A Rational Design Procedure for Aerated Lagoons
495
320
I
2
3
tj or t£ (days)
Fig.5. Effluent BOD from Basin 1 versus Time in either Basin
compute the retention time (t 2 ) required to reduce the BOD to the desired concentration
(Sei ->Se 2 ).
8. Estimate Xv in Basin Two (this estimate will be equal to Xv from Basin One plus
approximately one-half the BOD removed in Basin Two).
9. Check the assumed basin temperature in Equation (14) and recalculate as per step (7)
if required. Plot the detention time of Basin Two (t 2 ) as a function of the influent BOD
from Basin One (Sex). See Fig.5.
10. Compute the total retention time as t x + t 2 and plot versus tj as shown in Fig.5.
Select another detention time for Basin One and repeat steps 6 through 9. A minimum
total retention time will be established as shown in Fig.5.
11. Select the minimum total detention time from Fig.5 as the design period.
12. Compute the oxygen requirements from Equation (10). In actual practice summer
conditions will control oxygen requirements based on higher BOD removals, bottom
deposit feedback, and greater oxygen solubility.
13. Calculate the required horsepower. If surface aerators are to be used the oxygenation
efficiency is:
N
= N„
C S W "
C L . q . l . 0 2 (
T -
2 Q )
9.1
(15)
and
N 0 = KP V + N s
(16)