TM 5-814-3/AFM 88-11, Volume III
1
E2 '
0.5
W
1 % 0.0085
VF
1
0.31 '
0.5
1,085
1 % 0.0085
2.08V
V = 0.122 acre ft;
0.122 43,560 = 886 sq ft; use 1 filter.
Filter area A =
6
Filter diameter D = 33.6 ft; use 35 ft filter.
The design of a two--stage system requires careful economic considerations to insure that minimal filter
volume is required and that proper recirculation rates are selected to optimize filter volume and pumping
requirements, resulting in the lowest--cost, most flexible system.
C-7. Plastic media trickling filters. (Refer to para 12-2f[2].)
a. Design requirements and criteria. Design a plastic media trickling filter to treat 0.2 mgd of primary
settled effluent, assuming the following conditions:
Raw wastewater BOD = 250 mg/L;
Primary clarifier BOD removal efficiency = 30 percent;
Required final effluent BOD = 25 mg/L;
Winter design temperature = 10EC.
b. Calculations and results. The formula presented in paragraph 12-2f(2) states the following: Le and
Lo in units of mg/L; K20 as day_1; D as ft; and Q as gpm/sq ft.
(eq C-16)
t&20
& (O )K20 D
Le
' exp
Qn
Lo
The raw waste BOD = 250 mg/b; 30 percent removal is obtained in the primary clarifiers; therefore:
Lo = 250 (1 -- 0.3) = 175 mg/L;
Le = 25 mg/L, based on local, state or Federal requirements.
Assume a filter depth of 12 ft:
&[1.0353(10&20)](0.088)(12)
25
' exp
Q 0.67
175
therefore,
&0.75
0.143 ' exp
Q 0.67
C-20
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