Geoscience Reference
In-Depth Information
Over a given period, the average grit removal rate at a plant (at least a seasonal average) can be
determined and used for planning purposes. Typically, grit removal is calculated as cubic yards
because excavation is normally expressed in terms of cubic yards:
3
Totalgrit (ft )
27 ft /yd
3
Grit (yd)
=
(24.7)
3
■
EXAMPLE 24.6
Problem:
A treatment plant removes 10 ft
3
of grit in one day. How many ft
3
of grit are removed per
million gallons if the plant flow is 9 MGD?
Solution:
3
3
Grit volume (ft )
Flow (MG)
10
ft
9MG
3
Grit removed
=
=
=
1.1 ft /MG
■
EXAMPLE 24.7
Problem:
The total daily grit removed for a plant is 250 gal. If the plant flow is 12.2 MGD, how
many cubic feet of grit are removed per MG flow?
Solution:
First, convert gallon grit removed to ft
3
:
(250 gal) ÷ (7.48 gal/ft
3
) = 33 ft
3
Next, complete the calculation of ft
3
/MG:
3
3
Grit volume (ft )
Flow (MG)
ft
12.2 MG
33
3
Grit removed
=
=
=
2.7 ft /MG
■
EXAMPLE 24.8
Problem:
The daily average grit removal is 2.5 ft
3
/MG. If the monthly average flow is 2,500,000
gpd, how many cubic yards must be available for grit disposal if the disposal pit is to have a 90-day
capacity?
Solution:
First, calculate the grit generated each day:
(2.5 ft
3
/MG) × (2.5 MGD) = 6.25 ft
3
each day
The ft
3
grit generated for 90 days would be
(6.25 ft
3
/day) × (90 days) = 562.5 ft
3
Convert ft
3
to yd
3
grit:
(562.5 ft
3
) ÷ (27 ft
3
/yd
3
) = 21 yd
3
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