Ultraviolet Disinfection Systems Flashcards

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

Answer: Damaging DNA and RNA to prevent replication

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

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

Answer: 253–265 nm (UV-C peak)

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

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

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

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.

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

Answer: 99.9%

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

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

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

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

In a low-pressure UV lamp, what gas is sealed inside the lamp to produce UV emission?

Answer: Mercury vapor at low pressure

Low-pressure UV lamps contain mercury vapor at low pressure, which emits predominantly at 254 nm when electrically excited.

Which condition most directly causes UV lamp output to decrease without bulb failure?

Answer: Lamp aging and fouling of the quartz sleeve

As UV lamps age they lose intensity, and mineral or biological fouling on the quartz sleeve further reduces UV transmission to the water.