Practice Exam Questions And Correct

Louisiana Wastewater Operator Class IV Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of a grit chamber in a wastewater

treatment plant?

• To remove organic matter
• To remove heavy inorganic solids
• To settle sludge
• To disinfect wastewater

Rationale: Grit chambers are designed to remove heavy inorganic

solids like sand, gravel, and other debris that could damage equipment or accumulate in tanks. 1 / 4

• Which microorganism is primarily responsible for nitrification?
• Escherichia coli
• Clostridium
• Nitrosomonas and Nitrobacter
• Bacillus

Rationale: Nitrosomonas oxidizes ammonia to nitrite, and

Nitrobacter oxidizes nitrite to nitrate during nitrification.

3. The term "BOD5" refers to:

• Total solids in wastewater
• Chemical oxygen demand
• The amount of oxygen consumed in 5 days by microorganisms
• Suspended solids concentration

Rationale: BOD5 measures the biodegradable organic matter in

wastewater, indicating the oxygen demand over 5 days.

• What is the typical pH range for optimal activated sludge treatment?

A. 3.0–4.0

B. 9.0–10.0

C. 6.5–8.5

D. 5.0–6.0

Rationale: Microorganisms in activated sludge function best in a

near-neutral pH range, typically 6.5–8.5.

• Which of the following is a secondary treatment process?
• Screening 2 / 4

• Grit removal
• Activated sludge process
• Chlorination

Rationale: Secondary treatment focuses on removing dissolved and

suspended organic matter, which is the role of activated sludge.

6. The main function of a clarifier is to:

• Remove dissolved oxygen
• Separate solids from liquid
• Oxidize ammonia
• Neutralize pH

Rationale: Clarifiers settle solids, producing a clear effluent and

concentrated sludge.

• What is the typical sludge age in a Class IV activated sludge system?
• 1–2 days
• 3–5 days
• 10–20 days
• 30–40 days

Rationale: Longer sludge ages are required in advanced treatment

plants for complete nitrification and stable biological treatment.

• Which disinfectant is most commonly used in wastewater treatment?
• Iodine
• Ozone
• Chlorine 3 / 4

• Hydrogen peroxide

Rationale: Chlorine is widely used due to its effectiveness and cost

efficiency.

• What is the primary cause of septicity in wastewater?
• High dissolved oxygen
• Anaerobic conditions
• High pH
• Excess nitrates

Rationale: Septicity occurs when anaerobic bacteria produce

hydrogen sulfide and other gases in oxygen-depleted wastewater.

10. A composite sample is:

• A single grab at a point
• A combination of multiple samples over time
• Taken only in the morning
• Used for pH analysis only

Rationale: Composite samples better represent average wastewater

characteristics over a period.

11. The function of an aeration tank is to:

• Remove grit
• Supply oxygen to microorganisms
• Disinfect effluent
• Settle solids
• / 4