Alabama Wastewater Operator Grade III
Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. Which preliminary treatment process is primarily designed to remove
large floating and suspended debris from incoming wastewater?
A. Secondary clarification
B. Screening
C. Chlorination
D. Aeration
Rationale: Screening is the first treatment step and removes large objects
such as rags, sticks, plastics, and other debris that could damage
downstream equipment or interfere with treatment processes.
2. The primary purpose of a grit chamber is to remove:
,A. Dissolved organic matter
B. Pathogens
C. Sand, gravel, and other heavy inorganic particles
D. Nutrients
Rationale: Grit chambers are designed to settle heavy inorganic materials
before they enter pumps and treatment units, reducing equipment wear
and preventing accumulation in tanks.
3. Which treatment process primarily removes dissolved and suspended
biodegradable organic matter?
A. Screening
B. Grit removal
C. Biological secondary treatment
D. Sludge drying
Rationale: Secondary biological treatment uses microorganisms to
consume organic pollutants, significantly reducing biochemical oxygen
demand (BOD) and suspended solids.
4. Biochemical Oxygen Demand (BOD) measures:
A. Total dissolved solids
B. Oxygen concentration in treated water
,C. Oxygen required by microorganisms to decompose organic matter
D. Chlorine demand
Rationale: BOD indicates the amount of oxygen microorganisms consume
while breaking down biodegradable organic material, making it an
important indicator of wastewater strength.
5. Which microorganism group performs most of the organic matter
removal in an activated sludge process?
A. Algae
B. Bacteria
C. Protozoa
D. Viruses
Rationale: Bacteria are the primary organisms responsible for oxidizing
dissolved and suspended organic materials during biological treatment.
6. Mixed Liquor Suspended Solids (MLSS) refers to:
A. Solids in the influent only
B. Solids in the clarifier effluent
C. Suspended solids in the aeration basin
D. Sludge removed from digesters
, Rationale: MLSS represents the concentration of suspended
microorganisms and organic material in the aeration tank, serving as a key
operational control parameter.
7. Return Activated Sludge (RAS) is recycled to:
A. Increase chlorine demand
B. Maintain the biological population in the aeration basin
C. Reduce sludge production
D. Lower influent flow
Rationale: RAS returns settled microorganisms from the secondary clarifier
to the aeration basin to maintain an adequate microbial population for
treatment.
8. Waste Activated Sludge (WAS) is removed primarily to:
A. Increase dissolved oxygen
B. Control sludge age and MLSS concentration
C. Improve screening efficiency
D. Eliminate grit
Rationale: Wasting excess sludge prevents excessive biomass accumulation
and maintains the desired solids retention time and treatment efficiency.
9. Which instrument is commonly used to measure dissolved oxygen in
an aeration basin?
Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. Which preliminary treatment process is primarily designed to remove
large floating and suspended debris from incoming wastewater?
A. Secondary clarification
B. Screening
C. Chlorination
D. Aeration
Rationale: Screening is the first treatment step and removes large objects
such as rags, sticks, plastics, and other debris that could damage
downstream equipment or interfere with treatment processes.
2. The primary purpose of a grit chamber is to remove:
,A. Dissolved organic matter
B. Pathogens
C. Sand, gravel, and other heavy inorganic particles
D. Nutrients
Rationale: Grit chambers are designed to settle heavy inorganic materials
before they enter pumps and treatment units, reducing equipment wear
and preventing accumulation in tanks.
3. Which treatment process primarily removes dissolved and suspended
biodegradable organic matter?
A. Screening
B. Grit removal
C. Biological secondary treatment
D. Sludge drying
Rationale: Secondary biological treatment uses microorganisms to
consume organic pollutants, significantly reducing biochemical oxygen
demand (BOD) and suspended solids.
4. Biochemical Oxygen Demand (BOD) measures:
A. Total dissolved solids
B. Oxygen concentration in treated water
,C. Oxygen required by microorganisms to decompose organic matter
D. Chlorine demand
Rationale: BOD indicates the amount of oxygen microorganisms consume
while breaking down biodegradable organic material, making it an
important indicator of wastewater strength.
5. Which microorganism group performs most of the organic matter
removal in an activated sludge process?
A. Algae
B. Bacteria
C. Protozoa
D. Viruses
Rationale: Bacteria are the primary organisms responsible for oxidizing
dissolved and suspended organic materials during biological treatment.
6. Mixed Liquor Suspended Solids (MLSS) refers to:
A. Solids in the influent only
B. Solids in the clarifier effluent
C. Suspended solids in the aeration basin
D. Sludge removed from digesters
, Rationale: MLSS represents the concentration of suspended
microorganisms and organic material in the aeration tank, serving as a key
operational control parameter.
7. Return Activated Sludge (RAS) is recycled to:
A. Increase chlorine demand
B. Maintain the biological population in the aeration basin
C. Reduce sludge production
D. Lower influent flow
Rationale: RAS returns settled microorganisms from the secondary clarifier
to the aeration basin to maintain an adequate microbial population for
treatment.
8. Waste Activated Sludge (WAS) is removed primarily to:
A. Increase dissolved oxygen
B. Control sludge age and MLSS concentration
C. Improve screening efficiency
D. Eliminate grit
Rationale: Wasting excess sludge prevents excessive biomass accumulation
and maintains the desired solids retention time and treatment efficiency.
9. Which instrument is commonly used to measure dissolved oxygen in
an aeration basin?
