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Virginia Wastewater Works Operator Class 4 Practice Exam 100 Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf
- What is the primary purpose of wastewater treatment?
- Generate electricity
- Remove pollutants before discharge
- Produce fertilizers
- Increase water hardness
Answer: B
Rationale: Wastewater treatment aims to protect public health and the
environment by removing contaminants before water is released or reused.
- Which process is typically the first step in a wastewater treatment
plant? 1 / 4
- Disinfection
- Primary clarification
- Preliminary screening
- Biological treatment
Answer: C
Rationale: Screening removes large debris early to protect downstream
equipment.
3. Grit removal is used primarily to remove:
- Fats, oils, and grease
- Sand and small inorganic particles
- Pathogens
- Dissolved solids
Answer: B
Rationale: Grit chambers target heavy inorganic materials that cause
abrasion and wear.
4. The main purpose of primary clarifiers is to:
- Aerate wastewater
- Remove settleable solids
- Kill pathogens
- Remove ammonia
Answer: B
Rationale: Primary clarification reduces solids loading on downstream
biological processes. 2 / 4
5. Secondary treatment is primarily:
- Chemical precipitation
- Biological treatment
- Filtration
- Sludge composting
Answer: B
Rationale: Secondary treatment relies on microorganisms to break down
organic matter.
6. The activated sludge process depends mainly on:
- Chemical oxidation
- Mechanical filtration
- Microbial metabolism
- UV irradiation
Answer: C
Rationale: Activated sludge uses microbes that consume organic
pollutants.
- Dissolved oxygen (DO) concentration in aeration tanks is typically kept
around:
- 0 mg/L
- 1–2 mg/L
- 5–10 mg/L
- 12–15 mg/L 3 / 4
Answer: B
Rationale: Maintaining 1–2 mg/L DO supports aerobic microbial activity
without excessive energy use.
8. Too low DO in aeration tanks commonly causes:
- Filamentous bulking
- Toxicity
- Excessive nitrification
- High chlorine demand
Answer: A
Rationale: Low oxygen conditions favor filamentous organisms, causing
sludge settling issues.
9. Sludge that settles poorly in the secondary clarifier indicates:
- High DO
- Good floc formation
- Sludge bulking
- Proper F/M ratio
Answer: C
Rationale: Bulking sludge does not compact well, leading to poor settling.
10. The F/M ratio compares food to:
- Flow
- Microorganisms
- Metals
- / 4
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