TM 5-814-3/AFM 88-11, Volume III
c. Pumps. Recirculation pumps will be sized to provide constant rate recirculation. Vertical-shaft, single
suction units with motors mounted on top of the pumps, installed in a dry well or on an upper floor, will be
used. Each pump will be provided with its individual pipe connection to the wet well.
C-6. Two stage stone-media trickling filters. (Refer to para 12-2.)
a. Design requirements and criteria. Design a two-stage trickling filter to treat 3.0 mgd of primary
settled effluent, assuming the following conditions.
Raw wastewater BOD5 = 250 mg/L;
Primary clarified BOD removal efficiency = 30 percent;
Required effluent BOD5 = 30 mg/L;
Design temperature = 20EC.
b. Calculations and results.
Primary clairfier effluent BOD = 250 (1 - 0.3 = 175 mg/L;
Overall trickling filter efficiency = 175 & 30 ' 0.828;
175
Filter depth = 6 ft;
Recirculation = 1:2.
Assuming that the first stage filter efficiency = 75 percent:
Overall efficiency = 0.828 = E1 + E2 (1 - E1) = 0.75 + E2 (1 -- 0.75) E2 = 0.31;
1%R
1%2
'
' 2.08;
Recirculation factor F =
2
2
(1 % 0.1R)
1 % 0.1 2)
Organic loading to first stage filter,
W = 3.0 mgd x 8.34 x 250(1 -- 0.30) = 4,379; use 4,380 lb/day.
Now, using the NRC formula:
1
E1 '
0.5
W
1%0.085
VF
0.5
1
4,380
0.75 '
1 % 0.0085 2.08V
V = 1.37 acre ft;
1.35 43,560 = 9,946 sq ft; use 2 filters, 5,000 sq ft each.
Filter area =
6
Filter diameter = 80 ft, use 80 ft (each filter).
Design second stage filter:
Organic loading, W = W (1 - 0.75);
= 4,380 (1 - 0.75);
= 1,095 lb/day.
C-19
Previous Page
