Wastewater Calculations - Mathematics and Statistics for the Environment - page 666

Primary Treatment Secondary Treatment

Influent

Air Chlorine Euent

Primary
Settling

Collection
System

Screening &
Comminution

Grit
Chamber

Secondary
Settling

Chlorine
Contact Tank

Aeration

Activated Sludge

Screenings

Grit

Anaerobic
Digester

Sludge
Dewatering

ickener

Sludge
Disposal

FIGURE 24.1 Illustration of a wastewater treatment process providing primary and secondary treatment
using activated sludge process.

3

Screenings (ft )

3

Screenings removed (ft /MG) = (24.2)

Flow (MG)

■ EXAMPLE 24.1
Problem: A total of 65 gal of screenings is removed from the wastewater flow during a 24-hr period.
What is the screenings removal reported as ft 3 /day?

Solution: First convert gallon screenings to cubic feet:

(65 gal)/(7.48 gal/ft 3 ) = 8.7 ft 3 screenings

Then calculate screenings removed as ft 3 /day:

3

8.7 ft
1day

3 3

Screenings removed (ft /day) = = .. 7ft/day 8

■ EXAMPLE 24.2
Problem: During 1 week, a total of 310 gal of screenings was removed from the wastewater screens.
What is the average screenings removal in ft 3 /day?

Solution: First convert gallon screenings to cubic feet:

(310 gal) ÷ (7.48 gal/ft 3 ) = 41.4 ft 3 screenings

Then calculate screenings removed as ft 3 /day:

3

41.4 ft
7days

3 3

Screenings removed (ft /day) = = 5.9 ft /day