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Advective transport in activated sludge flocs

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The liquid flow through activated sludge floes from fullscale conventional treatment plants was evaluated on the basis of the information obtained from settling tests. In the samples of the mixed liquors studied, only a part of the activated sludge flocs was found permeable to fluid drainage. Basically, small flocs were not permeable but all the flocs in the size range from 100-150 μm showed different degrees of permeability. The permeability of flocs increased with an increase in the dynamic sludge age and decreased with an increase in the shear rate measured as the mean velocity gradient in the aeration tanks. The most sensitive assumption for the estimation of the permeability of the flocs was the size of the primary particles in the aggregates, with the sphericity of the flocs being less important. It was also found that the CarmanKozeny model reflected well the porosity-permeability relationship of most activated sludge flocs, except those that contained substantial amounts of filamentous growth. During free gravitational settling, flocs with the longest dimensions in the size range of 50 to 1000 showed a drainage rate in the range of 102 to 107 μm3/s, which followed the Carman-Kozeny model with a power relationship of 4.08.
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Keywords: activated sludge; flocs; particle size; permeability; porosity; settling

Document Type: Research Article

Publication date: 01 May 1992

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  • Water Environment Research (WER) is published monthly, including an annual Literature Review. A subscription to WER includes access to the latest content back to 1992, as well as access to fast track articles. An individual subscription is valid for 12 months from month of purchase.

    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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