WASTEWATER TREATMENT OPERATOR
CERTIFICATION EXAMINATION
QUESTION AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES
2026 Q&A INSTANT DOWNLOAD PDF
1. The primary purpose of preliminary treatment in a wastewater plant is to
A. Remove dissolved organic matter
B. Protect downstream equipment from damage
C. Disinfect wastewater
D. Remove nutrients
Rationale: Preliminary treatment such as screening and grit removal
protects pumps and equipment from large debris.
2. Which unit process removes large floating and suspended solids?
A. Aeration basin
B. Bar screen
C. Secondary clarifier
D. Chlorination tank
Rationale: Bar screens physically remove large debris like rags and
plastics.
3. Grit removal is important because grit
A. Adds nutrients
B. Causes abrasion and wear on equipment
C. Improves settling
D. Increases BOD
Rationale: Grit can damage pumps and reduce treatment efficiency.
,4. Primary clarification mainly removes
A. Dissolved solids
B. Settleable and floatable solids
C. Pathogens
D. Nutrients
Rationale: Primary clarifiers allow heavier solids to settle and lighter
materials to float.
5. BOD measures
A. Total solids
B. Oxygen required to biologically decompose organic matter
C. pH level
D. Toxicity
Rationale: BOD indicates organic pollution strength.
6. High BOD in influent indicates
A. Clean water
B. High organic load
C. Low bacteria
D. Excess chlorine
Rationale: More biodegradable material increases oxygen demand.
7. Secondary treatment primarily relies on
A. Chemical reactions
B. Biological processes
C. Physical screening
D. Disinfection
Rationale: Microorganisms consume organic matter in secondary
treatment.
8. Activated sludge systems require
A. No oxygen
B. Adequate dissolved oxygen
C. High chlorine
, D. High temperature
Rationale: Aerobic bacteria need oxygen to metabolize organics.
9. The main function of aeration is to
A. Settle solids
B. Supply oxygen and mix biomass
C. Disinfect effluent
D. Remove grit
Rationale: Aeration supports microbial activity and keeps solids
suspended.
10.Mixed liquor is
A. Influent wastewater
B. Mixture of wastewater and biological solids in aeration basin
C. Sludge in digester
D. Treated effluent
Rationale: Mixed liquor contains microorganisms actively treating
wastewater.
11.MLSS refers to
A. Dissolved oxygen
B. Mixed liquor suspended solids
C. Volatile acids
D. Sludge age
Rationale: MLSS measures concentration of solids in aeration basin.
12.Secondary clarifiers are used to
A. Add oxygen
B. Separate treated water from biomass
C. Disinfect effluent
D. Remove grit
Rationale: Clarifiers settle biological floc after aeration.
13.Return activated sludge (RAS) is used to
A. Waste solids
CERTIFICATION EXAMINATION
QUESTION AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES
2026 Q&A INSTANT DOWNLOAD PDF
1. The primary purpose of preliminary treatment in a wastewater plant is to
A. Remove dissolved organic matter
B. Protect downstream equipment from damage
C. Disinfect wastewater
D. Remove nutrients
Rationale: Preliminary treatment such as screening and grit removal
protects pumps and equipment from large debris.
2. Which unit process removes large floating and suspended solids?
A. Aeration basin
B. Bar screen
C. Secondary clarifier
D. Chlorination tank
Rationale: Bar screens physically remove large debris like rags and
plastics.
3. Grit removal is important because grit
A. Adds nutrients
B. Causes abrasion and wear on equipment
C. Improves settling
D. Increases BOD
Rationale: Grit can damage pumps and reduce treatment efficiency.
,4. Primary clarification mainly removes
A. Dissolved solids
B. Settleable and floatable solids
C. Pathogens
D. Nutrients
Rationale: Primary clarifiers allow heavier solids to settle and lighter
materials to float.
5. BOD measures
A. Total solids
B. Oxygen required to biologically decompose organic matter
C. pH level
D. Toxicity
Rationale: BOD indicates organic pollution strength.
6. High BOD in influent indicates
A. Clean water
B. High organic load
C. Low bacteria
D. Excess chlorine
Rationale: More biodegradable material increases oxygen demand.
7. Secondary treatment primarily relies on
A. Chemical reactions
B. Biological processes
C. Physical screening
D. Disinfection
Rationale: Microorganisms consume organic matter in secondary
treatment.
8. Activated sludge systems require
A. No oxygen
B. Adequate dissolved oxygen
C. High chlorine
, D. High temperature
Rationale: Aerobic bacteria need oxygen to metabolize organics.
9. The main function of aeration is to
A. Settle solids
B. Supply oxygen and mix biomass
C. Disinfect effluent
D. Remove grit
Rationale: Aeration supports microbial activity and keeps solids
suspended.
10.Mixed liquor is
A. Influent wastewater
B. Mixture of wastewater and biological solids in aeration basin
C. Sludge in digester
D. Treated effluent
Rationale: Mixed liquor contains microorganisms actively treating
wastewater.
11.MLSS refers to
A. Dissolved oxygen
B. Mixed liquor suspended solids
C. Volatile acids
D. Sludge age
Rationale: MLSS measures concentration of solids in aeration basin.
12.Secondary clarifiers are used to
A. Add oxygen
B. Separate treated water from biomass
C. Disinfect effluent
D. Remove grit
Rationale: Clarifiers settle biological floc after aeration.
13.Return activated sludge (RAS) is used to
A. Waste solids
