Hawaii Wastewater Treatment Operator Exam
Newest (2025 - 2026 Update) From Real Past
Papers Questions – A Set Of 100 Most
Common Exam Frequently Tested Questions
And Answers In Details 100% Verified Exam
Highly Recommendable For Grade A+
1. What is the primary purpose of preliminary treatment in a wastewater
treatment plant?
A. Remove dissolved nutrients
B. Destroy pathogens
C. Remove large debris and grit
D. Add chlorine
Answer: C. Remove large debris and grit
Preliminary treatment protects downstream equipment by removing rags, sticks,
sand, gravel, and other large materials before the wastewater enters primary
treatment.
2. Which process mainly removes settleable solids?
A. Activated sludge
B. Primary sedimentation
C. Chlorination
D. Aeration
,Answer: B. Primary sedimentation
Primary clarifiers allow heavier solids to settle while lighter materials float for
removal.
3. Biochemical Oxygen Demand (BOD) measures:
A. Total nitrogen
B. Acidity
C. Oxygen required by microorganisms to decompose organic matter
D. Dissolved solids
Answer: C. Oxygen required by microorganisms to decompose organic matter
BOD is one of the most important indicators of wastewater strength.
4. High dissolved oxygen in an aeration basin generally indicates:
A. Poor aeration
B. Septic conditions
C. Adequate oxygen supply for microorganisms
D. High grease concentration
Answer: C. Adequate oxygen supply for microorganisms
Proper dissolved oxygen levels support biological treatment and prevent odor
formation.
5. Which equipment removes grit?
A. Chlorine contact tank
B. Grit chamber
C. Digestor
D. Clarifier
Answer: B. Grit chamber
,Grit chambers slow the flow enough for heavy inorganic particles to settle.
6. Activated sludge consists primarily of:
A. Sand particles
B. Industrial chemicals
C. Microorganisms that consume organic matter
D. Chlorine compounds
Answer: C. Microorganisms that consume organic matter
Bacteria and other microorganisms biologically treat wastewater by consuming
organic pollutants.
7. Return Activated Sludge (RAS) is returned to:
A. Final clarifier
B. Aeration basin
C. Headworks
D. Sludge drying bed
Answer: B. Aeration basin
RAS maintains the proper microorganism population in the biological treatment
process.
8. Excess biological solids removed from the system are called:
A. Influent
B. Effluent
C. Waste Activated Sludge (WAS)
D. Screenings
Answer: C. Waste Activated Sludge (WAS)
WAS removes excess biomass to maintain process stability.
, 9. Which laboratory test measures suspended particles?
A. pH
B. Total Suspended Solids (TSS)
C. Conductivity
D. Alkalinity
Answer: B. Total Suspended Solids (TSS)
TSS indicates the concentration of suspended solids remaining in wastewater.
10.What is the normal pH range favorable for biological treatment?
A. 3.0–4.5
B. 5.0–5.5
C. 6.5–8.5
D. 10.5–12.0
Answer: C. 6.5–8.5
Most treatment microorganisms function best near neutral pH.
11.Chlorination is primarily used for:
A. Removing grit
B. Thickening sludge
C. Disinfection
D. Increasing BOD
Answer: C. Disinfection
Chlorine destroys disease-causing organisms before treated water is discharged.
12.Dechlorination is necessary because excess chlorine:
A. Improves algae growth
Newest (2025 - 2026 Update) From Real Past
Papers Questions – A Set Of 100 Most
Common Exam Frequently Tested Questions
And Answers In Details 100% Verified Exam
Highly Recommendable For Grade A+
1. What is the primary purpose of preliminary treatment in a wastewater
treatment plant?
A. Remove dissolved nutrients
B. Destroy pathogens
C. Remove large debris and grit
D. Add chlorine
Answer: C. Remove large debris and grit
Preliminary treatment protects downstream equipment by removing rags, sticks,
sand, gravel, and other large materials before the wastewater enters primary
treatment.
2. Which process mainly removes settleable solids?
A. Activated sludge
B. Primary sedimentation
C. Chlorination
D. Aeration
,Answer: B. Primary sedimentation
Primary clarifiers allow heavier solids to settle while lighter materials float for
removal.
3. Biochemical Oxygen Demand (BOD) measures:
A. Total nitrogen
B. Acidity
C. Oxygen required by microorganisms to decompose organic matter
D. Dissolved solids
Answer: C. Oxygen required by microorganisms to decompose organic matter
BOD is one of the most important indicators of wastewater strength.
4. High dissolved oxygen in an aeration basin generally indicates:
A. Poor aeration
B. Septic conditions
C. Adequate oxygen supply for microorganisms
D. High grease concentration
Answer: C. Adequate oxygen supply for microorganisms
Proper dissolved oxygen levels support biological treatment and prevent odor
formation.
5. Which equipment removes grit?
A. Chlorine contact tank
B. Grit chamber
C. Digestor
D. Clarifier
Answer: B. Grit chamber
,Grit chambers slow the flow enough for heavy inorganic particles to settle.
6. Activated sludge consists primarily of:
A. Sand particles
B. Industrial chemicals
C. Microorganisms that consume organic matter
D. Chlorine compounds
Answer: C. Microorganisms that consume organic matter
Bacteria and other microorganisms biologically treat wastewater by consuming
organic pollutants.
7. Return Activated Sludge (RAS) is returned to:
A. Final clarifier
B. Aeration basin
C. Headworks
D. Sludge drying bed
Answer: B. Aeration basin
RAS maintains the proper microorganism population in the biological treatment
process.
8. Excess biological solids removed from the system are called:
A. Influent
B. Effluent
C. Waste Activated Sludge (WAS)
D. Screenings
Answer: C. Waste Activated Sludge (WAS)
WAS removes excess biomass to maintain process stability.
, 9. Which laboratory test measures suspended particles?
A. pH
B. Total Suspended Solids (TSS)
C. Conductivity
D. Alkalinity
Answer: B. Total Suspended Solids (TSS)
TSS indicates the concentration of suspended solids remaining in wastewater.
10.What is the normal pH range favorable for biological treatment?
A. 3.0–4.5
B. 5.0–5.5
C. 6.5–8.5
D. 10.5–12.0
Answer: C. 6.5–8.5
Most treatment microorganisms function best near neutral pH.
11.Chlorination is primarily used for:
A. Removing grit
B. Thickening sludge
C. Disinfection
D. Increasing BOD
Answer: C. Disinfection
Chlorine destroys disease-causing organisms before treated water is discharged.
12.Dechlorination is necessary because excess chlorine:
A. Improves algae growth
