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 nutrients
b. Remove fine solids
c. Remove large solids and debris
d. Remove dissolved organics
Rationale: Preliminary treatment is designed to protect downstream
equipment by removing large solids and debris, such as sticks, rags, and
plastics.
,2. Which type of grit is most commonly removed during grit chambers?
a. Organic matter
b. Sludge
c. Sand and small stones
d. Fats, oils, and grease
Rationale: Grit chambers allow heavier inorganic particles like sand and
small stones to settle out before biological treatment.
3. What is the main function of a primary clarifier?
a. Remove dissolved organics
b. Remove settleable solids
c. Disinfect effluent
d. Remove nutrients
Rationale: Primary clarifiers remove settleable solids by gravity settling,
reducing the load on secondary treatment processes.
4. Which type of biological treatment uses microorganisms attached to
media?
a. Activated sludge
b. Trickling filter
c. Membrane bioreactor
d. Lagoon
Rationale: Trickling filters provide a surface for microorganisms to attach
and metabolize organic matter as wastewater flows over the media.
,5. In activated sludge systems, what does "MLSS" stand for?
a. Maximum liquid suspended solids
b. Mixed liquor suspended solids
c. Minimum level solids standard
d. Microbial life suspended solids
Rationale: MLSS represents the concentration of suspended
microorganisms in the aeration tank of an activated sludge system.
6. What is the typical purpose of aeration in activated sludge systems?
a. Remove grit
b. Remove nutrients
c. Supply oxygen for microbial activity
d. Disinfect wastewater
Rationale: Aeration provides oxygen necessary for aerobic microorganisms
to break down organic matter.
7. Which factor has the greatest influence on sludge settling in a secondary
clarifier?
a. pH
b. Temperature
c. MLSS concentration and flocculation
d. Dissolved oxygen
Rationale: Proper floc formation and MLSS concentration are key for
effective settling in secondary clarifiers.
, 8. What is the typical range of BOD5 removal in a conventional activated
sludge process?
a. 20–30%
b. 40–50%
c. 85–95%
d. 100%
Rationale: Conventional activated sludge processes typically remove 85–
95% of BOD5 under normal operating conditions.
9. Which disinfectant is commonly used in municipal wastewater
treatment?
a. Ammonia
b. Ozone
c. Chlorine
d. Hydrogen peroxide
Rationale: Chlorine is widely used for disinfection due to its effectiveness
and ease of application.
10. Which of the following is a common method for sludge stabilization?
a. Screening
b. Anaerobic digestion
c. Grit removal
d. Aeration
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 nutrients
b. Remove fine solids
c. Remove large solids and debris
d. Remove dissolved organics
Rationale: Preliminary treatment is designed to protect downstream
equipment by removing large solids and debris, such as sticks, rags, and
plastics.
,2. Which type of grit is most commonly removed during grit chambers?
a. Organic matter
b. Sludge
c. Sand and small stones
d. Fats, oils, and grease
Rationale: Grit chambers allow heavier inorganic particles like sand and
small stones to settle out before biological treatment.
3. What is the main function of a primary clarifier?
a. Remove dissolved organics
b. Remove settleable solids
c. Disinfect effluent
d. Remove nutrients
Rationale: Primary clarifiers remove settleable solids by gravity settling,
reducing the load on secondary treatment processes.
4. Which type of biological treatment uses microorganisms attached to
media?
a. Activated sludge
b. Trickling filter
c. Membrane bioreactor
d. Lagoon
Rationale: Trickling filters provide a surface for microorganisms to attach
and metabolize organic matter as wastewater flows over the media.
,5. In activated sludge systems, what does "MLSS" stand for?
a. Maximum liquid suspended solids
b. Mixed liquor suspended solids
c. Minimum level solids standard
d. Microbial life suspended solids
Rationale: MLSS represents the concentration of suspended
microorganisms in the aeration tank of an activated sludge system.
6. What is the typical purpose of aeration in activated sludge systems?
a. Remove grit
b. Remove nutrients
c. Supply oxygen for microbial activity
d. Disinfect wastewater
Rationale: Aeration provides oxygen necessary for aerobic microorganisms
to break down organic matter.
7. Which factor has the greatest influence on sludge settling in a secondary
clarifier?
a. pH
b. Temperature
c. MLSS concentration and flocculation
d. Dissolved oxygen
Rationale: Proper floc formation and MLSS concentration are key for
effective settling in secondary clarifiers.
, 8. What is the typical range of BOD5 removal in a conventional activated
sludge process?
a. 20–30%
b. 40–50%
c. 85–95%
d. 100%
Rationale: Conventional activated sludge processes typically remove 85–
95% of BOD5 under normal operating conditions.
9. Which disinfectant is commonly used in municipal wastewater
treatment?
a. Ammonia
b. Ozone
c. Chlorine
d. Hydrogen peroxide
Rationale: Chlorine is widely used for disinfection due to its effectiveness
and ease of application.
10. Which of the following is a common method for sludge stabilization?
a. Screening
b. Anaerobic digestion
c. Grit removal
d. Aeration
