Practice Exam Questions And Correct

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

• What is the primary purpose of nitrification in wastewater treatment?
• Remove phosphorus
• Denature organic compounds
• Convert ammonia to nitrate
• Raise alkalinity

Rationale: Nitrification is the biological conversion of ammonia first to

nitrite and then to nitrate.

• Which microorganisms are responsible for converting ammonia to

nitrite? 1 / 4

• Nitrosospira
• Nitrosomonas
• Nitrobacter
• Thiothrix

Rationale: Nitrosomonas bacteria perform the first nitrification step: ammonia to nitrite.

• What is the typical F/M ratio range for an extended aeration process?

A. 0.5–1.0

B. 0.2–0.4

C. 0.05–0.15

D. 0.01–0.03

Rationale: Extended aeration uses a very low F/M ratio around 0.05–0.15.

• In conventional activated sludge, what effect does low DO (<1.0 mg/L)

have?

• Increased settling
• Filamentous growth
• Increased nitrification
• Reduced denitrification

Rationale: Low dissolved oxygen encourages filamentous bacteria, causing

bulking.

• The purpose of RAS (return activated sludge) is to: 2 / 4

• Increase DO
• Reduce BOD
• Remove nitrates
• Maintain MLSS concentration

Rationale: RAS returns microorganisms to the aeration basin to maintain

proper MLSS levels.

• What is the typical sludge age (SRT) for a nitrifying activated sludge

plant?

• 2–4 days
• 4–6 days
• 6–10 days
• 10–20 days

Rationale: Nitrifiers are slow-growing and require higher SRT, usually 10–

20 days.

• What does a rising sludge blanket in secondary clarifiers usually

indicate?

• Hydraulic overload
• Denitrification
• Poor aeration
• RAS pump failure

Rationale: Denitrification gas bubbles cause sludge to float and rise.

8. The acronym SVI stands for: 3 / 4

• Settling Velocity Index
• Sludge Volume Index
• Solids Volume Indicator
• Sludge Viscosity Index

Rationale: SVI measures settling characteristics of activated sludge.

• What SVI value typically indicates a well-settling sludge?
• <50

B. 80–150

C. 150–200

• >250

Rationale: Normal, healthy sludge settles with SVI between 80 and 150.

• Which lab test is required to determine MLSS concentration?
• BOD test
• Total suspended solids test
• COD test
• Volatile acids test

Rationale: MLSS is measured using the TSS procedure on mixed liquor

samples.

• Primary clarifiers typically remove what percentage of BOD?

A. 5–10%

• 10–20%
• / 4