NYC DEP Wastewater Treatment Plant
Operator Grade Two Certification Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
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 completely eliminate biological oxygen demand (BOD) from influent
wastewater
D) To disinfect wastewater prior to biological treatment
Preliminary treatment focuses on protecting pumps, pipes, and
downstream processes by removing coarse materials like rags, sticks, and
grit rather than altering dissolved or biological content.
2. A Grade Two wastewater operator observes a sudden drop in dissolved
oxygen (DO) in an aeration tank. What is the most appropriate first
action?
,A) Immediately increase chlorine dosage
B) Reduce sludge wasting rate without further checks
C) Inspect aeration equipment for mechanical failure or reduced air supply
D) Bypass the primary clarifier to increase flow
A rapid DO drop is most commonly caused by aeration system malfunction
or loss of oxygen transfer efficiency, so equipment verification is the
priority before process adjustments.
3. What parameter is most directly used to evaluate the organic strength
of influent wastewater?
A) Total dissolved solids (TDS)
B) Biochemical oxygen demand (BOD)
C) Turbidity
D) Chlorine residual
BOD measures the oxygen required by microorganisms to decompose
organic matter and is a key indicator of wastewater strength.
4. In wastewater treatment, what is the main function of screening units?
A) To adjust pH levels of incoming wastewater
B) To remove dissolved solids and nutrients
C) To remove large solid materials such as rags, plastics, and debris
D) To disinfect effluent prior to discharge
Screens prevent damage and clogging in downstream equipment by
removing large solids early in the treatment process.
5. Which condition is most likely to cause septic conditions in a collection
system or influent line?
A) Excess dissolved oxygen
B) High pH levels
C) Lack of oxygen leading to anaerobic decomposition and hydrogen sulfide
, formation
D) High chlorine residual
When oxygen is depleted, anaerobic bacteria produce hydrogen sulfide and
other compounds that cause septic odors and corrosion.
6. What is the primary purpose of primary clarification in wastewater
treatment?
A) Biological oxidation of ammonia
B) Physical settling of suspended solids and removal of floatable materials
C) Chemical precipitation of phosphorus
D) Ultraviolet disinfection
Primary clarifiers rely on gravity to settle solids and remove scum before
secondary biological treatment.
7. Which gas is most commonly associated with confined space hazards
in wastewater facilities?
A) Oxygen
B) Nitrogen
C) Hydrogen sulfide (H₂S)
D) Helium
Hydrogen sulfide is toxic, corrosive, and can accumulate in confined spaces
such as wet wells and manholes, posing a serious safety risk.
8. What does the term “MLSS” refer to in activated sludge systems?
A) Maximum liquid settling standard
B) Mixed laboratory sampling solution
C) Mixed Liquor Suspended Solids concentration in the aeration tank
D) Microbial loading safety standard
Operator Grade Two Certification Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
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 completely eliminate biological oxygen demand (BOD) from influent
wastewater
D) To disinfect wastewater prior to biological treatment
Preliminary treatment focuses on protecting pumps, pipes, and
downstream processes by removing coarse materials like rags, sticks, and
grit rather than altering dissolved or biological content.
2. A Grade Two wastewater operator observes a sudden drop in dissolved
oxygen (DO) in an aeration tank. What is the most appropriate first
action?
,A) Immediately increase chlorine dosage
B) Reduce sludge wasting rate without further checks
C) Inspect aeration equipment for mechanical failure or reduced air supply
D) Bypass the primary clarifier to increase flow
A rapid DO drop is most commonly caused by aeration system malfunction
or loss of oxygen transfer efficiency, so equipment verification is the
priority before process adjustments.
3. What parameter is most directly used to evaluate the organic strength
of influent wastewater?
A) Total dissolved solids (TDS)
B) Biochemical oxygen demand (BOD)
C) Turbidity
D) Chlorine residual
BOD measures the oxygen required by microorganisms to decompose
organic matter and is a key indicator of wastewater strength.
4. In wastewater treatment, what is the main function of screening units?
A) To adjust pH levels of incoming wastewater
B) To remove dissolved solids and nutrients
C) To remove large solid materials such as rags, plastics, and debris
D) To disinfect effluent prior to discharge
Screens prevent damage and clogging in downstream equipment by
removing large solids early in the treatment process.
5. Which condition is most likely to cause septic conditions in a collection
system or influent line?
A) Excess dissolved oxygen
B) High pH levels
C) Lack of oxygen leading to anaerobic decomposition and hydrogen sulfide
, formation
D) High chlorine residual
When oxygen is depleted, anaerobic bacteria produce hydrogen sulfide and
other compounds that cause septic odors and corrosion.
6. What is the primary purpose of primary clarification in wastewater
treatment?
A) Biological oxidation of ammonia
B) Physical settling of suspended solids and removal of floatable materials
C) Chemical precipitation of phosphorus
D) Ultraviolet disinfection
Primary clarifiers rely on gravity to settle solids and remove scum before
secondary biological treatment.
7. Which gas is most commonly associated with confined space hazards
in wastewater facilities?
A) Oxygen
B) Nitrogen
C) Hydrogen sulfide (H₂S)
D) Helium
Hydrogen sulfide is toxic, corrosive, and can accumulate in confined spaces
such as wet wells and manholes, posing a serious safety risk.
8. What does the term “MLSS” refer to in activated sludge systems?
A) Maximum liquid settling standard
B) Mixed laboratory sampling solution
C) Mixed Liquor Suspended Solids concentration in the aeration tank
D) Microbial loading safety standard
