Page 1 of 143
Delaware Wastewater Operator Class II Exam ACTUAL EXAM
COMPLETE QUESTIONS AND CORRECT ANSWERS LATEST
UPDATE THIS YEAR
Delaware Wastewater Operator Class II Exam,
Summarized Exam Topics Covered (Point Form – Accurate for Class II Exam)
• Regulatory Framework: Delaware Surface Water Quality Standards, 7 DE Admin. Code 7201,
DNREC permitting, NPDES, effluent limits, sludge management
• Treatment Levels: Primary (sedimentation), Secondary (biological), Tertiary (advanced),
disinfection (chlorination/UV/dechlorination)
• Biological Treatment: Activated sludge (conventional, extended aeration), trickling filters, RBC,
lagoon systems, nitrification/denitrification
• Process Control: MLSS, MLVSS, SVI, DO control (2.0 mg/L minimum), F/M ratio, sludge age
(MCRT), return activated sludge (RAS), waste activated sludge (WAS)
• Sedimentation & Clarification: Detention time (2-4 hours), weir overflow rate, sludge blanket
depth, denitrification in final clarifiers
• Nutrient Removal: Biological and chemical phosphorus removal, nitrification/denitrification for
nitrogen
• Solids Handling: Sludge thickening (gravity, DAF), dewatering (belt press, centrifuge, drying
beds), anaerobic/aerobic digestion (VS reduction, gas production)
• Disinfection: Chlorination (dosage, contact time, dechlorination), UV transmittance, dose, lamp
maintenance
• Pumps & Hydraulics: Centrifugal pump curves, cavitation, wet well level control, VFDs, flow
measurement (Parshall flume)
• Laboratory: DO (Membrane electrode, Winkler), BOD (5-day, seeded), TSS (gravimetric), pH,
alkalinity, microscopic exam (filamentous bacteria, protozoa)
• Safety: Confined space (permit, testing, attendant), H₂S detection, lockout/tagout (LOTO), PPE,
SCBA
• Calculations: Detention time, organic loading (BOD/lb/1000 ft³), SVI (mL/g), MCRT (days), WAS
rate (gpm), sludge age
• Maintenance: Pump packing, greasing, V-belt tension, instrument calibration (DO probes, flow
meters)
• Troubleshooting & Odor Control: Rising sludge (denitrification/over-aeration), bulking
(filamentous), pin floc (under-aeration), chlorination of return sludge, H₂S scrubbers
1. A Class II operator notices that the activated sludge in the aeration basin has a dark brown color and a
“septic” odor. What is the most likely condition?
A) Normal healthy activated sludge
B) Old sludge (excess sludge age, low F/M)
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C) Young sludge (high F/M)
D) Bulking sludge due to filamentous bacteria
Answer: B
Rationale: Dark brown/black color and septic odor indicate old sludge (excess sludge age, low F/M).
Healthy sludge is light brown with an earthy smell.
2. The operator measures the dissolved oxygen (DO) in the aeration basin at 0.5 mg/L. The permit
requires a minimum of 2.0 mg/L. What is the immediate operational adjustment?
A) Increase the return activated sludge (RAS) rate
B) Increase the aeration rate (blower output)
C) Increase the waste activated sludge (WAS) rate
D) Reduce the influent flow if possible
Answer: B
Rationale: Low DO is corrected by increasing aeration (blower speed or valve position). RAS and WAS
adjustments affect sludge age, not directly DO.
3. A final clarifier has patches of black, rising sludge that bubble and float to the surface. Microscopic
exam shows no filamentous bacteria but many protozoa. What is the most likely cause?
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A) Bulking sludge
B) Denitrification in the final clarifier
C) Young sludge (high F/M)
D) Grease or oil accumulation
Answer: B
Rationale: Rising sludge with bubbles (often black) indicates denitrification in the clarifier, producing N₂
gas that lifts sludge. Correct by reducing aeration or increasing RAS.
4. A secondary clarifier weir overflow rate is 12,000 gpd/ft. Is this within typical design standards for
final clarifiers?
A) Yes, 10,000-15,000 gpd/ft is typical
B) No, maximum is 5,000 gpd/ft
C) Yes, as long as the solids loading is below 50 lb/day/ft²
D) No, final clarifiers should have weir rates below 5,000 gpd/ft
Answer: A
*Rationale: Typical weir overflow rates for final clarifiers are 10,000-15,000 gpd/ft. Higher rates may
cause solids carryover.*
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5. Compute the SVI (Sludge Volume Index) if a 1-L sample has an MLSS of 3,000 mg/L and settles to
200 mL in 30 minutes. SVI = (settled volume (mL/L) × 1,000) / MLSS (mg/L)
A) 66.7 mL/g
B) 100 mL/g
C) 150 mL/g
D) 300 mL/g
Answer: A
*Rationale: SVI = (settled volume (mL/L) × 1,000) / MLSS (mg/L). (200 × 1,000) / 3,000 = 66.7 mL/g.
Normal SVI is 80-120 mL/g.*
6. An operator notices that the secondary clarifier has a thin, billowy white foam on the surface. What is
the most likely cause?
