CALIFORNIA WASTEWATER TREATMENT OPERATOR
GRADE II EXAM — PRACTICE TEST (2025 PAST
PAPERS–BASED) NEWEST 2025- 2026 UPDATE 100
QUESTIONS & 100% CORRECT ANSWERS GRADED
A+ (BRAND NEW!!)
Most Tested Areas: Activated sludge process control,
disinfection, solids handling, laboratory analysis, safety, pumps,
hydraulics, trickling filters, regulations, troubleshooting, math
calculations.
1. What is the primary purpose of primary sedimentation?
Answer: Removal of settleable solids and floatable material
Explanation: Primary clarifiers reduce suspended solids and BOD by
settling heavy particles and skimming grease.
2. Which parameter best indicates organic strength of wastewater?
Answer: Biochemical Oxygen Demand (BOD)
Explanation: BOD measures oxygen required by microorganisms to
decompose organic matter.
3. What does MLSS stand for?
Answer: Mixed Liquor Suspended Solids
Explanation: MLSS represents the concentration of biomass in the
aeration tank.
4. What is the main function of return activated sludge (RAS)?
Answer: Maintain adequate biomass in the aeration tank
, Explanation: RAS recycles settled microorganisms back to sustain
treatment.
5. Excessive sludge age typically causes what condition?
Answer: Old sludge with poor settling
Explanation: High solids retention time leads to filamentous growth and
low activity.
6. Dissolved oxygen in an aeration tank should generally be
maintained above what level?
Answer: 2.0 mg/L
Explanation: Adequate oxygen ensures aerobic microbial activity.
7. What is the purpose of wasting sludge (WAS)?
Answer: Control solids concentration and sludge age
Explanation: Removing excess biomass prevents system overload.
8. Nitrification converts ammonia into what substance first?
Answer: Nitrite
Explanation: Ammonia is oxidized to nitrite, then to nitrate.
9. Denitrification occurs under what conditions?
Answer: Anoxic conditions
Explanation: Nitrate is converted to nitrogen gas without dissolved
oxygen.
10. What is a common cause of sludge bulking?
Answer: Filamentous bacteria overgrowth
Explanation: Filaments prevent compact settling.
11. Chlorine demand refers to what?
Answer: Amount of chlorine consumed before residual remains
Explanation: Organic and inorganic substances react with chlorine first.
GRADE II EXAM — PRACTICE TEST (2025 PAST
PAPERS–BASED) NEWEST 2025- 2026 UPDATE 100
QUESTIONS & 100% CORRECT ANSWERS GRADED
A+ (BRAND NEW!!)
Most Tested Areas: Activated sludge process control,
disinfection, solids handling, laboratory analysis, safety, pumps,
hydraulics, trickling filters, regulations, troubleshooting, math
calculations.
1. What is the primary purpose of primary sedimentation?
Answer: Removal of settleable solids and floatable material
Explanation: Primary clarifiers reduce suspended solids and BOD by
settling heavy particles and skimming grease.
2. Which parameter best indicates organic strength of wastewater?
Answer: Biochemical Oxygen Demand (BOD)
Explanation: BOD measures oxygen required by microorganisms to
decompose organic matter.
3. What does MLSS stand for?
Answer: Mixed Liquor Suspended Solids
Explanation: MLSS represents the concentration of biomass in the
aeration tank.
4. What is the main function of return activated sludge (RAS)?
Answer: Maintain adequate biomass in the aeration tank
, Explanation: RAS recycles settled microorganisms back to sustain
treatment.
5. Excessive sludge age typically causes what condition?
Answer: Old sludge with poor settling
Explanation: High solids retention time leads to filamentous growth and
low activity.
6. Dissolved oxygen in an aeration tank should generally be
maintained above what level?
Answer: 2.0 mg/L
Explanation: Adequate oxygen ensures aerobic microbial activity.
7. What is the purpose of wasting sludge (WAS)?
Answer: Control solids concentration and sludge age
Explanation: Removing excess biomass prevents system overload.
8. Nitrification converts ammonia into what substance first?
Answer: Nitrite
Explanation: Ammonia is oxidized to nitrite, then to nitrate.
9. Denitrification occurs under what conditions?
Answer: Anoxic conditions
Explanation: Nitrate is converted to nitrogen gas without dissolved
oxygen.
10. What is a common cause of sludge bulking?
Answer: Filamentous bacteria overgrowth
Explanation: Filaments prevent compact settling.
11. Chlorine demand refers to what?
Answer: Amount of chlorine consumed before residual remains
Explanation: Organic and inorganic substances react with chlorine first.
