Page 446 - Civil Engineering Formulas

372 CHAPTER THIRTEEN

Recycle Recycle

Influent Primary First- Second- Effluent
clarifier stage stage Clarifier
filter filter

Recycle Recycle

First- Second-
Influent Primary Effluent
stage Clarifier stage Clarifier
clarifier
filter filter
FIGURE 13.5 Two-stage trickling filter process flow schematics. (Hicks—Handbook of
Civil Engineering Calculations, McGraw-Hill.)

The NRC equations for trickling filter performance are empirical equations,
which are primarily applicable to single and multistage rock systems with recir-
culation.
The overall efficiency of the two-stage trickling filter is
influent BOD 5 effluent BOD 5
Overall efficiency 100 (13.45)
influent BOD 5
Also, overall efficiency E E (1 – E ); and E E . (13.46)
1 2 1 1 2
where E the efficiency of the first filter stage, including recirculation and set-
1
tling (%)
E the efficiency of the second filter stage, including recirculation and
2
settling (%)
For a single stage or first stage rock trickling filter, the NRC equation is
100
E 1 (13.47)
W
1 0.0561
BVF
where W BOD loading to the filter, lb/d (kg/d)
5
3
3
3
V volume of the filter media, 10 ft (m )
F recirculation factor
Recirculation factor represents the average number of passes of the influent
organic matter through the trickling filter. The recirculation factor is
1 R
F (13.48)
[1 (R 10)] 2