CWS Iron, Manganese & Hydrogen Sulfide Removal 1 — Questions and Answers
Question 1: What is the EPA secondary maximum contaminant level (SMCL) for iron in drinking water?
- 0.1 mg/L
- 0.3 mg/L (Correct answer)
- 0.5 mg/L
- 1.0 mg/L
Correct answer: 0.3 mg/L
The EPA secondary MCL for iron is 0.3 mg/L; above this level, iron causes staining and aesthetic issues.
Question 2: Which odor is most characteristic of hydrogen sulfide gas in a water supply?
- Musty or earthy smell
- Chlorine bleach odor
- Rotten egg smell (Correct answer)
- Metallic or bitter taste
Correct answer: Rotten egg smell
Hydrogen sulfide (H2S) produces a distinctive rotten egg odor even at very low concentrations.
Question 3: Which form of iron passes through a standard sediment filter without being captured?
- Ferric iron (oxidized particulate)
- Ferrous iron (dissolved) (Correct answer)
- Colloidal iron
- Bacterial iron deposits
Correct answer: Ferrous iron (dissolved)
Ferrous (dissolved) iron remains in solution and cannot be filtered until it is oxidized to ferric (particulate) form.
Question 4: What is the EPA secondary maximum contaminant level (SMCL) for manganese in drinking water?
- 0.01 mg/L
- 0.05 mg/L (Correct answer)
- 0.1 mg/L
- 0.3 mg/L
Correct answer: 0.05 mg/L
The EPA SMCL for manganese is 0.05 mg/L; exceeding this causes black staining and undesirable taste.
Question 5: Which oxidation method is most commonly used to convert dissolved ferrous iron to filterable ferric iron?
- Ultraviolet radiation
- Reverse osmosis
- Aeration (Correct answer)
- Ion exchange
Correct answer: Aeration
Aeration exposes water to oxygen, converting soluble ferrous iron into insoluble ferric iron that can then be filtered.
Question 6: Greensand filtration media is primarily used to remove which group of contaminants from water?
- Nitrates and phosphates
- Iron, manganese, and hydrogen sulfide (Correct answer)
- Chlorine and volatile organic compounds
- Calcium and magnesium hardness
Correct answer: Iron, manganese, and hydrogen sulfide
Greensand (glauconite coated with manganese dioxide) acts as a catalytic oxidizer and filter for iron, manganese, and hydrogen sulfide.
Question 7: What pH range is most favorable for effective oxidation and removal of dissolved iron from water?
- pH 4.0–5.5
- pH 5.5–6.0
- pH 6.0–7.0
- pH 7.0–8.5 (Correct answer)
Correct answer: pH 7.0–8.5
Iron oxidizes and precipitates most efficiently at neutral to slightly alkaline pH (7.0–8.5); low pH keeps iron in solution.
CWS Iron, Manganese & Hydrogen Sulfide Removal 1
What is the EPA secondary maximum contaminant level (SMCL) for iron in drinking water?