A) Old sludge
B) Young sludge (high F/M)
C) Denitrification
D) Grease and oil
Answer: B
Delaware Wastewater Operator Class II Exam ACTUAL EXAM
COMPLETE QUESTIONS AND CORRECT ANSWERS LATEST
UPDATE THIS YEAR
Delaware Wastewater Operator Class II Exam,
Summarized Exam Topics Covered (Point Form – Accurate for Class II Exam)
• Regulatory Framework: Delaware Surface Water Quality Standards, 7 DE Admin. Code 7201,
DNREC permitting, NPDES, effluent limits, sludge management
• Treatment Levels: Primary (sedimentation), Secondary (biological), Tertiary (advanced),
disinfection (chlorination/UV/dechlorination)
• Biological Treatment: Activated sludge (conventional, extended aeration), trickling filters, RBC,
lagoon systems, nitrification/denitrification
• Process Control: MLSS, MLVSS, SVI, DO control (2.0 mg/L minimum), F/M ratio, sludge age
(MCRT), return activated sludge (RAS), waste activated sludge (WAS)
• Sedimentation & Clarification: Detention time (2-4 hours), weir overflow rate, sludge blanket
depth, denitrification in final clarifiers
• Nutrient Removal: Biological and chemical phosphorus removal, nitrification/denitrification for
nitrogen
• Solids Handling: Sludge thickening (gravity, DAF), dewatering (belt press, centrifuge, drying
beds), anaerobic/aerobic digestion (VS reduction, gas production)
• Disinfection: Chlorination (dosage, contact time, dechlorination), UV transmittance, dose, lamp
maintenance
• Pumps & Hydraulics: Centrifugal pump curves, cavitation, wet well level control, VFDs, flow
measurement (Parshall flume)
• Laboratory: DO (Membrane electrode, Winkler), BOD (5-day, seeded), TSS (gravimetric), pH,
alkalinity, microscopic exam (filamentous bacteria, protozoa)
• Safety: Confined space (permit, testing, attendant), H₂S detection, lockout/tagout (LOTO), PPE,
SCBA
• Calculations: Detention time, organic loading (BOD/lb/1000 ft³), SVI (mL/g), MCRT (days), WAS
rate (gpm), sludge age
• Maintenance: Pump packing, greasing, V-belt tension, instrument calibration (DO probes, flow
meters)
• Troubleshooting & Odor Control: Rising sludge (denitrification/over-aeration), bulking
(filamentous), pin floc (under-aeration), chlorination of return sludge, H₂S scrubbers
1. A Class II operator notices that the activated sludge in the aeration basin has a dark brown color and a
“septic” odor. What is the most likely condition?
A) Normal healthy activated sludge
B) Old sludge (excess sludge age, low F/M)
, Page 2 of 143
C) Young sludge (high F/M)
D) Bulking sludge due to filamentous bacteria
Answer: B
Rationale: Dark brown/black color and septic odor indicate old sludge (excess sludge age, low F/M).
Healthy sludge is light brown with an earthy smell.
2. The operator measures the dissolved oxygen (DO) in the aeration basin at 0.5 mg/L. The permit
requires a minimum of 2.0 mg/L. What is the immediate operational adjustment?
A) Increase the return activated sludge (RAS) rate
B) Increase the aeration rate (blower output)
C) Increase the waste activated sludge (WAS) rate
D) Reduce the influent flow if possible
Answer: B
Rationale: Low DO is corrected by increasing aeration (blower speed or valve position). RAS and WAS
adjustments affect sludge age, not directly DO.
3. A final clarifier has patches of black, rising sludge that bubble and float to the surface. Microscopic
exam shows no filamentous bacteria but many protozoa. What is the most likely cause?
, Page 3 of 143
A) Bulking sludge
B) Denitrification in the final clarifier
C) Young sludge (high F/M)
D) Grease or oil accumulation
Answer: B
Rationale: Rising sludge with bubbles (often black) indicates denitrification in the clarifier, producing N₂
gas that lifts sludge. Correct by reducing aeration or increasing RAS.
4. A secondary clarifier weir overflow rate is 12,000 gpd/ft. Is this within typical design standards for
final clarifiers?
A) Yes, 10,000-15,000 gpd/ft is typical
B) No, maximum is 5,000 gpd/ft
C) Yes, as long as the solids loading is below 50 lb/day/ft²
D) No, final clarifiers should have weir rates below 5,000 gpd/ft
Answer: A
*Rationale: Typical weir overflow rates for final clarifiers are 10,000-15,000 gpd/ft. Higher rates may
cause solids carryover.*
, Page 4 of 143
5. Compute the SVI (Sludge Volume Index) if a 1-L sample has an MLSS of 3,000 mg/L and settles to
200 mL in 30 minutes. SVI = (settled volume (mL/L) × 1,000) / MLSS (mg/L)
A) 66.7 mL/g
B) 100 mL/g
C) 150 mL/g
D) 300 mL/g
Answer: A
*Rationale: SVI = (settled volume (mL/L) × 1,000) / MLSS (mg/L). (200 × 1,000) / 3,000 = 66.7 mL/g.
Normal SVI is 80-120 mL/g.*
6. An operator notices that the secondary clarifier has a thin, billowy white foam on the surface. What is
the most likely cause?
A) Old sludge
B) Young sludge (high F/M)
C) Denitrification
D) Grease and oil
Answer: B
