South Carolina Biological Wastewater
Operator Class C Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which of the following is the primary purpose of a clarifier in
wastewater treatment?
A. Increase dissolved oxygen
B. Remove suspended solids
C. Reduce pH
D. Kill bacteria
Rationale: Clarifiers are designed to settle out suspended solids from
wastewater, allowing for cleaner effluent and reducing the load on
subsequent treatment processes.
2. What is the most common type of microorganism responsible for BOD
removal in an activated sludge system?
, A. Protozoa
B. Algae
C. Bacteria
D. Fungi
Rationale: Bacteria are the primary organisms that metabolize
organic matter in activated sludge, reducing biological oxygen
demand (BOD).
3. Which process is most effective for nutrient removal in biological
wastewater treatment?
A. Sedimentation
B. Filtration
C. Biological nitrogen and phosphorus removal
D. Chlorination
Rationale: Biological nutrient removal uses specific bacteria to
convert nitrogen and phosphorus into forms that can be removed
from wastewater.
4. Which of the following is a symptom of filamentous bacteria
overgrowth in activated sludge?
A. High pH
B. Sludge bulking
C. Low BOD
D. Increased effluent chlorine demand
, Rationale: Filamentous bacteria can cause sludge to become fluffy
and resist settling, leading to sludge bulking.
5. What is the function of aeration in an activated sludge system?
A. Remove chlorine
B. Provide oxygen for aerobic bacteria
C. Reduce sludge volume
D. Remove heavy metals
Rationale: Aeration supplies dissolved oxygen needed by aerobic
microorganisms to degrade organic matter.
6. Which form of nitrogen is toxic to aquatic life at high concentrations?
A. Nitrate
B. Ammonia
C. Nitrite
D. Organic nitrogen
Rationale: Free ammonia (NH3) is toxic to fish and other aquatic
organisms, especially at higher pH and temperature.
7. In an anaerobic digester, the primary gas produced is:
A. Oxygen
B. Nitrogen
C. Methane
D. Carbon dioxide
Rationale: Anaerobic digestion breaks down organic matter in the
, absence of oxygen, producing methane as a major biogas
component.
8. What does MCRT (Mean Cell Residence Time) control in activated
sludge?
A. Influent flow rate
B. Effluent pH
C. Sludge age
D. Chlorine dosage
Rationale: MCRT represents the average time solids remain in the
system, influencing sludge characteristics and process stability.
9. Which is the primary advantage of a trickling filter over activated
sludge?
A. Lower land requirements
B. Lower energy requirements
C. Faster BOD removal
D. Better nutrient removal
Rationale: Trickling filters require less mechanical energy because
they rely on passive biofilm processes.
10. A sudden drop in dissolved oxygen in an aeration tank may
indicate:
A. Over-aeration
B. Low BOD load
C. Mechanical failure or high organic load
Operator Class C Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which of the following is the primary purpose of a clarifier in
wastewater treatment?
A. Increase dissolved oxygen
B. Remove suspended solids
C. Reduce pH
D. Kill bacteria
Rationale: Clarifiers are designed to settle out suspended solids from
wastewater, allowing for cleaner effluent and reducing the load on
subsequent treatment processes.
2. What is the most common type of microorganism responsible for BOD
removal in an activated sludge system?
, A. Protozoa
B. Algae
C. Bacteria
D. Fungi
Rationale: Bacteria are the primary organisms that metabolize
organic matter in activated sludge, reducing biological oxygen
demand (BOD).
3. Which process is most effective for nutrient removal in biological
wastewater treatment?
A. Sedimentation
B. Filtration
C. Biological nitrogen and phosphorus removal
D. Chlorination
Rationale: Biological nutrient removal uses specific bacteria to
convert nitrogen and phosphorus into forms that can be removed
from wastewater.
4. Which of the following is a symptom of filamentous bacteria
overgrowth in activated sludge?
A. High pH
B. Sludge bulking
C. Low BOD
D. Increased effluent chlorine demand
, Rationale: Filamentous bacteria can cause sludge to become fluffy
and resist settling, leading to sludge bulking.
5. What is the function of aeration in an activated sludge system?
A. Remove chlorine
B. Provide oxygen for aerobic bacteria
C. Reduce sludge volume
D. Remove heavy metals
Rationale: Aeration supplies dissolved oxygen needed by aerobic
microorganisms to degrade organic matter.
6. Which form of nitrogen is toxic to aquatic life at high concentrations?
A. Nitrate
B. Ammonia
C. Nitrite
D. Organic nitrogen
Rationale: Free ammonia (NH3) is toxic to fish and other aquatic
organisms, especially at higher pH and temperature.
7. In an anaerobic digester, the primary gas produced is:
A. Oxygen
B. Nitrogen
C. Methane
D. Carbon dioxide
Rationale: Anaerobic digestion breaks down organic matter in the
, absence of oxygen, producing methane as a major biogas
component.
8. What does MCRT (Mean Cell Residence Time) control in activated
sludge?
A. Influent flow rate
B. Effluent pH
C. Sludge age
D. Chlorine dosage
Rationale: MCRT represents the average time solids remain in the
system, influencing sludge characteristics and process stability.
9. Which is the primary advantage of a trickling filter over activated
sludge?
A. Lower land requirements
B. Lower energy requirements
C. Faster BOD removal
D. Better nutrient removal
Rationale: Trickling filters require less mechanical energy because
they rely on passive biofilm processes.
10. A sudden drop in dissolved oxygen in an aeration tank may
indicate:
A. Over-aeration
B. Low BOD load
C. Mechanical failure or high organic load
