Virginia Wastewater Works Operator Class
3 Practice Examination 100 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
plant?
A. Biological removal of nutrients
B. Removal of settleable solids
C. Removal of large debris
D. Chemical flocculation
Answer: C
Rationale: Preliminary treatment protects downstream equipment by
removing rags, sticks, and large debris.
2. What device is commonly used for measuring wastewater flow in open
channels?
,A. Pitot tube
B. Variable-area meter
C. Parshall flume
D. Positive displacement meter
Answer: C
Rationale: Parshall flumes provide accurate open-channel flow
measurement with predictable head-flow relationships.
3. Which organism type is most desirable in a healthy activated sludge
system?
A. Filamentous bacteria
B. Free-swimming ciliates
C. Rotifers
D. Stalked ciliates
Answer: D
Rationale: Stalked ciliates indicate a stable, mature activated-sludge
environment with good settling characteristics.
4. What is the typical dissolved oxygen (DO) range for an aerobic activated
sludge aeration tank?
A. 0.1–0.5 mg/L
B. 1–3 mg/L
C. 5–10 mg/L
D. 10–15 mg/L
Answer: B
,Rationale: DO between 1–3 mg/L maintains aerobic conditions without
excessive energy consumption.
5. Which parameter best indicates organic strength of wastewater?
A. TSS
B. pH
C. BOD
D. Alkalinity
Answer: C
Rationale: BOD measures biodegradable organic load entering treatment.
6. In primary clarification, what is the typical percent removal of
suspended solids?
A. 5–10%
B. 20–30%
C. 50–70%
D. 90–95%
Answer: C
Rationale: Primary clarifiers normally remove half to two-thirds of
suspended solids.
7. Which piece of equipment thickens sludge by allowing solids to settle
and compact?
A. Belt filter press
B. Clarifier
, C. Gravity thickener
D. Aeration tank
Answer: C
Rationale: Gravity thickeners concentrate sludge using settling.
8. What is the primary gas produced during anaerobic digestion?
A. Nitrogen
B. Methane
C. Hydrogen
D. CO₂
Answer: B
Rationale: Methane is the main energy-rich gas from anaerobic digestion.
9. What effect does low pH have on nitrification?
A. No effect
B. Speeds it up
C. Slows or inhibits it
D. Completely stops denitrification
Answer: C
Rationale: Nitrifying bacteria require near-neutral pH; low pH suppresses
their activity.
10. What does sludge volume index (SVI) evaluate?
A. Organic loading
B. Sludge settling characteristics
3 Practice Examination 100 Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download
1. What is the primary purpose of preliminary treatment in a wastewater
plant?
A. Biological removal of nutrients
B. Removal of settleable solids
C. Removal of large debris
D. Chemical flocculation
Answer: C
Rationale: Preliminary treatment protects downstream equipment by
removing rags, sticks, and large debris.
2. What device is commonly used for measuring wastewater flow in open
channels?
,A. Pitot tube
B. Variable-area meter
C. Parshall flume
D. Positive displacement meter
Answer: C
Rationale: Parshall flumes provide accurate open-channel flow
measurement with predictable head-flow relationships.
3. Which organism type is most desirable in a healthy activated sludge
system?
A. Filamentous bacteria
B. Free-swimming ciliates
C. Rotifers
D. Stalked ciliates
Answer: D
Rationale: Stalked ciliates indicate a stable, mature activated-sludge
environment with good settling characteristics.
4. What is the typical dissolved oxygen (DO) range for an aerobic activated
sludge aeration tank?
A. 0.1–0.5 mg/L
B. 1–3 mg/L
C. 5–10 mg/L
D. 10–15 mg/L
Answer: B
,Rationale: DO between 1–3 mg/L maintains aerobic conditions without
excessive energy consumption.
5. Which parameter best indicates organic strength of wastewater?
A. TSS
B. pH
C. BOD
D. Alkalinity
Answer: C
Rationale: BOD measures biodegradable organic load entering treatment.
6. In primary clarification, what is the typical percent removal of
suspended solids?
A. 5–10%
B. 20–30%
C. 50–70%
D. 90–95%
Answer: C
Rationale: Primary clarifiers normally remove half to two-thirds of
suspended solids.
7. Which piece of equipment thickens sludge by allowing solids to settle
and compact?
A. Belt filter press
B. Clarifier
, C. Gravity thickener
D. Aeration tank
Answer: C
Rationale: Gravity thickeners concentrate sludge using settling.
8. What is the primary gas produced during anaerobic digestion?
A. Nitrogen
B. Methane
C. Hydrogen
D. CO₂
Answer: B
Rationale: Methane is the main energy-rich gas from anaerobic digestion.
9. What effect does low pH have on nitrification?
A. No effect
B. Speeds it up
C. Slows or inhibits it
D. Completely stops denitrification
Answer: C
Rationale: Nitrifying bacteria require near-neutral pH; low pH suppresses
their activity.
10. What does sludge volume index (SVI) evaluate?
A. Organic loading
B. Sludge settling characteristics
