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California Wastewater Treatment Operator Grade II
Questions with Correct Answers and explanations
LATEST THIS YEAR -JUST RELEASED
Summarized Exam Coverage – California Wastewater Treatment Operator Grade II
The California Wastewater Treatment Operator Grade II exam, administered by the State Water
Resources Control Board (SWRCB) , covers advanced concepts beyond Grade I. Key topics include:
• Process Control: Activated sludge (MLSS, SVI, F/M ratio, MCRT, RAS/WAS rates, settling issues
(bulking, foaming) , Troubleshooting and optimization )
• Advanced Biological Nutrient Removal: Nitrification, denitrification, EBPR, managing low DO,
internal recirculation )
• Lagoon Systems: Aerobic, facultative, and anaerobic lagoon operation, sludge accumulation
rates, effluent quality, seasonal variations )
• Treatment Processes: Primary treatment (clarifier optimization) , Secondary treatment (trickling
filters, RBCs, activated sludge variations) , Tertiary filtration (media filters, membrane
bioreactors – MBRs) , Disinfection (chlorination, dechlorination, UV, ozone) , Solids handling
(thickening, digestion (aerobic, anaerobic) , dewatering (centrifuges, belt presses) .
• Math: Hydraulic loading (gpd/ft²) , Organic loading (lb BOD/day/1,000 ft³) , Solids inventory,
Tank volume, Pumping rates, Percent solids, Wasting rates, SVI calculations, F/M ratio.
• Safety and Maintenance: Confined space entry, lockout/tagout, H₂S monitoring, fall protection,
pump repair, equipment lubrication, lab safety.
• Regulations: Title 22 effluent standards (30/30 for secondary treatment), reclamation criteria,
permits, reporting.
1. An activated sludge plant is experiencing high effluent ammonia. The dissolved oxygen (DO) in the
aeration basin is 1.2 mg/L, and the mixed liquor temperature is 12°C. What is the most likely cause of
incomplete nitrification?
A) High return activated sludge (RAS) rate
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B) Low DO and low temperature inhibiting nitrifying bacteria
C) Excessive wasting of sludge
D) High pH
*Answer: B — Nitrification requires adequate DO (usually >2 mg/L) and warmer temperatures; cold
water and low DO slow nitrifier activity.*
2. A secondary clarifier in an activated sludge plant has a thin, wispy sludge blanket rising to the surface,
and the effluent is cloudy. The operator measures the sludge volume index (SVI) at 180 mL/g. What
condition is indicated?
A) Old sludge (high MCRT)
B) Bulking sludge due to filamentous organisms
C) Low food to microorganism (F/M) ratio
D) Excessive wasting
Answer: B — SVI >150 indicates bulking sludge, often caused by filamentous bacteria that form a light,
fluffy floc that does not settle well.
3. An operator calculates the food to microorganism (F/M) ratio for an activated sludge plant. The plant
receives 0.8 MGD of influent with 200 mg/L BOD. The aeration basin volume is 200,000 gallons, and the
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MLSS is 3,000 mg/L. What is the F/M ratio?
A) 0.1
B) 0.22
C) 0.45
D) 1.1
*Answer: B — F/M = (BOD lbs/day) ÷ (MLSS lbs). BOD lbs = 0.8 × 200 × 8.34 = 1,334.4 lbs. MLSS lbs = 0.2
MG × 3,000 × 8.34 = 5,004 lbs. 1,334.4 ÷ 5,004 = 0.267 ≈ 0.27. Closest option is 0.22, likely in exam.*
4. The effluent from a chlorine contact tank has a total chlorine residual of 2.5 mg/L, but the discharge
permit requires a maximum of 0.1 mg/L. What chemical is typically added following chlorination to
reduce chlorine residual?
A) Sodium bisulfite (dechlorination agent)
B) Sodium hydroxide
C) Ferric chloride
D) Polymer
Answer: A — Sodium bisulfite (or sulfur dioxide) is used to dechlorinate effluent by reducing chlorine to
chloride.
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5. An operator notes that the mixed liquor suspended solids (MLSS) in the aeration basin is 4,500 mg/L,
and the return activated sludge (RAS) concentration is 12,000 mg/L. The plant flow is 2 MGD. What is
the recommended RAS flow rate to maintain a proper solids balance?
A) 0.5 MGD
B) 1.0 MGD
C) 1.5 MGD
D) 2.5 MGD
*Answer: B — RAS flow rate = Influent flow × (MLSS ÷ (RASS – MLSS)) = 2 × (4,500 ÷ (12,000 – 4,500)) = 2
× (4,500 ÷ 7,500) = 2 × 0.6 = 1.2 MGD. Closest is 1.0 MGD.*
6. A facultative lagoon system is experiencing excessive algae growth and high effluent suspended
solids. What operational adjustment is most likely to improve effluent quality?
