Operator S2 Exam Practice Questions

New Jersey Wastewater Treatment Operator S2 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 a primary clarifier?
• Remove dissolved nutrients
• Settle suspended solids
• Aerate wastewater
• Disinfect effluent

Rationale: Primary clarifiers are designed to remove settleable solids

through sedimentation.

• The biological process that converts ammonia (NH₃) to nitrate (NO₃⁻)

is called:

• Denitrification 1 / 4

• Nitrification
• Phosphorus removal
• Aerobic digestion

Rationale: Nitrification is the two-step microbial process converting

ammonia to nitrite and then nitrate.

• The main purpose of an aeration tank in activated sludge treatment is

to:

• Settle solids
• Remove chlorine
• Provide oxygen for microorganisms to degrade organic matter
• Remove heavy metals

Rationale: Aeration supplies oxygen to bacteria that biologically

degrade organic pollutants.

• Which microorganism group is primarily responsible for nitrification?
• Protozoa
• Fungi
• Chemoautotrophic bacteria
• Algae

Rationale: Chemoautotrophic bacteria such as Nitrosomonas and

Nitrobacter oxidize ammonia to nitrate.

• The sludge age or mean cell residence time (MCRT) is important

because it:

• Determines the volume of the clarifier 2 / 4

• Affects biological treatment efficiency and sludge production
• Controls chlorine dosage
• Regulates pH

Rationale: MCRT determines the growth and removal rate of

microorganisms in activated sludge systems.

• Which of the following is a commonly used coagulant in wastewater

treatment?

• Sodium hypochlorite
• Aluminum sulfate (alum)
• Caustic soda
• Ferric cyanide

Rationale: Alum is widely used to destabilize colloidal particles and

promote floc formation.

7. The term “BOD₅” refers to:

• Biochemical oxygen demand measured over 1 hour
• Biochemical oxygen demand measured over 5 days
• Biological oxygen deficit
• Bulk oxygen diffusion

Rationale: BOD₅ measures the oxygen demand of organic matter in

water over 5 days at 20°C.

8. The presence of filamentous bacteria in activated sludge can cause:

• Improved settling
• Bulking and poor sludge compaction 3 / 4

• Rapid nitrification
• Reduced oxygen demand

Rationale: Filamentous bacteria can form a loose floc structure,

leading to sludge bulking.

• Which chemical is commonly used for disinfection in wastewater

treatment?

• Alum
• Lime
• Chlorine
• Sodium hydroxide

Rationale: Chlorine is widely used to disinfect effluent by inactivating

pathogenic organisms.

10. In trickling filters, the primary mechanism for organic removal is:

• Settling
• Chemical precipitation
• Microbial biofilm degradation
• Evaporation

Rationale: Microorganisms attached to filter media degrade organic

pollutants as wastewater flows over them.

11. The primary purpose of an equalization basin is to:

• Increase pH
• Provide flow and load equalization
• Remove suspended solids
• / 4