Florida Wastewater Treatment Plant
Operator Class B Certification
Examination Practice Questions &
[Verified Answers], Plus Explained
Rationales|2026 Latest Update| Instant
Download PDF
1. A wastewater treatment plant receives an average flow of 2.4
MGD. Approximately how many gallons per day must the plant
process?
A. 240,000 gallons
B. 1,200,000 gallons
C. 2,400,000 gallons
D. 24,000,000 gallons
Rationale: MGD means million gallons per day. Therefore, 2.4 MGD
equals 2.4 million gallons per day, or 2,400,000 gallons per day.
2. What is the primary purpose of preliminary treatment at a
wastewater treatment facility?
A. Remove dissolved ammonia
B. Remove large debris, rags, grit, and other materials that could
damage downstream equipment
1|Page
,C. Convert nitrate to nitrogen gas
D. Disinfect the final effluent
Rationale: Preliminary treatment protects downstream equipment
and processes by removing screenings, grit, and other coarse
materials before they enter primary or secondary treatment.
3. Which unit process is primarily responsible for removing settleable
solids during primary treatment?
A. Chlorine contact tank
B. Aeration basin
C. Primary clarifier
D. Tertiary filter
Rationale: Primary clarifiers slow wastewater velocity sufficiently to
allow heavier settleable solids to settle while floatable materials rise
and can be removed.
4. A primary clarifier develops excessive sludge accumulation. What is
the most likely concern?
A. Increased dissolved oxygen
B. Improved settling
C. Septic sludge conditions and possible solids carryover
D. Increased chlorine residual
Rationale: Excessive sludge storage can promote anaerobic
decomposition and septic conditions. Rising gases can also cause
previously settled solids to float and leave the clarifier.
2|Page
,5. Which parameter is especially important when evaluating
activated-sludge process performance?
A. Color of the laboratory walls
B. Dissolved oxygen
C. Atmospheric pressure only
D. Chloride concentration only
Rationale: Dissolved oxygen is essential for aerobic biological
treatment and helps operators determine whether microorganisms
are receiving adequate oxygen.
6. What is the principal purpose of aeration in a conventional
activated-sludge process?
A. Remove grit
B. Destroy all pathogens instantly
C. Provide oxygen and maintain biological mixing
D. Increase wastewater temperature
Rationale: Aeration supplies oxygen needed by aerobic
microorganisms and provides mixing so that microorganisms,
wastewater, and oxygen remain in contact.
7. An aeration basin has a dissolved oxygen concentration that is
consistently near zero. What is the most appropriate operator
concern?
A. Excessive chlorination
B. Insufficient oxygen transfer or excessive oxygen demand
C. Excessive primary settling
D. Excessive UV intensity
3|Page
, Rationale: Very low dissolved oxygen may indicate inadequate
aeration, excessive organic loading, equipment problems, or excessive
oxygen demand.
8. What does BOD₅ primarily measure?
A. Total dissolved salts
B. Chlorine concentration
C. Biodegradable oxygen demand exerted by microorganisms over the
test period
D. Total suspended grit
Rationale: BOD₅ estimates the amount of oxygen microorganisms
require to biologically stabilize biodegradable organic matter during
the standard five-day test.
9. A wastewater sample has a BOD₅ of 250 mg/L and a flow of 1 MGD.
Approximately what is the daily BOD loading?
A. 25 lb/day
B. 125 lb/day
C. 2,085 lb/day
D. 20,850 lb/day
Rationale: The standard loading equation is lb/day = mg/L × MGD ×
8.34. Thus, 250 × 1 × 8.34 = 2,085 lb/day.
10. What is the main purpose of return activated sludge (RAS)?
A. Return primary screenings to the headworks
B. Return settled biological solids from the secondary clarifier to the
4|Page
Operator Class B Certification
Examination Practice Questions &
[Verified Answers], Plus Explained
Rationales|2026 Latest Update| Instant
Download PDF
1. A wastewater treatment plant receives an average flow of 2.4
MGD. Approximately how many gallons per day must the plant
process?
A. 240,000 gallons
B. 1,200,000 gallons
C. 2,400,000 gallons
D. 24,000,000 gallons
Rationale: MGD means million gallons per day. Therefore, 2.4 MGD
equals 2.4 million gallons per day, or 2,400,000 gallons per day.
2. What is the primary purpose of preliminary treatment at a
wastewater treatment facility?
A. Remove dissolved ammonia
B. Remove large debris, rags, grit, and other materials that could
damage downstream equipment
1|Page
,C. Convert nitrate to nitrogen gas
D. Disinfect the final effluent
Rationale: Preliminary treatment protects downstream equipment
and processes by removing screenings, grit, and other coarse
materials before they enter primary or secondary treatment.
3. Which unit process is primarily responsible for removing settleable
solids during primary treatment?
A. Chlorine contact tank
B. Aeration basin
C. Primary clarifier
D. Tertiary filter
Rationale: Primary clarifiers slow wastewater velocity sufficiently to
allow heavier settleable solids to settle while floatable materials rise
and can be removed.
4. A primary clarifier develops excessive sludge accumulation. What is
the most likely concern?
A. Increased dissolved oxygen
B. Improved settling
C. Septic sludge conditions and possible solids carryover
D. Increased chlorine residual
Rationale: Excessive sludge storage can promote anaerobic
decomposition and septic conditions. Rising gases can also cause
previously settled solids to float and leave the clarifier.
2|Page
,5. Which parameter is especially important when evaluating
activated-sludge process performance?
A. Color of the laboratory walls
B. Dissolved oxygen
C. Atmospheric pressure only
D. Chloride concentration only
Rationale: Dissolved oxygen is essential for aerobic biological
treatment and helps operators determine whether microorganisms
are receiving adequate oxygen.
6. What is the principal purpose of aeration in a conventional
activated-sludge process?
A. Remove grit
B. Destroy all pathogens instantly
C. Provide oxygen and maintain biological mixing
D. Increase wastewater temperature
Rationale: Aeration supplies oxygen needed by aerobic
microorganisms and provides mixing so that microorganisms,
wastewater, and oxygen remain in contact.
7. An aeration basin has a dissolved oxygen concentration that is
consistently near zero. What is the most appropriate operator
concern?
A. Excessive chlorination
B. Insufficient oxygen transfer or excessive oxygen demand
C. Excessive primary settling
D. Excessive UV intensity
3|Page
, Rationale: Very low dissolved oxygen may indicate inadequate
aeration, excessive organic loading, equipment problems, or excessive
oxygen demand.
8. What does BOD₅ primarily measure?
A. Total dissolved salts
B. Chlorine concentration
C. Biodegradable oxygen demand exerted by microorganisms over the
test period
D. Total suspended grit
Rationale: BOD₅ estimates the amount of oxygen microorganisms
require to biologically stabilize biodegradable organic matter during
the standard five-day test.
9. A wastewater sample has a BOD₅ of 250 mg/L and a flow of 1 MGD.
Approximately what is the daily BOD loading?
A. 25 lb/day
B. 125 lb/day
C. 2,085 lb/day
D. 20,850 lb/day
Rationale: The standard loading equation is lb/day = mg/L × MGD ×
8.34. Thus, 250 × 1 × 8.34 = 2,085 lb/day.
10. What is the main purpose of return activated sludge (RAS)?
A. Return primary screenings to the headworks
B. Return settled biological solids from the secondary clarifier to the
4|Page
