Operator S3 Exam Practice Questions

New Jersey Wastewater Treatment Operator S3 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 treatment plant?

• Remove large solids and grit
• Reduce biochemical oxygen demand (BOD)
• Remove nutrients
• Disinfect effluent

Rationale: Preliminary treatment removes large solids and grit to

protect downstream equipment and improve treatment efficiency.

2. In activated sludge processes, the term “sludge age” refers to:

• Time wastewater spends in aeration tank 1 / 4

• Time solids spend in secondary clarifier
• Average time microorganisms remain in the system
• Hydraulic retention time of influent

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

average duration microorganisms stay in the system, affecting treatment efficiency.

3. The main function of an aeration tank in secondary treatment is to:

• Remove grit and screenings
• Promote biological oxidation of organic matter
• Settle suspended solids
• Remove phosphorus

Rationale: Aeration tanks provide oxygen to microorganisms,

enabling them to biologically oxidize organic pollutants.

4. The purpose of a secondary clarifier is to:

• Remove oil and grease
• Settle biological solids after aeration
• Filter effluent
• Neutralize pH

Rationale: Secondary clarifiers separate activated sludge from

treated water to return solids to the aeration tank or send to sludge handling.

• Which parameter is commonly used to measure the organic strength

of wastewater? 2 / 4

• Total suspended solids
• Biochemical oxygen demand (BOD)
• pH
• Temperature

Rationale: BOD indicates the amount of oxygen microorganisms

need to decompose organic matter in water.

6. Grit chambers are designed to remove:

• Oil and grease
• Organic matter
• Sand, gravel, and other heavy inorganic solids
• Dissolved nutrients

Rationale: Grit chambers remove heavy inorganic solids to prevent

abrasion and wear on pumps and equipment.

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

• Remove suspended solids
• Reduce BOD
• Disinfect effluent
• Remove nitrogen

Rationale: Chlorination kills pathogenic microorganisms, reducing

the risk of disease transmission from effluent.

• Which of the following is a typical concentration unit for measuring

TSS (Total Suspended Solids)?

• mg/L 3 / 4

• ppm
• Both A and B
• pH units

Rationale: TSS is commonly expressed in milligrams per liter (mg/L)

or parts per million (ppm), equivalent measures for dilute solutions.

• In the activated sludge process, returning settled sludge to the

aeration tank is called:

• Sludge wasting
• Return activated sludge (RAS)
• Settling
• Filtration

Rationale: RAS recycles microorganisms back to the aeration tank to

maintain biomass concentration for effective treatment.

10. The function of a bar screen in preliminary treatment is to:

• Settle solids
• Remove large debris
• Oxidize organics
• Disinfect water

Rationale: Bar screens mechanically remove large debris such as

rags, sticks, and plastics to protect downstream equipment.

• The most common chemical used for disinfection in wastewater

plants is:

• Ozone
• / 4