CWEA ADVANCED WATER TREATMENT | COMPLETE EXAM
PREPARATION - QUESTIONS WITH EXPLAINED VERIFIED
ANSWERS - UPDATED EDITION
CWEA Advanced Water Treatment
1. What is the primary purpose of advanced wastewater treatment?
A. Increase wastewater temperature
B. Remove contaminants remaining after conventional treatment
C. Increase suspended solids
D. Reduce plant capacity
ANSWER : B. Remove contaminants remaining after conventional
treatment.
Explanation: Advanced treatment provides additional removal of
nutrients, pathogens, dissolved contaminants, and other constituents after
conventional treatment.
2. Which process is commonly used for nitrogen removal?
A. Chlorination
B. Nitrification and denitrification
C. Grit removal
D. Screening
ANSWER : B. Nitrification and denitrification.
Explanation: Nitrification converts ammonia to nitrate, while
denitrification converts nitrate to nitrogen gas.
3. During nitrification, ammonia is primarily converted first into:
A. Nitrogen gas
B. Nitrite
C. Phosphate
D. Sulfide
ANSWER : B. Nitrite.
,Explanation: Ammonia-oxidizing microorganisms convert ammonia to
nitrite. Other nitrifiers then convert nitrite to nitrate.
4. Which organisms perform nitrification?
A. Nitrifying bacteria
B. Methanogens
C. Fungi only
D. Protozoa only
ANSWER : A. Nitrifying bacteria.
Explanation: Specialized autotrophic microorganisms perform ammonia
and nitrite oxidation.
5. Denitrification requires:
A. Anoxic conditions and an electron donor
B. High dissolved oxygen
C. Ultraviolet light only
D. Chlorine residual
ANSWER : A. Anoxic conditions and an electron donor.
Explanation: Denitrifying organisms reduce nitrate under oxygen-limited
conditions while using an available electron donor.
6. What is the primary end product of complete denitrification?
A. Ammonia
B. Nitrite
C. Nitrogen gas
D. Phosphorus
ANSWER : C. Nitrogen gas.
Explanation: Complete denitrification converts nitrate through
intermediate nitrogen compounds to nitrogen gas.
7. Which condition is most important for nitrification?
A. Adequate dissolved oxygen
B. Zero alkalinity
C. High chlorine residual
D. Complete absence of biomass
ANSWER : A. Adequate dissolved oxygen.
Explanation: Nitrifying organisms require oxygen for ammonia oxidation.
, 8. Why is alkalinity important during nitrification?
A. Nitrification consumes alkalinity
B. Nitrification produces chlorine
C. Alkalinity removes grit
D. Alkalinity eliminates all pathogens
ANSWER : A. Nitrification consumes alkalinity.
Explanation: Nitrification produces acidity and consumes alkalinity, so
insufficient alkalinity may cause pH to decline.
9. A rapid decrease in nitrification performance often results from:
A. Increased nitrifier population
B. Toxic compounds entering the process
C. Increased alkalinity
D. Improved aeration
ANSWER : B. Toxic compounds entering the process.
Explanation: Nitrifiers are sensitive to certain toxic compounds and
environmental changes.
10. What does SRT represent?
A. Sludge retention time
B. Screening removal technique
C. Solids recycling temperature
D. Surface reaction test
ANSWER : A. Sludge retention time.
Explanation: SRT represents the average time solids remain in the
biological treatment system.
11. Why is adequate SRT important for nitrification?
A. Nitrifiers grow slowly
B. Nitrifiers grow instantly
C. Nitrifiers do not require biomass
D. Nitrifiers require chlorine
ANSWER : A. Nitrifiers grow slowly.
Explanation: Nitrifiers reproduce more slowly than many ordinary
heterotrophic organisms, so sufficient SRT is needed to retain them.
12. Which measurement provides information about oxygen
availability in an aeration basin?
, A. DO
B. TSS only
C. pH paper only
D. Turbidity only
ANSWER : A. DO.
Explanation: Dissolved oxygen indicates the amount of oxygen available in
the liquid for biological reactions.
13. Excessive DO in an anoxic zone may:
A. Improve denitrification
B. Reduce denitrification efficiency
C. Increase nitrate removal automatically
D. Eliminate alkalinity consumption
ANSWER : B. Reduce denitrification efficiency.
Explanation: Denitrifying organisms prefer anoxic conditions. Excess
oxygen competes with nitrate as an electron acceptor.
14. What is the purpose of internal nitrate recycle in many
nitrogen-removal systems?
A. Return nitrate to an anoxic zone
B. Remove grit
C. Add chlorine
D. Increase influent flow
ANSWER : A. Return nitrate to an anoxic zone.
Explanation: Internal recycle moves nitrate-containing mixed liquor from
an aerobic zone to an anoxic zone for denitrification.
15. Which nutrient is primarily responsible for eutrophication?
A. Nitrogen and phosphorus
B. Sodium only
C. Chloride only
D. Calcium only
ANSWER : A. Nitrogen and phosphorus.
Explanation: Excess nitrogen and phosphorus stimulate excessive aquatic
plant and algae growth.
