Ultraviolet Disinfection Systems Flashcards
7 cards from real CWS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Ultraviolet Disinfection Systems flashcards as text
What is the significance of the 'UVT254' measurement in UV system monitoring?
Answer: It quantifies water clarity at the germicidal wavelength to confirm real-time dose delivery assumptions
Online UVT254 monitoring ensures that dose calculations remain valid as source water quality fluctuates, triggering alarms or dose adjustments when UVT drops.
Which regulatory document provides the primary US guidance for UV disinfection of drinking water at large surface water systems?
Answer: USEPA UV Disinfection Guidance Manual (UVDGM), 2006
The USEPA UVDGM (2006) provides comprehensive guidance on reactor validation, dose monitoring, and operational requirements for compliance under the LT2ESWTR.
NSF/ANSI Standard 55 Class A UV systems are designed to deliver at least what minimum dose for point-of-entry disinfection?
Answer: 40 mJ/cm²
NSF/ANSI 55 Class A requires a minimum validated dose of 40 mJ/cm² to inactivate bacteria, viruses, and cysts in point-of-entry or point-of-use applications.
What does 'dark repair' mean in the context of UV-treated microorganisms?
Answer: Light-independent enzymatic repair of UV-induced DNA damage using nucleotide excision repair pathways
Dark repair (nucleotide excision repair) allows some microorganisms to fix UV-damaged DNA without light, occurring even in the absence of visible light post-treatment.
In a multiple-lamp UV reactor, what is the purpose of operating lamps in a 'power pulsing' or 'dimming' mode at low flows?
Answer: To extend lamp life and save energy while maintaining required dose at reduced flow rates
Dimming or pulsing reduces lamp intensity at low flows to prevent overdosing while extending lamp life and reducing energy consumption, since dose = intensity × time.
What is the primary advantage of using amalgam UV lamps over standard low-pressure mercury lamps?
Answer: Amalgam lamps maintain higher UV output over a wider water temperature range and have longer service life
Amalgam lamps use a mercury-indium or mercury-bismuth amalgam to stabilize mercury vapor pressure, enabling consistent UV output from 5°C to 40°C water temperatures and lifetimes exceeding 12,000 hours.
When a UV system alarm indicates low UV intensity, what is the FIRST corrective action a CWS operator should take before assuming lamp failure?
Answer: Inspect and clean the quartz sleeve, then verify UVT and sensor calibration before replacing the lamp
Sleeve fouling and sensor drift are far more common causes of low-intensity alarms than lamp failure; cleaning and recalibrating should be verified first to avoid unnecessary lamp replacement costs.