AZ L-84 Water Treatment Contractor Exam
Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
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1. What is the primary purpose of coagulation in a conventional
water treatment process?
a. To disinfect finished water
b. To remove dissolved oxygen
c. To destabilize suspended and colloidal particles
d. To increase water hardness
Answer: c. To destabilize suspended and colloidal particles
Rationale: Coagulation uses chemicals such as alum, ferric salts, or
polymers to neutralize or destabilize particle charges. This allows very
small suspended and colloidal particles to combine during subsequent
flocculation and become easier to remove by sedimentation or
filtration.
, 2. Which process generally follows coagulation to promote the
formation of larger particles?
a. Chlorination
b. Flocculation
c. Aeration
d. Softening
Answer: b. Flocculation
Rationale: Flocculation provides gentle, controlled mixing after
coagulation. The destabilized particles collide and attach to one
another, forming larger flocs that can subsequently be removed
through sedimentation and filtration.
3. What is the main purpose of sedimentation in a water treatment
plant?
a. To remove settleable suspended solids
b. To increase chlorine residual
c. To remove all dissolved minerals
d. To raise the pH of water
Answer: a. To remove settleable suspended solids
Rationale: Sedimentation allows heavier particles and formed flocs to
settle by gravity. Properly designed sedimentation basins reduce the
,solids loading on downstream filters and improve overall treatment
efficiency.
4. Which measurement is commonly used to indicate the acidity or
alkalinity of water?
a. Turbidity
b. pH
c. Conductivity only
d. Total suspended solids
Answer: b. pH
Rationale: pH expresses the hydrogen-ion activity of water on a
logarithmic scale. It is important because coagulation, corrosion
control, disinfection, and many other treatment processes are strongly
affected by pH.
5. What does turbidity primarily measure?
a. Water temperature
b. The concentration of dissolved oxygen
c. The cloudiness caused by suspended and colloidal particles
d. Total chlorine concentration
Answer: c. The cloudiness caused by suspended and colloidal particles
, Rationale: Turbidity is an optical measurement related to light
scattering by particles in water. Elevated turbidity can interfere with
disinfection and indicate inadequate particle removal.
6. What is the principal purpose of disinfection in drinking-water
treatment?
a. To remove hardness
b. To destroy or inactivate pathogenic microorganisms
c. To remove all suspended solids
d. To increase alkalinity
Answer: b. To destroy or inactivate pathogenic microorganisms
Rationale: Disinfection is intended to control disease-causing
microorganisms such as bacteria, viruses, and certain protozoa.
Common disinfectants include chlorine, chloramines, ozone, and
ultraviolet light.
7. Which factor is especially important when evaluating chlorine
disinfection effectiveness?
a. Contact time
b. Pipe color
c. Tank wall thickness only
d. Pump brand
Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the primary purpose of coagulation in a conventional
water treatment process?
a. To disinfect finished water
b. To remove dissolved oxygen
c. To destabilize suspended and colloidal particles
d. To increase water hardness
Answer: c. To destabilize suspended and colloidal particles
Rationale: Coagulation uses chemicals such as alum, ferric salts, or
polymers to neutralize or destabilize particle charges. This allows very
small suspended and colloidal particles to combine during subsequent
flocculation and become easier to remove by sedimentation or
filtration.
, 2. Which process generally follows coagulation to promote the
formation of larger particles?
a. Chlorination
b. Flocculation
c. Aeration
d. Softening
Answer: b. Flocculation
Rationale: Flocculation provides gentle, controlled mixing after
coagulation. The destabilized particles collide and attach to one
another, forming larger flocs that can subsequently be removed
through sedimentation and filtration.
3. What is the main purpose of sedimentation in a water treatment
plant?
a. To remove settleable suspended solids
b. To increase chlorine residual
c. To remove all dissolved minerals
d. To raise the pH of water
Answer: a. To remove settleable suspended solids
Rationale: Sedimentation allows heavier particles and formed flocs to
settle by gravity. Properly designed sedimentation basins reduce the
,solids loading on downstream filters and improve overall treatment
efficiency.
4. Which measurement is commonly used to indicate the acidity or
alkalinity of water?
a. Turbidity
b. pH
c. Conductivity only
d. Total suspended solids
Answer: b. pH
Rationale: pH expresses the hydrogen-ion activity of water on a
logarithmic scale. It is important because coagulation, corrosion
control, disinfection, and many other treatment processes are strongly
affected by pH.
5. What does turbidity primarily measure?
a. Water temperature
b. The concentration of dissolved oxygen
c. The cloudiness caused by suspended and colloidal particles
d. Total chlorine concentration
Answer: c. The cloudiness caused by suspended and colloidal particles
, Rationale: Turbidity is an optical measurement related to light
scattering by particles in water. Elevated turbidity can interfere with
disinfection and indicate inadequate particle removal.
6. What is the principal purpose of disinfection in drinking-water
treatment?
a. To remove hardness
b. To destroy or inactivate pathogenic microorganisms
c. To remove all suspended solids
d. To increase alkalinity
Answer: b. To destroy or inactivate pathogenic microorganisms
Rationale: Disinfection is intended to control disease-causing
microorganisms such as bacteria, viruses, and certain protozoa.
Common disinfectants include chlorine, chloramines, ozone, and
ultraviolet light.
7. Which factor is especially important when evaluating chlorine
disinfection effectiveness?
a. Contact time
b. Pipe color
c. Tank wall thickness only
d. Pump brand
