NPDES Industrial Wastewater Operator
Certification Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. Which parameter is most commonly used to measure the oxygen-
demanding strength of wastewater?
A Total Suspended Solids (TSS)
B pH
C Biochemical Oxygen Demand (BOD)
D Chlorine residual
Biochemical Oxygen Demand measures the amount of oxygen
microorganisms require to decompose organic matter in wastewater,
making it the primary indicator of organic pollution strength.
2. What is the primary purpose of primary treatment in industrial
wastewater systems?
A Nutrient removal
, B Disinfection
C Removal of settleable solids and floatables
D Nitrogen conversion
Primary treatment focuses on physical separation processes such as
sedimentation and skimming to remove solids before biological
treatment.
3. Which process is most commonly used for secondary wastewater
treatment?
A Chemical precipitation
B Activated sludge process
C Filtration only
D Grit removal
The activated sludge process uses microorganisms in aerated tanks
to biologically degrade organic pollutants.
4. What does pH measure in wastewater?
A Temperature
B Oxygen content
C Hydrogen ion concentration (acidity or alkalinity)
D Conductivity
pH indicates whether wastewater is acidic or alkaline, which affects
biological treatment efficiency.
5. Which compound is most associated with high ammonia in industrial
wastewater?
, A Phosphates
B Nitrogenous waste from industrial or biological sources
C Chlorides
D Silica
Ammonia typically originates from industrial processes and
biological decomposition of nitrogen-containing compounds.
6. What is the main function of a clarifier?
A Aeration
B Disinfection
C Separation of suspended solids by gravity settling
D pH adjustment
Clarifiers allow solids to settle and be removed from wastewater
through sedimentation.
7. Which parameter is used to measure solids that remain suspended in
wastewater?
A BOD
B COD
C Total Suspended Solids (TSS)
D Alkalinity
TSS quantifies particulate matter suspended in wastewater that can
be filtered out.
8. What is the purpose of aeration in biological treatment?
A Increase pH
Certification Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which parameter is most commonly used to measure the oxygen-
demanding strength of wastewater?
A Total Suspended Solids (TSS)
B pH
C Biochemical Oxygen Demand (BOD)
D Chlorine residual
Biochemical Oxygen Demand measures the amount of oxygen
microorganisms require to decompose organic matter in wastewater,
making it the primary indicator of organic pollution strength.
2. What is the primary purpose of primary treatment in industrial
wastewater systems?
A Nutrient removal
, B Disinfection
C Removal of settleable solids and floatables
D Nitrogen conversion
Primary treatment focuses on physical separation processes such as
sedimentation and skimming to remove solids before biological
treatment.
3. Which process is most commonly used for secondary wastewater
treatment?
A Chemical precipitation
B Activated sludge process
C Filtration only
D Grit removal
The activated sludge process uses microorganisms in aerated tanks
to biologically degrade organic pollutants.
4. What does pH measure in wastewater?
A Temperature
B Oxygen content
C Hydrogen ion concentration (acidity or alkalinity)
D Conductivity
pH indicates whether wastewater is acidic or alkaline, which affects
biological treatment efficiency.
5. Which compound is most associated with high ammonia in industrial
wastewater?
, A Phosphates
B Nitrogenous waste from industrial or biological sources
C Chlorides
D Silica
Ammonia typically originates from industrial processes and
biological decomposition of nitrogen-containing compounds.
6. What is the main function of a clarifier?
A Aeration
B Disinfection
C Separation of suspended solids by gravity settling
D pH adjustment
Clarifiers allow solids to settle and be removed from wastewater
through sedimentation.
7. Which parameter is used to measure solids that remain suspended in
wastewater?
A BOD
B COD
C Total Suspended Solids (TSS)
D Alkalinity
TSS quantifies particulate matter suspended in wastewater that can
be filtered out.
8. What is the purpose of aeration in biological treatment?
A Increase pH
