Practice Exam Questions And Correct

Indiana Wastewater Operator Class I Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of preliminary treatment in a wastewater

facility?

• Remove dissolved solids
• Reduce nitrogen
• Remove large debris
• Disinfect wastewater
• Remove large debris

Preliminary treatment protects downstream equipment by removing rags, grit, and large solids.

• Which device is commonly used for grit removal? 1 / 4

• Trickling filter
• Aerated chamber
• Chlorine contact tank
• Membrane filter
• Aerated chamber

Aerated grit chambers slow flow and allow heavy inorganic particles to settle.

• Sludge with a strong rotten-egg odor is usually producing which gas?
• Methane
• Oxygen
• Nitrogen
• Hydrogen sulfide
• Hydrogen sulfide

H₂S forms under anaerobic conditions and produces a sulfur (rotten-egg) smell.

• The most common method of measuring wastewater flow in open

channels is:

• Magnetic meter
• Venturi tube
• Parshall flume
• Variable-area meter
• Parshall flume

Parshall flumes provide accurate flow measurement with low head loss. 2 / 4

5. BOD measures:

• Chemical oxidants
• Biological oxygen demand
• Nitrogen concentration
• Pathogen levels
• Biological oxygen demand

BOD indicates the oxygen microorganisms require to break down organic matter.

• Which lab test indicates the strength of organic material?
• pH
• DO

C. BOD

• Temperature

C. BOD

BOD is a key indicator of organic loading to the plant.

7. A composite sample is:

• Taken at one time
• Taken over time
• A grab sample duplicate
• A filtered sample
• Taken over time

Composite samples better represent changing wastewater conditions. 3 / 4

8. Standard pH range for activated sludge operation:

A. 3–4

B. 5–6

C. 6.5–8.5

D. 9–10

C. 6.5–8.5

Most biological systems function best within this near-neutral range.

9. The purpose of secondary treatment is to remove:

• Floating debris
• Heavy inorganic solids
• Dissolved and colloidal organics
• Pathogens
• Dissolved and colloidal organics

Secondary treatment relies on microbes to break down organic pollutants.

10. The activated sludge process depends on:

• Anaerobic bacteria
• Facultative algae
• Aerobic microorganisms
• Viruses
• Aerobic microorganisms

Activated sludge requires oxygen-using microbes for organic removal.

• Settleability of activated sludge is commonly measured using:
• / 4