Calculate chemical feed rate (lb/day or gal/day) from dosage, flow rate, and solution strength.
The target concentration of chemical to be added to the water in milligrams per liter (mg/L), equivalent to parts per million (ppm).
mg/L
The volume of water being treated per day in million gallons per day (MGD). 1 MGD = 1,000,000 gal/day = 694.4 GPM.
MGD
The percentage of active ingredient in the chemical product. Use 100% for pure/dry chemicals. Liquid sodium hypochlorite is typically 10-15% strength.
(0.1 - 100)%
Density of the liquid chemical relative to water (water = 1.0). Used to convert weight feed rate to volume. Example: 12.5% sodium hypochlorite has SG of about 1.17.
SG
Results
Dry Feed Rate-lb/day
Dry Feed Rate-kg/day
Liquid Feed Rate-gal/day
Liquid Feed Rate-mL/min
Actual Chemical Used-lb/day
Formulas & References
Dry Feed Rate (lb/day) = Dose (mg/L) x Flow (MGD) x 8.34 lb/gal
Actual Chemical (lb/day) = Dry Feed Rate / (Purity / 100)
Liquid Volume (gal/day) = Actual Chemical (lb/day) / (8.34 x Specific Gravity)
The constant 8.34 lb/gal is the weight of one gallon of water.
Reference: AWWA Water Treatment Plant Design, 5th Ed; Sacramento State Water Treatment Operator Handbook