WTO Chemical Feed Systems & Dosing 1 — Questions and Answers
Question 1: What is the standard conversion factor used to calculate chemical feed rates in pounds per day from a dosage in mg/L and flow in MGD?
- 3.785
- 8.34 (Correct answer)
- 7.48
- 2.31
Correct answer: 8.34
The factor 8.34 lb/gal is the weight of one gallon of water, used in the formula: Dose (mg/L) × Flow (MGD) × 8.34 = Feed rate (lbs/day).
Question 2: A treatment plant processes 3 MGD and must apply 12 mg/L of alum. How many pounds of alum are required per day?
- 250.0 lbs/day
- 300.0 lbs/day
- 300.24 lbs/day (Correct answer)
- 360.0 lbs/day
Correct answer: 300.24 lbs/day
Using the formula Dose × Flow × 8.34: 12 mg/L × 3 MGD × 8.34 = 300.24 lbs/day.
Question 3: Which type of chemical feeder is most appropriate for feeding powdered activated carbon (PAC)?
- Solution feeder
- Gas feeder
- Dry chemical feeder (Correct answer)
- Peristaltic pump
Correct answer: Dry chemical feeder
Dry chemical feeders are designed to accurately meter powdered or granular chemicals such as PAC into the treatment stream.
Question 4: What is the primary purpose of a day tank in a chemical feed system?
- To store bulk chemicals for long-term use
- To dilute concentrated chemicals and provide a measured daily supply (Correct answer)
- To neutralize chemical spills in the feed area
- To measure chemical demand in the raw water
Correct answer: To dilute concentrated chemicals and provide a measured daily supply
Day tanks hold a diluted chemical solution prepared for approximately one day's use, ensuring consistent and safe dosing to the process.
Question 5: What is the EPA-recommended target concentration for fluoride in drinking water, updated in 2015?
- 1.0 mg/L
- 0.5 mg/L
- 0.7 mg/L (Correct answer)
- 1.5 mg/L
Correct answer: 0.7 mg/L
The EPA updated the recommended fluoride level to 0.7 mg/L in 2015 to prevent dental fluorosis while still providing cavity protection.
Question 6: A solution feeder pumps 60 gallons per day of a 5% sodium hypochlorite solution. What is the daily feed rate in pounds of hypochlorite solution?
- 3.0 lbs/day
- 15.0 lbs/day
- 25.0 lbs/day
- 25.02 lbs/day (Correct answer)
Correct answer: 25.02 lbs/day
Multiply volume by the weight of water and the solution concentration: 60 gal/day × 8.34 lb/gal × 0.05 = 25.02 lbs/day.
Question 7: Which chemical is commonly used as a primary coagulant in water treatment?
- Sodium fluoride
- Ferric sulfate (Correct answer)
- Potassium permanganate
- Sodium hydroxide
Correct answer: Ferric sulfate
Ferric sulfate is a primary coagulant that destabilizes negatively charged suspended particles, allowing them to aggregate for removal.
WTO Chemical Feed Systems & Dosing 1
What is the standard conversion factor used to calculate chemical feed rates in pounds per day from a dosage in mg/L and flow in MGD?