CWS Filtration Media & Technologies 2 — Questions and Answers
Question 1: What is the primary mechanism by which activated carbon removes chloramines from water?
- Ion exchange
- Chemical reduction catalysis (Correct answer)
- Mechanical straining
- Adsorption only
Correct answer: Chemical reduction catalysis
Activated carbon removes chloramines primarily through chemical reduction catalysis, not just adsorption, which is why carbon used for chloramine reduction depletes faster than for chlorine removal.
Question 2: Which filtration media is BEST suited for removing dissolved iron in its ferrous (Fe²⁺) state directly without prior oxidation?
- Greensand
- Birm
- Catalytic carbon (Correct answer)
- Manganese dioxide
Correct answer: Catalytic carbon
Catalytic carbon can reduce dissolved ferrous iron directly through catalytic oxidation, whereas most other media require pre-oxidation to convert Fe²⁺ to Fe³⁺ before filtration.
Question 3: In a multimedia filter, what is the correct layering order from top to bottom?
- Fine sand, anthracite, garnet
- Garnet, fine sand, anthracite
- Anthracite, fine sand, garnet (Correct answer)
- Fine sand, garnet, anthracite
Correct answer: Anthracite, fine sand, garnet
Multimedia filters layer coarse, lighter anthracite on top, then fine sand, then dense garnet at the bottom, allowing coarser solids to be trapped at the top and finer particles deeper in the bed.
Question 4: What is the typical effective size range for sand used in a standard residential sand filter?
- 0.05–0.1 mm
- 0.35–0.5 mm (Correct answer)
- 1.0–2.0 mm
- 2.0–4.0 mm
Correct answer: 0.35–0.5 mm
Standard residential filter sand has an effective size of approximately 0.35–0.5 mm, which provides adequate filtration without excessive head loss.
Question 5: A customer's birm filter is failing to remove iron adequately. The most likely cause is:
- Feed water pH is above 8.5
- Dissolved oxygen in feed water is below 15% saturation (Correct answer)
- Flow rate is too low
- Backwash frequency is too high
Correct answer: Dissolved oxygen in feed water is below 15% saturation
Birm requires a minimum dissolved oxygen level of about 15% saturation to catalyze iron oxidation; insufficient DO is the most common cause of poor iron removal performance.
Question 6: Which characteristic is described by the 'uniformity coefficient' (UC) of a filter media?
- The ratio of the d60 to d10 particle sizes (Correct answer)
- The ratio of the d90 to d50 particle sizes
- The percentage of media retained on a #20 sieve
- The bulk density relative to silica sand
Correct answer: The ratio of the d60 to d10 particle sizes
The uniformity coefficient is d60/d10, where d60 is the sieve size passing 60% of the media and d10 is the effective size; a lower UC indicates a more uniform particle distribution.
Question 7: Zeolite filtration media is primarily used in water treatment for which purpose?
- Removing trihalomethanes
- Softening and ammonia removal via ion exchange (Correct answer)
- Oxidizing manganese
- Reducing turbidity below 0.1 NTU
Correct answer: Softening and ammonia removal via ion exchange
Natural zeolites (clinoptilolite) are used for ion-exchange softening and selective ammonia (NH₄⁺) removal because of their high cation exchange capacity and selectivity.
CWS Filtration Media & Technologies 2
What is the primary mechanism by which activated carbon removes chloramines from water?