Hanovia News - a Halma PR news blog

Introduction

Ultraviolet (UV) technology is now a well established method of swimming pool water treatment. From its early successes in high-load recreation pools, it is now widely used throughout the leisure industry, from hydrotherapy spas to Olympic size competition pools. This growth in popularity has been largely due to UV’s reliability and ease of use. Another major factor is the reduced reliance on traditional chemical treatments it affords, particularly chlorine.

Although the need for chlorine is greatly reduced with UV, residual amounts are still necessary to ensure effective disinfection. Some of the more unpleasant by-products of chlorination are chloramines, formed when 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 smells commonly associated with indoor public pools. They are also corrosive and in time can lead to damage to pool buildings and structures such as ventilation ducts.

How UV works

UV kills microorganisms 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. Within this region, UV is effective against virtually all known microorganisms, including bacteria, viruses, moulds and their spores.

In addition to microbial destruction, UV has the second, equally important function of chloramine reduction.

Chloramines are compounds containing 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. The action of UV on chloramines is 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 centimeter (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.

As Hanovia is the only supplier of UV systems to manufacture its own arc tubes, they are all custom-made with outputs optimized to promote the specific chemical reactions required by the user. Its photo-active arc tubes are unique to Hanovia SP pool treatment systems, with high outputs in the wavelengths required for disinfection, chloramine photolysis and hydroxyl radical production.

In recognition of the effectiveness of it’s UV systems, Hanovia has recently been awarded certification in the USA by NSF International, an independent public health and safety company, for its ‘Photon’ range. It is the first UV system from any manufacturer to be certified under NSF/ANSI Standard 50: Circulation System Components and Related Materials for Swimming Pools, Spas/Hot Tubs. The certification was based on a year-long series of tests, including of a  review of the system’s materials, a production facility audit, and tests of the system’s performance and health effects.

Link between chloramines and asthma

A recent study by researchers at the Catholic University of Louvain in Belgium found an increased incidence of asthma in children who swam regularly in chlorinated pools (1). 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.

Automatic wiping

Swimming pool water normally contains high levels of organic pollutants and these can foul the quartz sleeve protecting the UV lamp, 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.

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.

UV systems are ideally suited to both disinfection and dechloramination. 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 like Cryptosporidium is also eliminated.

The units are compact and can usually be installed within existing pipework. Operation and maintenance is simple and can easily be 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.

Following the installation of two UV systems at the Sunbury Leisure Centre in Surrey, the manager commented, “The water quality has definitely improved since we switched to UV. It is much clearer than it used to be and you can’t smell chlorine or feel it in your eyes when you enter the pool areas – visitors have really noticed the difference. The drop in the level of chlorine dosing has also made disinfecting the pools easier and safer to manage. Before UV we were adding chlorine at 2.5ppm. This has now dropped to 0.8ppm, a significant reduction.”

The manager of the Les Quennevais Sports Centre in Jersey, when asked about improvements since switching from an ozone to a Hanovia UV water treatment system, said that the water quality and clarity had improved “110%”.

Comments like these speak for themselves and are a glowing endorsement to the very real benefits of UV.

References:

* There are two main types of UV lamp: low pressure and medium pressure. Low pressure lamps produce a single peak of UV output at 254nm, while medium pressure lamps produce a broader spread of UV output, between 210 and 310nm. Medium pressure lamps are therefore much better suited to pool applications, as their output spans the entire range of wavelengths necessary for both chloramine removal and permanent microbial destruction.

1. 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.