Article - Issue 51, June 2012

HOW DOES THAT WORK? - Pool sterilisation

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Pathogenic contaminants are associated with numerous recreational water-borne illnesses such as otitis externa, commonly called ‘swimmer’s ear’. A number of methods are used to sterilise swimming pool water and for the London 2012 Olympics a combination of treatments will be used.

During the 20th century, seawater swimming pools were common in UK coastal towns; the salt water killed pathogens by action on the bacterial outer membrane. Chlorination is the most widespread system used today, but creates strong odours and can cause skin and eye irritation. Sodium hypochlorite is added to pool water at the rate of three parts per million and needs to be carefully monitored. The chlorine disinfects by reacting with organic compounds. However, its volatile nature causes it to disappear quickly from the water system, and so requires constant replenishment.

An alternative system that has been used in competition pools is the germicidal disinfection of water employing UV-C radiation. UV has a wavelength in the 240 nm to 280 nm range generated by mercury vapour lamps inside a sealed water conduit. This initiates a photochemical reaction that destroys the reproductive capability of bacteria and algae by disrupting their genetic code. The sterilised micro-organisms are then physically filtered from the water. This treatment, supplemented by light chlorination, will be used in the Aquatic Centre for the London 2012 Games.

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