CALIFORNIA WASTEWATER TREATMENT
OPERATOR GRADE III PRACTICE EXAMINATION
NEWEST 2025 – 2026 QUESTIONS FROM ACTUAL
EXAMS COMPLETE 100 QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS)
|ALREADY GRADED A+||BRAND NEW!!
Content Covered (Most Tested Areas): Activated Sludge Process,
Secondary Treatment Operations, Process Control Calculations
(F/M, MCRT, SVI), Clarifier Operation, Sludge Handling,
Disinfection, Nutrient Removal, Laboratory Testing, Safety, Pumps
and Equipment, Troubleshooting Plant Operations
1. What is the primary purpose of the activated sludge process in wastewater treatment?
A. Remove grit and sand
B. Remove dissolved oxygen
C. Biologically remove organic matter
D. Remove large debris
Answer: C. Biologically remove organic matter
Explanation: The activated sludge process uses microorganisms to biologically
degrade organic material measured as BOD or COD.
2. The food-to-microorganism ratio (F/M) compares:
A. BOD load to microorganism mass
B. Flow rate to sludge age
C. Oxygen to nitrogen concentration
D. Clarifier depth to MLSS
Answer: A. BOD load to microorganism mass
Explanation: F/M ratio is the pounds of BOD entering the aeration tank divided by
pounds of microorganisms (MLVSS) present.
3. Mixed Liquor Suspended Solids (MLSS) represents:
A. Solids in the primary clarifier
B. Solids in the aeration tank mixture
,C. Solids in the final effluent
D. Solids removed in digestion
Answer: B. Solids in the aeration tank mixture
Explanation: MLSS includes microorganisms and suspended solids present in the
aeration tank.
4. Sludge Volume Index (SVI) is used to determine:
A. Oxygen demand
B. Sludge settling characteristics
C. Chlorine dosage
D. Flow velocity
Answer: B. Sludge settling characteristics
Explanation: SVI measures the volume occupied by settled sludge after 30 minutes
relative to MLSS concentration.
5. Excessive sludge bulking in a clarifier is often caused by:
A. Low temperature
B. Filamentous bacteria growth
C. High chlorine residual
D. Low pH only
Answer: B. Filamentous bacteria growth
Explanation: Filamentous organisms prevent proper settling, causing bulky sludge.
6. Return Activated Sludge (RAS) is recycled to:
A. Primary clarifier
B. Headworks
C. Aeration tank
D. Sludge digester
Answer: C. Aeration tank
Explanation: RAS returns settled microorganisms to maintain biological
population in aeration.
7. Mean Cell Residence Time (MCRT) refers to:
A. Time solids remain in the system
B. Flow retention time in pipes
, C. Pump operating time
D. Disinfection contact time
Answer: A. Time solids remain in the system
Explanation: MCRT indicates average time microorganisms remain in the
biological system.
8. A high SVI value indicates:
A. Good settling sludge
B. Bulking sludge
C. Excellent compaction
D. Low MLSS
Answer: B. Bulking sludge
Explanation: High SVI means sludge settles poorly and occupies larger volume.
9. Primary treatment mainly removes:
A. Dissolved nutrients
B. Suspended solids
C. Dissolved oxygen
D. Pathogens
Answer: B. Suspended solids
Explanation: Primary clarifiers remove settleable and floating solids.
10. Nitrification converts:
A. Nitrogen gas to ammonia
B. Ammonia to nitrate
C. Nitrate to nitrogen gas
D. Nitrite to ammonia
Answer: B. Ammonia to nitrate
Explanation: Nitrifying bacteria oxidize ammonia to nitrite and then nitrate.
11. Denitrification converts nitrate into:
A. Ammonia
B. Nitrite
C. Nitrogen gas
D. Oxygen
OPERATOR GRADE III PRACTICE EXAMINATION
NEWEST 2025 – 2026 QUESTIONS FROM ACTUAL
EXAMS COMPLETE 100 QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS)
|ALREADY GRADED A+||BRAND NEW!!
Content Covered (Most Tested Areas): Activated Sludge Process,
Secondary Treatment Operations, Process Control Calculations
(F/M, MCRT, SVI), Clarifier Operation, Sludge Handling,
Disinfection, Nutrient Removal, Laboratory Testing, Safety, Pumps
and Equipment, Troubleshooting Plant Operations
1. What is the primary purpose of the activated sludge process in wastewater treatment?
A. Remove grit and sand
B. Remove dissolved oxygen
C. Biologically remove organic matter
D. Remove large debris
Answer: C. Biologically remove organic matter
Explanation: The activated sludge process uses microorganisms to biologically
degrade organic material measured as BOD or COD.
2. The food-to-microorganism ratio (F/M) compares:
A. BOD load to microorganism mass
B. Flow rate to sludge age
C. Oxygen to nitrogen concentration
D. Clarifier depth to MLSS
Answer: A. BOD load to microorganism mass
Explanation: F/M ratio is the pounds of BOD entering the aeration tank divided by
pounds of microorganisms (MLVSS) present.
3. Mixed Liquor Suspended Solids (MLSS) represents:
A. Solids in the primary clarifier
B. Solids in the aeration tank mixture
,C. Solids in the final effluent
D. Solids removed in digestion
Answer: B. Solids in the aeration tank mixture
Explanation: MLSS includes microorganisms and suspended solids present in the
aeration tank.
4. Sludge Volume Index (SVI) is used to determine:
A. Oxygen demand
B. Sludge settling characteristics
C. Chlorine dosage
D. Flow velocity
Answer: B. Sludge settling characteristics
Explanation: SVI measures the volume occupied by settled sludge after 30 minutes
relative to MLSS concentration.
5. Excessive sludge bulking in a clarifier is often caused by:
A. Low temperature
B. Filamentous bacteria growth
C. High chlorine residual
D. Low pH only
Answer: B. Filamentous bacteria growth
Explanation: Filamentous organisms prevent proper settling, causing bulky sludge.
6. Return Activated Sludge (RAS) is recycled to:
A. Primary clarifier
B. Headworks
C. Aeration tank
D. Sludge digester
Answer: C. Aeration tank
Explanation: RAS returns settled microorganisms to maintain biological
population in aeration.
7. Mean Cell Residence Time (MCRT) refers to:
A. Time solids remain in the system
B. Flow retention time in pipes
, C. Pump operating time
D. Disinfection contact time
Answer: A. Time solids remain in the system
Explanation: MCRT indicates average time microorganisms remain in the
biological system.
8. A high SVI value indicates:
A. Good settling sludge
B. Bulking sludge
C. Excellent compaction
D. Low MLSS
Answer: B. Bulking sludge
Explanation: High SVI means sludge settles poorly and occupies larger volume.
9. Primary treatment mainly removes:
A. Dissolved nutrients
B. Suspended solids
C. Dissolved oxygen
D. Pathogens
Answer: B. Suspended solids
Explanation: Primary clarifiers remove settleable and floating solids.
10. Nitrification converts:
A. Nitrogen gas to ammonia
B. Ammonia to nitrate
C. Nitrate to nitrogen gas
D. Nitrite to ammonia
Answer: B. Ammonia to nitrate
Explanation: Nitrifying bacteria oxidize ammonia to nitrite and then nitrate.
11. Denitrification converts nitrate into:
A. Ammonia
B. Nitrite
C. Nitrogen gas
D. Oxygen
