WTO Water Quality & Treatment Principles 3 — Questions and Answers
Question 1: Which pathogen is most resistant to chlorine disinfection and requires UV or ozone treatment for effective inactivation?
- Giardia lamblia
- Cryptosporidium parvum (Correct answer)
- Escherichia coli
- Legionella pneumophila
Correct answer: Cryptosporidium parvum
Cryptosporidium parvum oocysts are highly resistant to chlorine disinfection; UV light or ozone are required for effective inactivation.
Question 2: What does the term 'breakthrough' indicate during granular activated carbon (GAC) filtration?
- When GAC begins to release adsorbed contaminants back into the water
- When the filter develops channeling and bypasses the media
- When the GAC media has reached its adsorption capacity and contaminants pass through (Correct answer)
- When backwash pressure exceeds design limits
Correct answer: When the GAC media has reached its adsorption capacity and contaminants pass through
Breakthrough occurs when the GAC bed is exhausted and can no longer adsorb contaminants, allowing them to pass through into the finished water.
Question 3: Which of the following best describes 'hardness' in water?
- The concentration of total dissolved solids
- The concentration of dissolved calcium and magnesium ions (Correct answer)
- The measure of water's resistance to pH change
- The amount of iron and manganese in water
Correct answer: The concentration of dissolved calcium and magnesium ions
Water hardness is caused primarily by dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions, and is typically expressed as mg/L of calcium carbonate equivalent.
Question 4: What is the purpose of a residual disinfectant maintained in a drinking water distribution system?
- To remove taste and odor compounds
- To provide ongoing protection against microbial regrowth and contamination (Correct answer)
- To prevent corrosion of iron pipes
- To reduce the concentration of nitrates
Correct answer: To provide ongoing protection against microbial regrowth and contamination
A disinfectant residual in the distribution system provides a continuing barrier against microbial contamination and regrowth as water travels to consumers.
Question 5: In a conventional treatment plant, what is the correct order of treatment processes?
- Filtration → Coagulation → Sedimentation → Disinfection
- Coagulation → Flocculation → Sedimentation → Filtration → Disinfection (Correct answer)
- Sedimentation → Coagulation → Flocculation → Filtration → Disinfection
- Disinfection → Coagulation → Sedimentation → Filtration
Correct answer: Coagulation → Flocculation → Sedimentation → Filtration → Disinfection
The conventional treatment sequence is coagulation, flocculation, sedimentation, filtration, and then disinfection to produce safe drinking water.
Question 6: What pH range is generally optimal for chlorine disinfection effectiveness in water treatment?
- pH 8.5–9.5
- pH 6.5–7.5 (Correct answer)
- pH 5.0–6.0
- pH 9.0–10.0
Correct answer: pH 6.5–7.5
Chlorine is most effective as a disinfectant in the pH range of 6.5–7.5 because free chlorine exists primarily as hypochlorous acid (HOCl), the more germicidal form.
Question 7: Which regulation establishes the treatment technique requirements for control of Legionella in drinking water systems?
- Lead and Copper Rule
- Surface Water Treatment Rule (SWTR) (Correct answer)
- Stage 2 D/DBP Rule
- Groundwater Rule
Correct answer: Surface Water Treatment Rule (SWTR)
The Surface Water Treatment Rule requires proper filtration and disinfection that also controls Legionella, as this organism thrives in inadequately treated water.
WTO Water Quality & Treatment Principles 3
Which pathogen is most resistant to chlorine disinfection and requires UV or ozone treatment for effective inactivation?