Page 1 of 80
Ohio Wastewater Operator Class A ACTUAL EXAM
QUESTIONS AND CORRECT DETAILED ANSWERS LATEST
UPDATE THIS YEAR
Ohio Wastewater Operator Class A Exam
10-Line Exam Coverage
1. Preliminary Treatment – Bar screens remove large debris; grit chambers protect pumps
from abrasive wear and sedimentation .
2. Primary Treatment – Clarifiers use gravity to settle 50-70% of suspended solids with 1-2
hour detention times .
3. Secondary Biological Treatment – Activated sludge and trickling filters use
microorganisms to consume BOD; RAS returns biomass to aeration tanks .
4. Activated Sludge Process Control – F/M ratio, SRT (sludge age), MLSS, and DO monitoring
optimize microbial performance .
5. Disinfection – Chlorine and UV light kill pathogens; dechlorination required before
effluent discharge to aquatic life .
6. Sludge Handling – Gravity thickening, anaerobic digestion (methane production), and
dewatering reduce sludge volume .
7. Laboratory Procedures – BOD (5-day test), TSS (filtration/drying), DO, pH, and chlorine
residual analysis .
8. Regulatory Requirements – Ohio EPA permits, NPDES limits, and operator certification
under OAC 3745-7 .
9. Safety – Confined space entry (H₂S, O₂ monitoring), lockout/tagout, and PPE for
chemical/biological hazards.
10. Math & Calculations – Detention time, overflow rates, organic loading (lbs/day = mg/L ×
MGD × 8.34), and SVI.
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200 MCQs with Rationales – Ohio Class A Wastewater Exam
Section 1: Preliminary Treatment (Q 1-20)
1. What is the main purpose of preliminary treatment in wastewater facilities?
A) Remove nutrients
B) Remove large debris and grit
C) Disinfect the water
D) Reduce BOD
Correct Answer: B) Remove large debris and grit
Rationale: Preliminary treatment removes large debris and grit, protecting downstream
equipment from damage and wear .
2. Which device is typically used to remove rags, sticks, and large solids at the headworks?
A) Grit chamber
B) Bar screen
C) Trickling filter
D) Sand filter
Correct Answer: B) Bar screen
Rationale: Bar screens are installed at the headworks to physically remove large objects from
incoming wastewater before further treatment .
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3. What is the main risk if grit is not removed during preliminary treatment?
A) Increase in BOD
B) Equipment abrasion and wear
C) Excess foaming
D) High pH
Correct Answer: B) Equipment abrasion and wear
Rationale: Grit (sand, gravel, eggshells) causes abrasion, clogging, and excessive wear on pumps
and mechanical equipment .
4. Which preliminary device removes floating oils and grease?
A) Bar screen
B) Grit chamber
C) Skimming device
D) Chlorinator
Correct Answer: C) Skimming device
Rationale: Skimming devices (often in primary clarifiers) remove floating oils, grease, and scum
from the wastewater surface .
5. What is the typical detention time in a grit chamber?
A) 30 seconds
B) 1 minute
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C) 5 minutes
D) 30 minutes
Correct Answer: B) 1 minute
Rationale: Grit chambers are designed for short detention times (30-90 seconds) to settle only
heavy inorganic solids while keeping organics suspended .
6. Which type of grit removal system uses air to roll grit to a collection hopper?
A) Horizontal flow grit chamber
B) Aerated grit chamber
C) Vortex grit chamber
D) Cyclone separator
Correct Answer: B) Aerated grit chamber
Rationale: Air induces a spiral flow pattern that rolls grit to one side while keeping organics in
suspension .
7. A comminutor is used to:
A) Remove grit
B) Cut and grind solids into smaller particles
C) Remove oil and grease
D) Measure flow
Ohio Wastewater Operator Class A ACTUAL EXAM
QUESTIONS AND CORRECT DETAILED ANSWERS LATEST
UPDATE THIS YEAR
Ohio Wastewater Operator Class A Exam
10-Line Exam Coverage
1. Preliminary Treatment – Bar screens remove large debris; grit chambers protect pumps
from abrasive wear and sedimentation .
2. Primary Treatment – Clarifiers use gravity to settle 50-70% of suspended solids with 1-2
hour detention times .
3. Secondary Biological Treatment – Activated sludge and trickling filters use
microorganisms to consume BOD; RAS returns biomass to aeration tanks .
4. Activated Sludge Process Control – F/M ratio, SRT (sludge age), MLSS, and DO monitoring
optimize microbial performance .
5. Disinfection – Chlorine and UV light kill pathogens; dechlorination required before
effluent discharge to aquatic life .
6. Sludge Handling – Gravity thickening, anaerobic digestion (methane production), and
dewatering reduce sludge volume .
7. Laboratory Procedures – BOD (5-day test), TSS (filtration/drying), DO, pH, and chlorine
residual analysis .
8. Regulatory Requirements – Ohio EPA permits, NPDES limits, and operator certification
under OAC 3745-7 .
9. Safety – Confined space entry (H₂S, O₂ monitoring), lockout/tagout, and PPE for
chemical/biological hazards.
10. Math & Calculations – Detention time, overflow rates, organic loading (lbs/day = mg/L ×
MGD × 8.34), and SVI.
, Page 2 of 80
200 MCQs with Rationales – Ohio Class A Wastewater Exam
Section 1: Preliminary Treatment (Q 1-20)
1. What is the main purpose of preliminary treatment in wastewater facilities?
A) Remove nutrients
B) Remove large debris and grit
C) Disinfect the water
D) Reduce BOD
Correct Answer: B) Remove large debris and grit
Rationale: Preliminary treatment removes large debris and grit, protecting downstream
equipment from damage and wear .
2. Which device is typically used to remove rags, sticks, and large solids at the headworks?
A) Grit chamber
B) Bar screen
C) Trickling filter
D) Sand filter
Correct Answer: B) Bar screen
Rationale: Bar screens are installed at the headworks to physically remove large objects from
incoming wastewater before further treatment .
, Page 3 of 80
3. What is the main risk if grit is not removed during preliminary treatment?
A) Increase in BOD
B) Equipment abrasion and wear
C) Excess foaming
D) High pH
Correct Answer: B) Equipment abrasion and wear
Rationale: Grit (sand, gravel, eggshells) causes abrasion, clogging, and excessive wear on pumps
and mechanical equipment .
4. Which preliminary device removes floating oils and grease?
A) Bar screen
B) Grit chamber
C) Skimming device
D) Chlorinator
Correct Answer: C) Skimming device
Rationale: Skimming devices (often in primary clarifiers) remove floating oils, grease, and scum
from the wastewater surface .
5. What is the typical detention time in a grit chamber?
A) 30 seconds
B) 1 minute
, Page 4 of 80
C) 5 minutes
D) 30 minutes
Correct Answer: B) 1 minute
Rationale: Grit chambers are designed for short detention times (30-90 seconds) to settle only
heavy inorganic solids while keeping organics suspended .
6. Which type of grit removal system uses air to roll grit to a collection hopper?
A) Horizontal flow grit chamber
B) Aerated grit chamber
C) Vortex grit chamber
D) Cyclone separator
Correct Answer: B) Aerated grit chamber
Rationale: Air induces a spiral flow pattern that rolls grit to one side while keeping organics in
suspension .
7. A comminutor is used to:
A) Remove grit
B) Cut and grind solids into smaller particles
C) Remove oil and grease
D) Measure flow
