocity equation is based on the Rouse equation. The removal efficiency equation yields the minimum particle size completely remove d by the sedimentation tank. Using these equations the design equation s have been obtained for the length and width of the settling tank. Be sides other parameters, the design equations involve the completely re moved minimum particle size, the specific gravity of the sediment part icles, and the kinematic viscosity of water. These equations will be u seful for the design of grit chambers and settling basins undergoing c lass-I settling.