Grade 2 Exam Practice Questions And

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

• What is the primary purpose of preliminary treatment?
• Remove dissolved solids
• Remove nutrients
• Remove large debris that could damage equipment
• Disinfect wastewater

Rationale: Preliminary treatment removes rags, grit, and large solids to

protect downstream equipment.

2. Grit chambers are designed mainly to remove:

• Organic solids
• Colloidal particles 1 / 4

• Inorganic heavy particles such as sand and gravel
• Viruses

Rationale: Grit is primarily sand, gravel, and inorganic material that settles

quickly.

3. The typical pH range for activated sludge microorganisms is:

A. 4–5

B. 5–6

C. 6.5–8.5

D. 9–11

Rationale: Biological processes operate best between pH 6.5 and 8.5.

4. The main purpose of primary clarifiers is to:

• Aerate wastewater
• Settle out heavy solids and float grease/scum
• Disinfect the effluent
• Remove nutrients

Rationale: Primary clarifiers settle suspended solids and remove floatables.

5. Sludge that settles poorly and forms a fluffy layer is usually caused by:

• Good settling
• Bulking sludge
• Sand accumulation
• High chlorine levels 2 / 4

Rationale: Bulking sludge prevents proper settling and creates a fluffy

blanket.

6. The food-to-microorganism ratio (F/M) is used to monitor:

• Chlorine dosage
• Activated sludge loading
• Flow variations
• Solids buildup in digesters

Rationale: F/M helps operators understand how much “food” is available

for biological treatment.

7. A high chlorine demand usually indicates:

• Low organic load
• Cold temperatures
• High organic or ammonia levels
• Stable effluent

Rationale: More chlorine is used up when more organic matter or

ammonia is present.

• What organism is most associated with excellent sludge settling?
• Amoebas
• Flagellates
• Stalked ciliates
• Rotifers 3 / 4

Rationale: Stalked ciliates indicate a stable, mature activated sludge

process.

9. The term BOD stands for:

• Biological Organic Density
• Biochemical Oxygen Demand
• Biological Oxidation Data
• Bio-Oxygen Decomposition

Rationale: BOD measures oxygen needed by bacteria to break down

organics.

10. Short-circuiting in a clarifier will:

• Improve settling
• Reduce detention time and hurt efficiency
• Increase sludge blanket depth
• Decrease flow

Rationale: Short-circuiting reduces effective settling time, harming

performance.

11. Dissolved oxygen in aeration tanks should generally be kept:

• Under 0.5 mg/L
• 0.5–1.0 mg/L
• 2.0 mg/L or higher
• / 4