Practice Exam Questions And Correct

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

• Which of the following is the most common method of primary

treatment in wastewater plants?

• Trickling filter
• Activated sludge
• Sedimentation
• Aerated lagoon

Sedimentation is used to remove settleable solids from wastewater in primary treatment.

2. The primary purpose of a grit chamber is to:

• Remove suspended organic matter 1 / 4

• Remove sand, gravel, and other heavy inorganic solids
• Reduce BOD
• Treat pathogens

Grit chambers prevent damage and abrasion to downstream equipment by removing heavy inorganic solids.

3. BOD stands for:

• Biological Oxidation Demand
• Biochemical Oxygen Demand
• Basic Oxidation Demand
• Biological Oxygen Dilution

BOD measures the amount of oxygen microorganisms consume to decompose organic matter in wastewater.

4. A high BOD indicates:

• Low organic content
• High organic content
• Low nitrogen content
• High phosphorus content

High BOD means more oxygen is required to decompose organic material, indicating high organic content.

5. The first step in wastewater treatment after preliminary screening is:

• Disinfection
• Primary sedimentation
• Trickling filter 2 / 4

• Sludge digestion

After screening removes large debris, wastewater enters primary sedimentation to settle solids.

6. Chlorination in wastewater treatment is primarily used for:

• Disinfection
• Odor control
• Nutrient removal
• Sludge thickening

Chlorination kills or inactivates disease-causing microorganisms in the effluent.

7. The term “influent” refers to:

• Sludge leaving the plant
• Wastewater entering the plant
• Effluent discharged to a river
• Treated solids

Influent is raw wastewater entering the treatment facility.

• Which of the following is a primary source of nitrogen in wastewater?
• Industrial solvents
• Heavy metals
• Human waste and urine
• Pesticides

Nitrogen primarily comes from ammonia in human waste and urine. 3 / 4

9. The function of a secondary clarifier is to:

• Add chlorine
• Separate biological solids from treated wastewater
• Remove grit
• Measure flow

Secondary clarifiers settle out biomass from activated sludge or other biological treatment processes.

10. Sludge digestion primarily reduces:

• Organic content and volume
• Chlorine demand
• BOD in effluent
• Heavy metals

Digestion stabilizes sludge by reducing organic content and volume, making disposal safer.

11. The pH of most domestic wastewater is typically:

A. 2–4

B. 5–6

C. 6–8

D. 9–11

Domestic wastewater is usually near neutral, ranging from 6 to 8.

• The most common method of measuring flow in wastewater

plants is:

• Magnetic flow meter
• / 4