Operator Group I Exam Practice Questions

Washington Wastewater Treatment Plant Operator Group I Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following best describes the primary purpose of a

wastewater treatment plant?

• Produce drinking water
• Remove solid waste from sewage
• Protect public health and the environment by treating wastewater
• Generate electricity from sewage

Rationale: The primary purpose of a wastewater treatment plant is

to remove pollutants and protect public health and the environment.

• What is the most common method used to remove suspended solids

in primary treatment?

• Sedimentation 1 / 4

• Filtration
• Chlorination
• Aeration

Rationale: Sedimentation allows solids to settle by gravity, which is

the primary method used in primary treatment.

• What type of microorganisms are primarily responsible for breaking

down organic matter in secondary treatment?

• Algae
• Protozoa
• Bacteria
• Viruses

Rationale: Bacteria metabolize organic matter in wastewater during

secondary treatment.

4. The term BOD stands for:

• Biological Oxidation Demand
• Biochemical Oxygen Demand
• Biological Organic Decomposition
• Basic Oxidation Determination

Rationale: BOD measures the amount of oxygen required by bacteria

to decompose organic matter in water.

5. Nitrification in wastewater treatment is a process in which:

• Ammonia is converted to organic nitrogen
• Ammonia is converted to nitrate 2 / 4

• Nitrate is converted to ammonia
• Nitrogen gas is converted to nitrate

Rationale: Nitrification is a two-step biological process where

ammonia is oxidized to nitrite and then nitrate.

• What is the main function of aeration in activated sludge systems?
• Remove heavy metals
• Supply oxygen to microorganisms
• Settle solids
• Chlorinate wastewater

Rationale: Aeration provides dissolved oxygen necessary for aerobic

bacteria to metabolize organic matter.

• Which chemical is commonly used for disinfection in wastewater

treatment?

• Fluoride
• Chlorine
• Aluminum sulfate
• Sodium hydroxide

Rationale: Chlorine is widely used to kill pathogenic microorganisms

in treated wastewater.

8. The term TSS in wastewater treatment stands for:

• Total Soluble Substances
• Total Suspended Solids
• Total Sewage Solids 3 / 4

• Total Salinity Standard

Rationale: TSS refers to the solids that remain suspended in water

and can be removed by settling or filtration.

• What is the purpose of sludge digestion?
• Increase TSS
• Reduce organic content and odor
• Increase ammonia
• Produce chlorine

Rationale: Sludge digestion reduces the volume of solids and

stabilizes organic material, reducing odors.

• In an activated sludge system, what does SVI (Sludge Volume

Index) indicate?

• Oxygen demand of sludge
• Settling characteristics of sludge
• Concentration of ammonia
• Chlorine demand

Rationale: SVI measures the volume occupied by a unit weight of

sludge after settling, indicating settling efficiency.

• Which of the following is a common coagulant used in

wastewater treatment?

• Sodium hypochlorite
• Aluminum sulfate (alum)
• Calcium carbonate
• / 4