Operator Grade 4 Practice Exam

New York Wastewater Treatment Plant Operator Grade 4 Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

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

treatment plant?

• Remove dissolved nutrients
• Remove settleable solids
• Disinfect effluent
• Remove heavy metals

Answer: B

Rationale: Primary treatment primarily removes settleable solids through

physical processes such as sedimentation. 1 / 4

• Which type of bacteria is most responsible for nitrification?
• Sulfate-reducing bacteria
• Coliform bacteria
• Nitrosomonas and Nitrobacter
• Methanogens

Answer: C

Rationale: Nitrosomonas convert ammonia to nitrite, and Nitrobacter

convert nitrite to nitrate, completing nitrification.

• What is the main concern with high levels of total suspended solids (TSS)

in wastewater effluent?

• Reduced pH
• Interference with disinfection and aquatic life harm
• Increased odor only
• Faster biological oxygen demand removal

Answer: B

Rationale: High TSS can shield pathogens from disinfection and reduce

light penetration, harming aquatic ecosystems.

• Which process is primarily used to remove phosphorus from

wastewater?

• Aeration
• Chemical precipitation
• Filtration
• Sedimentation 2 / 4

Answer: B

Rationale: Phosphorus is often removed by adding chemicals such as alum

or ferric chloride to form insoluble precipitates.

• What is the main objective of secondary treatment?
• Remove settleable solids
• Remove dissolved and colloidal organic matter
• Add chlorine
• Remove heavy metals

Answer: B

Rationale: Secondary treatment uses biological processes to oxidize

dissolved and colloidal organics.

• Activated sludge processes rely primarily on which type of

microorganism?

• Viruses
• Protozoa
• Bacteria
• Fungi

Answer: C

Rationale: Bacteria metabolize organic matter, forming flocs that settle in

secondary clarifiers.

• In wastewater treatment, what is sludge age (mean cell residence time)?
• Time sludge spends in anaerobic digesters 3 / 4

• Average time solids remain in the activated sludge system
• Time for chlorine contact
• Time for primary sedimentation

Answer: B

Rationale: Sludge age influences microbial population, nitrification, and

overall process stability.

• What is the purpose of a bar screen in preliminary treatment?
• Reduce TSS
• Remove large debris
• Aerate wastewater
• Adjust pH

Answer: B

Rationale: Bar screens prevent rags, sticks, and other large solids from

damaging downstream equipment.

• What is the typical pH range for biological wastewater treatment

processes?

A. 2.0 – 4.0

B. 9.0 – 11.0

C. 6.5 – 8.5

• 10.0 – 12.0
• / 4