WTO - Water Treatment Operator Disinfection Processes Questions and Answers

Question 1

A water treatment plant is using chlorine gas to disinfect water with a flow of 2.5 MGD.
The operator needs to maintain a chlorine residual of 1.2 mg/L.
If the chlorine demand of the water is 1.8 mg/L, what is the required chlorine dose in mg/L?

Accepted Answer

3.0 mg/L

Answer

0.6 mg/L

Answer

1.2 mg/L

Answer

1.8 mg/L

Question 2

Which of the following factors would decrease the effectiveness of chlorine disinfection?

Accepted Answer

High pH

Answer

Increased water temperature

Answer

Low turbidity

Answer

Increased contact time

Question 3

A water utility is considering switching from chlorine to chloramine for secondary disinfection in its distribution system. What is a primary advantage of using chloramines?

Accepted Answer

They produce a more stable, longer-lasting residual.

Answer

They are a stronger and faster-acting disinfectant than chlorine.

Answer

They are completely free from forming any disinfection byproducts.

Answer

They are easier to remove from water for dialysis patients.

Question 4

Disinfection byproducts (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) are formed when:

Accepted Answer

Chlorine reacts with natural organic matter (NOM) present in the water.

Answer

UV light reacts with inorganic matter in the water.

Answer

Ozone is used as the primary disinfectant in low-alkalinity water.

Answer

Ammonia is added to water that has already been chlorinated.

Question 5

An operator is calculating the CT value to ensure adequate inactivation of Giardia. If the free chlorine residual (Concentration) is 1.5 mg/L and the contact time (Time) is 40 minutes, what is the calculated CT value in mg-min/L?

Accepted Answer

60.0

Answer

26.7

Answer

41.5

Answer

15.0

Question 6

Which of the following is a significant limitation of using Ultraviolet (UV) light for disinfection in a water treatment plant?

Accepted Answer

It does not provide a residual disinfectant to protect water in the distribution system.

Answer

It is ineffective against chlorine-resistant pathogens like Cryptosporidium.

Answer

It significantly alters the taste and odor of the water.

Answer

It requires the handling of hazardous chemicals for operation.

A water treatment plant is using chlorine gas to disinfect water with a flow of 2.5 MGD.The operator needs to maintain a chlorine residual of 1.2 mg/L.If the chlorine demand of the water is 1.8 mg/L, what is the required chlorine dose in mg/L?

A water treatment plant is using chlorine gas to disinfect water with a flow of 2.5 MGD.
The operator needs to maintain a chlorine residual of 1.2 mg/L.
If the chlorine demand of the water is 1.8 mg/L, what is the required chlorine dose in mg/L?