Also, overall efficiency = El+ E 2 (I -E 1 ), and E 1 =E 2.where E 1 = The efficiency of the first filter stage, including recirculation and settling (%)
E 2 = The efficiency of the second filter stage, including recirculation and settling
(%)Substituting E 1 for E 2 , setting up as a quadratic equation, and solving for E 1 :E\ - 2E 1 + 0.917 = O = E 1 = 0.712 or 71.2%Therefore, the efficiency of each trickling filter stage is 71.2 percent.
- Analyze the first stage filter
For a single stage or first stage rock trickling filter, the NRC equation is
100
El= 1+0.0561 /E
V VFwhere W= BOD 5 loading to the filter, Ib/d (kg/d)
V= Volume of the filter media, 103 ft^3 (m^3 )
F= Recirculation factor
2a. Compute the recirculation factor of the filter
Recirculation factor represents the average number of passes of the influent organic mat-
ter through the trickling filter. The recirculation factor is calculated using
F=
1+
*
[1 + (fl/10)]
2where R = Recirculation ratio = QJQ
Qr = Recirculation flow
Q = Wastewater flow
Using values from above, the recirculation factor is
F=_JL±2__=^208
[1+(2/1O)]^2
2b. Compute the BOD 5 loading for the first stage filter
The BOD 5 loading for the first stage filter is calculated using
W - (Influent BOD 5 , mg/L)(Wastewater flow, Mgd)(8.34 Ib/Mgal/mg/L)Using values from above, the BOD 5 loading for the first stage filter is
W= (240 mg/L)(1.0 Mgd)(8.34) - 2,002 Ib BOD 5 /d (908.9 kg/d)2c. Compute the volume and diameter of the first stage filter
Therefore, the volume of the first stage trickling filter is calculated as follows: