Minnesota Wastewater Operator Class
A Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. What is the primary purpose of preliminary treatment in a wastewater
treatment plant?
A. Remove dissolved nutrients
B. Destroy pathogens completely
C. Remove large solids and debris
D. Stabilize activated sludge
Answer: C. Remove large solids and debris
Preliminary treatment protects downstream equipment by removing
materials such as rags, sticks, plastics, and grit that can damage pumps
and interfere with treatment processes.
, 2. Which wastewater treatment process uses microorganisms to break
down organic matter?
A. Screening
B. Biological treatment
C. Chlorination
D. Filtration
Answer: B. Biological treatment
Biological treatment relies on microorganisms to consume and convert
organic pollutants into more stable forms.
3. The measurement of oxygen required by microorganisms to
decompose organic matter is called:
A. TSS
B. BOD
C. pH
D. DO
Answer: B. BOD
Biochemical Oxygen Demand (BOD) measures the amount of oxygen
microorganisms need to break down biodegradable organic material.
, 4. A wastewater operator measures dissolved oxygen primarily to
determine:
A. Chlorine concentration
B. Organic loading
C. Available oxygen for biological activity
D. Sludge age
Answer: C. Available oxygen for biological activity
Dissolved oxygen indicates whether aerobic microorganisms have enough
oxygen to effectively treat wastewater.
5. The activated sludge process depends mainly on:
A. Chemical precipitation
B. Aerobic microorganisms
C. Ultraviolet radiation
D. Physical settling only
Answer: B. Aerobic microorganisms
Activated sludge uses aerobic bacteria and other organisms to remove
dissolved and suspended organic matter.
6. What is the purpose of a secondary clarifier?
, A. Add oxygen
B. Remove settled biological solids
C. Remove screenings
D. Increase chlorine contact time
Answer: B. Remove settled biological solids
Secondary clarifiers separate treated water from biological solids produced
during the activated sludge process.
7. Sludge return from a clarifier back to the aeration tank is called:
A. WAS
B. RAS
C. MLSS
D. SVI
Answer: B. RAS
Return Activated Sludge (RAS) maintains the microorganism population in
the aeration basin.
8. Waste activated sludge is removed from the treatment system to
control:
A. Temperature
B. Sludge age and solids concentration
A Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of preliminary treatment in a wastewater
treatment plant?
A. Remove dissolved nutrients
B. Destroy pathogens completely
C. Remove large solids and debris
D. Stabilize activated sludge
Answer: C. Remove large solids and debris
Preliminary treatment protects downstream equipment by removing
materials such as rags, sticks, plastics, and grit that can damage pumps
and interfere with treatment processes.
, 2. Which wastewater treatment process uses microorganisms to break
down organic matter?
A. Screening
B. Biological treatment
C. Chlorination
D. Filtration
Answer: B. Biological treatment
Biological treatment relies on microorganisms to consume and convert
organic pollutants into more stable forms.
3. The measurement of oxygen required by microorganisms to
decompose organic matter is called:
A. TSS
B. BOD
C. pH
D. DO
Answer: B. BOD
Biochemical Oxygen Demand (BOD) measures the amount of oxygen
microorganisms need to break down biodegradable organic material.
, 4. A wastewater operator measures dissolved oxygen primarily to
determine:
A. Chlorine concentration
B. Organic loading
C. Available oxygen for biological activity
D. Sludge age
Answer: C. Available oxygen for biological activity
Dissolved oxygen indicates whether aerobic microorganisms have enough
oxygen to effectively treat wastewater.
5. The activated sludge process depends mainly on:
A. Chemical precipitation
B. Aerobic microorganisms
C. Ultraviolet radiation
D. Physical settling only
Answer: B. Aerobic microorganisms
Activated sludge uses aerobic bacteria and other organisms to remove
dissolved and suspended organic matter.
6. What is the purpose of a secondary clarifier?
, A. Add oxygen
B. Remove settled biological solids
C. Remove screenings
D. Increase chlorine contact time
Answer: B. Remove settled biological solids
Secondary clarifiers separate treated water from biological solids produced
during the activated sludge process.
7. Sludge return from a clarifier back to the aeration tank is called:
A. WAS
B. RAS
C. MLSS
D. SVI
Answer: B. RAS
Return Activated Sludge (RAS) maintains the microorganism population in
the aeration basin.
8. Waste activated sludge is removed from the treatment system to
control:
A. Temperature
B. Sludge age and solids concentration
