Fundamental Concepts of Rectangular Settling Tanks

This investigation of fundamental theories of sedimentation, scour by turbulent eddies, inlet and outlet disturbances, and sludge-thickening phenomena indicates that settling tanks should be designed on the basis of surface area and that rectangular settling tanks should be long and narrow. The authors suggest that the minimum depth of such tanks is limited not by bed-load movement resulting from direct shear, as previously supposed, but by scour resulting from turbulent eddies in accordance with the suspended-load equation. There is evidence that tanks can be made relatively shallow if the deposited sludge is protected from resuspension by means of multiple inclined baffles. These baffles also serve to produce thicker sludge.