Marine Wastewater Discharges from Multiport Diffusers. I: Unstratified Stationary Water |
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Authors: | Xiaodong Tian Philip J. W. Roberts Gregory J. Daviero |
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Affiliation: | 1Postdoctoral Researcher, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, 30332. 2Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, 30332. 3Malcolm Pirnie, Inc., 104 Corporate Park, Dr., White Plains, NY 10602-0751
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Abstract: | Laboratory experiments on the near-field mixing of buoyant plumes discharged from multiport diffusers into unstratified stationary water are reported. Dilution was measured by a newly developed three-dimensional laser-induced fluorescence system and a microconductivity probe. Significant additional mixing (and dilution) occurs beyond the point where the plume impacts the water surface. This mixing ceases when the turbulence generated by the plumes collapses in the surface spreading layer. The port spacing, s, was varied through a range encompassing line to point source conditions. In all cases, the concentration distribution in the surface layer eventually becomes laterally uniform. Measurements of the near-field dilution, length, and layer thickness, and semiempirical equations to predict them are presented. The discharge behaves as a line plume when s/H ? 0.3, and as a point plume when s/H ≥ 1.0. The additional near-field mixing for a point plume is much greater than for a line plume. Basing diffuser design on near-field dilution rather than impact-point dilution allows the use of far fewer ports, or risers, with considerable potential cost savings, particularly for tunneled outfalls. |
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Keywords: | Ocean disposal Outfall sewers Wastewater disposal Model studies Dilution Multi-port diffuser |
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