Wastewater Operator Certification Disinfection Processes 2

Question 1

At what approximate wavelength does UV radiation most effectively inactivate microorganisms?

Accepted Answer

254 nm

Answer

UV radiation at approximately 254 nm is most effective because it falls within the peak absorption range of DNA and RNA, maximizing nucleic acid damage in microorganisms.

Question 2

What is the primary mechanism by which UV disinfection inactivates microorganisms?

Accepted Answer

Damaging DNA and RNA, preventing reproduction

Answer

UV radiation causes the formation of thymine dimers and other photoproducts in DNA/RNA, preventing replication and rendering organisms unable to reproduce.

Question 3

Which effluent quality parameter most significantly limits UV disinfection performance?

Accepted Answer

Turbidity and UV transmittance (UVT)

Answer

Turbidity and low UV transmittance shield microorganisms from UV exposure, directly reducing the delivered UV dose and disinfection efficacy.

Question 4

A major operational advantage of UV disinfection over chlorination is:

Accepted Answer

No chemical residual or formation of harmful disinfection byproducts

Answer

UV disinfection adds no chemicals to the effluent, eliminating concerns about chlorine toxicity to aquatic life and the formation of disinfection byproducts like trihalomethanes.

Question 5

Why must ozone (O₃) used for disinfection be generated on-site?

Accepted Answer

It is an unstable gas that decomposes rapidly and cannot be stored

Answer

Ozone has a very short half-life (approximately 20-30 minutes in water) and cannot be stored or transported, requiring on-site generation from oxygen or air.

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Disinfection Processes 2