TM 5-814-3/AFM 88-11, Volume III
Effluent requirements:
# 10 mg/b;
BOD5
# 5 mg/b;
TKN
# mg/b;
NH3-N
# 20 mg/b.
TSS
Waste characteristics:
Y = 0.8 lb solids produced/lb BOD5 removed;
= total sludge produced;
kd = 0.05 day-1.
Clarifier characteristics:
Overflow rate # 450 gpd/sq ft @ Qavg;
Solid loading # 30 lb/sq ft-day.
Flow divided equally into two units in parallel, or Q = 0.5 mgd average daily flow each; the calculation
shown below applies to either unit:
Qavg = 0.5 mgd = 347.2 gpm;
Organic load = 0.5 mgd 250 mg/b 8.34 = 1042.5 lb BOD/day.
b. Calculation of oxidation ditch volume.
Use 20 lb BOD/1,000 cu ft--day;
1042.5 lb/day
' 52,125 cu ft;
V'
20lb/1,000 cu ft&day
Hydraulic detention time = 52,125 7.48 24 ' 18.75 hr.
0.5 106
c. Calculation of rotor requirements.
Rotor mixing requirement = 16,000 gal/ft of rotor; recommended by bakeside Equipment Corporation for
maintaining a channel velocity of 1.0 fps.
52,125 7.48
Length of rotor '
' 24.4; use 25 ft.
16,000
Oxygenation requirement = 2.35 lb O2/lb BOD-recommended for domestic sewage. Assume the
following operating conditions:
RPM = 72;
Immersion = 8 in.
Oxygenation = 3.75 lb O2/hr-ft (from fig C-2), using a 42-in diameter MAGNA rotor.
C-22
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