By Zach Hansen and Karen Rigsby
Supplemental systems can go a long way towards improving the water quality of a given pool or spa. Understanding how these systems work and how to use them effectively are vital to any diligent pool or spa operator. While these systems will not replace a registered sanitizer, they can be very effective tools, ones that should be used to their full advantage.
Ultraviolet (UV) technology
UV disinfection is used extensively and increasingly throughout the world in a vast array of water treatment applications. Most notable for its use in the drinking water industry, UV is a particularly effective supplemental sanitation system when used on pools and spas. The technology utilizes specifically targeted UV radiation to inactivate microbial contaminants and reduce certain disinfection byproducts such as chloramines, allowing for a safer, more comfortable swimming environment. Its effectiveness as a proven treatment against chlorine-resistant parasites, such as Cryptosporidium and Giardia, has received the attention of health departments across North America, where there is a growing debate as to whether such systems, or others with similar disinfection profiles, should be required at public facilities. As a result, UV technology will likely become more prevalent on commercial and residential pools for years to come.
How it works
A natural emission of the sun, UV light is further broken down into bands of decreasing wavelength. UVA and UVB garner the most notoriety, as these bands reach the Earth’s surface and are responsible for chronic skin ailments, such as accelerated aging and cancer. Other bands—namely, UVC and vacuum UV—also exist, but are filtered by the Earth’s upper atmosphere. UV disinfection systems use radiation within the UVC band that exhibits a wavelength range from 200 to 280 nanometres (nm), which is why this band is more commonly referred to as ‘germicidal UV.’ UV energy within this range inactivates micro-organisms by damaging their DNA/RNA, thereby rendering them unable to replicate. If a micro-organism cannot replicate, it cannot cause infection.
The effect of UVC radiation on chloramines is another positive benefit. Trichloramine is a particularly strong absorber of UV energy, whereas free chlorine tends to be a relatively poor absorber of UVC. Thus, free chlorine sanitizer shows minimal photodegradation when exposed to UVC. However, the ensuing effect on trichloramine is much greater. Data developed from a study published by Jing Li and Ernest R. Blatchley in Environmental Science & Technology (‘UV Photodegradation of Inorganic Chloramines’) show significant degradation of trichloramine when exposed to UVC. This is noteworthy, as trichloramine is the main chloramine component present in the air directly above the pool surface, and has been has been identified as an irritant of mucous membranes and the upper respiratory system.