CWS Iron, Manganese & Hydrogen Sulfide Removal 2 — Questions and Answers
Question 1: When iron bacteria are confirmed in a water supply, which treatment approach is most appropriate?
- Aeration alone followed by greensand filtration
- Chlorine injection followed by contact time and filtration (Correct answer)
- Water softener regeneration with salt
- Reverse osmosis as the sole treatment
Correct answer: Chlorine injection followed by contact time and filtration
Iron bacteria require disinfection with chlorine (or another oxidant) to destroy the organisms before filtration removes the resulting solids.
Question 2: Potassium permanganate (KMnO4) is used in water treatment primarily to:
- Soften water by removing calcium ions
- Oxidize iron, manganese, and hydrogen sulfide (Correct answer)
- Lower water pH to acceptable levels
- Add beneficial trace minerals to drinking water
Correct answer: Oxidize iron, manganese, and hydrogen sulfide
Potassium permanganate is a strong oxidizer that converts dissolved iron, manganese, and hydrogen sulfide into filterable precipitates.
Question 3: To avoid pink or purple staining of fixtures, how should potassium permanganate dosing be controlled?
- Maintain a slight pink residual in the water
- Achieve complete oxidation with no excess residual (Correct answer)
- Dose as much as possible for maximum effectiveness
- Use only pre-dosed cartridge media with no liquid feed
Correct answer: Achieve complete oxidation with no excess residual
Excess potassium permanganate residual in treated water will stain fixtures pink or purple, so dosing must not exceed what is consumed during oxidation.
Question 4: Birm filtration media removes iron and manganese primarily through which mechanism?
- Ion exchange
- Catalytic oxidation (Correct answer)
- Adsorption onto carbon
- Biological filtration
Correct answer: Catalytic oxidation
Birm uses dissolved oxygen already present in the water as a catalytic oxidizer to convert dissolved metals into filterable particles.
Question 5: A customer reports persistent black staining on fixtures and darkened laundry. Which contaminant is the most likely cause?
- High iron levels above 1.0 mg/L
- High chlorine residual in the water
- Elevated manganese levels (Correct answer)
- Hydrogen sulfide gas
Correct answer: Elevated manganese levels
Manganese oxidizes to form black or brownish-black precipitates that stain fixtures, laundry, and plumbing components.
Question 6: For aeration to effectively oxidize iron, the dissolved oxygen (DO) level in the water should be:
- Below 1 mg/L to avoid over-oxidation
- Above 2 mg/L to support oxidation (Correct answer)
- Exactly 0.5 mg/L for optimal reaction
- Dissolved oxygen level has no effect on iron oxidation
Correct answer: Above 2 mg/L to support oxidation
Adequate dissolved oxygen (above approximately 2 mg/L) is required to drive the oxidation of ferrous iron to ferric iron.
Question 7: Which type of iron filter requires periodic regeneration with a potassium permanganate solution to restore oxidizing capacity?
- Birm filter
- Greensand filter (Correct answer)
- Activated carbon filter
- Sediment cartridge filter
Correct answer: Greensand filter
Greensand media is coated with manganese dioxide, which is depleted over time and must be restored through backwashing and regeneration with potassium permanganate.
CWS Iron, Manganese & Hydrogen Sulfide Removal 2
When iron bacteria are confirmed in a water supply, which treatment approach is most appropriate?