Geoscience Reference
In-Depth Information
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EXAMPLE 23.105
Problem:
A chlorinator setting is 30 lb per 24 hr. If the flow being chlorinated is 1.25 MGD, what
is the chlorine dosage expressed as mg/L?
Solution:
Chlorine (lb/day) = Chlorine (mg/L) × Flow (MGD) × 8.34 lb/gal
30 lb/day =
x
mg/L × 1.25 MGD × 8.34 lb/gal
x
= 30/(1.25 × 8.34) = 2.9 mg/L
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EXAMPLE 23.106
Problem:
A flow of 1600 gpm is to be chlorinated. At a chlorinator setting of 48 lb per 24 hr, what
would be the chlorine dosage in mg/L?
Solution:
Convert the gpm flow rate to MGD flow rate:
1600 gpm × 1440 min/day = 2,304,000 gpd = 2.304 MGD
Now calculate the chlorine dosage in mg/L:
Chlorine (lb/day) = Chlorine (mg/L) × Flow (MGD)
48 lb/day =
x
mg/L × 2.304 MGD × 8.34 lb/gal
x
= 48/(2.304 × 8.34) = 2.5 mg/L
23.7.3 C
alCulating
C
hlorine
d
ose
, d
emand
,
and
r
esidual
Common terms used in chlorination include the following:
•
Chlorine dose—
The amount of chlorine added to the system. It can be determined by
adding the desired residual for the finished water to the chlorine demand of the untreated
water. Dosage can be either milligrams per liter (mg/L) or pounds per day (lb/day). The
most common is mg/L:
Chlorine dose (mg/L) = Chlorine demand (mg/L) + Chlorine residual (mg/L)
(23.88)
•
Chlorine demand
—The amount of chlorine used by iron, manganese, turbidity, algae, and
microorganisms in the water. Because the reaction between chlorine and microorganisms
is not instantaneous, demand is relative to time; for example, the demand 5 min after
applying chlorine will be less than the demand after 20 min. Demand, like dosage, is
expressed in mg/L:
Chlorine demand (mg/L) = Chlorine dose (mg/L) - Chlorine residual (mg/L)
The following examples illustrate the calculation of chlorine dose, demand, and residual using
Equation 23.88.
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EXAMPLE 23.107
Problem:
A water sample is tested and found to have a chlorine demand of 1.7 mg/L. If the desired
chlorine residual is 0.9 mg/L, what is the desired chlorine dose in mg/L?
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