AZ L-85 Wastewater Treatment
Contractor Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2027 Q&A | Instant
Download Pdf
1. What is the primary purpose of a wastewater treatment plant?
A. Increase drinking-water pressure
B. Remove contaminants from wastewater before discharge or reuse
C. Store potable water
D. Produce electrical power
Answer: B. Remove contaminants from wastewater before discharge or
reuse
Rationale: Wastewater treatment reduces physical, chemical, and
biological pollutants so the treated effluent can meet applicable discharge
or reuse requirements.
,2. Which process primarily removes large floating and suspended debris at
the beginning of treatment?
A. Disinfection
B. Screening
C. Aeration
D. Chlorination
Answer: B. Screening
Rationale: Screens remove rags, plastics, sticks, and other large debris
before wastewater enters downstream equipment.
3. What is the main purpose of grit removal?
A. Remove dissolved ammonia
B. Remove sand, gravel, and other heavy inorganic particles
C. Increase dissolved oxygen
D. Destroy pathogens
Answer: B. Remove sand, gravel, and other heavy inorganic particles
Rationale: Grit removal protects pumps and mechanical equipment from
abrasion and prevents accumulation in tanks and channels.
,4. Primary clarification mainly removes:
A. Dissolved salts
B. Settleable solids and floatable material
C. Dissolved oxygen
D. Chlorine residual
Answer: B. Settleable solids and floatable material
Rationale: Primary clarifiers allow heavier solids to settle and lighter
materials such as grease and scum to float for removal.
5. What is the primary function of an aeration basin in an activated-sludge
process?
A. Remove grit
B. Supply oxygen for biological treatment
C. Store sludge permanently
D. Increase wastewater temperature
Answer: B. Supply oxygen for biological treatment
Rationale: Aeration supplies oxygen needed by microorganisms that
metabolize biodegradable organic matter.
, 6. Dissolved oxygen in an aerobic treatment process is important because
it:
A. Prevents all settling
B. Supports aerobic microorganisms
C. Eliminates all suspended solids instantly
D. Replaces screening
Answer: B. Supports aerobic microorganisms
Rationale: Aerobic microorganisms require adequate dissolved oxygen to
efficiently perform biological treatment.
7. What does BOD measure?
A. Biological oxygen demand
B. Bacterial operating density
C. Basin oxygen depth
D. Biological oxidation discharge
Answer: A. Biological oxygen demand
Rationale: BOD indicates the amount of oxygen microorganisms require to
biologically stabilize biodegradable organic matter in wastewater.
Contractor Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2027 Q&A | Instant
Download Pdf
1. What is the primary purpose of a wastewater treatment plant?
A. Increase drinking-water pressure
B. Remove contaminants from wastewater before discharge or reuse
C. Store potable water
D. Produce electrical power
Answer: B. Remove contaminants from wastewater before discharge or
reuse
Rationale: Wastewater treatment reduces physical, chemical, and
biological pollutants so the treated effluent can meet applicable discharge
or reuse requirements.
,2. Which process primarily removes large floating and suspended debris at
the beginning of treatment?
A. Disinfection
B. Screening
C. Aeration
D. Chlorination
Answer: B. Screening
Rationale: Screens remove rags, plastics, sticks, and other large debris
before wastewater enters downstream equipment.
3. What is the main purpose of grit removal?
A. Remove dissolved ammonia
B. Remove sand, gravel, and other heavy inorganic particles
C. Increase dissolved oxygen
D. Destroy pathogens
Answer: B. Remove sand, gravel, and other heavy inorganic particles
Rationale: Grit removal protects pumps and mechanical equipment from
abrasion and prevents accumulation in tanks and channels.
,4. Primary clarification mainly removes:
A. Dissolved salts
B. Settleable solids and floatable material
C. Dissolved oxygen
D. Chlorine residual
Answer: B. Settleable solids and floatable material
Rationale: Primary clarifiers allow heavier solids to settle and lighter
materials such as grease and scum to float for removal.
5. What is the primary function of an aeration basin in an activated-sludge
process?
A. Remove grit
B. Supply oxygen for biological treatment
C. Store sludge permanently
D. Increase wastewater temperature
Answer: B. Supply oxygen for biological treatment
Rationale: Aeration supplies oxygen needed by microorganisms that
metabolize biodegradable organic matter.
, 6. Dissolved oxygen in an aerobic treatment process is important because
it:
A. Prevents all settling
B. Supports aerobic microorganisms
C. Eliminates all suspended solids instantly
D. Replaces screening
Answer: B. Supports aerobic microorganisms
Rationale: Aerobic microorganisms require adequate dissolved oxygen to
efficiently perform biological treatment.
7. What does BOD measure?
A. Biological oxygen demand
B. Bacterial operating density
C. Basin oxygen depth
D. Biological oxidation discharge
Answer: A. Biological oxygen demand
Rationale: BOD indicates the amount of oxygen microorganisms require to
biologically stabilize biodegradable organic matter in wastewater.
