Wastewater math
Chlorine dose in mg/L from demand and residual, and the feed rate in lb/day from the flow and the product's purity.
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The formula
Dose, mg/L = Demand, mg/L + Residual, mg/LOperator Master Disinfection course, Chlorine Demand page: demand is the difference between the applied dose and the residual
Feed Rate, lb/day = (Dosage, mg/L)(Flow, MGD)(8.34 lb/gal) ÷ Purity (decimal)WPI Formula/Conversion Table (2023), Printed page 2 of 10, Feed Rate, lb/day
Worked example
Chlorine demand is 6.5 mg/L and you want a 1.5 mg/L residual at 2.5 MGD. How many lb/day of 65% calcium hypochlorite do you feed?
Add demand and residual for the dose: 6.5 mg/L + 1.5 mg/L = 8.0 mg/L.
Find pounds of pure chlorine: 8.0 mg/L × 2.5 MGD × 8.34 lb/gal = 166.8 lb/day.
Divide by the purity as a decimal: 166.8 lb/day ÷ 0.65 = 256.6 lb/day.
Answer: 256.6 lb/day of 65% calcium hypochlorite
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