CO Water Treatment Contractor Exam
Practice Questions And Correct
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1. Which treatment process is primarily used to remove suspended
solids and turbidity from raw surface water before disinfection?
A. Fluoridation
B. Coagulation and sedimentation
C. Chlorination only
D. Aeration
Answer: B. Coagulation and sedimentation
Coagulation destabilizes fine particles so they can form larger flocs,
while sedimentation allows those flocs to settle before the water
proceeds to filtration and disinfection.
2. What is the principal purpose of coagulation in a conventional
drinking-water treatment plant?
A. To increase dissolved oxygen
B. To destroy all microorganisms immediately
C. To destabilize colloidal particles and promote floc formation
D. To increase water hardness
,Answer: C. To destabilize colloidal particles and promote floc formation
Coagulants neutralize or reduce the electrical forces that keep small
particles suspended, allowing them to collide and form larger particles
that can be removed by subsequent treatment.
3. Which chemical is commonly used as a coagulant in conventional
water treatment?
A. Aluminum sulfate
B. Sodium chloride
C. Calcium carbonate
D. Potassium chloride
Answer: A. Aluminum sulfate
Aluminum sulfate, commonly called alum, is widely used as a coagulant
because it reacts in water to form species that destabilize particles and
produce settleable floc.
4. Why is rapid mixing used immediately after a coagulant is added?
A. To evaporate excess chlorine
B. To distribute the chemical rapidly and uniformly throughout the
water
C. To remove settled sludge
D. To increase water temperature
Answer: B. To distribute the chemical rapidly and uniformly throughout
the water
,Rapid mixing provides intense turbulence so the coagulant is dispersed
quickly and contacts the suspended particles throughout the treatment
flow.
5. What is the primary purpose of flocculation?
A. To increase chlorine concentration
B. To gently bring destabilized particles together into larger flocs
C. To remove dissolved minerals by evaporation
D. To sterilize filter media
Answer: B. To gently bring destabilized particles together into larger
flocs
Flocculation uses controlled, relatively gentle mixing to encourage
particle collisions without breaking apart the developing floc.
6. Excessive mixing during flocculation can cause what problem?
A. Formation of stronger and larger flocs
B. Breakup of previously formed flocs
C. Complete removal of dissolved oxygen
D. Increased alkalinity
Answer: B. Breakup of previously formed flocs
Flocs can be physically damaged by excessive shear, producing smaller
particles that are more difficult to settle and filter.
7. What is the primary function of a sedimentation basin in a
conventional treatment plant?
A. Remove settleable floc and suspended solids
, B. Add fluoride
C. Increase water pressure
D. Generate chlorine
Answer: A. Remove settleable floc and suspended solids
Sedimentation reduces the solids loading on downstream filters by
providing sufficient detention and quiescent conditions for heavier
particles and flocs to settle.
8. Which factor most directly affects the settling performance of a
sedimentation basin?
A. Paint color of the basin
B. Surface overflow rate
C. Electrical service voltage
D. Chlorine cylinder size
Answer: B. Surface overflow rate
Surface overflow rate is an important hydraulic design and operating
parameter because it relates the basin flow to its surface area and
influences whether particles can settle before leaving the basin.
9. What is the primary purpose of filtration following sedimentation?
A. Remove remaining suspended particles and microorganisms
B. Increase raw-water turbidity
C. Add hardness to water
D. Produce wastewater sludge
Answer: A. Remove remaining suspended particles and microorganisms
Practice Questions And Correct
Answers (Verified Answers) Plus
Rationale 2027 Q&A| Instant
Download Pdf.
1. Which treatment process is primarily used to remove suspended
solids and turbidity from raw surface water before disinfection?
A. Fluoridation
B. Coagulation and sedimentation
C. Chlorination only
D. Aeration
Answer: B. Coagulation and sedimentation
Coagulation destabilizes fine particles so they can form larger flocs,
while sedimentation allows those flocs to settle before the water
proceeds to filtration and disinfection.
2. What is the principal purpose of coagulation in a conventional
drinking-water treatment plant?
A. To increase dissolved oxygen
B. To destroy all microorganisms immediately
C. To destabilize colloidal particles and promote floc formation
D. To increase water hardness
,Answer: C. To destabilize colloidal particles and promote floc formation
Coagulants neutralize or reduce the electrical forces that keep small
particles suspended, allowing them to collide and form larger particles
that can be removed by subsequent treatment.
3. Which chemical is commonly used as a coagulant in conventional
water treatment?
A. Aluminum sulfate
B. Sodium chloride
C. Calcium carbonate
D. Potassium chloride
Answer: A. Aluminum sulfate
Aluminum sulfate, commonly called alum, is widely used as a coagulant
because it reacts in water to form species that destabilize particles and
produce settleable floc.
4. Why is rapid mixing used immediately after a coagulant is added?
A. To evaporate excess chlorine
B. To distribute the chemical rapidly and uniformly throughout the
water
C. To remove settled sludge
D. To increase water temperature
Answer: B. To distribute the chemical rapidly and uniformly throughout
the water
,Rapid mixing provides intense turbulence so the coagulant is dispersed
quickly and contacts the suspended particles throughout the treatment
flow.
5. What is the primary purpose of flocculation?
A. To increase chlorine concentration
B. To gently bring destabilized particles together into larger flocs
C. To remove dissolved minerals by evaporation
D. To sterilize filter media
Answer: B. To gently bring destabilized particles together into larger
flocs
Flocculation uses controlled, relatively gentle mixing to encourage
particle collisions without breaking apart the developing floc.
6. Excessive mixing during flocculation can cause what problem?
A. Formation of stronger and larger flocs
B. Breakup of previously formed flocs
C. Complete removal of dissolved oxygen
D. Increased alkalinity
Answer: B. Breakup of previously formed flocs
Flocs can be physically damaged by excessive shear, producing smaller
particles that are more difficult to settle and filter.
7. What is the primary function of a sedimentation basin in a
conventional treatment plant?
A. Remove settleable floc and suspended solids
, B. Add fluoride
C. Increase water pressure
D. Generate chlorine
Answer: A. Remove settleable floc and suspended solids
Sedimentation reduces the solids loading on downstream filters by
providing sufficient detention and quiescent conditions for heavier
particles and flocs to settle.
8. Which factor most directly affects the settling performance of a
sedimentation basin?
A. Paint color of the basin
B. Surface overflow rate
C. Electrical service voltage
D. Chlorine cylinder size
Answer: B. Surface overflow rate
Surface overflow rate is an important hydraulic design and operating
parameter because it relates the basin flow to its surface area and
influences whether particles can settle before leaving the basin.
9. What is the primary purpose of filtration following sedimentation?
A. Remove remaining suspended particles and microorganisms
B. Increase raw-water turbidity
C. Add hardness to water
D. Produce wastewater sludge
Answer: A. Remove remaining suspended particles and microorganisms
