CWS Ultraviolet Disinfection Systems 3

Question 1

What is 'UV fluence' (also called UV dose) and how is it expressed?

Accepted Answer

The product of UV irradiance and exposure time, expressed in mJ/cm²

Answer

UV fluence is the product of irradiance (mW/cm²) and contact time (seconds), yielding a dose in mJ/cm² that determines inactivation efficacy.

Question 2

Why is a quartz sleeve used around UV lamps in water systems rather than direct lamp-to-water contact?

Accepted Answer

It isolates the lamp from water while transmitting UV-C, protecting the lamp and allowing safe replacement

Answer

The quartz sleeve keeps the lamp dry and at optimal operating temperature while transmitting UV-C radiation through to the water with minimal attenuation.

Question 3

A UV system's 'validated dose' is established through what process?

Accepted Answer

USEPA/DVGW-compliant bioassay challenge testing at a certified hydraulics test facility

Answer

Validated doses must be established by third-party bioassay testing at certified facilities following USEPA UV Disinfection Guidance Manual or equivalent protocols.

Question 4

Which water quality parameter, if elevated, most reduces UV system effectiveness by absorbing UV light before it reaches pathogens?

Accepted Answer

Color and dissolved organic carbon (DOC)

Answer

Dissolved organic carbon, tannins, and color compounds absorb UV at 254 nm, lowering UVT and reducing germicidal dose delivered to microorganisms.

Question 5

What operational advantage do medium-pressure (MP) UV lamps have over low-pressure (LP) lamps?

Accepted Answer

Polychromatic UV output that addresses photoreactivation more effectively and requires fewer lamps

Answer

MP lamps emit UV across a broad spectrum (200–400 nm), which can damage multiple DNA repair pathways and reduce photoreactivation, often allowing fewer lamps per installation.

(CWS) Certified Water Specialist Practice Test

(CWS) Certified Water Specialist Practice Test

CWS Ultraviolet Disinfection Systems 3