WTO Disinfection Processes 3

Question 1

Chlorine dioxide (ClO₂) used for disinfection must be generated on-site because:

Accepted Answer

It is an unstable gas that cannot be safely stored or transported

Answer

Chlorine dioxide is a highly reactive gas that decomposes rapidly and poses explosion risks, making on-site generation mandatory.

Question 2

What byproduct concern is unique to chlorine dioxide disinfection?

Accepted Answer

Formation of chlorite and chlorate ions

Answer

Chlorine dioxide produces chlorite (ClO₂⁻) and chlorate (ClO₃⁻) as byproducts, which are regulated under the DBPR.

Question 3

What is the purpose of a chlorine contact chamber (CCC) in a water treatment plant?

Accepted Answer

To ensure sufficient contact time between chlorine and water for pathogen inactivation

Answer

The CCC is designed to maximize contact time between chlorine and water, achieving the required CT for inactivation credit under surface water treatment rules.

Question 4

An operator notices breakpoint chlorination requires more chlorine than expected. The most likely cause is:

Accepted Answer

Elevated ammonia or organic nitrogen in the source water

Answer

Elevated ammonia or organic nitrogen demands more chlorine to reach breakpoint because chloramines must first be formed and then destroyed before free chlorine residual appears.

Question 5

Which factor does NOT affect ozone disinfection effectiveness?

Accepted Answer

Water fluoride concentration

Answer

Fluoride concentration does not influence ozone disinfection; temperature, pH, and organic matter (contributing to color) all affect ozone demand and CT.

(WTO) Water Treatment Operator Certification Practice Test

(WTO) Water Treatment Operator Certification Practice Test

WTO Disinfection Processes 3