WTO Chemical Feed Systems & Dosing 2 — Questions and Answers
Question 1: What type of pump is most commonly used for metering chemicals in water treatment plants?
- Centrifugal pump
- Diaphragm metering pump (Correct answer)
- Vertical turbine pump
- Submersible pump
Correct answer: Diaphragm metering pump
Diaphragm metering pumps deliver accurate, adjustable flow rates at high pressures, making them ideal for precise chemical dosing.
Question 2: Which chemical is typically added to water to raise pH for corrosion control in the distribution system?
- Carbon dioxide
- Sulfuric acid
- Lime (calcium hydroxide) (Correct answer)
- Alum
Correct answer: Lime (calcium hydroxide)
Lime increases water pH, which reduces corrosion of distribution system pipes and limits lead and copper leaching into drinking water.
Question 3: When a 150-lb chlorine cylinder is being connected and there is risk of chlorine gas release, which personal protective equipment is required?
- Latex gloves and safety glasses
- SCBA or supplied-air respirator with full-face protection (Correct answer)
- Dust mask and chemical splash goggles
- Face shield and chemical-resistant gloves only
Correct answer: SCBA or supplied-air respirator with full-face protection
Chlorine gas is immediately dangerous to life and health (IDLH) at 10 ppm; SCBA or supplied-air respirators with full-face protection are required.
Question 4: A gas chlorinator feeds at 8 lbs/day and plant flow is 2 MGD. What is the applied chlorine dose in mg/L?
- 0.48 mg/L (Correct answer)
- 0.96 mg/L
- 1.20 mg/L
- 4.17 mg/L
Correct answer: 0.48 mg/L
Dose (mg/L) = Feed rate ÷ (Flow × 8.34): 8 lbs/day ÷ (2 MGD × 8.34) = 8 ÷ 16.68 = 0.48 mg/L.
Question 5: What does 'flow-paced' chemical feeding mean?
- Feeding chemicals at a fixed rate regardless of flow changes
- Automatically adjusting chemical feed rate proportional to plant flow (Correct answer)
- Feeding chemicals only during peak flow periods
- Manually adjusting the feed rate once per shift
Correct answer: Automatically adjusting chemical feed rate proportional to plant flow
Flow-paced feeders automatically vary the chemical feed rate in direct proportion to water flow, maintaining a consistent dose as flow changes.
Question 6: Which chemical is used as an oxidizing agent for taste and odor control and iron/manganese removal in water treatment?
- Sodium fluoride
- Calcium hypochlorite
- Potassium permanganate (Correct answer)
- Ferric chloride
Correct answer: Potassium permanganate
Potassium permanganate (KMnO4) is a strong oxidizer used to remove iron, manganese, and hydrogen sulfide and to control taste and odor.
Question 7: Sodium hypochlorite solution degrades most rapidly when exposed to which conditions?
- Low temperatures and darkness
- High temperature and direct sunlight (Correct answer)
- Neutral pH and cool temperatures
- High pressure and low humidity
Correct answer: High temperature and direct sunlight
Heat and UV light accelerate decomposition of sodium hypochlorite, reducing available chlorine concentration over time.
WTO Chemical Feed Systems & Dosing 2
What type of pump is most commonly used for metering chemicals in water treatment plants?