Wastewater Calculations - Mathematics and Statistics for the Environment - page 702

■ EXAMPLE 24.58
Problem: A wastewater treatment pond has an average width of 370 ft and an average length of 730
ft. The influent flow rate to the pond is 0.10 MGD with a BOD concentration of 165 mg/L. What is
the organic loading rate to the pond in pounds per day per acre (lb/day/ac)?

Solution:

1ac
43,560 ft

730 ft × 370 ft × = 6.2 ac

2

0.10 MGD × 165 mg/L × 8.34 lb/gal = 138 lb/day

138 lb/day
6.2 ac

= 22.3 lb/day/ac

24.9.2.4 BOD Removal Efficiency
The efficiency of any treatment process is its effectiveness in removing various constituents from
the water or wastewater. BOD removal efficiency is therefore a measure of the effectiveness of the
wastewater treatment pond in removing BOD from the wastewater:

BODremoved(mg/L)
BODtotal (

%BOD removed = × 100

mg/L)

■ EXAMPLE 24.59
Problem: The BOD entering a waste treatment pond is 194 mg/L. If the BOD in the pond effluent
is 45 mg/L, what is the BOD removal efficiency of the pond?

Solution:

BODremoved(mg/L)
BODtotal (

149 mg/L
194 mg/L

%BOD removed = ×= ×= 100 100 77%

mg/L)

24.9.2.5 Population Loading

BOD(mg/ L) × influent flow (MGD) × 8.34

Populationloading (people/ac/day) = (2 4.81)

Pond area (ac)

24.9.2.6 Hydraulic Loading (In./Day) (Overflow Rate)

Influent flow ( ac-in./day)

Pond area (ac)

(24.82)

Hydraulic loading(in./day) =

24.9.3 a erated p onds
Depending on the hydraulic retention time, the effluent from an aerated pond will contain from one-
third to one-half the concentration of the influent BOD in the form of cell tissue (Metcalf & Eddy,
1991). These solids must be removed by settling before the effluent is discharged. The mathemati-
cal relationship for BOD removal in a complete-mix-activated pond is derived from the following
equation: