UV: Chloramine Reduction, Disinfection And Water Savings In One Neat Package
Introduction
UV is now a well established method of water treatment for indoor pools. From hydrotherapy spas to the largest Olympic-sized competition pools, it is fast becoming the water treatment method of choice. UV not only destroys chloramines, the unpleasant by-products of chlorination, but is also a highly effective disinfectant in its own right, which means pool operators can drastically reduce chlorine usage (commonly down to as little as 0.5ppm). Virtually no microorganisms are immune to UV, even chlorine-resistant pathogens. Another major benefit of UV is that it significantly reduces the need for backwashing and dilution, saving hundreds of pounds a month for pool operators.
Although the need for chlorine is greatly reduced with UV, small amounts are still needed to ensure residual disinfection. Chloramines are formed when free chlorine reacts with sweat or urine in pool water. Trichloramines in particular are powerful irritants which are responsible for eye and respiratory complaints and the unpleasant ‘chlorine smell’ commonly associated with indoor pools. Chloramines are also corrosive and in time can lead to damage to pool buildings and structures such as ventilation ducts. Any water treatment system that reduces reliance on chlorine is therefore welcome.
How UV works
A typical UV system consists of a UV lamp in a protective quartz sleeve which is mounted within a cylindrical stainless steel chamber. The water to be treated enters at one end and passes along the entire length of the chamber before exiting at the other end, receiving a dose of UV energy along the way.
There are two main types of UV technology, based on the type of UV lamps used: low pressure and medium pressure. Low pressure lamps have a monochromatic UV output (limited to a single wavelength at 254nm), while medium pressure lamps have a polychromatic UV output (with an output between 185-400nm).
Chloramine destruction
Chloramines contain chlorine (Cl), nitrogen (N) and hydrogen (H) in varying amounts. They can contain one, two or three Cl atoms and are known as mono, di or trichloramines respectively. UV destroys these compounds in a two-fold process:
1. High energy UV breaks the Cl-N (or Cl-H) bonds of the chloramines (a process known as photolysis).
2. Short wavelength UV energy (less than 230nm) breaks the bonds in water to form OH (hydroxyl) radicals. The hydroxyl radicals produced are themselves powerful oxidizing agents which attack chloramines in the water (known as photo-oxidation).
Research by the Society of Soft Drink Technologists in the USA has shown the optimum wavelengths for chloramine photolysis are as follows:
Type of chloramine: UV wavelength for optimum photolysis (nm):
Monochloramine 245nm
Dichloramine 297nm
Trichloramine 260nm and 340nm
The UV dose required for chloramine photolysis is double the dose required for disinfection. (Dose is a function of UV intensity multiplied by exposure time and is expressed in millijoules per square centimetre (mJ/cm2).) For this reason UV pool treatment systems are normally sized to achieve a minimum dose of 60mJ/cm2, compared to 30mJ/cm2 for straightforward disinfection.
Disinfection
UV is a highly efficient natural disinfectant and kills virtually all known microorganisms, including bacteria, viruses, moulds and their spores, by permanently destroying their DNA. It is most powerful in the region of the electromagnetic spectrum between about 210nm and 310nm, the so-called ‘germicidal’ wavelengths.
Microbial recovery from UV treatment
It is well-known that water-borne microorganisms contain enzymes that can repair UV-damaged DNA – a process known as ‘ DNA reactivation’. Some of these enzymes need visible light to perform the repairs (’photoreactivation’), while others can do so without light (known as ‘dark repair’). Both of these phenomena pose obvious concerns for pool owners who are using UV for disinfection in addition to chloramine reduction.
Recent research, however, comparing photoreactivation of E.coli DNA after exposure to UV wavelengths emitted by low and medium pressure lamps shows that the DNA underwent extensive repair following exposure to UV from low pressure UV lamps, but virtually none following exposure to UV from medium pressure lamps (1, 2).
The researchers concluded that it was the broad UV output of medium pressure lamps that has this desirable effect. By emitting UV over a wide range of the UV spectrum, these lamps appear to damage other intracellular molecules, such as enzymes, in addition to DNA. It is this ‘extra’ damage which seems to permanently inactivate the cells’ DNA repair mechanisms. Low pressure UV lamps, on the other hand, produce only a single UV peak at 254nm which only affects DNA.
These preliminary results have serious consequences for pool owners using low pressure UV disinfection systems. If, following exposure to low pressure UV lamps, microorganisms are capable of recovering, operators need to seriously consider upgrading to medium pressure technology. By providing permanent microbial deactivation, medium pressure UV offers peace of mind, something low pressure UV does not do.
The Hanovia SwimPure range only uses medium pressure UV technology and all the lamps are optimised to promote the specific chemical reactions required for chloramine photolysis, hydroxyl radical production and disinfection. In addition, Hanovia is the only supplier of UV systems to manufacture its own UV lamps, so quality control is never compromised.
A link between chloramines and asthma?
A recent study in Belgium – the cause of much controversy – seems to confirm earlier research linking chlorine by-products in indoor swimming pools with asthma in children (3, 4). The researchers from the Catholic University of Louvain analysed the rates of wheezing, asthma and other ailments in almost 190,000 13 and 14 year olds in 21 European countries. The results showed rates of asthma and wheezing rose by around 2.7% and 3.39% respectively among regular indoor pool users. In some cases the damage was equivalent to that found in heavy smokers. Even people sitting at the sides of pools, such as lifeguards and instructors, were found to be at risk.
