NPDES Package Plant 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 evaluate the organic
strength of wastewater influent?
A. Total Suspended Solids (TSS)
B. pH
C. Biochemical Oxygen Demand (BOD)
D. Chlorine residual
BOD measures the amount of oxygen required by microorganisms to
decompose organic matter and is the standard indicator of organic
pollution strength.
2. The primary purpose of an aeration tank in a package treatment plant
is to:
A. Remove grit
, B. Settle solids
C. Provide oxygen for biological treatment
D. Disinfect effluent
Aeration tanks supply dissolved oxygen to support aerobic
microorganisms that break down organic waste.
3. A low dissolved oxygen level in the aeration basin typically results in:
A. Increased nitrification
B. Improved effluent quality
C. Poor treatment and possible odor production
D. Increased chlorine demand
Low DO causes anaerobic conditions, leading to odors and reduced
treatment efficiency.
4. The function of a secondary clarifier is to:
A. Add chemicals
B. Aerate wastewater
C. Separate biological solids from treated water
D. Remove grit
Secondary clarifiers allow activated sludge flocs to settle, producing
clear effluent.
5. What does MLSS stand for?
A. Mixed Liquid Settled Solids
B. Maximum Liquid Suspended Solids
C. Mixed Liquor Suspended Solids
, D. Mixed Lagoon Solids System
MLSS represents the concentration of suspended biological solids in
the aeration tank.
6. Sludge Age is also known as:
A. Flow rate
B. Solids Retention Time (SRT)
C. Hydraulic loading
D. BOD removal rate
SRT refers to the average time solids remain in the treatment system.
7. The most common disinfectant used in package plants is:
A. Oxygen
B. Aluminum sulfate
C. Chlorine
D. Lime
Chlorine is widely used due to its effectiveness and ease of
application.
8. A high sludge volume index (SVI) indicates:
A. Good settling sludge
B. Dense sludge
C. Poor settling sludge (bulking condition)
D. Low solids concentration
High SVI means sludge is fluffy and does not settle well.
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 evaluate the organic
strength of wastewater influent?
A. Total Suspended Solids (TSS)
B. pH
C. Biochemical Oxygen Demand (BOD)
D. Chlorine residual
BOD measures the amount of oxygen required by microorganisms to
decompose organic matter and is the standard indicator of organic
pollution strength.
2. The primary purpose of an aeration tank in a package treatment plant
is to:
A. Remove grit
, B. Settle solids
C. Provide oxygen for biological treatment
D. Disinfect effluent
Aeration tanks supply dissolved oxygen to support aerobic
microorganisms that break down organic waste.
3. A low dissolved oxygen level in the aeration basin typically results in:
A. Increased nitrification
B. Improved effluent quality
C. Poor treatment and possible odor production
D. Increased chlorine demand
Low DO causes anaerobic conditions, leading to odors and reduced
treatment efficiency.
4. The function of a secondary clarifier is to:
A. Add chemicals
B. Aerate wastewater
C. Separate biological solids from treated water
D. Remove grit
Secondary clarifiers allow activated sludge flocs to settle, producing
clear effluent.
5. What does MLSS stand for?
A. Mixed Liquid Settled Solids
B. Maximum Liquid Suspended Solids
C. Mixed Liquor Suspended Solids
, D. Mixed Lagoon Solids System
MLSS represents the concentration of suspended biological solids in
the aeration tank.
6. Sludge Age is also known as:
A. Flow rate
B. Solids Retention Time (SRT)
C. Hydraulic loading
D. BOD removal rate
SRT refers to the average time solids remain in the treatment system.
7. The most common disinfectant used in package plants is:
A. Oxygen
B. Aluminum sulfate
C. Chlorine
D. Lime
Chlorine is widely used due to its effectiveness and ease of
application.
8. A high sludge volume index (SVI) indicates:
A. Good settling sludge
B. Dense sludge
C. Poor settling sludge (bulking condition)
D. Low solids concentration
High SVI means sludge is fluffy and does not settle well.
