Practice Exam Questions And Correct

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

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

facility?

• Remove dissolved solids
• Reduce nitrogen levels
• Remove large debris and grit
• Reduce BOD

Rationale: Preliminary treatment protects downstream equipment by

removing rags, debris, and grit.

2. The measure of oxygen-using organic matter in wastewater is:

A. TSS

B. BOD 1 / 3

• Alkalinity
• Turbidity

Rationale: BOD quantifies biodegradable organic material requiring

oxygen for decomposition.

3. In an activated sludge process, the MLSS is measured in:

• mg/L as CaCO₃
• mg/L as nitrogen
• mg/L
• ppm as chlorine residual

Rationale: MLSS concentration is expressed in mg/L of suspended solids in

aeration.

4. A wastewater flow rate of 2.5 MGD equals approximately:

• 1.25 cfs
• 2.5 cfs
• 3.9 cfs
• 5.0 cfs

Rationale: 1 MGD ≈ 1.547 cfs; 2.5 × 1.547 ≈ 3.9 cfs.

5. The most common cause of filaments in activated sludge is:

• High chlorine feed
• Low DO conditions
• Excess alkalinity 2 / 3

• Low temperature

Rationale: Filamentous bacteria thrive under low DO levels.

6. The process used to thicken sludge by gravity is called:

• Digestion
• Dewatering
• Gravity thickening
• Conditioning

Rationale: Gravity thickening uses settling to increase solids concentration.

7. The main purpose of disinfection is to:

• Remove ammonia
• Kill pathogenic organisms
• Remove TSS
• Reduce odors

Rationale: Disinfection neutralizes disease-causing organisms.

8. A chlorine residual of 0.2 mg/L typically indicates:

• Over-chlorination
• Equipment failure
• Adequate minimum final effluent residual
• No disinfection occurring

Rationale: 0.2 mg/L is commonly required as a minimum effluent chlorine

residual.

9. Sludge bulking is most often due to:

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