16. Biological phosphorus removal depends on:
A. Phosphorus-accumulating organisms
PREPARATION - QUESTIONS WITH EXPLAINED VERIFIED
ANSWERS - UPDATED EDITION
CWEA Advanced Water Treatment
1. What is the primary purpose of advanced wastewater treatment?
A. Increase wastewater temperature
B. Remove contaminants remaining after conventional treatment
C. Increase suspended solids
D. Reduce plant capacity
ANSWER : B. Remove contaminants remaining after conventional
treatment.
Explanation: Advanced treatment provides additional removal of
nutrients, pathogens, dissolved contaminants, and other constituents after
conventional treatment.
2. Which process is commonly used for nitrogen removal?
A. Chlorination
B. Nitrification and denitrification
C. Grit removal
D. Screening
ANSWER : B. Nitrification and denitrification.
Explanation: Nitrification converts ammonia to nitrate, while
denitrification converts nitrate to nitrogen gas.
3. During nitrification, ammonia is primarily converted first into:
A. Nitrogen gas
B. Nitrite
C. Phosphate
D. Sulfide
ANSWER : B. Nitrite.
,Explanation: Ammonia-oxidizing microorganisms convert ammonia to
nitrite. Other nitrifiers then convert nitrite to nitrate.
4. Which organisms perform nitrification?
A. Nitrifying bacteria
B. Methanogens
C. Fungi only
D. Protozoa only
ANSWER : A. Nitrifying bacteria.
Explanation: Specialized autotrophic microorganisms perform ammonia
and nitrite oxidation.
5. Denitrification requires:
A. Anoxic conditions and an electron donor
B. High dissolved oxygen
C. Ultraviolet light only
D. Chlorine residual
ANSWER : A. Anoxic conditions and an electron donor.
Explanation: Denitrifying organisms reduce nitrate under oxygen-limited
conditions while using an available electron donor.
6. What is the primary end product of complete denitrification?
A. Ammonia
B. Nitrite
C. Nitrogen gas
D. Phosphorus
ANSWER : C. Nitrogen gas.
Explanation: Complete denitrification converts nitrate through
intermediate nitrogen compounds to nitrogen gas.
7. Which condition is most important for nitrification?
A. Adequate dissolved oxygen
B. Zero alkalinity
C. High chlorine residual
D. Complete absence of biomass
ANSWER : A. Adequate dissolved oxygen.
Explanation: Nitrifying organisms require oxygen for ammonia oxidation.
, 8. Why is alkalinity important during nitrification?
A. Nitrification consumes alkalinity
B. Nitrification produces chlorine
C. Alkalinity removes grit
D. Alkalinity eliminates all pathogens
ANSWER : A. Nitrification consumes alkalinity.
Explanation: Nitrification produces acidity and consumes alkalinity, so
insufficient alkalinity may cause pH to decline.
9. A rapid decrease in nitrification performance often results from:
A. Increased nitrifier population
B. Toxic compounds entering the process
C. Increased alkalinity
D. Improved aeration
ANSWER : B. Toxic compounds entering the process.
Explanation: Nitrifiers are sensitive to certain toxic compounds and
environmental changes.
10. What does SRT represent?
A. Sludge retention time
B. Screening removal technique
C. Solids recycling temperature
D. Surface reaction test
ANSWER : A. Sludge retention time.
Explanation: SRT represents the average time solids remain in the
biological treatment system.
11. Why is adequate SRT important for nitrification?
A. Nitrifiers grow slowly
B. Nitrifiers grow instantly
C. Nitrifiers do not require biomass
D. Nitrifiers require chlorine
ANSWER : A. Nitrifiers grow slowly.
Explanation: Nitrifiers reproduce more slowly than many ordinary
heterotrophic organisms, so sufficient SRT is needed to retain them.
12. Which measurement provides information about oxygen
availability in an aeration basin?
, A. DO
B. TSS only
C. pH paper only
D. Turbidity only
ANSWER : A. DO.
Explanation: Dissolved oxygen indicates the amount of oxygen available in
the liquid for biological reactions.
13. Excessive DO in an anoxic zone may:
A. Improve denitrification
B. Reduce denitrification efficiency
C. Increase nitrate removal automatically
D. Eliminate alkalinity consumption
ANSWER : B. Reduce denitrification efficiency.
Explanation: Denitrifying organisms prefer anoxic conditions. Excess
oxygen competes with nitrate as an electron acceptor.
14. What is the purpose of internal nitrate recycle in many
nitrogen-removal systems?
A. Return nitrate to an anoxic zone
B. Remove grit
C. Add chlorine
D. Increase influent flow
ANSWER : A. Return nitrate to an anoxic zone.
Explanation: Internal recycle moves nitrate-containing mixed liquor from
an aerobic zone to an anoxic zone for denitrification.
15. Which nutrient is primarily responsible for eutrophication?
A. Nitrogen and phosphorus
B. Sodium only
C. Chloride only
D. Calcium only
ANSWER : A. Nitrogen and phosphorus.
Explanation: Excess nitrogen and phosphorus stimulate excessive aquatic
plant and algae growth.
16. Biological phosphorus removal depends on:
A. Phosphorus-accumulating organisms
