Page 1 of 59
NYC DEP WASTEWATER TREATMENT PLANT OPERATOR
GRADE TWO CERTIFICATION EXAM 2026/2027 COMPLETE
(150) CURRENT TESTING QUESTIONS AND CORRECT
ANSWERS WITH DETAILED RATIONALES.
WASTEWATER
Prepare effectively for the NYC DEP Wastewater Treatment Plant Operator Grade Two
Certification Exam with this focused practice resource. It supports review of
wastewater treatment processes, plant operations, process control, equipment
maintenance, water quality, safety procedures, and regulatory requirements. Use the
material to reinforce your technical knowledge, practice key concepts, and identify
areas that may require additional study. This resource is suited for wastewater
treatment operators, environmental professionals, plant technicians, and candidates
preparing for NYC DEP Grade Two certification examinations.
MULTIPLE CHOICE.
SECTION 1: GENERAL WASTEWATER TREATMENT (Questions 1–30)
1. Which of the following BEST describes the primary objective of
preliminary treatment in a wastewater treatment plant?
(A) To remove dissolved inorganic nutrients such as nitrates and phosphates
(B) To remove large debris, grit, and floatable materials to protect downstream
equipment
(C) To biologically oxidize organic matter
(D) To disinfect the wastewater before discharge
Answer: (B) To remove large debris, grit, and floatable materials to protect
downstream equipment
Rationale: Preliminary treatment is designed to protect downstream
equipment from damage and clogging by removing large solids, grit, and
floatable materials. Nutrient removal (A) occurs in tertiary treatment.
, Page 2 of 59
Biological oxidation (C) occurs in secondary treatment. Disinfection (D) is the
final treatment step.
2. What is the typical pH range of municipal wastewater?
(A) 2.0–4.0
(B) 4.0–6.0
(C) 6.5–8.5
(D) 9.0–11.0
Answer: (C) 6.5–8.5
Rationale: Municipal wastewater typically has a pH in the neutral range of
6.5–8.5. This range supports biological treatment processes and meets
discharge requirements.
3. What is the primary purpose of a grit chamber in wastewater
treatment?
(A) To remove dissolved organic matter
(B) To remove heavy inorganic particles such as sand and gravel
(C) To remove oil and grease
(D) To disinfect the wastewater
Answer: (B) To remove heavy inorganic particles such as sand and gravel
Rationale: Grit chambers are designed to settle out heavy inorganic particles
(grit) such as sand, gravel, and other materials that can damage equipment if
not removed.
4. Which parameter most directly indicates the organic loading of raw
wastewater?
, Page 3 of 59
(A) Total suspended solids (TSS)
(B) Biochemical oxygen demand (BOD)
(C) Dissolved oxygen (DO)
(D) pH
Answer: (B) Biochemical oxygen demand (BOD)
Rationale: BOD measures the amount of oxygen required by microorganisms
to decompose organic matter and is the primary indicator of organic loading
in wastewater. TSS (A) measures suspended solids but not organic content
directly.
5. In activated sludge systems, what is the main function of aeration?
(A) To mix chemicals
(B) To provide oxygen for microorganisms
(C) To remove suspended solids
(D) To disinfect the wastewater
Answer: (B) To provide oxygen for microorganisms
Rationale: Aeration supplies oxygen to microorganisms in the activated
sludge process, allowing them to biologically degrade organic matter.
6. A wastewater treatment plant operator notices that dissolved oxygen
(DO) levels in the aeration basin have dropped below the desired
operating range. What is the MOST appropriate first action?
(A) Increase the return activated sludge (RAS) rate
(B) Increase the aeration rate
(C) Decrease the influent flow
(D) Add more chemicals
, Page 4 of 59
Answer: (B) Increase the aeration rate
Rationale: A drop in DO indicates that oxygen demand exceeds supply. The
first action is to increase the aeration rate to restore DO levels.
7. What is the primary purpose of primary clarification?
(A) To remove dissolved organic matter
(B) To settle and remove settleable solids by gravity
(C) To disinfect the wastewater
(D) To remove nutrients
Answer: (B) To settle and remove settleable solids by gravity
Rationale: Primary clarification is a physical treatment process that allows
settleable solids to settle out by gravity, removing a significant portion of
suspended solids and BOD.
8. Which of the following is a common secondary biological treatment
process?
(A) Bar screening
(B) Grit removal
(C) Activated sludge
(D) Chlorination
Answer: (C) Activated sludge
Rationale: Activated sludge is a common biological secondary treatment
process that uses microorganisms to oxidize organic matter. Bar screening (A)
and grit removal (B) are preliminary treatment processes. Chlorination (D) is
disinfection.
