OHIO WASTEWATER OPERATOR CLASS A EXAMINATION
COMPLETE QUESTIONS AND DETAILED SOLUTIONS
LATEST UPDATE THIS YEAR JUST RELEASED
Examination Coverage Areas
1. Preliminary and Primary Treatment — screening, grit removal, clarification, scum removal, and
hydraulic loading.
2. Biological Treatment — activated sludge, aeration, microorganisms, F/M ratio, SRT, nitrification,
and denitrification.
3. Secondary Clarification — settling characteristics, sludge blanket control, RAS, WAS, bulking,
and rising sludge.
4. Advanced Nutrient Removal — biological nitrogen and phosphorus removal and process
control.
5. Disinfection and Effluent Treatment — chlorine, UV, contact time, residuals, dechlorination,
and pathogen control.
6. Solids Processing — thickening, digestion, dewatering, stabilization, biosolids handling, and
odor control.
7. Wastewater Mathematics — flow, loading, detention time, pounds per day, concentrations,
volumes, and process calculations.
8. Laboratory and Process Control — BOD, TSS, DO, pH, ammonia, alkalinity, MLSS, MLVSS, SVI,
and sampling.
9. Regulatory and Operational Requirements — NPDES compliance, records, reporting, operator
responsibilities, bypasses, and permit conditions.
10. Safety, Maintenance, and Troubleshooting — confined spaces, chemical hazards, electrical
safety, equipment failures, alarms, and emergency response.
1. Which operational objective is most important when a wastewater plant
receives unusually high influent flow during a major storm event?
A. Increase sludge wasting immediately without measuring process conditions
B. Maintain treatment performance while preventing hydraulic overloading of
downstream processes
C. Shut down all biological treatment equipment until flow returns to normal
D. Increase effluent chlorine concentration regardless of actual contact conditions
Answer: B
,Rationale: Excessive hydraulic flow can reduce detention time, disturb clarifier
settling, and overload biological and disinfection processes. Operators should
maintain treatment while managing hydraulic loading carefully.
2. Why is effective screening particularly important before wastewater enters
pumps and downstream mechanical treatment equipment?
A. Screens increase the dissolved oxygen concentration entering aeration basins
B. Screens remove large debris that could damage equipment or interfere with
treatment
C. Screens convert ammonia directly into nitrate before biological treatment
D. Screens eliminate the need for primary clarification
Answer: B
Rationale: Bar screens remove rags, plastics, sticks, and other large debris that
can clog pumps, damage mechanical equipment, and interfere with subsequent
treatment processes.
3. An operator observes excessive grit accumulation in downstream channels
despite apparently normal influent flow conditions. What should be
investigated first?
A. Grit removal process velocity and equipment operation
B. Chlorine residual in the final effluent
C. Digester alkalinity only
D. Final effluent ultraviolet lamp intensity
Answer: A
Rationale: Grit removal depends heavily on controlling hydraulic conditions and
maintaining properly functioning grit collection equipment. Excessive
downstream grit indicates inadequate preliminary removal.
,4. Which wastewater characteristic most directly affects the ability of a primary
clarifier to remove settleable suspended solids?
A. Hydraulic and surface overflow loading
B. Ultraviolet transmittance
C. Chlorine demand
D. Digester volatile-acid concentration
Answer: A
Rationale: Primary clarifier performance depends strongly on hydraulic loading,
detention characteristics, settling properties, and proper solids removal.
5. What operational problem can occur when primary clarifier sludge remains in
the tank for excessive periods before being removed?
A. Increased dissolved oxygen transfer
B. Anaerobic decomposition, gas formation, odors, and solids flotation
C. Improved nitrification throughout the aeration basin
D. Elimination of scum formation
Answer: B
Rationale: Excessive sludge detention can cause anaerobic conditions and gas
production. Gas bubbles can attach to solids and carry them to the surface,
producing floating sludge and odors.
6. A primary clarifier develops a thick layer of floating material even though the
sludge pumps appear operational. What should the operator investigate?
A. Sludge withdrawal frequency and scum removal effectiveness
B. UV lamp sleeve cleanliness only
C. Secondary aeration basin alkalinity only
D. Effluent ammonia sampling frequency only
, Answer: A
Rationale: Floating solids may result from inadequate scum removal or prolonged
solids detention. Operators should verify sludge and scum collection equipment
and operating schedules.
7. Which condition would most likely cause settleable solids to pass through a
primary clarifier without adequate removal?
A. Excessively high hydraulic loading
B. Proper sludge withdrawal
C. Stable influent conditions
D. Correctly maintained scum removal
Answer: A
Rationale: Excessive flow increases surface overflow rate and reduces effective
settling opportunity, allowing more solids to escape with the clarifier effluent.
8. Why should an operator routinely inspect mechanical screening equipment
rather than relying exclusively on automatic alarms?
A. Automatic controls cannot detect every mechanical or process-related problem
B. Manual inspections eliminate all maintenance requirements
C. Screening equipment never experiences mechanical failures
D. Automatic alarms are prohibited at wastewater facilities
Answer: A
Rationale: Visual inspection can identify unusual vibration, accumulation, wear,
bypassing, odors, and other conditions before they become major failures.
