Practice Exam Questions And Correct

Illinois Wastewater Operator Class 2 Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of a wastewater treatment plant?
• To generate electricity
• To remove pollutants and protect public health
• To store water for industrial use
• To desalinate water
• To remove pollutants and protect public health

Rationale: Wastewater treatment plants are designed to remove physical,

chemical, and biological contaminants to protect human health and the environment. 1 / 4

• Which microorganism is most commonly used in the activated sludge

process?

• Algae
• Protozoa
• Bacteria
• Viruses
• Bacteria

Rationale: Bacteria are the primary organisms responsible for breaking

down organic matter in activated sludge systems.

3. In wastewater terminology, BOD stands for:

• Biochemical Oxidation Demand
• Biological Oxygen Demand
• Basic Organic Degradation
• Biohazardous Oxidation Detection
• Biological Oxygen Demand

Rationale: BOD measures the amount of dissolved oxygen required by

microorganisms to decompose organic matter in water.

• Which of the following is a common method for primary treatment?
• Trickling filter
• Sedimentation
• Activated sludge
• Chlorination
• Sedimentation 2 / 4

Rationale: Primary treatment uses physical processes like sedimentation to

remove settleable solids from wastewater.

5. Nitrification in wastewater treatment converts:

• Ammonia to nitrite and nitrate
• Nitrate to nitrogen gas
• Phosphate to ammonia
• BOD to TSS
• Ammonia to nitrite and nitrate

Rationale: Nitrification is a two-step biological process converting

ammonia first to nitrite and then to nitrate using autotrophic bacteria.

• Which chemical is commonly used for disinfection of wastewater?
• Sulfuric acid
• Chlorine
• Ammonia
• Sodium hydroxide
• Chlorine

Rationale: Chlorine is widely used to disinfect treated wastewater by

killing pathogenic microorganisms.

• What is the primary purpose of an aeration tank in the activated sludge

process?

• Remove sludge
• Mix chemicals
• Provide oxygen to microorganisms 3 / 4

• Filter solids
• Provide oxygen to microorganisms

Rationale: Aeration tanks supply oxygen to aerobic bacteria, enabling

them to metabolize organic pollutants.

• Which parameter indicates the concentration of suspended solids in

water?

A. TSS

B. COD

• pH
• DO

A. TSS

Rationale: Total Suspended Solids (TSS) measure the amount of particles

suspended in water, a key indicator of water quality.

• Which of the following pH values indicates neutral water?
• 3
• 7
• 9
• 11
• 7

Rationale: A pH of 7 is neutral, below 7 is acidic, and above 7 is alkaline.

10. The main advantage of trickling filters over activated sludge is:

• Requires less land
• Requires less energy and maintenance
• / 4