Exam Practice Questions And Correct

Iowa Wastewater Operator Grade IV Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• The primary purpose of an aeration basin in a wastewater treatment

plant is to:

a) Remove grit

b) Settle solids

c) Promote biological oxidation of organic matter

d) Disinfect effluent

Rationale: Aeration basins provide oxygen to microorganisms, which

break down organic pollutants biologically.

2. Nitrification in a wastewater treatment plant converts:

a) Nitrite to nitrate 1 / 4

b) Ammonia to nitrate

c) Nitrate to ammonia

d) Organic nitrogen to ammonia

Rationale: Nitrification is a two-step biological process where

ammonia is first converted to nitrite, then nitrite to nitrate.

3. The main function of a primary clarifier is to:

a) Promote microbial growth

b) Oxidize ammonia

c) Remove settleable solids

d) Neutralize pH

Rationale: Primary clarifiers allow solids to settle out by gravity

before secondary treatment.

4. The purpose of chlorination in wastewater treatment is to:

a) Reduce BOD

b) Remove solids

c) Disinfect effluent

d) Promote nitrification

Rationale: Chlorine is used to kill pathogens and disinfect the treated

effluent.

• Which of the following is the primary cause of odor in wastewater?

a) High BOD

b) Hydrogen sulfide (H₂S)

c) Nitrates 2 / 4

d) Suspended solids

Rationale: Hydrogen sulfide, produced under anaerobic conditions, is

a major contributor to odor.

6. Activated sludge is composed mainly of:

a) Sand and grit

b) Microorganisms and water

c) Chemicals

d) Sludge only

Rationale: Activated sludge contains a high concentration of

microorganisms used for biological treatment.

7. The most common method for sludge thickening is:

a) Filtration

b) Gravity thickening

c) Reverse osmosis

d) Incineration

Rationale: Gravity thickening allows solids to concentrate without

chemical addition or complex equipment.

8. The term “BOD₅” refers to:

a) Biochemical oxygen demand over 1 day

b) Biochemical oxygen demand over 5 days

c) Total oxygen in wastewater

d) Oxygen required to nitrify ammonia 3 / 4

Rationale: BOD₅ measures the oxygen consumed by microorganisms

to degrade organic matter over 5 days at 20°C.

• Which of the following processes is primarily used for phosphorus

removal?

a) Nitrification

b) Chemical precipitation

c) Filtration

d) Chlorination

Rationale: Phosphorus is typically removed by adding chemicals that

form insoluble precipitates.

10. Sludge digestion primarily reduces:

a) Suspended solids

b) Volatile solids

c) Pathogens

d) Inorganic solids

Rationale: Anaerobic digestion breaks down volatile solids, reducing

sludge volume and stabilizing it.

• What is the primary function of a grit chamber?

a) Reduce BOD

b) Remove sand and grit

c) Settle organic solids

d) Disinfect water

• / 4