Practice Exam Questions And Correct

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

• Which of the following best describes BOD (Biochemical Oxygen

Demand)?

• The amount of oxygen required by microorganisms to stabilize

organic matter in wastewater

• The total dissolved solids in wastewater
• The amount of oxygen consumed by microorganisms to degrade

organic matter in a specific time period

• The amount of oxygen in raw wastewater 1 / 4

Rationale: BOD measures the oxygen microorganisms use to decompose

organic matter over a set time (usually 5 days). It is a key indicator of wastewater strength.

• The primary purpose of a bar screen in a wastewater treatment plant

is to:

• Remove dissolved organic matter
• Remove large solids and debris from influent wastewater
• Settle sludge
• Disinfect wastewater

Rationale: Bar screens prevent large debris from damaging downstream

equipment and interfering with treatment processes.

• Which type of bacteria predominates in an anaerobic digester?
• Nitrifying bacteria
• Methanogenic bacteria
• Facultative bacteria
• Coliform bacteria

Rationale: Methanogenic bacteria thrive in anaerobic conditions and

produce methane during sludge digestion.

• What is the function of the aeration basin in an activated sludge

process?

• Settle solids
• Remove large debris 2 / 4

• Provide oxygen to microorganisms for the breakdown of organic

matter

• Filter wastewater

Rationale: Aeration basins supply oxygen, promoting microbial

degradation of organic matter in the activated sludge process.

5. Chlorination of wastewater is primarily used to:

• Increase pH
• Remove nitrogen
• Disinfect and kill pathogenic organisms
• Remove heavy metals

Rationale: Chlorination is a common disinfection method to reduce

disease-causing bacteria before discharge.

6. Nitrification in wastewater treatment converts:

• Ammonia to organic nitrogen
• Ammonia to nitrate
• Nitrate to ammonia
• Nitrite to phosphorus

Rationale: Nitrification is an aerobic process where ammonia is oxidized

first to nitrite, then to nitrate.

• Which chemical is commonly used to remove phosphorus from

wastewater?

• Chlorine 3 / 4

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

Rationale: Alum reacts with phosphate to form insoluble aluminum

phosphate, which settles out of the water.

8. Sludge thickening primarily aims to:

• Disinfect sludge
• Oxidize organic matter
• Reduce water content and increase solids concentration
• Neutralize pH

Rationale: Thickening concentrates solids to reduce volume and improve

subsequent handling and digestion efficiency.

• The most common indicator organism for fecal contamination in

wastewater is:

• Salmonella
• Escherichia coli (E. coli)
• Methanogens
• Clostridium

Rationale: E. coli is used as a coliform indicator because it is abundant in

human intestines and signals potential pathogen presence.

• What is the primary purpose of a primary clarifier?
• Remove dissolved oxygen
• / 4