Geoscience Reference
In-Depth Information
23.4.4.3 Determining Dry Chemical Feeder Setting (lb/day)
When adding (dosing) chemicals to the water flow, a measured amount of chemical is called
for. The amount of chemical required depends on such factors as the type of chemical used, the
reason for dosing, and the flow rate being treated. To convert from mg/L to lb/day, the following
equation is used:
Chemical added (lb/day) = Chemical (mg/L) × Flow (MGD) × 8.34 lb/gal
(23.25)
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EXAMPLE 23.28
Problem:
Jar tests indicate that the best alum dose for water is 8 mg/L. If the flow to be treated is
2,100,000 gpd, what should the lb/day setting be on the dry alum feeder?
Solution:
Chemical added = Chemical (mg/L) × Flow (MGD) × 8.34 lb/gal
= 8 mg/L × 2.10 MGD × 8.34 lb/gal = 140 lb/day
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EXAMPLE 23.29
Problem:
Determine the desired lb/day setting on a dry chemical feeder if jar tests indicate an opti-
mum polymer dose of 12 mg/L and the flow to be treated is 4.15 MGD.
Solution:
Polymer (lb/day) = 12 mg/L × 4.15 MGD × 8.34 lb/gal = 415 lb/day
23.4.4.4 Determining Chemical Solution Feeder Setting (gpd)
When solution concentration is expressed as pound chemical per gallon solution, the required feed
rate can be determined using the following equations:
Chemical (lb/day) = Chemical (mg/L) × Flow (MGD) × 8.34 lb/gal
(23.26)
Then convert the lb/day dry chemical to gpd solution:
Solution (gpd) = Chemical (lb/day)/lb Chemical per gal solution
(23.27)
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EXAMPLE 23.30
Problem:
Jar tests indicate that the best alum dose for water is 7 mg/L. The flow 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:
Dry alum = Chemical (mg/L) × Flow (MGD) × 8.34 lb/gal
= 7 mg/L × 1.52 MGD × 8.34 lb/gal = 89 lb/day
Then calculate gpd solution required:
Alum solution = 89 lb/day/5.36 lb alum per gal solution = 16.6 gpd
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