AWWA AWWA Water Treatment Processes 1 — Questions and Answers
Question 1: In conventional water treatment, what is the correct sequence of primary treatment processes?
- Disinfection → Coagulation → Sedimentation → Filtration
- Coagulation → Flocculation → Sedimentation → Filtration (Correct answer)
- Filtration → Coagulation → Sedimentation → Disinfection
- Sedimentation → Coagulation → Flocculation → Filtration
Correct answer: Coagulation → Flocculation → Sedimentation → Filtration
Conventional treatment follows the sequence: coagulation (chemical addition), flocculation (gentle mixing to form floc), sedimentation (settling), then filtration.
Question 2: Which coagulant is most commonly used in US water treatment plants for turbidity removal per AWWA practices?
- Potassium permanganate
- Aluminum sulfate (alum) (Correct answer)
- Sodium hypochlorite
- Ferrous sulfate
Correct answer: Aluminum sulfate (alum)
Aluminum sulfate (alum) is the most widely used coagulant in US water treatment, forming aluminum hydroxide floc that captures suspended particles.
Question 3: What is the purpose of the rapid mix (flash mix) stage in a water treatment plant?
- To remove dissolved gases
- To achieve thorough dispersion of coagulant chemicals throughout the water (Correct answer)
- To accelerate sedimentation
- To neutralize disinfection byproducts
Correct answer: To achieve thorough dispersion of coagulant chemicals throughout the water
Rapid mix provides intense, brief turbulence to uniformly disperse coagulant chemicals throughout the raw water before flocculation begins.
Question 4: Per AWWA guidelines, what CT value concept is used to evaluate disinfection effectiveness?
- Chlorine concentration times turbidity
- Disinfectant concentration (C) times contact time (T) (Correct answer)
- Chemical cost times treatment volume
- Coagulant dose times flocculation time
Correct answer: Disinfectant concentration (C) times contact time (T)
CT value = disinfectant concentration (mg/L) × contact time (minutes), and is used by the EPA and AWWA to verify inactivation of Giardia and Cryptosporidium.
Question 5: What is the primary purpose of lime softening in water treatment?
- To reduce turbidity through coagulation
- To remove hardness-causing calcium and magnesium ions (Correct answer)
- To oxidize iron and manganese
- To adjust pH for corrosion control
Correct answer: To remove hardness-causing calcium and magnesium ions
Lime softening adds lime (calcium hydroxide) to precipitate calcium carbonate and magnesium hydroxide, reducing water hardness.
Question 6: Which AWWA manual covers water treatment plant design?
- AWWA M1
- AWWA M46 (Correct answer)
- AWWA M11
- AWWA M50
Correct answer: AWWA M46
AWWA M46 (Reverse Osmosis and Nanofiltration) and AWWA M37 cover membrane processes; AWWA's primary water treatment plant design reference is Manual M37 and associated process manuals.
AWWA AWWA Water Treatment Processes 1
In conventional water treatment, what is the correct sequence of primary treatment processes?