A treatment plant uses 318 lb/d of chlorine and treats 23.4 ft^3/s. The resulting chlorine dose is approximately which mg/L?

• A. 2.52 mg/L
• B. 0.40 mg/L
• C. 175.4 mg/L
• D. 2542.0 mg/L

Answer: (A)

Dose in mg/L is found by dividing the mass of chlorine applied per day by the volume of water treated per day, with both quantities in compatible units.

First convert the amount of chlorine to milligrams per day: 318 pounds per day × 453,592 mg per pound ≈ 144,242,000 mg/day.

Next convert the flow to liters per day: 23.4 ft^3/s × 86,400 s/day × 7.48052 gal/ft^3 × 3.78541 L/gal ≈ 57,238,000 L/day.

Now divide: 144,242,000 mg/day ÷ 57,238,000 L/day ≈ 2.52 mg/L.

So the resulting chlorine dose is about 2.52 mg/L.