CIVIL ENGINEERING FORMULAS

376 CHAPTER THIRTEEN

Adjustment for depth. The treatability constant is then adjusted from the
standard depth of 20 ft (6.1 m) to the example filter depth of 25 ft (7.6 m) using
the following equation:

(13.62)

wherek30/25treatability constant at 30°C (86°F) and 25 ft (7.6 m) filter depth
(as example value)
k30/20treatability constant at 30°C (86°F) and 20 ft (6.1 m) filter depth
D 1 depth of reference filter (20 ft) (6.1 m)
D 2 depth of actual filter (25 ft) (7.6 m) (as example value)
xempirical constant (0.3 for plastic medium filters)

The empirical formula used for sizing plastic media trickling filters is

(13.63)

where SeBOD 5 of settled effluent from trickling filter (mg/L)
SiBOD 5 of influent wastewater to trickling filter (mg/L)
k 20 treatability constant adjusted for wastewater temperature and filter
depth(k30/25)
Ddepth of filter (ft)
Qvvolumetric flowrate applied per unit of filter area (gal/minsq ft)
(L/sm^2 )Q/A
Qflowrate applied to filter without recirculation (gal/min)(L/s)
Aarea of filter (sqft) (m^2 )
nempirical constant (usually 0.5)

Rearranging and solving for the trickling filter area (A):

(13.64)

The hydraulic loading of the filter in gpm/ft^2 , or L/sm^2 is

Hydraulic loading Q/A (13.65)

For plastic media trickling filters, the hydraulic loading ranges from 0.2 to
1.20 gal/minsqft (0.14 to 0.82 L/sm^2 ).
The organic loading to the trickling filter is calculated by dividing the BOD 5
load to the filter by the filter volume as follows:

Organic loading BOD 5 /(A) (filter length, ft) (13.66)

For plastic media trickling filters, the organic loading ranges from 30 to
200 lb/10^3 ft^3 d (146.6 to 977.4 kg/m^2 d).
To optimize the treatment performance of a trickling filter, there should be a
continual and uniform growth of biomass and sloughing of excess biomass; to

AQ

ln(Se/Si

(k30/25)D

1/n

Se

Si

exp[kD(Qv)n]

k30/25k30/20(D 1 /D 2 )x