By Tom Schaefer
An increasing number of indoor aquatic facilities are using ultraviolet (UV) technology to improve indoor air quality, as its energy can naturally breakdown some byproducts of chlorine use including, odour, bather irritation and enhanced corrosion associated with these environments.
While chlorine use is hailed as one of the greatest achievements of modern man, studies have documented its disinfection byproducts (DBPs) are harmful in high concentrations. For example, athletic asthma on competitive swim teams and respiratory ailments by aquatic staff can be traced to poor air quality. The primary benefit of using a UV system in an indoor aquatic facility is to improve air and water quality by lowering the concentrations of harmful DBPs.
Another benefit of using UV, whether for an indoor or outdoor pool, is that it also disinfects to a very high level. UV light can be subdivided in a number of ways, for example, UVC (the short wave or germicidal band) forms a near instant bond in the DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) of pathogens; preventing them from replicating and effectively killing a wide range of pathogens. Chlorine is still required, however, because UV does not leave a residual effect in the water and only treats the water passing through the filter return line.
Another benefit of UV technology is its effectiveness against some pathogens that are resistant to chlorine. There is also a movement among health departments to address these ‘chlorine resistant’ pathogens, not only in municipal drinking water, but public pools as well. Throughout North America there have been numerous aquatic outbreaks of Cryptosporidium (Crypto) over the last few years. In 2007, it is estimated 20,000 people were afflicted during an outbreak in Utah.
Cryptosporidium is a naturally occurring protozoan parasite, which can cause an intense gastro-intestinal illness that is potentially life threatening to infants, the elderly and immune-compromised individuals. Crypto has a hard outer shell, which protects it from the disinfecting capabilities of chlorine.
The U.S. Centers for Disease Control (CDC) notes chlorine achieves a 99.9 per cent disinfection rate of Crypto, with one parts per million (ppm) of free chlorine in 10.6 days. UV systems for swimming pools are sized to provide a minimum of five times the level of energy required to achieve a 99.9 per cent disinfection level, which is continuously applied to the filtered water.
An accidental discharge of Crytpo can easily result in millions of oocytes being shed into the pool. Ingesting these in small numbers can result in patrons being afflicted with Cryptosporidiosis. Often times, a discharge in a swimming pool is not known until people start becoming ill. With symptoms appearing, on average, seven days after ingestion, hundreds or thousands of bathers can be exposed before the presence of Crypto is identified.
UV cannot eliminate the risk, but it can dramatically reduce the number of viable oocytes in a short period of time as it continuously treats 100 per cent of the filtered water, which significantly reduces the threat within a few turnovers of the pool’s water.
UV science
Similar to a household lamp for interior lighting, UV systems use more powerful mercury lamps made of quartz, which unlike glass, allows UVC energy to pass through into the water.
Many are familiar with the terms UVA (long wave or black light) and UVB (medium wave) energy, which causes skin to tan or burn, depending on the length of exposure in the sun. UVC energy, however, is more powerful and beneficial for breaking down chloramines, as well as disinfecting a wide range of bacteria, viruses, moulds and protozoas. It is worth noting UVC energy from the sun is easily absorbed by earth’s atmosphere, which eliminates human exposure.
The range of UVC energy is about 100 wavelengths in width along the light energy spectrum, which is located between 200 to 300 nanometers (nm). A bell curve of germicidal energy exists within this range and is most powerful for disinfecting around 260 to 265 nm. Chloramine control is most effective below 240 nm, as photon energy increases as the size of the wavelength is reduced. Significantly more energy is absorbed to disrupt the chemical structure of chloramines near 200 nm and decreases significantly above 240 nm.