COMPLETE QUESTIONS AND DETAILED SOLUTIONS
LATEST UPDATE THIS YEAR JUST RELEASED
Examination Coverage Areas
1. Preliminary and Primary Treatment — screening, grit removal, clarification, scum removal, and
hydraulic loading.
2. Biological Treatment — activated sludge, aeration, microorganisms, F/M ratio, SRT, nitrification,
and denitrification.
3. Secondary Clarification — settling characteristics, sludge blanket control, RAS, WAS, bulking,
and rising sludge.
4. Advanced Nutrient Removal — biological nitrogen and phosphorus removal and process
control.
5. Disinfection and Effluent Treatment — chlorine, UV, contact time, residuals, dechlorination,
and pathogen control.
6. Solids Processing — thickening, digestion, dewatering, stabilization, biosolids handling, and
odor control.
7. Wastewater Mathematics — flow, loading, detention time, pounds per day, concentrations,
volumes, and process calculations.
8. Laboratory and Process Control — BOD, TSS, DO, pH, ammonia, alkalinity, MLSS, MLVSS, SVI,
and sampling.
9. Regulatory and Operational Requirements — NPDES compliance, records, reporting, operator
responsibilities, bypasses, and permit conditions.
10. Safety, Maintenance, and Troubleshooting — confined spaces, chemical hazards, electrical
safety, equipment failures, alarms, and emergency response.
1. Which operational objective is most important when a wastewater plant
receives unusually high influent flow during a major storm event?
A. Increase sludge wasting immediately without measuring process conditions
B. Maintain treatment performance while preventing hydraulic overloading of
downstream processes
C. Shut down all biological treatment equipment until flow returns to normal
D. Increase effluent chlorine concentration regardless of actual contact conditions
Answer: B
,Rationale: Excessive hydraulic flow can reduce detention time, disturb clarifier
settling, and overload biological and disinfection processes. Operators should
maintain treatment while managing hydraulic loading carefully.
2. Why is effective screening particularly important before wastewater enters
pumps and downstream mechanical treatment equipment?
A. Screens increase the dissolved oxygen concentration entering aeration basins
B. Screens remove large debris that could damage equipment or interfere with
treatment
C. Screens convert ammonia directly into nitrate before biological treatment
D. Screens eliminate the need for primary clarification
Answer: B
Rationale: Bar screens remove rags, plastics, sticks, and other large debris that
can clog pumps, damage mechanical equipment, and interfere with subsequent
treatment processes.
3. An operator observes excessive grit accumulation in downstream channels
despite apparently normal influent flow conditions. What should be
investigated first?
A. Grit removal process velocity and equipment operation
B. Chlorine residual in the final effluent
C. Digester alkalinity only
D. Final effluent ultraviolet lamp intensity
Answer: A
Rationale: Grit removal depends heavily on controlling hydraulic conditions and
maintaining properly functioning grit collection equipment. Excessive
downstream grit indicates inadequate preliminary removal.
,4. Which wastewater characteristic most directly affects the ability of a primary
clarifier to remove settleable suspended solids?
A. Hydraulic and surface overflow loading
B. Ultraviolet transmittance
C. Chlorine demand
D. Digester volatile-acid concentration
Answer: A
Rationale: Primary clarifier performance depends strongly on hydraulic loading,
detention characteristics, settling properties, and proper solids removal.
5. What operational problem can occur when primary clarifier sludge remains in
the tank for excessive periods before being removed?
A. Increased dissolved oxygen transfer
B. Anaerobic decomposition, gas formation, odors, and solids flotation
C. Improved nitrification throughout the aeration basin
D. Elimination of scum formation
Answer: B
Rationale: Excessive sludge detention can cause anaerobic conditions and gas
production. Gas bubbles can attach to solids and carry them to the surface,
producing floating sludge and odors.
6. A primary clarifier develops a thick layer of floating material even though the
sludge pumps appear operational. What should the operator investigate?
A. Sludge withdrawal frequency and scum removal effectiveness
B. UV lamp sleeve cleanliness only
C. Secondary aeration basin alkalinity only
D. Effluent ammonia sampling frequency only
, Answer: A
Rationale: Floating solids may result from inadequate scum removal or prolonged
solids detention. Operators should verify sludge and scum collection equipment
and operating schedules.
7. Which condition would most likely cause settleable solids to pass through a
primary clarifier without adequate removal?
A. Excessively high hydraulic loading
B. Proper sludge withdrawal
C. Stable influent conditions
D. Correctly maintained scum removal
Answer: A
Rationale: Excessive flow increases surface overflow rate and reduces effective
settling opportunity, allowing more solids to escape with the clarifier effluent.
8. Why should an operator routinely inspect mechanical screening equipment
rather than relying exclusively on automatic alarms?
A. Automatic controls cannot detect every mechanical or process-related problem
B. Manual inspections eliminate all maintenance requirements
C. Screening equipment never experiences mechanical failures
D. Automatic alarms are prohibited at wastewater facilities
Answer: A
Rationale: Visual inspection can identify unusual vibration, accumulation, wear,
bypassing, odors, and other conditions before they become major failures.