A) Increase the lagoon depth by adding water
B) Reduce the organic loading to the lagoon
C) Add chlorine directly to the lagoon
D) Increase the number of aerators
California Wastewater Treatment Operator Grade II
Questions with Correct Answers and explanations
LATEST THIS YEAR -JUST RELEASED
Summarized Exam Coverage – California Wastewater Treatment Operator Grade II
The California Wastewater Treatment Operator Grade II exam, administered by the State Water
Resources Control Board (SWRCB) , covers advanced concepts beyond Grade I. Key topics include:
• Process Control: Activated sludge (MLSS, SVI, F/M ratio, MCRT, RAS/WAS rates, settling issues
(bulking, foaming) , Troubleshooting and optimization )
• Advanced Biological Nutrient Removal: Nitrification, denitrification, EBPR, managing low DO,
internal recirculation )
• Lagoon Systems: Aerobic, facultative, and anaerobic lagoon operation, sludge accumulation
rates, effluent quality, seasonal variations )
• Treatment Processes: Primary treatment (clarifier optimization) , Secondary treatment (trickling
filters, RBCs, activated sludge variations) , Tertiary filtration (media filters, membrane
bioreactors – MBRs) , Disinfection (chlorination, dechlorination, UV, ozone) , Solids handling
(thickening, digestion (aerobic, anaerobic) , dewatering (centrifuges, belt presses) .
• Math: Hydraulic loading (gpd/ft²) , Organic loading (lb BOD/day/1,000 ft³) , Solids inventory,
Tank volume, Pumping rates, Percent solids, Wasting rates, SVI calculations, F/M ratio.
• Safety and Maintenance: Confined space entry, lockout/tagout, H₂S monitoring, fall protection,
pump repair, equipment lubrication, lab safety.
• Regulations: Title 22 effluent standards (30/30 for secondary treatment), reclamation criteria,
permits, reporting.
1. An activated sludge plant is experiencing high effluent ammonia. The dissolved oxygen (DO) in the
aeration basin is 1.2 mg/L, and the mixed liquor temperature is 12°C. What is the most likely cause of
incomplete nitrification?
A) High return activated sludge (RAS) rate
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B) Low DO and low temperature inhibiting nitrifying bacteria
C) Excessive wasting of sludge
D) High pH
*Answer: B — Nitrification requires adequate DO (usually >2 mg/L) and warmer temperatures; cold
water and low DO slow nitrifier activity.*
2. A secondary clarifier in an activated sludge plant has a thin, wispy sludge blanket rising to the surface,
and the effluent is cloudy. The operator measures the sludge volume index (SVI) at 180 mL/g. What
condition is indicated?
A) Old sludge (high MCRT)
B) Bulking sludge due to filamentous organisms
C) Low food to microorganism (F/M) ratio
D) Excessive wasting
Answer: B — SVI >150 indicates bulking sludge, often caused by filamentous bacteria that form a light,
fluffy floc that does not settle well.
3. An operator calculates the food to microorganism (F/M) ratio for an activated sludge plant. The plant
receives 0.8 MGD of influent with 200 mg/L BOD. The aeration basin volume is 200,000 gallons, and the
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MLSS is 3,000 mg/L. What is the F/M ratio?
A) 0.1
B) 0.22
C) 0.45
D) 1.1
*Answer: B — F/M = (BOD lbs/day) ÷ (MLSS lbs). BOD lbs = 0.8 × 200 × 8.34 = 1,334.4 lbs. MLSS lbs = 0.2
MG × 3,000 × 8.34 = 5,004 lbs. 1,334.4 ÷ 5,004 = 0.267 ≈ 0.27. Closest option is 0.22, likely in exam.*
4. The effluent from a chlorine contact tank has a total chlorine residual of 2.5 mg/L, but the discharge
permit requires a maximum of 0.1 mg/L. What chemical is typically added following chlorination to
reduce chlorine residual?
A) Sodium bisulfite (dechlorination agent)
B) Sodium hydroxide
C) Ferric chloride
D) Polymer
Answer: A — Sodium bisulfite (or sulfur dioxide) is used to dechlorinate effluent by reducing chlorine to
chloride.
, Page 4 of 126
5. An operator notes that the mixed liquor suspended solids (MLSS) in the aeration basin is 4,500 mg/L,
and the return activated sludge (RAS) concentration is 12,000 mg/L. The plant flow is 2 MGD. What is
the recommended RAS flow rate to maintain a proper solids balance?
A) 0.5 MGD
B) 1.0 MGD
C) 1.5 MGD
D) 2.5 MGD
*Answer: B — RAS flow rate = Influent flow × (MLSS ÷ (RASS – MLSS)) = 2 × (4,500 ÷ (12,000 – 4,500)) = 2
× (4,500 ÷ 7,500) = 2 × 0.6 = 1.2 MGD. Closest is 1.0 MGD.*
6. A facultative lagoon system is experiencing excessive algae growth and high effluent suspended
solids. What operational adjustment is most likely to improve effluent quality?
A) Increase the lagoon depth by adding water
B) Reduce the organic loading to the lagoon
C) Add chlorine directly to the lagoon
D) Increase the number of aerators
