South Carolina Biological Wastewater
Operator Class B 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 primary clarifier in a wastewater
treatment plant?
a. Increase dissolved oxygen levels
b. Remove settleable solids from wastewater
c. Neutralize pH
d. Kill pathogens
Rationale: The primary clarifier allows suspended solids to settle,
removing them before biological treatment.
2. Which microorganism is primarily responsible for nitrification in a
biological treatment process?
a. Escherichia coli
, b. Nitrosomonas
c. Bacillus subtilis
d. Clostridium
Rationale: Nitrosomonas oxidizes ammonia to nitrite, a key step in
nitrification.
3. What is the typical range for mixed liquor suspended solids (MLSS) in
an activated sludge process for a Class B plant?
a. 50–100 mg/L
b. 100–200 mg/L
c. 200–500 mg/L
d. 2000–4000 mg/L
Rationale: Class B plants generally operate with MLSS in the 2000–
4000 mg/L range to maintain proper biological activity.
4. Which parameter is most critical for maintaining a healthy activated
sludge process?
a. Temperature
b. Dissolved oxygen
c. pH
d. Conductivity
Rationale: Adequate dissolved oxygen is essential for aerobic
microorganisms to metabolize organic matter.
5. Chlorination is primarily used in wastewater treatment to:
a. Reduce BOD
, b. Disinfect the effluent
c. Reduce TSS
d. Adjust pH
Rationale: Chlorination kills or inactivates pathogens, ensuring
effluent meets public health standards.
6. The main purpose of aeration in secondary treatment is to:
a. Remove heavy metals
b. Provide oxygen for microorganisms
c. Settle solids
d. Filter wastewater
Rationale: Aeration supplies oxygen to support the metabolism of
aerobic bacteria in the activated sludge process.
7. Which of the following is a sign of sludge bulking in an activated sludge
system?
a. Clear effluent
b. Rapid settling
c. Fluffy, non-settling sludge
d. Decreased MLSS
Rationale: Bulking occurs when filamentous bacteria dominate,
resulting in poor settling sludge.
8. What does BOD5 measure?
a. Total suspended solids
b. Oxygen demand after 24 hours
, c. Oxygen demand after 5 days
d. Effluent nitrogen
Rationale: BOD5 measures the oxygen required by microorganisms
to decompose organic matter over 5 days.
9. The first step in the nitrogen cycle in wastewater treatment is:
a. Denitrification
b. Ammonification
c. Nitrification
d. Assimilation
Rationale: Ammonification converts organic nitrogen into ammonia,
which can then be nitrified.
10. What is the typical detention time in a primary clarifier?
a. 10–20 minutes
b. 30–60 minutes
c. 1–3 hours
d. 6–8 hours
Rationale: A 1–3 hour detention allows settleable solids to
adequately separate from the liquid.
11. In an aerobic digester, the main purpose of aeration is to:
a. Remove heavy metals
b. Stabilize sludge by biological oxidation
c. Sediment solids
d. Adjust pH
Operator Class B Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a primary clarifier in a wastewater
treatment plant?
a. Increase dissolved oxygen levels
b. Remove settleable solids from wastewater
c. Neutralize pH
d. Kill pathogens
Rationale: The primary clarifier allows suspended solids to settle,
removing them before biological treatment.
2. Which microorganism is primarily responsible for nitrification in a
biological treatment process?
a. Escherichia coli
, b. Nitrosomonas
c. Bacillus subtilis
d. Clostridium
Rationale: Nitrosomonas oxidizes ammonia to nitrite, a key step in
nitrification.
3. What is the typical range for mixed liquor suspended solids (MLSS) in
an activated sludge process for a Class B plant?
a. 50–100 mg/L
b. 100–200 mg/L
c. 200–500 mg/L
d. 2000–4000 mg/L
Rationale: Class B plants generally operate with MLSS in the 2000–
4000 mg/L range to maintain proper biological activity.
4. Which parameter is most critical for maintaining a healthy activated
sludge process?
a. Temperature
b. Dissolved oxygen
c. pH
d. Conductivity
Rationale: Adequate dissolved oxygen is essential for aerobic
microorganisms to metabolize organic matter.
5. Chlorination is primarily used in wastewater treatment to:
a. Reduce BOD
, b. Disinfect the effluent
c. Reduce TSS
d. Adjust pH
Rationale: Chlorination kills or inactivates pathogens, ensuring
effluent meets public health standards.
6. The main purpose of aeration in secondary treatment is to:
a. Remove heavy metals
b. Provide oxygen for microorganisms
c. Settle solids
d. Filter wastewater
Rationale: Aeration supplies oxygen to support the metabolism of
aerobic bacteria in the activated sludge process.
7. Which of the following is a sign of sludge bulking in an activated sludge
system?
a. Clear effluent
b. Rapid settling
c. Fluffy, non-settling sludge
d. Decreased MLSS
Rationale: Bulking occurs when filamentous bacteria dominate,
resulting in poor settling sludge.
8. What does BOD5 measure?
a. Total suspended solids
b. Oxygen demand after 24 hours
, c. Oxygen demand after 5 days
d. Effluent nitrogen
Rationale: BOD5 measures the oxygen required by microorganisms
to decompose organic matter over 5 days.
9. The first step in the nitrogen cycle in wastewater treatment is:
a. Denitrification
b. Ammonification
c. Nitrification
d. Assimilation
Rationale: Ammonification converts organic nitrogen into ammonia,
which can then be nitrified.
10. What is the typical detention time in a primary clarifier?
a. 10–20 minutes
b. 30–60 minutes
c. 1–3 hours
d. 6–8 hours
Rationale: A 1–3 hour detention allows settleable solids to
adequately separate from the liquid.
11. In an aerobic digester, the main purpose of aeration is to:
a. Remove heavy metals
b. Stabilize sludge by biological oxidation
c. Sediment solids
d. Adjust pH
