Environmental Engineering Reference
In-Depth Information
Milligrams per liter (mg/L)
Pounds per day (lb/day)
To convert from mg/L (or ppm) concentration to lb/day, we use Equation 16.20:
Chlorine (lb/day) = Chlorine (mg/L) × Flow (MGD) × 8.34 lb/gal
(16.20)
Note: At one time, it was normal practice to use the expression parts per million
(ppm) as an expression of concentration, as 1 mg/L = 1 ppm; however, current
practice is to use mg/L as the preferred expression of concentration.
Example 16.21
Problem: Determine the chlorinator setting (lb/day) required to treat a flow of 8
MGD with a chlorine dose of 6 mg/L.
Solution:
Chlorine (lb/day) = Chlorine (mg/L) × Flow (MGD) × 8.34 lb/gal
Chlorine (lb/day) = 6 mg/L × 8 MGD × 8.34 lb/gal = 400 lb/day
Example 16.22
Problem: What should the chlorinator setting be (in lb/day) to treat a flow of 3 MGD
if the chlorine demand is 12 mg/L and a chlorine residual of 2 mg/L is desired?
Note: The chlorine demand is the amount of chlorine used in reacting with vari-
ous components of the wastewater such as harmful organisms and other organic
and inorganic substances. When the chlorine demand has been satisfied, these
reactions stop.
Solution: Remember that
Chlorine (lb/day) = Chlorine (mg/L) × Flow (MGD) × 8.34 lb/gal
To find the unknown value of lb/day, we must first determine chlorine dose. To do
this we must use Equation 16.21:
Chlorine dose (mg/L) = Chlorine demand (mg/L) + Chlorine residual (mg/L)
(16.21)
Chlorine dose = 12 mg/L + 2 mg/L = 14 mg/L
Then we can make the mg/L to lb/day calculation:
Chlorine (lb/day) = 12 mg/L × 3 MGD × 8.34 lb/gal = 300 lb/day
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