AWWA AWWA Water Treatment Processes

Question 1

In conventional water treatment, what is the correct sequence of primary treatment processes?

Accepted Answer

Coagulation → Flocculation → Sedimentation → Filtration

Answer

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?

Accepted Answer

Aluminum sulfate (alum)

Answer

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?

Accepted Answer

To achieve thorough dispersion of coagulant chemicals throughout the water

Answer

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?

Accepted Answer

Disinfectant concentration (C) times contact time (T)

Answer

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?

Accepted Answer

To remove hardness-causing calcium and magnesium ions

Answer

Lime softening adds lime (calcium hydroxide) to precipitate calcium carbonate and magnesium hydroxide, reducing water hardness.

(AWWA) American Water Works Association Practice Test

(AWWA) American Water Works Association Practice Test

AWWA AWWA Water Treatment Processes