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Underflow geometry in secondary sedimentation

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Previous work by the authors suggested that activated sludge sedimentation might be highly sensitive to underflow geometry. Field, physical model, and stratified flow numerical model tests were conducted to evaluate this hypothesis. Field work included solids settling velocity, dye dispersion, and flow pattern/solids distribution tests. Physical tests included operation of a pie-shaped 1:12.5 scale model of a circular, center-feed tank with sludge withdrawal simulating countercurrent, uniform, and cocurrent geometries. A stratified flow numerical model that simulated the effects of density currents was calibrated to the results of the full-scale testing. The results failed to confirm the experimental hypothesis. Model performance was relatively insensitive to underflow geometry in a circular tank when density effects were simulated.

Keywords: activated sludge; clarifiers; design; modeling; sedimentation; simulation; underflow

Document Type: Research Article


Publication date: May 1, 1992

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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