Strong sunlight is known to kill bacteria, viruses, moulds and spores. Almost a century ago scientists identified the part of the spectrum responsible for this well-known effect as primarily in the UV-C spectrum.
What is Ultra Violet (UV) light?
UV light is a naturally occurring component of solar radiation. It falls in the region between visible light and X-Rays in the electromagnetic spectrum between the wavelengths 100nm – 400nm. UV can be further categorized into UV-A, UV-B and UV-C and Vacuum UV.
What is UV-C light?
UVC between the wavelengths of 220nm and 290nm is recognised as having significant ‘germicidal’ properties. UV-C light is almost entirely filtered out by the Earth’s atmosphere, so to utilize its germicidal properties we have to artificially generate it here on earth using commercially produced UV lamps.
How does a UV-C light disinfect?
When UV light meets a microorganisms it penetrates its DNA, destroying the adenine and thymine bonds effectively inactivating bacteria, viruses, spores and moulds, by stopping them from multiplying and causing infection.
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How do we generate UVC Light?
There are two mainstream UVC lamp technologies used in Industrial and Municipal applications:
Amalgam lamps offer a monochromatic (Single wavelength) output at 254nm with 30%+ conversion of electricity to UVC. These lamps are efficient but their energy density is low which means they are relatively low power (100 to 800 W) and long. They are used when efficiency is key, but larger multi-lamp systems can be bulky and difficult to maintain.
Medium Pressure lamps offer a polychromatic output across a wide spectrum. This can be useful to match the sensitivity of a target organism, but they have a lower energy efficiency (~15%). Conversely they are high powered (1kw to 24KW) and short which means you need less lamps in a smaller reactor.
These two lamp technologies offer a choice of reactor design which allows us to weigh the pros and cons of size and efficiency for a given application. As we manufacture both types of lamp we are uniquely placed to assess these competing characteristics to arrive at our “Application Optimised UV” solutions.
Benefits of using Low Pressure or Medium Pressure lamps:
Low Pressure
Medium Pressure
Supporting Comments
Low power use
Low pressure lamps are more efficient, but are lower powered
Efficient at higher flow rates
Medium pressure lamps run at a much higher power density to low pressure lamps so one medium pressure lamp can treat a much higher flow than a single low pressure lamp.
Space restrictions
Medium pressure lamps for the same UV output are around a third of the length of a low pressure lamp and so systems are much smaller
Lamp life
Low pressure lamps typically last 9000 to 15000 hours while the latest generation medium pressure lamps last about 9000 hours
Save on maintenance & spares
For the same conditions medium pressure UV systems generally have a smaller footprint and use fewer lamps than Low pressure system
Disinfection efficiency
Medium pressure has a higher UV light energy output and not only breaks a microbe’s DNA bond but also ruptures the cell wall. Some microorganisms are much more sensitive to these multiple wavelengths produced by medium pressure lamps.
Low running temperature
Low pressure lamps run at about 120°C, whereas medium pressure runs at 600°C to 800°C
High water temperature
Medium pressure UV systems are hardly affected by the water temperature, whereas low pressure can only operate between 5-40°C
Status ‘ON’ after no water flow
In many cases LP systems can operate for longer without any water flow than MP systems.
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Key Features of a UV treatment System
UV Chamber: This is the reactor through which fluid flows and comes into contact with the UV Light. It has an inlet and an outlet with connections to suit your pipework and is designed and tested as a pressure vessel. Chambers can be Axial flow, Cross flow or U shaped.
UV lamp inside quartz sleeve: The UV lamp is sealed within a quartz sleeve protecting it from the water or fluid whilst allowing the UVC wavelengths to pass through. Some quartz can be doped to manage the wavelengths that pass. The quartz is held in position by lamp flanges or a supporting framework.
UV Intensity sensor: This instrument measures the intensity (W/cm2) of UV light passing through the water and arriving at the sensor. This intensity is used to calculate the UV dose (mJ/cm2) that is being delivered.
Temperature sensor: A hardwired trip switches the system off at high temperatures, whilst a built in thermocouple provides a temperature measurement on the control panel.
Auto-wiper: Like a wiper on a car cleans your windscreen an auto-wiper can be used to clean the quartz without having to interrupt the treatment process. Wipers are used in water pre-treatment and waste water systems where solids or scale deposits can form. Wipers are not required post RO or demineralisation. A chemically assisted wiper is available on some models.
Power supply & Control cabinet: Provides the user with information on the performance of the UV system and controls power to the lamps.
UVT Meter: Some systems will require a sensor to measure changes in the income water UV transmission (UVT). This feeds into the system controller and regulates the power to ensure that the required dose is maintained. Our PQ EO, PQ AF and PQ AL ranges have UVT corrections built in to validated algorithms and do not require a separate UVT instrument.
Flow meter: If your flow varies and you want to optimise your energy consumption you will also need a flow signal into the UV so that the power can be adjusted to match the flow rate.
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