Ultraviolet radiation water treatment systems are different from the other methods discussed because they purify the pool water as it passes through the plant room. Both deal with water contaminants without providing a disinfectant residual, and allow the water in the pool itself to operate with a lower level of conventional residual disinfectant than it otherwise would.
Both ozone and ultraviolet radiation are potentially hazardous and attention should be paid to the safety of plant room operators, particularly during maintenance. Ozone plant rooms should be ventilated to Occupational Health and Safety Regulations.
Of the two, ozone is the more established in Australian pools. Ultraviolet radiation is beginning to be explored in commercial pools.
Ultraviolet Radiation (UV)
The disinfectant ability of radiation from the ultraviolet section of the electromagnetic spectrum is well established. UV treatment has been used in drinking water, industrial and effluent applications.
The primary action of UV is to kill bacteria, viruses, moulds and spores, thus reducing the risk of transmission of stomach, skin and respiratory tract infections to pool users. UV has an important secondary action: it initiates photochemical and photo-oxidation reactions which destroy chloramines. This is particularly important in leisure pools where features such as water slides and waves give a greater surface area for the release of chloramines into the air. UV reduces the burden, making the atmosphere safer and more pleasant.
The limiting factor tends to be the water clarity, as dissolved and suspended material inhibits UV penetration. Filtration will remove some of these solids from swimming pool water; but to optimise the effectiveness of the UV it is important that the full flow of water returning to the pool is exposed to the ultraviolet radiation. This will ensure the pool water is treated on a regular and continuous basis. An automatic wiper removes solids that settle onto the quartz thimble around the UV arc tube.
A chlorine or bromine based disinfectant must be used in conjunction with UV systems to maintain a disinfectant residual in the pool. UV radiation inactivates bacteria and helps break down chloramines and other pollutants.