Geoscience Reference
In-Depth Information
Then calculate the filtration rate:
Flow rate (gpm)
Filter surfa
3947 gpm
45 ft
ft
2
Filtrationrate
=
=
=
4.4 gpm/
2
ce area (ft )
×
20 ft
■
EXAMPLE 23.75
Problem:
A filter is 40 ft long by 20 ft wide. During a test of flow rate, the influent valve to the filter
is closed for 6 min. The water level drop during this period is 16 in. What is the filtration rate for
the filter in gpm/ft
2
?
Solution:
First calculate the gpm flow rate using the
Q
=
A
×
V
equation:
Q
(gpm) = Length (ft) × Width (ft) × Drop velocity (ft/min) × 7.48 ga l /f (ft)
3
= (40 ft × 20 ft × 1.33 ft × 7.48 ga l /f ft
3
)/6 min = 1326 gpm
Then calculate the filtration rate:
Flow rate (gpm)
Filter surfa
1326 gpm
40 ft
ft
2
Filtrationrate
=
=
=
1.6 gpm/
2
ce area (ft )
×
20 ft
23.6.3 u
nit
F
filter
r
un
v
olume
(uFrv)
The unit filter run volume (UFRV) calculation indicates the total gallons passing through each
square foot of filter surface area during an entire filter run. This calculation is used to compare and
evaluate filter runs. UFRVs are usually at least 5000 gal/ft
2
and generally in the range of 10,000
gpd/ft
2
. The UFRV value will begin to decline as the performance of the filter begins to deteriorate.
The equation to be used in these calculations is shown below:
Unit filter run volume = Total gallons iltered/Filter surface area (ft
2
)
(23.68)
■
EXAMPLE 23.76
Problem:
The total water filtered during a filter run (between backwashes) is 2,220,000 gal. If the
filter is 18 ft by 18 ft, what is the unit filter run volume in gal/ft
2
?
Solution:
Unit filter run volume = Total gallons filtered/filter surface area (ft
2
)
= 2,220,000 gal/(18 ft × 18 ft) = 6852 gal/ft
2
■
EXAMPLE 23.77
Problem:
The total water filtered during a filter run is 4,850,000 gal. If the filter is 28 ft by 18 ft,
what is the unit filter run volume in gal/ft
2
?
Solution:
Unit filter run volume = Total gallons filtered/filter surface area (ft
2
)
= 4,850,000 gal/(28 ft × 18 ft) = 9623 gal/ft
2
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