Practice Exam Questions And Correct

Iowa Wastewater Operator Grade I 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:

• Remove dissolved nutrients
• Remove settleable solids
• Disinfect wastewater
• 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:

• The amount of oxygen in water 1 / 4

• The oxygen required by microorganisms to decompose organic

matter

• The dissolved oxygen saturation
• The chemical content of wastewater

Rationale: BOD quantifies the oxygen microorganisms consume when

breaking down organic matter in water.

• Which unit process removes most of the suspended solids in primary

treatment?

• Trickling filter
• Activated sludge
• Primary clarifier
• 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:

• Scum
• Return activated sludge
• Primary sludge
• Digested sludge

Rationale: Solids settled from raw wastewater in the primary clarifier are

called primary sludge. 2 / 4

5. The purpose of an aeration tank is to:

• Remove grit
• Provide oxygen to support microbial degradation of organic

matter

• Settle suspended solids
• Neutralize pH

Rationale: Aeration tanks introduce oxygen to promote the growth of

microorganisms that consume organic matter.

6. Secondary treatment primarily removes:

• Heavy metals
• Dissolved organic matter
• Grit
• Oils and grease

Rationale: Secondary treatment focuses on biological processes that

reduce dissolved organics, measured as BOD.

7. A measure of water clarity is:

• pH
• Turbidity
• Conductivity
• Alkalinity

Rationale: Turbidity indicates the amount of suspended particles in water,

affecting clarity. 3 / 4

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:

• Nitrogen gas to ammonia
• Ammonia to nitrate
• Nitrate to ammonia
• Organic nitrogen to phosphorus

Rationale: Nitrifying bacteria oxidize ammonia to nitrite and then to

nitrate.

10. Chlorination in wastewater treatment is used to:

• Reduce BOD
• Settle solids
• Disinfect effluent
• Remove nutrients

Rationale: Chlorine kills or inactivates pathogens to disinfect wastewater

before discharge.

• / 4