Chlorine or bromine treatment has long been the most common method of treating water in swimming pools however Ultraviolet, or UV water treatment systems are becoming increasingly popular, in part because they significantly reduce the need for chlorine consumption and therefore allow people to have an almost chlorine free swimming pool.
UV Secondary Disinfection Systems for Swimming Pools and Spas
Chlorine and Bromine remain the main forms of disinfection used in swimming pools and spas however, it is becoming increasingly popular to supplement chemical disinfection with technologies such as ultra-violet irradiation. Depending on the system chosen, these methods of disinfection can offer benefits such as:
• Lower sanitiser levels
• Greater reduction in bacteria levels
• Deactivation of chlorine-resistant microorganisms (such as Cryptosporidium Parvum and Giardia Lamblia)
• Oxidation of chloramines (chlorine by-products)
• Avoiding health and safety issues involved with handling dangerous chemicals
A UV pool system works by passing water through a vessel containing a UV lamp or lamps. These systems are split into two main groups: low pressure (LP) and medium pressure (MP). LP and MP refer to the internal pressure of the gasses within the lamps and not the water pressure of the system and each has different uses and benefits.
UV Water Treatment in Domestic Pools and Spas
UV treatment systems use a cylindrical container inside which is a UV lamp protected by a quartz sleeve. The pool water is simply pumped through the chamber and is dosed with UV energy as it passes through.
As the water passes through the system, one section of the UV spectrum breaks down the chloramines by a process known as photolysis. Shorter UV wavelengths produce hydroxyl radicals from the water itself, which are powerful oxidising agents and attack the chloramines in the water.
While domestic pools can use MP UV, the more common choice is a LP system. Lower bather loads usually mean disinfection is the main goal of the UV system. LP lamps emit UV light at a specific wavelength (254nm) which is highly effective at deactivating bacteria. The “dose” of UV light is measured in mj/cm2 and the critical minimum dose to maintain is 30mj/cm2. This dose is equal to drinking water standards and will give a 99.99% reduction in bacteria levels across the most common bacteria found in swimming pools.
UV radiation also acts as a highly efficient natural disinfectant that deactivates microorganisms by damaging their DNA.
Because UV is only able to treat water as it passes across the lamp, a residual amount of sanitiser (e.g. chlorine) must still be present to provide constant protection throughout the rest of the system. This residual, however, can be reduced by around 50-80% against a pool’s usual level, meaning it may be possible to lower the level down to as little as 0.5ppm depending on the pool. That means that a UV treated pool is using far less chemicals and therefore will also need less backwashing, which helps reduce water and heating costs.
UV Treatment in Commercial Pools and Spas
A Commercial UV System operates in much the same way as a domestic one, although larger and more powerful. The Pool Water Treatment Advisory Group (PWTAG) updated their guidelines in 2018 to include MP UV Systems for all commercial applications. The guidelines now state that the full flow of water should be treated with MP UV with a dose of 60mj/cm2 at a UV Transmittance rate (the amount of UV light able to pass through the water) of 94%.
MP lamps emit UV light across a broader wavelength which – coupled with the higher dose compared to a domestic systems – causes the oxidation of chloramines within the water as well as disinfection.
Commercial systems are usually manufactured from electro-polished stainless steel, but can also be manufactured from other materials such as titanium.
A UV water treatment system in operation.
A UV water treatment system for a swimming pool is relatively easy to install in both new plant rooms and when retrofitting.
The vessel, which is the heart of the UV system, can be plumbed into the plant room anywhere that is convenient although the best position is after the filter and before the heater. It is important to ensure adequate space is given for the removal of the lamps and any other required maintenance. Lamps should be changed in accordance with manufacturer’s guidelines to ensure optimum functionality. Over time, organic residue can build up on the quartz sleeve that protects the UV lamp. In order to make sure that the water gets the right dose of UV, in some commercial systems, an automatic wiping system keeps the sleeve clean but in other systems it is necessary to clean these manually.
UV treatment systems come in different sizes so that they can be matched to the usage of the pool and the flow rate of water through it. Even in a busy, high bather load, commercial pool, a correctly specified UV treatment will produce cleaner, clearer, more comfortable water than chlorine alone and the air in the poolroom or enclosure will be better with no unpleasant chloramine smells or eye irritation.
Triogen UV water treatment systems from Golden Coast.
With over twenty years experience in pool water treatment, Triogen is recognised as one of the world’s leading design and manufacturing companies specialising in ozone and UV systems for both domestic and commercial swimming pools.
The cost-effective UV Ultra units feature LP lamps, a pressure switch, lamp-on indicator, a choice of metric or imperial unions, and a robust, hardwearing, low-maintenance construction. Their reactor bodies are made from UV-inhibited polymeric materials, which are totally resistant to corrosion, and their UV lamps have a life of 13000 hours.
The Triogen range of Commercial UV Systems feature MP lamps and can be constructed from either stainless steel or titanium. Options include a manual or automatic wiper system for cleaning the quartz tube, a UV monitor, and a variety of control panel options with various alarms, lamp power settings, and status indications depending on the model and options selected.
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