CIVIL ENGINEERING FORMULAS

372 CHAPTER THIRTEEN

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

(13.45)

Also, overall efficiency E 1 E 2 (1 – E 1 ); and E 1 E 2. (13.46)

whereE 1 the efficiency of the first filter stage, including recirculation and set-
tling (%)
E 2 the efficiency of the second filter stage, including recirculation and
settling (%)

For a single stage or first stage rock trickling filter, the NRC equation is

(13.47)

whereWBOD 5 loading to the filter, lb/d (kg/d)
Vvolume of the filter media, 10^3 ft^3 (m^3 )
Frecirculation factor

Recirculation factor represents the average number of passes of the influent
organic matter through the trickling filter. The recirculation factor is

F (13.48)

1 R

[1(R10)]^2

E 1 

100

1 0.0561

B

W

VF

Overall efficiency

influent BOD 5 effluent BOD 5

influent BOD 5

 100

FIGURE 13.5 Two-stage trickling filter process flow schematics. (Hicks—Handbook of

Civil Engineering Calculations, McGraw-Hill.)

Recycle

Influent

Influent

Primary

clarifier

Primary

clarifier

First-

stage

filter

First-

stage

filter

Recycle Recycle

Effluent

Clarifier

Second-

stage

filter

Second-

stage

filter

Clarifier

Clarifier

Effluent

Recycle