Which expression correctly gives Feed Rate (lb/day) using Dose (mg/L), Flow (MGD), and %Purity?

Which expression correctly gives Feed Rate (lb/day) using Dose (mg/L), Flow (MGD), and %Purity?

• A. Dose × Flow × 8.34
• B. Dose × 8.34 × Flow
• C. Dose ÷ Flow × 8.34
• D. Dose × Flow × 8.34 × %Purity

Answer: (D)

To find Feed Rate in pounds per day, you combine how much chemical is needed per liter (the dose), how much water is treated each day (the flow), a conversion factor to turn mg/L over a million gallons into pounds, and the actual purity of the chemical. Dose in mg/L tells you how many milligrams of chemical are needed per liter of water. Flow in MGD tells you how many millions of gallons are treated each day. Multiplying dose by flow gives milligrams per day scaled to the volume being treated. The factor 8.34 converts mg/L over one million gallons into pounds per day, so Dose × Flow × 8.34 yields pounds per day if the chemical were pure. Then multiply by %Purity (as a decimal or fraction) to account for the actual strength of the chemical being fed. Put together, Dose × Flow × 8.34 × %Purity gives the correct feed rate in lb/day. Omitting the purity or misplacing operations would miss either the conversion to pounds or the adjustment for how pure the chemical is, which is why that complete expression is the right choice.

To find Feed Rate in pounds per day, you combine how much chemical is needed per liter (the dose), how much water is treated each day (the flow), a conversion factor to turn mg/L over a million gallons into pounds, and the actual purity of the chemical.

Dose in mg/L tells you how many milligrams of chemical are needed per liter of water. Flow in MGD tells you how many millions of gallons are treated each day. Multiplying dose by flow gives milligrams per day scaled to the volume being treated. The factor 8.34 converts mg/L over one million gallons into pounds per day, so Dose × Flow × 8.34 yields pounds per day if the chemical were pure. Then multiply by %Purity (as a decimal or fraction) to account for the actual strength of the chemical being fed. Put together, Dose × Flow × 8.34 × %Purity gives the correct feed rate in lb/day.

Omitting the purity or misplacing operations would miss either the conversion to pounds or the adjustment for how pure the chemical is, which is why that complete expression is the right choice.