The theoretical densimetric Froude number values with favourable effect on the clarifier performance |
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Affiliation: | 1. Deltares, Boussinesqweg 1, NL-2629 HV Delft, The Netherlands;2. Section of Environmental Fluid Mechanics, Delft University of Technology, P.O. Box, 5048, NL-2600 GA, Delft, The Netherlands |
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Abstract: | The performance of secondary clarifiers is strongly related to density effects in the sedimentation vessel. The upper level of the clarifier's chamber – once considered to be inactive at the sedimentation process – now appears to play an important role in solids removal. A fully developed three-layer flow phenomenon that develops in some cases is proved to promote settling. Therefore, investigation of flow patterns at different operative conditions was carried out. Experiments were conducted in a model of a circular, centre-feed settling tank with continuous operation. Ground hazelnut shells served as the settling matter; in one set of experiments only dye was used. All laboratory runs were filmed and analysed, qualitatively and quantitatively, by means of computer-aided visualisation. The results of the study showed that a determining factor of the conditions favourable for formation of a fully developed three-layer flow is the theoretical densimetric Froude number. If the hydraulic and solid loadings are soundly chosen in accordance with these findings, the clarifier performance can be evidently improved. |
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Keywords: | Clarifier Separation Fluid mechanics Wastewater treatment Visualisation Densimetric Froude number |
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