Wastewater Operator Certification Disinfection Processes 1

Question 1

What is the primary purpose of disinfection in wastewater treatment?

Accepted Answer

Inactivate pathogenic microorganisms

Answer

Disinfection targets the inactivation or destruction of pathogenic microorganisms to protect public health and receiving water bodies.

Question 2

Which form of chlorine is the most effective disinfectant in wastewater treatment?

Accepted Answer

Hypochlorous acid (HOCl)

Answer

Hypochlorous acid (HOCl) is the most germicidal form of chlorine because it is an uncharged molecule that penetrates cell membranes more easily than the hypochlorite ion.

Question 3

At what pH does hypochlorous acid (HOCl) predominate over the hypochlorite ion (OCl⁻)?

Accepted Answer

Below pH 7.5

Answer

Below pH 7.5, the equilibrium strongly favors HOCl, making lower pH conditions more favorable for chlorine disinfection effectiveness.

Question 4

The CT value used in disinfection calculations represents:

Accepted Answer

Disinfectant concentration (mg/L) multiplied by contact time (minutes)

Answer

CT is the product of residual disinfectant concentration (C) and the hydraulic contact time (T), used to predict pathogen inactivation efficacy.

Question 5

What occurs at the breakpoint in breakpoint chlorination?

Accepted Answer

Enough chlorine has been added to destroy all chloramines, producing a free chlorine residual

Answer

At breakpoint chlorination, all ammonia-nitrogen has been oxidized and combined chlorine (chloramines) have been destroyed; any additional chlorine added appears as free chlorine residual.

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Disinfection Processes 1