Wastewater Operator Certification Disinfection Processes

Question 1

What is the primary purpose of disinfection in wastewater treatment?

Accepted Answer

Inactivate pathogenic microorganisms

Answer

Remove suspended solids from effluent

Answer

Reduce biochemical oxygen demand

Answer

Remove nitrogen and phosphorus

Question 2

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

Accepted Answer

Hypochlorous acid (HOCl)

Answer

Combined chlorine (chloramines)

Answer

Hypochlorite ion (OCl⁻)

Answer

Chloride ions (Cl⁻)

Question 3

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

Accepted Answer

Below pH 7.5

Answer

Above pH 8.5

Answer

Above pH 9.0

Answer

Between pH 8.0 and 9.0

Question 4

The CT value used in disinfection calculations represents:

Accepted Answer

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

Answer

Chemical temperature of the disinfectant solution

Answer

Contact time alone in minutes

Answer

Chlorine total residual at the outlet

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

Chlorine begins to precipitate out of solution

Answer

The pH of the wastewater reaches neutral

Answer

Chlorine demand equals zero

Question 6

Chlorine demand is defined as:

Accepted Answer

The difference between the chlorine applied and the free chlorine residual remaining

Answer

The total chlorine concentration added to the influent

Answer

The free chlorine residual measured at the effluent

Answer

The amount of chlorine consumed by ammonia only

Question 7

Which disinfectant is most widely used in US municipal wastewater treatment plants?

Accepted Answer

Chlorine gas or sodium hypochlorite

Answer

Ozone (O₃)

Answer

Ultraviolet (UV) light

Answer

Peracetic acid