Interest in the use of ultraviolet light for supplemental water disinfection has increased in response to state and local health regulations covering public pools and spas. Halogens, such as chlorine and bromine, and sanitizers are used to treat waterborne pathogens in pool and hot tub water; however, many commercial pool operators and some residential pool owners are incorporating a supplemental disinfection system to assist in combating recreational water illnesses such as cryptosporidium and giardia. Ultraviolet (UV-C) water treatment technology is one such technique that has seen increased popularity thanks to its ease of use, reduced chemical consumption, health advantages and environmentally friendly benefits. UV-C light can improve water and air quality in aquatic facilities.

UV-C is an invisible light with a wavelength shorter than that of visible light but longer than X-rays. Its connection to water sanitation was discovered more than 100 years ago when European scientists learned the top surface of lake water was sterile when exposed to sunlight. This eventually led to the invention of UV-C bulbs.  The spectrum of UV light can be subdivided into four main categories, UV-A, UV-B, UV-C and Vacuum UV. The area between 280 and 100 nanometers is UV-C, also known as germicidal light.

How does it work?

UV sanitation systems eliminate chlorine-resistant microorganisms, which are common causes of pool closures. These systems reproduce UV radiation inside light chambers via powerful lamps, which emit germicidal UV-C light that is used to disinfect pool and spa water. Facilities equipped with these systems consume fewer chemicals and allow sanitizers to be more effective. How much more effective depends on the water’s hardness, pH and other water chemistry factors. UV-C causes permanent damage to a number of microorganisms almost instantly as the water circulates through the light chamber. By disrupting the microorganism’s DNA, protozoans, viruses and bacteria are unable to replicate and remain inert. This light, however, works only on water that flows through the chamber. Water in dead zones isn’t treated by the light and the light does not act as a residual, thus the need for the presence of a halogen. The effects of UV-C are immediate and do not alter the water’s composition.

UV can improve air quality

A variety of European organizations have certified UV-C technology to be effective in improving indoor air quality. Studies show UV-C light disinfects pool and hot tub water and removes chloramines — the leading cause of poor air quality at the surface of the pool and surrounding area, especially indoors. UV-C light destroys formation of chloramines at the molecular level before they evaporate and foul the air.

Choosing the right system

It is important to do research when considering a UV sanitation system because an inadequate system may not perform the job properly or comply with sanitation regulations. For instance, checking the system’s certifications (e.g. energy efficiency ratings, maximum flow rates, etc.) with the manufacturer is a good idea, while referring to NSF International’s website (www.nsf.org) for its list of approved UV water treatment systems is another. In addition to researching the product, other variables to consider include system size, low versus medium pressure lamps, wattage, spare parts/maintenance and cost/payback.

System size

The size of the UV system is determined by the type of pool (i.e. commercial or residential) as well as its use. For example, the needs of an indoor Olympic-sized pool with heavy bather loads will differ substantially from an outdoor, mid-sized pool at a hotel. 

Low versus medium pressure lamps

There are two types of UV lamps — a low-pressure, high-output lamp, which emits monochromatic UV rays at 254 nm, and a medium-pressure lamp, which emits UV rays between 200 and 600 nm. Generally, low pressure lamps are better suited for residential applications because of their lower initial cost and electricity use, while medium pressure lamps are typically designed for large commercial installations because of their greater sanitation abilities. The distinction can be chalked up to cost, flow requirements and the ability to destroy chloramines.  Due to its large light spectral, medium pressure lamps are more effective at reducing chloramines and improving air quality.

Conclusion

The standard protocol for water quality maintenance is premised on the assumption that appropriate filtration and residual halogen disinfection will inactivate all pathogens. However, it is known that:

It can take chlorine up to 45 minutes to deactivate giardia;

30 to 60 minutes to deactivate norovirus; andCrypto can linger in pool water for up to 10 days, as it is highly resistant to chlorine.

In-line UV disinfection is recognized as an effective and reliable method for deactivating pathogens in pool and hot tub water.

Moving beyond the basics of pool and spa water quality management will require revising the two-pillar approach, which includes filtration and halogen, followed by adopting a supplemental disinfection method.