Class C Exam Practice Questions And

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

• What is the primary purpose of preliminary treatment in a wastewater

treatment plant?

a) Remove nutrients

b) Reduce organic matter

c) Remove large solids and debris

d) Disinfect wastewater

Rationale: Preliminary treatment focuses on screening and grit

removal to protect downstream equipment and processes.

2. The BOD test measures:

a) Total suspended solids 1 / 4

b) The amount of oxygen required by microorganisms to decompose

organic matter

c) Nutrient concentration

• pH levels

Rationale: BOD (Biochemical Oxygen Demand) indicates the organic

strength of wastewater and potential oxygen depletion in receiving waters.

• Which of the following is a common unit process for removing grit

from wastewater?

a) Clarifier

b) Trickling filter

c) Grit chamber

d) Aeration basin

Rationale: Grit chambers use velocity control to settle sand, gravel,

and other heavy particles.

• Which pH range is typically optimal for biological treatment

processes?

• 4–5
• 9–10
• 6.5–8.5
• 2–3

Rationale: Most bacteria in activated sludge or biofilm processes

function best near neutral pH. 2 / 4

5. The main purpose of an aeration tank is to:

a) Settle solids

b) Provide oxygen to support microbial degradation of organic

matter

c) Remove grit

d) Disinfect wastewater

Rationale: Aeration tanks supply oxygen to microorganisms that

break down organic pollutants.

6. Activated sludge is:

a) A chemical coagulant

b) A mixture of microorganisms and wastewater used to treat

organic matter

c) Settled sludge in clarifiers

d) Disinfected wastewater

Rationale: Activated sludge contains aerobic bacteria that consume

organic pollutants.

• Which of the following is a characteristic of secondary clarifiers?

a) Used before preliminary treatment

b) Remove only dissolved oxygen

c) Settle biological solids after aeration

d) Filter water chemically

Rationale: Secondary clarifiers separate biomass from treated water

after biological treatment. 3 / 4

8. The term “sludge age” refers to:

a) The age of the plant

b) Age of the influent

c) Average time solids remain in the biological system

d) Time for chlorine contact

Rationale: Sludge age or mean cell residence time (MCRT) helps

control microbial population and treatment efficiency.

• What is the primary function of a bar screen in wastewater treatment?

a) Remove large debris like rags and sticks

b) Remove dissolved nutrients

c) Settle solids

d) Aerate water

Rationale: Bar screens prevent damage and clogging of downstream

equipment.

10. Nitrification in wastewater treatment is carried out by:

a) Protozoa

b) Specialized bacteria converting ammonia to nitrate

c) Fungi

d) Chlorine

Rationale: Ammonia-oxidizing and nitrite-oxidizing bacteria convert

nitrogen compounds in aerobic conditions.

• Denitrification occurs under which conditions?

a) Aerobic

• / 4