Wastewater Calculations - Mathematics and Statistics for the Environment - page 701

24.9.2 t reatment p ond p roCess C ontrol C alCulations
Although there are no recommended process control calculations for the treatment pond, several
calculations may be helpful in evaluating process performance or identifying causes of poor perfor-
mance. These include hydraulic detention time, BOD loading, organic loading rate, BOD removal
efficiency, population loading, and hydraulic loading rate. In the following, we provide a few cal-
culations that might be helpful in pond performance evaluation and identification of causes of poor
process performance along with other calculations and equations that may be helpful.

24.9.2.1 Hydraulic Detention Time (Days)

(ac-ft)
Influent flow (ac-ft/day)

Pond volume

Hydraulic detention time (days) = (24.78)

Key Point: Hydraulic detention time for stabilization ponds normally ranges from 30 to 120 days.

■ EXAMPLE 24.56
Problem: A stabilization pond has a volume of 54.5 ac-ft. What is the detention time in days when
the flow is 0.35 MGD?

Solution:

Flow = 0.35 MGD × 3069 ac-ft/MG = 1.07 ac-ft/day

54.5 ac-ft
1.07 ac-ft/

Detentiontime(days) = = 51 days

day

24.9.2.2 BOD Loading
When calculating BOD loading on a wastewater treatment pond, the following equation is used:

BOD (lb/day) = BOD (mg/L) × Flow (MGD) × 8.34 lb/gal (24.79)

■ EXAMPLE 24.57
Problem: Calculate the BOD loading (lb/day) on a pond if the influent flow is 0.3 MGD with a BOD
of 200 mg/L.

Solution:

BOD (lb/day) = BOD × Flow × 8.34 lb/gal = 200 mg/L × 0.3 MGD × 8.34 lb/gal = 500 lb/day

24.9.2.3 Organic Loading Rate
Organic loading can be expressed as pound of BOD per acre per day (most common), pounds of
BOD per acre-foot per day, or people per acre per day.

BOD(m g/L) × influent flow (MGD) × 8.34

Organicloading rate (lbBOD/ac/day) = (24.80)

Pond area (ac )

Key Point: The organic loading rate normally ranges from 10 to 50 lb BOD per day per acre.