Iowa Wastewater Operator Grade I
Practice Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. The main purpose of primary treatment in a wastewater plant is to:
A. Remove dissolved nutrients
B. Remove settleable solids
C. Disinfect wastewater
D. Reduce BOD
Rationale: Primary treatment uses physical processes like sedimentation to
remove settleable solids, while dissolved nutrients and BOD require
secondary treatment.
2. Biological oxygen demand (BOD) measures:
A. The amount of oxygen in water
, B. The oxygen required by microorganisms to decompose organic
matter
C. The dissolved oxygen saturation
D. The chemical content of wastewater
Rationale: BOD quantifies the oxygen microorganisms consume when
breaking down organic matter in water.
3. Which unit process removes most of the suspended solids in primary
treatment?
A. Trickling filter
B. Activated sludge
C. Primary clarifier
D. Aeration tank
Rationale: Primary clarifiers allow solids to settle out of wastewater before
secondary biological treatment.
4. Sludge that has settled in the primary clarifier is called:
A. Scum
B. Return activated sludge
C. Primary sludge
D. Digested sludge
Rationale: Solids settled from raw wastewater in the primary clarifier are
called primary sludge.
, 5. The purpose of an aeration tank is to:
A. Remove grit
B. Provide oxygen to support microbial degradation of organic
matter
C. Settle suspended solids
D. Neutralize pH
Rationale: Aeration tanks introduce oxygen to promote the growth of
microorganisms that consume organic matter.
6. Secondary treatment primarily removes:
A. Heavy metals
B. Dissolved organic matter
C. Grit
D. Oils and grease
Rationale: Secondary treatment focuses on biological processes that
reduce dissolved organics, measured as BOD.
7. A measure of water clarity is:
A. pH
B. Turbidity
C. Conductivity
D. Alkalinity
Rationale: Turbidity indicates the amount of suspended particles in water,
affecting clarity.
, 8. The pH of typical raw wastewater is usually:
A. 1–3
B. 4–5
C. 6–8
D. 9–11
Rationale: Most raw wastewater is near neutral, typically between 6 and
8.
9. Nitrification in wastewater treatment converts:
A. Nitrogen gas to ammonia
B. Ammonia to nitrate
C. Nitrate to ammonia
D. Organic nitrogen to phosphorus
Rationale: Nitrifying bacteria oxidize ammonia to nitrite and then to
nitrate.
10. Chlorination in wastewater treatment is used to:
A. Reduce BOD
B. Settle solids
C. Disinfect effluent
D. Remove nutrients
Rationale: Chlorine kills or inactivates pathogens to disinfect wastewater
before discharge.
Practice Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. The main purpose of primary treatment in a wastewater plant is to:
A. Remove dissolved nutrients
B. Remove settleable solids
C. Disinfect wastewater
D. Reduce BOD
Rationale: Primary treatment uses physical processes like sedimentation to
remove settleable solids, while dissolved nutrients and BOD require
secondary treatment.
2. Biological oxygen demand (BOD) measures:
A. The amount of oxygen in water
, B. The oxygen required by microorganisms to decompose organic
matter
C. The dissolved oxygen saturation
D. The chemical content of wastewater
Rationale: BOD quantifies the oxygen microorganisms consume when
breaking down organic matter in water.
3. Which unit process removes most of the suspended solids in primary
treatment?
A. Trickling filter
B. Activated sludge
C. Primary clarifier
D. Aeration tank
Rationale: Primary clarifiers allow solids to settle out of wastewater before
secondary biological treatment.
4. Sludge that has settled in the primary clarifier is called:
A. Scum
B. Return activated sludge
C. Primary sludge
D. Digested sludge
Rationale: Solids settled from raw wastewater in the primary clarifier are
called primary sludge.
, 5. The purpose of an aeration tank is to:
A. Remove grit
B. Provide oxygen to support microbial degradation of organic
matter
C. Settle suspended solids
D. Neutralize pH
Rationale: Aeration tanks introduce oxygen to promote the growth of
microorganisms that consume organic matter.
6. Secondary treatment primarily removes:
A. Heavy metals
B. Dissolved organic matter
C. Grit
D. Oils and grease
Rationale: Secondary treatment focuses on biological processes that
reduce dissolved organics, measured as BOD.
7. A measure of water clarity is:
A. pH
B. Turbidity
C. Conductivity
D. Alkalinity
Rationale: Turbidity indicates the amount of suspended particles in water,
affecting clarity.
, 8. The pH of typical raw wastewater is usually:
A. 1–3
B. 4–5
C. 6–8
D. 9–11
Rationale: Most raw wastewater is near neutral, typically between 6 and
8.
9. Nitrification in wastewater treatment converts:
A. Nitrogen gas to ammonia
B. Ammonia to nitrate
C. Nitrate to ammonia
D. Organic nitrogen to phosphorus
Rationale: Nitrifying bacteria oxidize ammonia to nitrite and then to
nitrate.
10. Chlorination in wastewater treatment is used to:
A. Reduce BOD
B. Settle solids
C. Disinfect effluent
D. Remove nutrients
Rationale: Chlorine kills or inactivates pathogens to disinfect wastewater
before discharge.
