CWS Ultraviolet Disinfection Systems 2

Question 1

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

Accepted Answer

Damaging DNA and RNA to prevent replication

Answer

UV light at 254 nm is absorbed by nucleic acids, causing thymine dimers and other DNA/RNA damage that prevents microbial replication.

Question 2

Which UV wavelength range is considered most germicidal for water disinfection?

Accepted Answer

253–265 nm (UV-C peak)

Answer

The 253–265 nm range within UV-C has the highest germicidal effectiveness because it coincides with peak DNA absorption.

Question 3

What does 'UV transmittance' (UVT) measure in a water system?

Accepted Answer

The fraction of UV light that passes through a 1 cm water sample at 254 nm

Answer

UVT is the percentage of 254 nm UV light transmitted through a 1 cm path length of water, indicating how easily UV penetrates the water.

Question 4

A UV system validated for a 3-log reduction of Cryptosporidium delivers what percentage inactivation?

Accepted Answer

99.9%

Answer

A 3-log (3 log10) reduction means 99.9% of the target organism is inactivated, leaving 0.1% viable.

Question 5

What is the purpose of a UV dose-response curve in system design?

Accepted Answer

To determine the UV fluence required to achieve a specific log inactivation of a target organism

Answer

Dose-response curves relate UV fluence (mJ/cm²) to log inactivation, allowing designers to specify the dose needed for regulatory compliance.

(CWS) Certified Water Specialist Practice Test