ARIZONA WATER TREATMENT OPERATOR EXAM
LEVEL II QUESTIONS AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES Q&A 2026
|INSTANT DOWNLOAD PDF
1. Which of the following best describes BOD (Biochemical
Oxygen Demand)?
A. The total amount of oxygen present in water
B. The amount of oxygen required for chemical oxidation
C. The amount of oxygen consumed by microorganisms to
decompose organic matter
D. The amount of oxygen in wastewater after treatment
Rationale: BOD measures the oxygen consumed by bacteria
when decomposing organic matter in water, reflecting the
pollution load.
Correct answer: C
2. Which process is primarily used to remove suspended solids
from wastewater?
A. Filtration
B. Sedimentation
C. Chlorination
D. Nitrification
,Rationale: Sedimentation allows heavier solids to settle, which
is the primary method for removing suspended solids.
Correct answer: B
3. Which microorganism is most commonly used in activated
sludge treatment to break down organic matter?
A. Protozoa
B. Algae
C. Bacteria
D. Fungi
Rationale: Bacteria are the primary decomposers of organic
material in activated sludge systems.
Correct answer: C
4. What is the primary purpose of chlorination in wastewater
treatment?
A. Remove suspended solids
B. Kill pathogens
C. Reduce BOD
D. Reduce nitrogen
Rationale: Chlorination is used mainly to disinfect treated
water by killing pathogenic microorganisms.
Correct answer: B
,5. Which of the following is a typical sign of sludge bulking in
an activated sludge system?
A. Clear effluent
B. Settling problems in clarifiers
C. Increased dissolved oxygen
D. Decreased BOD
Rationale: Sludge bulking occurs when the sludge does not
settle properly, causing poor clarifier performance.
Correct answer: B
6. What does TSS stand for in wastewater treatment?
A. Total Suspended Solids
B. Total Settled Solids
C. Total Soluble Substances
D. Total Sediment Standard
Rationale: TSS measures the total amount of particles
suspended in water, an important water quality parameter.
Correct answer: A
7. What is the function of a primary clarifier in wastewater
treatment?
A. Reduce pathogens
B. Remove organic nitrogen
C. Remove settleable solids
D. Add oxygen to water
, Rationale: Primary clarifiers remove settleable solids before
secondary biological treatment.
Correct answer: C
8. In wastewater, ammonia is primarily converted to nitrite
and then nitrate in a process called:
A. Denitrification
B. Nitrification
C. Ammonification
D. Oxidation
Rationale: Nitrification is a two-step microbial process that
converts ammonia to nitrite and then to nitrate.
Correct answer: B
9. What is the primary cause of foaming in activated sludge
tanks?
A. Excess dissolved oxygen
B. Growth of filamentous bacteria
C. High BOD influent
D. High nitrogen levels
Rationale: Filamentous bacteria can grow excessively and
create foam on the surface of aeration tanks.
Correct answer: B
LEVEL II QUESTIONS AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES Q&A 2026
|INSTANT DOWNLOAD PDF
1. Which of the following best describes BOD (Biochemical
Oxygen Demand)?
A. The total amount of oxygen present in water
B. The amount of oxygen required for chemical oxidation
C. The amount of oxygen consumed by microorganisms to
decompose organic matter
D. The amount of oxygen in wastewater after treatment
Rationale: BOD measures the oxygen consumed by bacteria
when decomposing organic matter in water, reflecting the
pollution load.
Correct answer: C
2. Which process is primarily used to remove suspended solids
from wastewater?
A. Filtration
B. Sedimentation
C. Chlorination
D. Nitrification
,Rationale: Sedimentation allows heavier solids to settle, which
is the primary method for removing suspended solids.
Correct answer: B
3. Which microorganism is most commonly used in activated
sludge treatment to break down organic matter?
A. Protozoa
B. Algae
C. Bacteria
D. Fungi
Rationale: Bacteria are the primary decomposers of organic
material in activated sludge systems.
Correct answer: C
4. What is the primary purpose of chlorination in wastewater
treatment?
A. Remove suspended solids
B. Kill pathogens
C. Reduce BOD
D. Reduce nitrogen
Rationale: Chlorination is used mainly to disinfect treated
water by killing pathogenic microorganisms.
Correct answer: B
,5. Which of the following is a typical sign of sludge bulking in
an activated sludge system?
A. Clear effluent
B. Settling problems in clarifiers
C. Increased dissolved oxygen
D. Decreased BOD
Rationale: Sludge bulking occurs when the sludge does not
settle properly, causing poor clarifier performance.
Correct answer: B
6. What does TSS stand for in wastewater treatment?
A. Total Suspended Solids
B. Total Settled Solids
C. Total Soluble Substances
D. Total Sediment Standard
Rationale: TSS measures the total amount of particles
suspended in water, an important water quality parameter.
Correct answer: A
7. What is the function of a primary clarifier in wastewater
treatment?
A. Reduce pathogens
B. Remove organic nitrogen
C. Remove settleable solids
D. Add oxygen to water
, Rationale: Primary clarifiers remove settleable solids before
secondary biological treatment.
Correct answer: C
8. In wastewater, ammonia is primarily converted to nitrite
and then nitrate in a process called:
A. Denitrification
B. Nitrification
C. Ammonification
D. Oxidation
Rationale: Nitrification is a two-step microbial process that
converts ammonia to nitrite and then to nitrate.
Correct answer: B
9. What is the primary cause of foaming in activated sludge
tanks?
A. Excess dissolved oxygen
B. Growth of filamentous bacteria
C. High BOD influent
D. High nitrogen levels
Rationale: Filamentous bacteria can grow excessively and
create foam on the surface of aeration tanks.
Correct answer: B
