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Gravity thickener analysis and design − a gravity thickener concentrates waste activated
sludge biosolids. Pertinent design and performance data are; waste activated sludge flow
rate = 250,000 gal/day, suspended solids concentration in the thickener influent = 10,000
mg/l, influent sludge specific gravity = 1.002, thickened sludge solids concentration =
25,000 mg/l, specific gravity of the thickened sludge = 1.005, supernatant suspended
solids concentration = 800 mg/l, supernatant specific gravity = 1.000, design overflow
rate = 600 gpd/ft2, design solids loading rate = 5.0 lb/day/ft2 Determine;
(a) thickened sludge flow rate (gal/day)
(b) diameter of the thickener (ft)
(c) thickener solids capture, Sc, which is defined as the fraction (or percentage) of the
influent suspended solids retained in the thickened sludge, i.e.,
Sc = mTSS,sludge / mTSS,i . Notice, then, that the fraction of the influent suspended
solids escaping in the thickener supernatant is (1−Sc).
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