II Certification Exam Practice Questions

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

• Which process is primarily responsible for removing settleable solids

from wastewater?

a) Activated sludge

b) Filtration

c) Sedimentation

d) Disinfection

Rationale: Sedimentation allows heavier solids to settle out of

wastewater by gravity, forming sludge.

• What is the primary purpose of aeration in the activated sludge

process? 1 / 4

a) Increase pH

b) Remove nutrients

c) Provide oxygen for microbial growth

d) Separate solids from liquids

Rationale: Aeration supplies oxygen to microorganisms, which is

essential for the biological treatment of organic matter.

• Which of the following parameters is most commonly used to measure

organic matter in wastewater?

• pH

b) Total suspended solids

c) Biochemical oxygen demand (BOD)

d) Turbidity

Rationale: BOD measures the amount of oxygen microorganisms

consume to break down organic matter, indicating the strength of wastewater.

• In wastewater treatment, what is the typical function of a grit

chamber?

a) Remove oil and grease

b) Remove sand, gravel, and heavy inorganic solids

c) Disinfect wastewater

d) Increase microbial activity

Rationale: Grit chambers remove heavy inorganic solids that could

damage pumps and equipment. 2 / 4

• Which form of nitrogen is typically removed during biological nitrogen

removal?

a) Nitrite only

b) Ammonia (NH₃/NH₄⁺)

c) Nitrate only

d) Organic nitrogen

Rationale: Ammonia is converted to nitrite and nitrate via nitrification,

then to nitrogen gas via denitrification.

6. Chlorination is primarily used in wastewater treatment to:

a) Remove solids

b) Reduce BOD

c) Disinfect effluent

d) Remove nitrogen

Rationale: Chlorine kills pathogens in treated wastewater to reduce

public health risks.

• What is the purpose of sludge thickening?

a) To disinfect sludge

b) To reduce water content and increase solids concentration

c) To aerate sludge

d) To remove nutrients

Rationale: Thickening concentrates solids, making subsequent

treatment (digestion, dewatering) more efficient. 3 / 4

• In the activated sludge process, what does the term “F/M ratio” refer

to?

a) Flow per meter

b) Food to microorganism ratio

c) Filtration/membrane ratio

d) Fixed mass

Rationale: The F/M ratio indicates the amount of organic matter

(food) available per unit mass of microorganisms, guiding process control.

• Which of the following is a common method of sludge stabilization?

a) Filtration

b) Sedimentation

c) Aerobic or anaerobic digestion

d) Chlorination

Rationale: Digestion stabilizes sludge by reducing pathogens and

odors through microbial breakdown of organic material.

• What is the typical function of a primary clarifier?

a) Aerate wastewater

b) Remove settleable solids

c) Remove dissolved organics

d) Remove pathogens

Rationale: Primary clarifiers allow solids to settle, reducing the load on

secondary treatment.

• / 4