Operator Class 2 Practice Exam

Maryland Wastewater Treatment Operator Class 2 Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

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

plant?

• Remove grit
• Reduce inorganic solids
• Clarify raw wastewater
• Reduce BOD and suspended solids

Rationale: Secondary treatment focuses on biological reduction of BOD

and TSS.

• The optimal dissolved oxygen (DO) level for an activated sludge aeration

basin is: 1 / 4

• 0.5–1.0 mg/L
• 6–8 mg/L
• 2–4 mg/L
• 10–12 mg/L

Rationale: Maintaining 2–4 mg/L DO supports efficient biological activity.

3. Sludge volume index (SVI) is used to evaluate:

• Centrifuge efficiency
• Settling characteristics of activated sludge
• Membrane fouling
• pH control efficiency

Rationale: SVI determines how well sludge settles in secondary clarifiers.

4. A high SVI usually indicates:

• Good settling
• Dense sludge
• Bulking conditions
• High chlorine demand

Rationale: High SVI means poor settling often due to filamentous growth.

5. The purpose of grit removal is to:

• Remove BOD
• Digest organics
• Prevent wear on pumps and equipment 2 / 4

• Remove colloidal solids

Rationale: Grit is abrasive and can damage mechanical components.

6. Typical pH range for biological treatment is:

A. 2.0–4.0

B. 4.0–5.0

C. 6.5–8.5

D. 9.5–12.0

Rationale: Microorganisms thrive in a near-neutral pH range.

• Which organism dominates a healthy activated sludge process?
• Amoebas
• Rotifers
• Bacteria
• Algae

Rationale: Bacteria perform most of the organic breakdown in secondary

treatment.

8. Alum is used in wastewater treatment primarily for:

• pH increase
• Coagulation and phosphorus removal
• Odor control
• Chlorine neutralization

Rationale: Alum coagulates particles and precipitates phosphorus.

• Too much return activated sludge (RAS) flow can cause: 3 / 4

• Heavy foam formation
• Overloading secondary clarifier
• Increased SVI
• High chlorine demand

Rationale: Excess RAS reduces clarifier detention time and impairs settling.

10. A dissolved oxygen reading of 0.5 mg/L in the aeration basin indicates:

• Normal operation
• Possible septic conditions
• Excess aeration
• No impact

Rationale: DO below 1 mg/L leads to anaerobic conditions and poor

treatment.

11. Primary clarifiers typically remove:

A. 5% BOD, 5% TSS

B. 90% BOD, 50% TSS

C. 25–35% BOD, 50–60% TSS

D. 70% BOD, 90% TSS

Rationale: Primary settling removes heavier solids and some organic load.

12. A rising sludge blanket in a secondary clarifier indicates:

• Low MLSS
• Denitrification occurring
• / 4