UV disinfection
UV (ultraviolet) disinfection units are an industry standard when it comes to combating microbiological contamination in private water supplies. By harnessing the power of UV light, micro-organisms that can cause and spread infection are neutralised and your water becomes safe for consumption.
Why does your water need UV disinfection?
Raw water - particularly water from surface sources - can contain a multitude of microbiological contaminants (e.g. viruses and bacteria), with the most common including e.coli, coliform bacteria and clostridium perfringens. These contaminants often derive from faeces, sewage effluents or animal remains entering your water supply; contamination which can occur anywhere between the water source and interior taps. In practice, all private water supplies require disinfection treatment because any level of microbiological content can cause and spread infection. Even lower-risk water sources such as groundwater supplies are unlikely to always be contaminant free.
A zero tolerance policy
Every water source will contain a unique composition of contaminants which all have their own resistance to disinfection. Due to this, water testing becomes an essential first step in the water filtration design process, as these tests are not only important for identifying the specific type and concentration of the contaminants present in your water, but consequently selecting the correct UV unit for effective disinfection.
How does UV disinfection work?
UV light operates on a spectrum; a spectrum which is divided into subgroups based on the unique characteristics and functions of UV energy at different wavelengths. UV light with a wavelength between 200 - 280 nm (nanometres) is categorised as the germicidal range, as at these levels UV rays can break through the cell membrane of micro-organisms and inactivate the DNA inside the cells, consequently inhibiting their ability to reproduce or cause infection.
For treatment of drinking water, UV lamps operate within the optimal germicidal range of wavelength 250 - 265 nm, with a wavelength of 254 nm being the most effective for disinfection.
What is a UV disinfection unit?
On the outside
A UV disinfection unit is made up of three components: a reaction chamber (usually made of stainless steel), a transparent quartz sleeve and a UV lamp.
On the inside
The UV lamp (which emits the UV light) is located at the centre of the unit, ensuring that your water has maximum exposure to the UV light as it flows through the cylindrical reaction chamber from the inlet to the outlet. The lamp is sealed within a transparent quartz sleeve, which acts as a barrier to protect the lamp from water damage without compromising the ability of the light to pass through to the water. The quartz sleeve also aids to minimise any cooling effects of the water as most UV lamps work at an optimal temperature of around 40 degrees celsius.
UV disinfection units: The essentials
Effective UV disinfection only occurs if the water has adequate exposure to the UV light.
Time
Disinfection will be ineffective if the water doesn’t spend enough time under the UV rays. Primarily, the aim is to avoid water running through the UV disinfection unit too quickly, which can happen if day-to-day demand exceeds the capacity of the UV unit. This increases the risk of microbiological contaminants making it to your tap. Since UV disinfection units are designed for different flow rates, water filtration system designs should always consider peak usage demands, maximum flow rate and the chemistry of your water.
Shine
Equally important to exposure duration, is the exposure intensity. The UV light should be able to radiate through the quartz sleeve and into the water uninterrupted and at optimum power. The biggest barrier to high UV transmittance (the ability of the UV rays to penetrate through to the water) is a dirty or discoloured quartz sleeve, with the buildup of sediment or any staining on the quartz shielding the microbiological contaminants from disinfection. For this reason, regular maintenance includes cleaning the quartz sleeve. Reduction of UV intensity can also result from ageing of the UV lamps, which typically last between 10 to 12 months. While the light may still work after this period, the output is around 70% of its original capacity, rendering the lamp's efficiency at disinfection significantly reduced.
Refine
UV efficiency can be significantly lowered if the incoming water contains high levels of natural colour, organics, turbidity (cloudiness) and/or particulate. Colour, organics and turbidity are problematic because they limit the ability of the UV rays to penetrate through the water, as the light struggles to reach the outer edges of the unit due to these particles absorbing the majority of the UV energy. Alternatively, any particulate acts as a physical shield for the microbiological content to hide behind, limiting the duration and intensity of any exposure the microorganisms may have to the UV light. The solution is to reduce colour, organics, turbidity and particulate by installing pre-filtration equipment.
It’s all under control
All UV disinfection units come with a control box which monitors the UV in real time. The functions and capabilities of the control box will depend on the type of unit you opt for. Basic units can feature an LED light that goes out when the UV lamp isn’t working or a small screen that displays a countdown to the next lamp replacement date.
Higher spec models can be set up to sound an alarm and/or show an alert message when the UV lamp needs to be changed or if there is a fault with the unit (e.g., the lamp stops working). These models can even be connected to an automatic solenoid valve which stops the water flow when it recognises an issue with the unit. This means that you are alerted to the problem quickly, ensuring that the issue is properly investigated before any bacteria can pass through to your taps.
A quick check
Aside from the control box, most UV models have a slightly transparent cap at one end of the unit which allows the UV light (when switched on) to peek through. The presence of a violet glow indicates that the lamp is working. It is important to note that you should never look at the UV light directly as it is not healthy for your eyes.
UV disinfection units: The accessories
The little extras that provide peace of mind and reliable performance.
Power supply
The UV disinfection unit should be switched on at all times. If the UV isn’t switched on, then the water is not being disinfected. Unlike chemical treatments which leave residual disinfectant in the water, UV treatment requires adequate contact time with the water in order to be effective. Additionally, switching the UV on and off for selective use will increase the likelihood of microbiological contaminants migrating through the unit whilst the unit it switched off. This can introduce bacteria into the pipework between the UV unit and the taps, increasing the risk of re-contamination when the treated water travels through the final parts of the distribution network. It is important to have a back up plan in place in case of any potential power outages, such as a portable power generator or automatic shut-off valve.
Kettle
If for any reason the UV disinfection unit stops working (e.g. there’s a power cut or the lamp fails), it is imperative that the water is boiled before it is used for drinking, cooking or brushing teeth. Boiling the water kills the microbiological content that the UV disinfection unit has been unable to treat during its downtime, making it safe for consumption.
Maintenance
Regular maintenance is crucial for equipment longevity and performance. Specific maintenance requirements and schedules will vary depending on your water chemistry, however there are standard recommended practices. UV lamps should be checked daily to ensure the lamp is on and the unit is working. The lamp itself usually lasts 10 - 12 months, and should be replaced after this duration to ensure effective disinfection. In the first year of operation, the quartz sleeve should be checked at the 6 month mark, to look for sediment build-up or discolouration. If the quartz sleeve is still clean, it is likely that it will only require annual cleaning. If the quartz sleeve is dirty, it is an indication that it will require more regular cleaning, such as 4-monthly.
What are the benefits of UV disinfection?
A precise impact
UV treatment doesn’t impact the taste, odour, colour or pH of the water. It will only treat the microbiological contamination.
Chemical free
UV disinfection doesn’t require the use of any chemicals, in fact it can be more effective than chemical treatments for some types of bacteria.
A clean solution
The process doesn’t produce any by-products that are harmful to human health.
Easy addition
The device is relatively small and wall mounted, taking up minimal space. They can be easily incorporated into any existing or new system.
Low maintenance
While maintenance is essential it is not colossal. Maintenance for many systems includes an annual quartz sleeve clean and UV lamp replacement.
Cost effective
Running costs for the unit are low, with their only requirement being a constant supply of electricity.
Ready to get started with UV disinfection?