Operator Class 5 Exam 100 Practice

Maryland Wastewater Treatment Operator Class 5 Exam 100 Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

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

Class 5 wastewater plant?

• Remove nutrients
• Remove large debris to protect downstream equipment
• Disinfect wastewater
• Reduce sludge volume

Rationale: Preliminary treatment protects equipment by removing rags,

grit, and large solids.

• Which device is most commonly used for flow measurement in large

wastewater facilities? 1 / 4

• Weir box
• Magnetic flow meter
• Rotameter
• Venturi tube

Rationale: Magnetic flow meters are highly accurate and suitable for large

pipe diameters.

• What is the typical purpose of grit removal?
• Remove organic solids
• Increase BOD
• Protect pumps and mechanical equipment
• Raise pH

Rationale: Grit removal prevents abrasion and damage to equipment.

• The primary treatment process typically removes what percentage of

TSS?

A. 10–20%

B. 20–30%

C. 50–60%

D. 80–90%

Rationale: Primary clarifiers typically remove about half of suspended

solids.

• Which microorganism group is primarily responsible for nitrification? 2 / 4

• Protozoa
• Autotrophic bacteria
• Anaerobic fungi
• Viruses

Rationale: Nitrosomonas and Nitrobacter are autotrophic nitrifying

bacteria.

• What is the correct sequence for biological nitrogen removal?
• Denitrification → Nitrification
• Settling → Denitrification
• Aeration → Clarification
• Nitrification → Denitrification

Rationale: First ammonia is oxidized (nitrification), then nitrate is reduced

to nitrogen gas (denitrification).

• Which condition is required for nitrification?
• pH < 5
• Anoxic conditions
• High dissolved oxygen
• Low temperature

Rationale: Nitrifying bacteria require high DO to oxidize ammonia.

• What is the typical DO target for nitrification?
• 0.5 mg/L
• 1.0 mg/L 3 / 4

• 2.0 mg/L or higher
• 5 mg/L minimum

Rationale: At least 2 mg/L DO is needed for stable nitrification.

9. Filamentous bulking is most often caused by:

• Excess DO
• Excess chlorine
• Low F/M ratio
• High pH

Rationale: Low F/M promotes filamentous organisms, causing poor

settling.

10. Sludge age (SRT) is defined as:

• Time water stays in aeration tank
• Average time solids remain in the biological system
• Time water stays in clarifier
• Time for disinfection

Rationale: SRT measures the retention time of biomass within the system.

11. A high SRT typically results in:

• High F/M
• Older sludge and improved nitrification
• Younger sludge
• High BOD in effluent

Rationale: Older sludge supports slow-growing nitrifying bacteria.

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