Certification Exam Practice Questions

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

• Which of the following is the primary purpose of preliminary

treatment in a wastewater plant?

• Reduce BOD
• Remove large solids and debris
• Kill pathogens
• Improve pH

Rationale: Preliminary treatment focuses on removing large solids,

rags, sticks, and grit to prevent damage to downstream equipment.

• The measure of the organic matter in wastewater that can be

biologically oxidized is called: 1 / 4

A. TSS

• pH

C. BOD

D. COD

Rationale: Biochemical Oxygen Demand (BOD) quantifies the amount

of oxygen needed by microorganisms to decompose organic matter.

• Which unit process is designed to remove grit from wastewater?
• Screening
• Sedimentation
• Grit chamber
• Filtration

Rationale: Grit chambers allow heavy inorganic particles such as

sand and gravel to settle out, protecting pumps and other equipment.

4. The main function of aeration in an activated sludge process is to:

• Remove nutrients
• Settle solids
• Provide oxygen for microbial growth
• Adjust pH

Rationale: Aeration supplies dissolved oxygen to aerobic

microorganisms to break down organic matter.

• Which of the following pathogens are commonly monitored in

wastewater? 2 / 4

• Influenza virus
• Coliform bacteria

C. HIV

• Salmonella typhi only

Rationale: Coliform bacteria, particularly fecal coliforms, are

indicators of pathogenic contamination in wastewater.

6. A properly functioning septic tank removes solids primarily by:

• Filtration
• Aeration
• Sedimentation
• Chlorination

Rationale: Solids settle to the bottom of the tank forming sludge,

while oils and grease float forming scum.

• Which chemical is most commonly used for disinfection in wastewater

treatment?

• Ozone
• Chlorine
• Alum
• Hydrogen peroxide

Rationale: Chlorine is widely used due to its effectiveness,

availability, and low cost.

8. The term “sludge age” refers to:

• Time sludge is in storage 3 / 4

• Time it takes for solids to settle
• Average time microorganisms remain in the system
• Time before sludge dewatering

Rationale: Sludge age, or mean cell residence time, affects the

stability and activity of microorganisms in activated sludge systems.

9. TSS stands for:

• Total Sanitation Standards
• Total Suspended Solids
• Total Soluble Solids
• Toxic Substance Score

Rationale: TSS measures the solids suspended in wastewater, an

important parameter for treatment efficiency.

• What is the typical pH range for most biological wastewater

treatment processes?

A. 3.0–5.0

B. 5.0–6.0

C. 6.5–8.5

D. 9.0–10.5

Rationale: Most bacteria thrive in a near-neutral pH environment.

• Which of the following processes is anaerobic?
• Trickling filter
• Activated sludge
• Anaerobic digester
• / 4