Minnesota Wastewater Operator Class
C 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. Remove large solids and debris
C. Destroy all microorganisms
D. Increase dissolved oxygen levels
Answer: B. Remove large solids and debris
Rationale: Preliminary treatment protects downstream equipment by
removing large objects such as rags, sticks, plastics, and grit that could
damage pumps and clog pipes.
, 2. Which wastewater characteristic measures the amount of oxygen
required by microorganisms to decompose organic matter?
A. Total suspended solids
B. pH
C. Biochemical oxygen demand
D. Chlorine residual
Answer: C. Biochemical oxygen demand
Rationale: Biochemical oxygen demand (BOD) indicates the amount of
oxygen microorganisms need to break down biodegradable organic
material in wastewater.
3. A bar screen in a wastewater plant is designed to remove:
A. Dissolved salts
B. Large floating materials
C. Pathogenic bacteria
D. Ammonia
Answer: B. Large floating materials
Rationale: Bar screens capture large solids such as rags, sticks, and other
debris before wastewater enters treatment processes.
4. Grit removal systems are mainly used to remove:
,A. Sand and heavy inorganic particles
B. Dissolved organic matter
C. Viruses
D. Nutrients
Answer: A. Sand and heavy inorganic particles
Rationale: Grit removal protects pumps and equipment by removing dense
inorganic materials that settle quickly.
5. The main purpose of primary sedimentation is to remove:
A. Settleable solids
B. Dissolved oxygen
C. Chlorine compounds
D. Bacteria only
Answer: A. Settleable solids
Rationale: Primary clarifiers allow heavier solids to settle and remove a
portion of suspended solids and organic matter.
6. Activated sludge treatment relies primarily on:
A. Chemical precipitation
B. Biological microorganisms
, C. Mechanical screening only
D. Ultraviolet radiation
Answer: B. Biological microorganisms
Rationale: Activated sludge uses microorganisms to consume organic
pollutants in wastewater under controlled conditions.
7. The aeration basin provides:
A. Chlorine contact time
B. Oxygen for microorganisms
C. Grit storage
D. Sludge drying
Answer: B. Oxygen for microorganisms
Rationale: Aeration supplies oxygen needed by microorganisms to break
down organic waste.
8. Dissolved oxygen in an aeration tank should generally be:
A. Completely absent
B. Maintained at an adequate level for biological activity
C. Removed before clarification
D. Replaced with chlorine
Answer: B. Maintained at an adequate level for biological activity
C 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. Remove large solids and debris
C. Destroy all microorganisms
D. Increase dissolved oxygen levels
Answer: B. Remove large solids and debris
Rationale: Preliminary treatment protects downstream equipment by
removing large objects such as rags, sticks, plastics, and grit that could
damage pumps and clog pipes.
, 2. Which wastewater characteristic measures the amount of oxygen
required by microorganisms to decompose organic matter?
A. Total suspended solids
B. pH
C. Biochemical oxygen demand
D. Chlorine residual
Answer: C. Biochemical oxygen demand
Rationale: Biochemical oxygen demand (BOD) indicates the amount of
oxygen microorganisms need to break down biodegradable organic
material in wastewater.
3. A bar screen in a wastewater plant is designed to remove:
A. Dissolved salts
B. Large floating materials
C. Pathogenic bacteria
D. Ammonia
Answer: B. Large floating materials
Rationale: Bar screens capture large solids such as rags, sticks, and other
debris before wastewater enters treatment processes.
4. Grit removal systems are mainly used to remove:
,A. Sand and heavy inorganic particles
B. Dissolved organic matter
C. Viruses
D. Nutrients
Answer: A. Sand and heavy inorganic particles
Rationale: Grit removal protects pumps and equipment by removing dense
inorganic materials that settle quickly.
5. The main purpose of primary sedimentation is to remove:
A. Settleable solids
B. Dissolved oxygen
C. Chlorine compounds
D. Bacteria only
Answer: A. Settleable solids
Rationale: Primary clarifiers allow heavier solids to settle and remove a
portion of suspended solids and organic matter.
6. Activated sludge treatment relies primarily on:
A. Chemical precipitation
B. Biological microorganisms
, C. Mechanical screening only
D. Ultraviolet radiation
Answer: B. Biological microorganisms
Rationale: Activated sludge uses microorganisms to consume organic
pollutants in wastewater under controlled conditions.
7. The aeration basin provides:
A. Chlorine contact time
B. Oxygen for microorganisms
C. Grit storage
D. Sludge drying
Answer: B. Oxygen for microorganisms
Rationale: Aeration supplies oxygen needed by microorganisms to break
down organic waste.
8. Dissolved oxygen in an aeration tank should generally be:
A. Completely absent
B. Maintained at an adequate level for biological activity
C. Removed before clarification
D. Replaced with chlorine
Answer: B. Maintained at an adequate level for biological activity
