III Certification Practice Exam Questions

Industrial Waste Treatment Operator Class III Certification Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• The main purpose of primary treatment in an industrial wastewater plant

is to:

• Remove dissolved organics
• Remove settleable and floatable solids
• Oxidize ammonia
• Disinfect pathogens

Rationale: Primary treatment uses sedimentation and skimming to

separate solids before biological or chemical treatment.

2. The primary function of secondary treatment is to:

• Filter suspended solids
• Biologically remove organic matter 1 / 4

• Neutralize acids
• Precipitate metals

Rationale: Secondary treatment employs microorganisms to metabolize

organic matter measured as BOD.

• Which parameter best indicates organic pollution in wastewater?

A. TSS

B. BOD

• Chloride
• Turbidity

Rationale: Biochemical Oxygen Demand (BOD) measures oxygen needed

for microbial degradation of organics.

4. The typical detention time in a primary clarifier is:

• 5–10 minutes
• 6–8 hours
• 1.5–2.5 hours
• 10–12 hours

Rationale: Primary clarifiers are designed for around 1.5–2.5 hours to

settle solids efficiently.

• / 4

5. The most common coagulant in chemical treatment is:

• Sodium hydroxide
• Aluminum sulfate (alum)
• Ferric chloride
• Lime

Rationale: Alum neutralizes negative charges on colloids to enhance

settling.

6. The activated sludge process relies primarily on:

• Aerobic microorganisms
• Anaerobic bacteria
• Chemical oxidation
• Adsorption

Rationale: Aerobic microbes oxidize organic material into CO₂, water, and

biomass.

7. The F/M ratio in activated sludge refers to:

• Flow per mass
• Food to microorganism ratio
• Filter to membrane ratio
• Flow to membrane ratio

Rationale: F/M ratio controls microbial loading and system stability. 3 / 4

8. Excessive F/M ratio can cause:

• Filamentous bulking
• Poor settling and high turbidity
• Low DO
• Sludge rising

Rationale: Too much food leads to dispersed growth and poor floc

formation.

9. Low DO in an aeration tank often results in:

• Rapid settling
• Filamentous bulking
• Improved BOD removal
• Chemical precipitation

Rationale: Low oxygen favors filamentous organisms, causing poor

settling.

10. The typical DO range in an aeration basin is:

• 0.1–0.5 mg/L
• 1.5–3.0 mg/L
• 4–6 mg/L
• 8–10 mg/L
• / 4