## 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/ft2·d) 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

If you have any suggestion, please email Professor Roy at droy@poly.edu