Class A Exam Practice Questions And

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

• The primary purpose of preliminary treatment in a wastewater

treatment plant is to:

a) Remove dissolved nutrients

b) Remove pathogens

c) Remove large solids and grit

d) Reduce organic matter

Rationale: Preliminary treatment is designed to remove large solids,

debris, and grit to protect downstream equipment and processes.

• Which of the following best describes BOD (Biochemical Oxygen

Demand)? 1 / 4

a) Total oxygen in water

b) Oxygen added during aeration

c) Amount of oxygen required by microorganisms to decompose

organic matter

d) Oxygen content of effluent

Rationale: BOD measures the oxygen microorganisms need to

biologically degrade organic pollutants in water.

3. The main purpose of a grit chamber is to:

a) Reduce BOD

b) Remove heavy inorganic solids

c) Clarify wastewater

d) Disinfect effluent

Rationale: Grit chambers allow sand, gravel, and other heavy solids

to settle out, preventing wear on pumps and equipment.

• Which unit process uses biological organisms to remove dissolved and

particulate organic matter?

a) Sedimentation

b) Filtration

c) Activated sludge

d) Disinfection

Rationale: Activated sludge systems rely on microorganisms to

consume organic matter, reducing BOD and suspended solids. 2 / 4

5. Nitrification in a wastewater treatment plant converts:

a) Ammonia to nitrogen gas

b) Nitrogen gas to ammonia

c) Ammonia to nitrate

d) Nitrate to ammonia

Rationale: Nitrification is a two-step biological process where

ammonia is first converted to nitrite and then to nitrate by nitrifying bacteria.

6. Denitrification primarily occurs under:

a) Aerobic conditions

b) Photosynthetic conditions

c) Anoxic conditions

d) Anaerobic digestion

Rationale: Denitrification occurs in the absence of dissolved oxygen,

where nitrate is converted to nitrogen gas.

7. The purpose of chlorination in wastewater treatment is to:

a) Remove solids

b) Reduce BOD

c) Disinfect effluent

d) Remove nutrients

Rationale: Chlorination kills or inactivates pathogenic

microorganisms in treated wastewater before discharge. 3 / 4

8. Sludge thickening is performed to:

a) Remove toxic chemicals

b) Increase solids concentration before dewatering

c) Disinfect biosolids

d) Reduce BOD

Rationale: Thickening increases solids content, reducing volume and

improving handling in dewatering processes.

9. The term “MLSS” in activated sludge processes refers to:

a) Mixed liquid settleable solids

b) Maximum limit suspended solids

c) Mixed liquor suspended solids

d) Microbial limit for suspended solids

Rationale: MLSS represents the concentration of suspended

microorganisms and solids in the aeration tank.

10. The primary clarifier in a wastewater plant is used to:

a) Aerate the water

b) Remove dissolved oxygen

c) Allow solids to settle by gravity

d) Chlorinate effluent

Rationale: Primary clarifiers settle out heavy solids from raw

wastewater before biological treatment.

11. Sludge digestion primarily serves to:

a) Increase BOD

• / 4