Delaware Wastewater Operator Class II
Practice Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. What is the primary purpose of preliminary treatment in a wastewater
treatment plant?
A. To remove dissolved nutrients
B. To remove large solids and grit
C. To disinfect the effluent
D. To remove pathogens
Rationale: Preliminary treatment primarily removes large solids and
grit to prevent damage to downstream equipment and reduce
clogging.
,2. Which of the following is a common biological treatment process in
wastewater treatment?
A. Coagulation
B. Sedimentation
C. Activated sludge
D. Filtration
Rationale: Activated sludge is a biological process that uses
microorganisms to consume organic matter in wastewater.
3. What is the typical range for BOD5 (Biochemical Oxygen Demand over
5 days) in raw domestic wastewater?
A. 10–50 mg/L
B. 50–100 mg/L
C. 200–300 mg/L
D. 400–600 mg/L
Rationale: Raw domestic wastewater typically has a BOD5 in the
range of 200–300 mg/L.
4. Which unit operation is used to remove settleable solids after
preliminary treatment?
A. Trickling filter
B. Primary clarifier
C. Chlorination
D. Aeration tank
, Rationale: The primary clarifier allows settleable solids to settle out
by gravity, reducing the load on secondary treatment.
5. What is the main function of aeration in an activated sludge system?
A. To remove grit
B. To supply oxygen for microbial activity
C. To separate solids from liquids
D. To disinfect the effluent
Rationale: Aeration provides oxygen necessary for microorganisms to
metabolize organic matter in the wastewater.
6. Which of the following indicates proper operation of a secondary
clarifier?
A. High effluent TSS
B. Clear effluent with low suspended solids
C. Floating scum throughout the tank
D. Excessive foaming
Rationale: A properly functioning secondary clarifier produces clear
effluent with minimal suspended solids.
7. What is the main purpose of disinfection in wastewater treatment?
A. Remove organic matter
B. Destroy pathogenic organisms
C. Remove nutrients
D. Reduce turbidity
, Rationale: Disinfection targets harmful microorganisms to protect
public health before effluent is discharged.
8. Which disinfectant is most commonly used in small wastewater
treatment plants?
A. Ozone
B. UV light
C. Chlorine
D. Hydrogen peroxide
Rationale: Chlorine is commonly used due to its effectiveness, ease of
handling, and cost efficiency.
9. Nitrification is the biological conversion of:
A. Nitrogen gas to ammonia
B. Ammonia to nitrate
C. Nitrate to nitrogen gas
D. Ammonium to nitrogen gas
Rationale: Nitrification is a two-step biological process where
ammonia is oxidized to nitrite and then nitrate.
10. Denitrification in wastewater treatment results in the
production of:
A. Nitrate
B. Ammonia
C. Nitrogen gas
D. Phosphate
Practice Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of preliminary treatment in a wastewater
treatment plant?
A. To remove dissolved nutrients
B. To remove large solids and grit
C. To disinfect the effluent
D. To remove pathogens
Rationale: Preliminary treatment primarily removes large solids and
grit to prevent damage to downstream equipment and reduce
clogging.
,2. Which of the following is a common biological treatment process in
wastewater treatment?
A. Coagulation
B. Sedimentation
C. Activated sludge
D. Filtration
Rationale: Activated sludge is a biological process that uses
microorganisms to consume organic matter in wastewater.
3. What is the typical range for BOD5 (Biochemical Oxygen Demand over
5 days) in raw domestic wastewater?
A. 10–50 mg/L
B. 50–100 mg/L
C. 200–300 mg/L
D. 400–600 mg/L
Rationale: Raw domestic wastewater typically has a BOD5 in the
range of 200–300 mg/L.
4. Which unit operation is used to remove settleable solids after
preliminary treatment?
A. Trickling filter
B. Primary clarifier
C. Chlorination
D. Aeration tank
, Rationale: The primary clarifier allows settleable solids to settle out
by gravity, reducing the load on secondary treatment.
5. What is the main function of aeration in an activated sludge system?
A. To remove grit
B. To supply oxygen for microbial activity
C. To separate solids from liquids
D. To disinfect the effluent
Rationale: Aeration provides oxygen necessary for microorganisms to
metabolize organic matter in the wastewater.
6. Which of the following indicates proper operation of a secondary
clarifier?
A. High effluent TSS
B. Clear effluent with low suspended solids
C. Floating scum throughout the tank
D. Excessive foaming
Rationale: A properly functioning secondary clarifier produces clear
effluent with minimal suspended solids.
7. What is the main purpose of disinfection in wastewater treatment?
A. Remove organic matter
B. Destroy pathogenic organisms
C. Remove nutrients
D. Reduce turbidity
, Rationale: Disinfection targets harmful microorganisms to protect
public health before effluent is discharged.
8. Which disinfectant is most commonly used in small wastewater
treatment plants?
A. Ozone
B. UV light
C. Chlorine
D. Hydrogen peroxide
Rationale: Chlorine is commonly used due to its effectiveness, ease of
handling, and cost efficiency.
9. Nitrification is the biological conversion of:
A. Nitrogen gas to ammonia
B. Ammonia to nitrate
C. Nitrate to nitrogen gas
D. Ammonium to nitrogen gas
Rationale: Nitrification is a two-step biological process where
ammonia is oxidized to nitrite and then nitrate.
10. Denitrification in wastewater treatment results in the
production of:
A. Nitrate
B. Ammonia
C. Nitrogen gas
D. Phosphate
