Settling Tank - Dimension 2


2. Determine the Depth of Final Settling Tank

     Depth = clarifying depth + thickening depth + sludge storage

     a). Depth for clarifying

     DT = 2 hr for average flowrate

     SOFR DT = 550 1.547 10-6 2 3,600 = 6.2 ft

SOFR(gal/ft2d) DT(hr)

(ft)

     b). Depth for thickening

     The mass of sludge required to thicken = (1 + R)Q MLSS DT(clarifying)

     Consider thickening zone average sludge concentration: MLSSA = (2,500 + 7,000)/2 = 4,750 mg/l

R DT(hr) MLSS(mg/l) MLSSr Q(gal/day) Area(ft2)

(ft)

     c). Depth for storage

     Storage zone is provided to handle the excess sludge produced when sustained peak mass loading and flowrate occurs and if the capacity of sludge-processing facilities is not enough.

     Select two days storage capacity

     Total storage sludge = 2(days) Qp/QAd QW   = 2 10/5 QW  = 4 2,655 = 10,620 (lb)

     Consider MLSSr = 6,000 mg/l

#of Days Qp/QAd MLSSr QW(lb/day) Area(ft2)

(ft) Total Weight of Storage Sludge(lb)

     4). Depth of the settling tank

     Depth = h1 + h2 + h3 = 6.2 +3.3 + 2.2 = 11.7 (ft) 12 (ft)

3. Dimension of Settling Tank

     4 tanks

     A = 14,000/4 = 3,500 ft2

     W = 25'

     L = 140'

     L : W = 1,140 : 25 = 5.6 : 1

     D = 12'

     Ok for the design

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