Class D Exam Practice Questions And

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

• What is the primary purpose of a wastewater treatment plant?
• Generate electricity
• Remove pollutants from wastewater before discharge
• Provide drinking water
• Produce drinking water-quality effluent

Rationale: The main goal of a wastewater treatment plant is to remove

pollutants and protect public health and the environment.

• Which of the following is a characteristic of domestic wastewater?
• High metal content
• Contains organic matter from human waste and household 1 / 4

activities

• Only stormwater
• Pure water

Rationale: Domestic wastewater primarily comes from household sources

and contains organic material, nutrients, and pathogens.

• What is the purpose of screening in wastewater treatment?
• Remove large solids and debris from influent wastewater
• Remove dissolved chemicals
• Reduce odor
• Kill pathogens

Rationale: Screening prevents damage to downstream equipment and

removes large floating or suspended objects.

4. In wastewater treatment, grit chambers are used to remove:

• Bacteria
• Sand, gravel, and other heavy inorganic particles
• Oil and grease
• Dissolved solids

Rationale: Grit chambers slow down flow so heavy inorganic particles

settle, protecting pumps and pipes.

• Which parameter measures the amount of oxygen required by

bacteria to decompose organic matter in wastewater?

• pH 2 / 4

B. TSS

• BOD (Biochemical Oxygen Demand)

D. COD

Rationale: BOD quantifies the oxygen consumed by microorganisms during

the breakdown of organic matter, indicating wastewater strength.

• The primary treatment process removes approximately what

percentage of suspended solids?

A. 10–20%

B. 30–40%

C. 50–60%

D. 80–90%

Rationale: Primary treatment, using sedimentation, removes about half of

the suspended solids and some organic material.

7. Secondary treatment in wastewater treatment primarily targets:

• Heavy metals
• Dissolved and suspended organic matter
• Large debris
• Pathogens

Rationale: Secondary treatment uses biological processes, such as

activated sludge or trickling filters, to reduce organic matter.

• What is the main function of an aeration tank?
• Remove grit 3 / 4

• Settle solids
• Provide oxygen to bacteria for biological treatment
• Disinfect effluent

Rationale: Aeration tanks introduce air to support aerobic bacteria that

decompose organic matter.

9. Chlorination in wastewater treatment is used for:

• Removing solids
• Disinfecting the effluent to kill pathogens
• Increasing BOD
• Enhancing sedimentation

Rationale: Chlorine is commonly used as a disinfectant to protect public

health before discharge.

• Sludge is the solid byproduct of which process?
• Screening only
• Primary and secondary treatment
• Grit removal only
• Chlorination

Rationale: Sludge forms from settled solids in primary treatment and

biological solids from secondary treatment.

• Which of the following is a common cause of wastewater odor?
• Excess chlorine
• Anaerobic decomposition of organic matter
• / 4