Minnesota Wastewater Operator Class
D 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 a wastewater treatment plant?
A. Increase wastewater temperature
B. Remove pollutants before discharge
C. Add chemicals to drinking water
D. Store wastewater permanently
Answer: B. Remove pollutants before discharge
The primary purpose of a wastewater treatment plant is to remove
physical, chemical, and biological contaminants so treated effluent can be
safely released into the environment.
2. Which stage of wastewater treatment removes large debris such as
sticks and rags?
, A. Disinfection
B. Secondary treatment
C. Screening
D. Sludge digestion
Answer: C. Screening
Screening is the first treatment step and removes large solids that could
damage equipment or interfere with later processes.
3. The main goal of primary treatment is to remove:
A. Dissolved oxygen
B. Settleable and suspended solids
C. Bacteria only
D. Nutrients only
Answer: B. Settleable and suspended solids
Primary treatment uses physical processes such as sedimentation to
remove solids that can settle or float.
4. Secondary wastewater treatment primarily uses:
A. Physical filtration only
B. Chemical precipitation only
C. Biological microorganisms
D. Chlorine only
,Answer: C. Biological microorganisms
Secondary treatment relies on microorganisms to break down dissolved
and suspended organic matter in wastewater.
5. BOD stands for:
A. Biological Oxygen Demand
B. Basic Oxygen Density
C. Bacterial Organic Digestion
D. Biological Oxidation Division
Answer: A. Biological Oxygen Demand
BOD measures the amount of oxygen microorganisms need to break down
organic material in wastewater.
6. High BOD levels in receiving waters can cause:
A. Increased dissolved oxygen
B. Oxygen depletion
C. Reduced algae growth always
D. Lower organic matter
Answer: B. Oxygen depletion
High BOD consumes dissolved oxygen as microorganisms decompose
organic matter, which can harm aquatic life.
, 7. Dissolved oxygen is important in an activated sludge system because
it:
A. Kills all organisms
B. Supports aerobic microorganisms
C. Removes grit
D. Prevents flow
Answer: B. Supports aerobic microorganisms
Aerobic bacteria require dissolved oxygen to break down organic
pollutants effectively.
8. A grit chamber removes:
A. Fine bacteria
B. Sand and heavy inorganic particles
C. Dissolved chemicals
D. Viruses
Answer: B. Sand and heavy inorganic particles
Grit chambers protect pumps and equipment by removing heavy inorganic
solids such as sand and gravel.
9. The activated sludge process uses:
A. Aeration and microorganisms
B. Only settling tanks
D Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a wastewater treatment plant?
A. Increase wastewater temperature
B. Remove pollutants before discharge
C. Add chemicals to drinking water
D. Store wastewater permanently
Answer: B. Remove pollutants before discharge
The primary purpose of a wastewater treatment plant is to remove
physical, chemical, and biological contaminants so treated effluent can be
safely released into the environment.
2. Which stage of wastewater treatment removes large debris such as
sticks and rags?
, A. Disinfection
B. Secondary treatment
C. Screening
D. Sludge digestion
Answer: C. Screening
Screening is the first treatment step and removes large solids that could
damage equipment or interfere with later processes.
3. The main goal of primary treatment is to remove:
A. Dissolved oxygen
B. Settleable and suspended solids
C. Bacteria only
D. Nutrients only
Answer: B. Settleable and suspended solids
Primary treatment uses physical processes such as sedimentation to
remove solids that can settle or float.
4. Secondary wastewater treatment primarily uses:
A. Physical filtration only
B. Chemical precipitation only
C. Biological microorganisms
D. Chlorine only
,Answer: C. Biological microorganisms
Secondary treatment relies on microorganisms to break down dissolved
and suspended organic matter in wastewater.
5. BOD stands for:
A. Biological Oxygen Demand
B. Basic Oxygen Density
C. Bacterial Organic Digestion
D. Biological Oxidation Division
Answer: A. Biological Oxygen Demand
BOD measures the amount of oxygen microorganisms need to break down
organic material in wastewater.
6. High BOD levels in receiving waters can cause:
A. Increased dissolved oxygen
B. Oxygen depletion
C. Reduced algae growth always
D. Lower organic matter
Answer: B. Oxygen depletion
High BOD consumes dissolved oxygen as microorganisms decompose
organic matter, which can harm aquatic life.
, 7. Dissolved oxygen is important in an activated sludge system because
it:
A. Kills all organisms
B. Supports aerobic microorganisms
C. Removes grit
D. Prevents flow
Answer: B. Supports aerobic microorganisms
Aerobic bacteria require dissolved oxygen to break down organic
pollutants effectively.
8. A grit chamber removes:
A. Fine bacteria
B. Sand and heavy inorganic particles
C. Dissolved chemicals
D. Viruses
Answer: B. Sand and heavy inorganic particles
Grit chambers protect pumps and equipment by removing heavy inorganic
solids such as sand and gravel.
9. The activated sludge process uses:
A. Aeration and microorganisms
B. Only settling tanks
