UV’s mechanism of action is the breaking of DNA and RNA bonds within the target micro-organisms. Coincidentally, the energy required to vibrate certain bonds within DNA and RNA to the point at which they break, leading to micro-organism inactivation, can be generated by any UV lamp that emits ultraviolet light at the 254 nanometer (nm) wavelength (see Figure 3). Both low-pressure and medium-pressure UV lamps are available and used for this purpose. The pros and cons of these two different lamp types are covered elsewhere.
Referring to Table 3, the minimum established UV dose required by the U.S. Environmental Protection Agency (EPA) for 99.9 per cent Cryptosporidium inactivation in drinking water is listed as 12 mJ/cm.2 This amount of UV is lower than the dose required to inactivate Pseudomonas aeruginosa to the same level (99.9 per cent). What is most interesting and relevant about these data is the National Sanitation Foundation (NSF), a respected authority for qualifying commercial pool equipment in the U.S., requires a 99.9 per cent or greater destruction of Pseudomonas aeruginosa for certification of UV pool equipment. By extension, devices that pass the 99.9 per cent requirement for Pseudomonas aeruginosa inactivation would have successfully inactivated 99.9 per cent or greater of Cryptosporidium—a U.S. drinking water requirement.
It should be self-evident that not all micro-organisms are readily destroyed by UV light. For example, adenoviruses can require a UV dose eight to 14 times greater than Cryptosporidium. In short, like chlorine, UV is not the end all solution to sanitization, but as a partner to chlorine in the fight against Cryptosporidium, the leading causal agent in pool disease outbreaks, it is a great choice.
UV light is also a great partner to chlorine in that it helps destroy chloramines. Chloramines, formed when chlorine combines with nitrogen (N)-containing compounds such as urea from sweat and urine, are broken down by the UV light. Most commercial facilities monitor chloramines as a measure of water quality. Generally, in a pool, chloramines should not exceed about 0.5 ppm. Pool operators should shock or super-chlorinate the pool to destroy these contaminants when that concentration is exceeded. The benefit of adding a UV system to pool water treatment is the chloramines are better held in check and less frequent shocking is needed.
Ozone represents another important strategy in enhancing pool water quality. Chemically, ozone (O3) consists of three atoms of oxygen. This arrangement is very reactive compared to its diatomic relative, oxygen (O2). As an oxidizer, ozone contributes its oxygen to other molecules it comes in contact with in a process called oxidation. Oxidation can be thought of as ‘chemical burning,’ whereby the result of the oxidation is simply carbon dioxide (CO2) and water. This process is valuable in pools and spas/hot tubs where a myriad of organic contaminants can exist, which need to be ‘burnt’ away via oxidation.
Ozone has to be removed before going back into the pool. UV really does not have an application in swimming pools or spas due to the turbidity of the water. Before taking a leap into ozone or UV read ALL the positives and negatives regarding the system. Do not attempt to apply single pass drinking water regulations for UV and follow the Ozone mfg recommendations on Linked In. Ozone is not allowed in pool or spa water it must be removed by GAC granular activated carbon.