Class IV Certification Practice Examination

Industrial Wastewater Treatment Operator Class IV Certification Practice Examination Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1. The main purpose of primary treatment in wastewater treatment is to:

a) Remove dissolved organics

b) Remove pathogens

c) Remove settleable and floatable solids

d) Oxidize ammonia

Rationale: Primary treatment uses physical processes like sedimentation to

remove settleable and floatable solids before biological treatment.

• The primary clarifier typically removes what percentage of suspended

solids?

• 10–20%
• 25–35% 1 / 4

• 50–70%
• 80–90%

Rationale: Primary clarification typically achieves 50–70% TSS removal

through sedimentation.

• In an activated sludge system, the microorganism population primarily

responsible for BOD removal is:

a) Algae

b) Viruses

c) Bacteria

d) Protozoa

Rationale: Bacteria consume and oxidize organic matter, reducing BOD

levels in the process.

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

a) Food to microorganism ratio

b) Flow to mass ratio

c) Feed to metal ratio

d) Fuel to methane ratio

Rationale: The F/M ratio indicates the balance between available food

(BOD) and microorganisms, critical for process control.

• / 4

5. Sludge bulking is commonly caused by:

a) Excess chlorine

b) Filamentous bacteria overgrowth

c) Too high DO

d) Short aeration time

Rationale: Filamentous bacteria dominate under low DO or nutrient

imbalance, causing poor settling.

6. The secondary clarifier’s main function is to:

a) Remove grit

b) Separate biological solids from treated water

c) Chlorinate the effluent

d) Aerate the water

Rationale: Secondary clarifiers settle activated sludge solids for return or

wasting.

• What is the primary cause of sludge rising in secondary clarifiers?

a) High DO

b) Denitrification

c) Excess chlorine

d) Low MLSS

Rationale: Denitrification produces nitrogen gas, which attaches to sludge

particles and causes them to float. 3 / 4

8. The main function of a grit chamber is to:

a) Remove heavy inorganic materials

b) Remove dissolved organics

c) Control odors

d) Promote biological growth

Rationale: Grit chambers use velocity control to remove sand, gravel, and

other inorganics.

9. The standard method for measuring BOD involves incubation for:

• 1 day
• 3 days
• 5 days
• 7 days

Rationale: The BOD₅ test measures oxygen demand over 5 days at 20°C.

10. A low DO concentration in an aeration tank usually results in:

a) Reduced nitrification

b) Poor floc formation and odor production

c) Increased settling

d) Higher pH

• / 4