Water and Wastewater Conveyance by Frank R. Spellman

Author:Frank R. Spellman
Language: eng
Format: epub
Publisher: CRC Press

TRANSPORT OF SEWER SOLIDS

Sewer flow-carrying velocities for solid-phase matter were first evaluated at a sewer pilot system in 1967 (FMC, 1967a). Results indicated that the flow velocity for resuspension of the settled solids was much greater than the flow velocity in which solids would settle (i.e., solids resuspension ≥ 0.44 m/s [1.44 ft/s] vs. solids settling < 0.27 m/s [0.88 ft/s]). Microscopic examination of the sewer sediment samples collected from the test pilot sewer line found sand-like particles with a size range of 40 to 900 µm with a specific gravity range of 2.4 to 2.6. These particles required the highest flow velocity to be resuspended from the bottom of the test sewer line. Another investigation was conducted to determine the settling characteristics (including size and specific gravity distributions) of solids in sanitary wastewater, CSO, and stormwater runoff (Dalrymple et al., 1975). The settling velocity distributions for road dust (10 to 20 µm) and wastewater solids (74 to 149 µm) appeared to relate to Stokes’ law for spherical particles at these size ranges. According to Stokes’ law, for Reynolds numbers (Re) < 1, particle settling velocity (vs) can be expressed as

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