The symptoms are caused, the researchers believe, by chloramines – particularly trichloramines. The problem is potentially so serious that the study’s authors suggested pool operators should seriously consider alternatives to chlorine-based disinfection. They also recommended better ventilation to help remove chloramine-laden air from pool surroundings, improved hygiene practices by bathers themselves – such as showering before swimming – and the regular renewal of pool water.
While further research is needed, these findings add further credence to the importance of reducing chloramines as much as possible.
Backwashing and diluting
Pool water currently costs approximately £3 per cubic metre and is likely to rise to £4 per cubic metre by 2009, even by conservative estimates. The costs are made up of water costs, heat, chemicals and management, as well as discharge costs. By using medium pressure UV, which significantly cuts chlorine usage, the requirement for backwashing and dilution is greatly reduced. Even old pools can reduce backwashing and dilution cost by hundreds of pounds a month by switching to UV – for many operators this saving may be the most compelling reason for installing UV.
Automatic wiping
Swimming pool water normally contains high levels of organic pollutants and these can foul the quartz sleeve protecting UV lamps, reducing UV output. For this reason all UV systems for pools should have an automatic wiping mechanism which keeps the quartz sleeve clean at all times. The wiper should also be capable of keeping the UV monitor clean. The monitor is a small ‘camera’ located on the wall of the disinfection chamber which detects UV levels and provides readings of UV dose. These features are all standard with Hanovia’s SwimPure range.
Case studies
Cotgrave Leisure Centre, Nottinghamshire
Since opening in 1998, the Cotgrave Leisure Centre near Nottingham has used Hanovia medium pressure UV to treat the water in its indoor pool. The technology has been so successful that Neil Gallagher, the centre’s Assistant Operations Manager, contacted Hanovia to tell the company how pleased he was.
“I’m really happy the centre decided to install UV right from the start,” said Neil. “We use it for primary disinfection, with 1ppm chlorine added for residual disinfection. We could probably go lower than this, but we prefer to keep it at 1ppm, especially at busy times, as part of our ‘belt and braces’ approach to hygiene.”
Neil added, “With UV, the pool water is much clearer than if we were using chlorine on its own. Also, because UV destroys any chloramines produced by the residual chlorination, the atmosphere around the pool is better, with none of the unwelcome smells or eye irritations normally associated with indoor pools. People often comment on it, and it has even become a bit of a selling point for the pool. I definitely think UV is the way forward.”
Dyrons Leisure Centre, Devon
Since Dyrons Leisure Centre in Devon installed a Hanovia medium pressure UV disinfection system, pool water quality has been transformed. The centre has also made significant energy cost savings.
“There has been a real improvement in water quality since we switched to medium pressure UV,” said Engineering Manager Brian Pady. “We have reduced residual chlorination to as little as 0.5 ppm and this reduction in chlorine usage has also resulted in significant cost savings on chemicals. The UV system is also more energy efficient than the old ozone plant, cutting our energy costs by about 30% over two years.”
Comments like these speak for themselves and are a glowing endorsement to the very real benefits of medium pressure UV.
Conclusion
Even though UV significantly reduces reliance on chlorine, residual amounts are still necessary to ensure effective disinfection of pool water. This leads to the production of chloramines, which must be removed if the pool environment is to remain acceptable to bathers.
Medium pressure UV systems are particularly suited to both chloramine destruction and disinfection. The resulting effect is a cleaner, more pleasant atmosphere both in and around the pool. The potential dangers caused by trichloramines are significantly reduced, and the danger of infection by harmful microorganisms is also eliminated.
All Hanovia medium pressure UV systems are compact and can usually be installed within existing pipework. Automatic wipers keep the quartz sleeves housing the UV lamps clean, so the only regular maintenance required is changing the lamp every nine to twelve months – a simple operation that is carried out by on-site staff. Reduced chlorine usage also results in significant cost savings for the pool operator, as well as cutting down on chemical handling.
Ends
References:
1. Oguma, K., Katayama, H. & Ohgaki, S. (2002). Photoreactivation of Escherichia coli after low- or medium-pressure UV disinfection determined by an endonuclease sensitive site assay. Applied & Environmental Microbiology, Vol. 68, No. 12, 6029-6035.
2. Zimmer, J. L. & Slawson, R. M. (2002). Potential repair of Escherichia coli DNA following exposure to UV radiation from both medium- and low-pressure UV sources used in drinking water treatment. Applied & Environmental Microbiology, Vol. 68, No. 7, 3293-3299.
3. Nickmilder, M., and Bernard, A. (2006). Ecological association between childhood asthma and availability of indoor chlorinated swimming pools in Europe. Occupational & Environmental Medicine, July 2006, Volume 63, doi:10.1136/oem.2005.025452.
4. Bernard, A., et al, (2003). Lung hyperpermeability and asthma prevalence in schoolchildren: unexpected associations with the attendance at indoor chlorinated swimming pools. Occupational & Environmental Medicine, 60, 385-394.