NYC DEP WASTEWATER TREATMENT PLANT OPERATOR
GRADE TWO CERTIFICATION EXAM 2026/2027 COMPLETE
(150) CURRENT TESTING QUESTIONS AND CORRECT
ANSWERS WITH DETAILED RATIONALES.
WASTEWATER
Prepare effectively for the NYC DEP Wastewater Treatment Plant Operator Grade Two
Certification Exam with this focused practice resource. It supports review of
wastewater treatment processes, plant operations, process control, equipment
maintenance, water quality, safety procedures, and regulatory requirements. Use the
material to reinforce your technical knowledge, practice key concepts, and identify
areas that may require additional study. This resource is suited for wastewater
treatment operators, environmental professionals, plant technicians, and candidates
preparing for NYC DEP Grade Two certification examinations.
MULTIPLE CHOICE.
SECTION 1: GENERAL WASTEWATER TREATMENT (Questions 1–30)
1. Which of the following BEST describes the primary objective of
preliminary treatment in a wastewater treatment plant?
(A) To remove dissolved inorganic nutrients such as nitrates and phosphates
(B) To remove large debris, grit, and floatable materials to protect downstream
equipment
(C) To biologically oxidize organic matter
(D) To disinfect the wastewater before discharge
Answer: (B) To remove large debris, grit, and floatable materials to protect
downstream equipment
Rationale: Preliminary treatment is designed to protect downstream
equipment from damage and clogging by removing large solids, grit, and
floatable materials. Nutrient removal (A) occurs in tertiary treatment.
, Page 2 of 59
Biological oxidation (C) occurs in secondary treatment. Disinfection (D) is the
final treatment step.
2. What is the typical pH range of municipal wastewater?
(A) 2.0–4.0
(B) 4.0–6.0
(C) 6.5–8.5
(D) 9.0–11.0
Answer: (C) 6.5–8.5
Rationale: Municipal wastewater typically has a pH in the neutral range of
6.5–8.5. This range supports biological treatment processes and meets
discharge requirements.
3. What is the primary purpose of a grit chamber in wastewater
treatment?
(A) To remove dissolved organic matter
(B) To remove heavy inorganic particles such as sand and gravel
(C) To remove oil and grease
(D) To disinfect the wastewater
Answer: (B) To remove heavy inorganic particles such as sand and gravel
Rationale: Grit chambers are designed to settle out heavy inorganic particles
(grit) such as sand, gravel, and other materials that can damage equipment if
not removed.
4. Which parameter most directly indicates the organic loading of raw
wastewater?
, Page 3 of 59
(A) Total suspended solids (TSS)
(B) Biochemical oxygen demand (BOD)
(C) Dissolved oxygen (DO)
(D) pH
Answer: (B) Biochemical oxygen demand (BOD)
Rationale: BOD measures the amount of oxygen required by microorganisms
to decompose organic matter and is the primary indicator of organic loading
in wastewater. TSS (A) measures suspended solids but not organic content
directly.
5. In activated sludge systems, what is the main function of aeration?
(A) To mix chemicals
(B) To provide oxygen for microorganisms
(C) To remove suspended solids
(D) To disinfect the wastewater
Answer: (B) To provide oxygen for microorganisms
Rationale: Aeration supplies oxygen to microorganisms in the activated
sludge process, allowing them to biologically degrade organic matter.
6. A wastewater treatment plant operator notices that dissolved oxygen
(DO) levels in the aeration basin have dropped below the desired
operating range. What is the MOST appropriate first action?
(A) Increase the return activated sludge (RAS) rate
(B) Increase the aeration rate
(C) Decrease the influent flow
(D) Add more chemicals
, Page 4 of 59
Answer: (B) Increase the aeration rate
Rationale: A drop in DO indicates that oxygen demand exceeds supply. The
first action is to increase the aeration rate to restore DO levels.
7. What is the primary purpose of primary clarification?
(A) To remove dissolved organic matter
(B) To settle and remove settleable solids by gravity
(C) To disinfect the wastewater
(D) To remove nutrients
Answer: (B) To settle and remove settleable solids by gravity
Rationale: Primary clarification is a physical treatment process that allows
settleable solids to settle out by gravity, removing a significant portion of
suspended solids and BOD.
8. Which of the following is a common secondary biological treatment
process?
(A) Bar screening
(B) Grit removal
(C) Activated sludge
(D) Chlorination
Answer: (C) Activated sludge
Rationale: Activated sludge is a common biological secondary treatment
process that uses microorganisms to oxidize organic matter. Bar screening (A)
and grit removal (B) are preliminary treatment processes. Chlorination (D) is
disinfection.
