Role of Activated Sludge Final Settling Tanks

by Richard I. Dick, (M.ASCE), Assoc. Prof. of Sanitary Engrg.; Dept. of Civ. Engrg., Univ. of Illinois, Urbana, IL,

Serial Information: Journal of the Sanitary Engineering Division, 1970, Vol. 96, Issue 2, Pg. 423-436

Document Type: Journal Paper


Both the thickening and clarification functions of final settling tanks influence the quality of effluent produced by the activated sludge process. The thickening function commonly is ignored in design. Failure to consider the thickening function can lead to excessive loss of solids over the final settling tank weir and to inability to withdraw thickened sludge at the desired concentration for recycle. By use of an illustrative problem it is shown that conventional design procedures for activated sludge final settling tanks can result in unsatisfactory performance of the entire process. Design for the thickening function of final settling tanks is based on the limiting solids handling capacity of the sludge. Several alternate methods are available for determining the limiting capacity. The batch flux plot technique is the most convenient method.

Subject Headings: Activated sludge | Sedimentation tanks | Wastewater treatment | Solid mechanics | Effluents | Weirs | Recycling

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