TM 5-814-3/AFM 88-11, Volume III
Winter conditions--In areas that experience prolonged cold and/or icing, windbreaks or dome covers for
trickling filters to prevent freezing problems will be considered. Consult TM 5-852-5/AFR 88-19, volume
5, for further information on the design of trickling filters for cold climates.
f. Plant efficiencies. Performance efficiencies, given as biochemical oxygen demand removal, or single-
stage and two-stage filters are to be estimated using formulas in the following section.
(1) National Research Council (NRC) formulas. The NRC formulas have resulted from extensive
analysis of operational records from stone-media trickling filter plants serving military installations. Since
these formulas are based on military installation data, they will be used to design all stone-media trickling
filters for military installations. Based on its data analyses, NRC developed the following formulas for
predicting the stone-media trickling filter performance at 20EC.
First of Single Stage:
100
E1 '
(eq 12-2)
1 % 0.0085(W/VF)0.5
Second Stage (includes intermediate clarifier):
100
E2 '
(eq 12-3)
0.0085
1%
1 & E1 (W )/VF)0.5
where:
E1
=
Percent BOD removal efficiency through the first or single-stage filter and clarifier;
W
=
BOD loading (lb/day) to the first or single-stage filter, not including recycle;
V
=
Volume of the particular filter stage (acre-ft);
F
=
Recirculation for a particular stage, where:
1%R
F'
(1 % 0.1R)2
Recirculation Flow
R=
Recirculation ratio =
Plant Influent Flow
E2 =
Percent BOD removal through the second-stage filter and clarifier;
W' =
BOD loading (lbs/day) to the second-stage filter, not including recycle.
A sample problem utilizing the NRC formula is presented in appendix C.
(2) Other design formulas. Other design formulas have been developed and used for design of
trickling filters and for performance prediction. Such expressions include the Ten-States Standards Formula
and those of Velz, Schulze, Germain, Galler and Gotaas, and Eckenfelder. Detailed descriptions and
evaluations of these formulas are presented in the Manual of Practice No. 8, published by the Water Pollution
Control Federation. Although the NRC formula is required for design of stone-media filters, the following
formula is appropriate for stacked synthetic media filters. Equation (12-4) is incomplete. Check Manual of
Practice No. 8.
(eq 12-4)
0(T&20)K20D
&
Qn
Le
'e
Lo
0=
Temperature constant equal to 1.035;
L0=
BOD of primary effluent (not including recirculation);
12-6
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