Wastewater Calculations - Mathematics and Statistics for the Environment - page 686

24.7.1.2 BOD, COD, or SS Loading
When calculating BOD, COD, or SS loading on an aeration process (or any other treatment process),
loading on the process is usually calculated as lb/day. The following equation is used:

BOD, COD, or SS loading (lb/day) = BOD, COD, or SS (mg/L) × Flow (MGD) × 8.34 lb/gal (24.31)

■ EXAMPLE 24.40
Problem: The BOD concentration of the wastewater entering an aerator is 210 mg/L. If the flow to
the aerator is 1,550,000 gpd, what is the lb/day BOD loading?

Solution:

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

BOD = 210 mg/L × 1.55 MGD × 8.34 lb/gal = 2715 lb/day

■ EXAMPLE 24.41
Problem: The flow to an aeration tank is 2750 gpm. If the BOD concentration of the wastewater is
140 mg/L, how many pounds of BOD are applied to the aeration tank daily?

Solution: First convert the gpm flow to gpd flow:

2750 gpm × 1440 min/day = 3,960,000 gpd

Then calculate lb/day BOD:

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

= 140 mg/L × 3.96 MGD × 8.34 lb/gal

= 4624 lb /day

24.7.1.3 Solids Inventory
In the activated biosolids process, it is important to control the amount of solids under aeration. The
suspended solids in an aeration tank are called mixed liquor suspended solids (MLSS). To calculate
the pounds of solids in the aeration tank, we need to know the mg/L MLSS concentration and the
aeration tank volume. Then lb MLSS can be calculated as follows:

MLSS (lb) = MLSS (mg/L) × Volume (MG) × 8.34 lb/gal (24.32)

■ EXAMPLE 24.42
Problem: If the mixed liquor suspended solids concentration is 1200 mg/L, and the aeration tank
has a volume of 550,000 gal, how many pounds of suspended solids are in the aeration tank?

Solution:

MLSS (lb) = MLSS (mg/L) × volume(MG) × 8.34 lb/g al

= 1200 mg/L × 0.550 MG × 8.34 lb/gal

= 5504 lb