Why swimming pool need UV-C light to treat water?

Many efforts have been made to replace chlorine, but few of these have gained substantial ground. This is because the solutions have been found to have the same drawbacks (e.g. bromine), or are expensive (e.g. hydrogen peroxide) or are less effective (e.g. metal ion-based processes, hydrogen peroxide).

UV radiation: an extremely powerful disinfectant

Ultraviolet radiation of a particular wavelength (UV-C – 253.7nm) that, when used to treat water, has a very strong biocide effect. It renders harmless microorganisms in the water, particularly those that are unaffected by chlorine. UV-C light is the most damaging part of sunlightthat doesn’t reach the earth, so a special electric lamp is needed to generate this radiation.

This means that in swimming pools, UV is an extremely powerful disinfectant. It is even effective against Cryptosporidium parvum and Giardia lamblia, for example. These are particularly nasty microorganisms that can survive in a swimming pool despite the use of chlorine.

In addition to its biocide action, UV-C has an extremely strong oxidizing effect. This means that it effectively removes organic pollution from the swimming pool water. When either ozone or UV-C is used in conjunction with chlorine in a swimming pool, the harmful chloramines that cause i.e. eye and skin irritation are destroyed.

The benefits of using a UV-C purifier in a swimming pool

• The protection of bathers against illnesses caused by microorganisms that are unaffected by chlorine.
• The virtual elimination of the eye, nose, skin, and respiratory system irritation caused by chloramines in the water.
• The elimination of the unpleasant “swimming pool smell”.
• The increased preservation of the fabric of the pool and pool hall by the reduction of the chloramines in the pool water.

So, if UV-C is that effective, why not stop using the chlorine altogether?

UV-C purifying does not add anything to the water to prevent further new infection. Although the water is disinfected, it is not disinfectant. The water from the UV-C purifier returns to the pool. Typically, it will remain for four hours in the swimming pool until it is treated again. So, any pathogens instantaneously introduced by bathers in the pool would not be treated until that water arrives back at the UV treatment unit in four hours’ time. This presents a threat to the health of pool users.

For that reason, it is always necessary to maintain a small residual concentration of a secondary disinfectant (such as chlorine) in the pool. For public pools, in most countries, this is in any case a requirement imposed by the regulatory public health authorities. The addition of a secondary disinfectant ensures that the water in the pool remains disinfectant as well as having been disinfected.

Although the use of UV-C does not remove the need for a secondary residual disinfectant such as chlorine, its total concentration in the pool water can usually be significantly reduced (in public pools to the minimum legally allowable concentration). Most of the disinfecting and oxidising load will be borne by the UV system. In particular, the destruction of harmful pathogens and the significant reduction of unpleasant chloramines in the pool water would be handled by the UV system.