3 Practice Examination 100 Questions And

Virginia Wastewater Works Operator Class

• Practice Examination 100 Questions And

Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of preliminary treatment in a wastewater

plant?

• Biological removal of nutrients
• Removal of settleable solids
• Removal of large debris
• Chemical flocculation

Answer: C

Rationale: Preliminary treatment protects downstream equipment by

removing rags, sticks, and large debris.

• What device is commonly used for measuring wastewater flow in open

channels? 1 / 4

• Pitot tube
• Variable-area meter
• Parshall flume
• Positive displacement meter

Answer: C

Rationale: Parshall flumes provide accurate open-channel flow

measurement with predictable head-flow relationships.

• Which organism type is most desirable in a healthy activated sludge

system?

• Filamentous bacteria
• Free-swimming ciliates
• Rotifers
• Stalked ciliates

Answer: D

Rationale: Stalked ciliates indicate a stable, mature activated-sludge

environment with good settling characteristics.

• What is the typical dissolved oxygen (DO) range for an aerobic activated

sludge aeration tank?

• 0.1–0.5 mg/L
• 1–3 mg/L
• 5–10 mg/L
• 10–15 mg/L

Answer: B 2 / 4

Rationale: DO between 1–3 mg/L maintains aerobic conditions without

excessive energy consumption.

• Which parameter best indicates organic strength of wastewater?

A. TSS

• pH

C. BOD

• Alkalinity

Answer: C

Rationale: BOD measures biodegradable organic load entering treatment.

• 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.

• Which piece of equipment thickens sludge by allowing solids to settle

and compact?

• Belt filter press
• Clarifier 3 / 4

• Gravity thickener
• Aeration tank

Answer: C

Rationale: Gravity thickeners concentrate sludge using settling.

• What is the primary gas produced during anaerobic digestion?
• Nitrogen
• Methane
• Hydrogen

D. CO₂

Answer: B

Rationale: Methane is the main energy-rich gas from anaerobic digestion.

• What effect does low pH have on nitrification?
• No effect
• Speeds it up
• Slows or inhibits it
• Completely stops denitrification

Answer: C

Rationale: Nitrifying bacteria require near-neutral pH; low pH suppresses

their activity.

• What does sludge volume index (SVI) evaluate?
• Organic loading
• Sludge settling characteristics
• / 4