Science of Water : Concepts and Applications

Water Treatment Calculations 341
Solution:
Polymer (lbday) ( 12 mgL)(4.15 MGD)(8.34 lbgal) 415 lb/day
Determining Chemical Solution Feeder Setting, gpd
When solution concentration is expressed as lb chemical/gal solution, the required feed rate can be
determined using the following equations:
Chemical, lbday (chemical, mgL)(flow, MGD)(8.34 lbgal) Then convert the lb/day dry chemical into gpd solution:
Example 10.30
chemical (lb day)
Solution (gpd)
lb chemical gal solution
(10.26)
(10.27)
Problem:
Jar tests indicate that the best alum dose for a water sample is 7 mg/L. The amount to be treated is
1.52 MGD. Determine the gpd setting for the alum solution feeder if the liquid alum contains 5.36 lb
of alum per gallon of solution.
Solution:
First calculate the lb/day of dry alum required, using the mg/L to lb/day equation:
Then calculate the gpd solution required.
Dry alum, lb/day ( mgL)(flow, MGD)(8.34 lbgal) ( 7 mgL)(1.52 MGD)(8.34 lbgal) 89 lb day
89 lbday Alum solution (gpd)
5.36 lb alumgal solution
16.6 gpd
Determining Chemical Solution Feeder Setting, mL/min
Some solution chemical feeders dispense chemical as milliliters per minute (mL/min). To calculate
the mL/min solution required, use the following procedure:
Example 10.31
(gpd)(3785 mLgal) Solution, mLmin
1440 minday (10.28)
Problem:
The desired solution feed rate was calculated to be 9 gpd. What is this feed rate expressed as mL/min?