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TO “B” OR NOT TO “B”? UV SYSTEMS DEMYSTIFIED
Written By Clifford Fasnacht, MWS
The question that often arises when there is need for an Ultraviolet (UV) disinfection system is which system is the best or the most appropriate. This article will address the differences and some rules to follow when making the choice.
Class A
“Class A” comes from NSF/ANSI Standard 55, which is widely accepted certification for residential and commercial UV disinfection systems. Also suitable for treating microbiologically unsafe or contaminated water (e.g., well water). The standard defines performance criteria for UV systems based on the level of microbial reduction:
Additionally, a class “A system must include the following:
• A UV sensor
• An alarm (visible or audible
• Flow restrictor
Class A systems are certified to inactivate a broad spectrum of microorganisms, including:
• Bacteria (e.g. E.coli)
• Viruses
• Protozoan cysts (e.g., Giardia and Cryptosporidium)
To earn Class A certification, the system must deliver a minimum UV dose (at the 254-nm wavelength) that’s high enough to achieve significant reduction (typically ≥99.99% for bacteria and viruses and ≥99.9% for protozoa) under specified test conditions. Use this when safety is critical.
Correct situations for Class A:
• Water source unknown, untreated, or unreliable (well water, rainwater or surface water)
• Possible biological contamination (bacteria, viruses, parasites)
• Drinking water for:
*Infants
*Elderly
*Immunocompromised people
• You want water that is microbiologically safe, not just better-tasting
Class B
A “Class B” UV water treatment system is a type of UV disinfection system certified under NSF/ANSI Standard 55 to provide a lower level of microbiological treatment (16 mJ/cm2 ) than a Class A system and intended for treating water that is potable and already microbiologically safe. Not certified for disinfection or virus inactivation of unsafe water but instead to improve quality, not safety.
Correct situations for Class B:
• Water supply already microbiologically safe (e.g., municipal water)
• Secondary treatment after filtration and/no disinfection
• Improves taste or odor
• Reduces non-pathogenic nuisance microorganisms
• Cosmetic clarity
• Manage chlorine-resistant parasites/organisms like Giardia and Cryptosporidium (in water that is already safe or pre-treated)
• No concern for unsafe or untreated water source(s)
• Reducing:
o Heterotrophic bacteria
o Algae
o Mold
o Iron or sulfur bacteria (odor-causing)
• Preventing microbial growth in plumbing systems
Incorrect situations for Class B:
• Bacteria or viruses (Does NOT reliably remove)
• should not be used where water is of unknown or unsafe quality
• Heavy metals (Does NOT reliably remove)
• Does not replace proper filtration or chemical disinfection for contaminated water
Important Limitations for Class B:
• Not certified to disinfect unsafe water (doesn’t reliably inactivate bacteria and viruses at required levels).
• Should not be used alone for drinking water from questionable sources (e.g., untreated wells)
• Requires pre-filtration if water is turbid or cloudy (UV light may not reach effectively)
Best Installation Practices
A minimum 5 micron prefilter is generally required.
Install the units with the understanding annual service will be required e.g. leave adequate room for the removal of the lamp and sleeve.
Always place the controller/power supply above the unit to protect from water spills and leaks.
Follow the manufacture installation instructions regarding orientation and discharge piping requirements.
A supplemental physical disinfection program may be needed to maintain a system and to provide a testable residual of disinfectant in the system that complies with local codes .
Conclusion
In conclusion, classification is based on their intended use and disinfection capability.
Both Class A and Class B systems share strict requirements for safety of materials in contact with drinking water and for structural integrity of systems connected to a pressurized water supply.
Both Class A & B must include flow restrictors to assure that the UV dosage cannot drop below that which results from testing. However, Class A systems require a higher UV dosage.
NSF/ANSI 55 requirements specify that Class A ultraviolet systems incorporate an alarm or fail-safe element into their design. Thus, all Class A systems include sensors that provide an audible and visual indication that the system is not performing to standard.
Although Class B systems are not required to have a UV sensor, if a class B system is equipped with a sensor, then it must meet the necessary requirements.
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