Understanding the power of UV technology
What is Ultra Violet light:
Ultra violet light is low wavelength electromagnetic radiation between 10nm and 400nm and has wavelengths below lights visible spectrum.
For disinfection purposes we often refer to UVC and the most useful wavelengths are between 200nm and 280nm.
How does UV light disinfect:
Ultra Violet light works by breaking the hydrogen bond linking the Adenine and Thymine pair in a pathogens DNA, this stops the pathogen from replicating. Once the pathogen has been inactivated by UV light it cannot replicate and has a typical life of only a few minutes so rendering it harmless.
The level of a pathogens inactivation depends on the UV dose (UV intensity x exposure time) applied and the pathogens susceptibility to this UV dose and it varies for every pathogen.
The advantages of UV light disinfection:
Ultra violet disinfection offers many advantages over conventional disinfection.
· Requires no chemicals
· Does not leave a taint or taste in the liquid
· Can be more efficient than chlorine
· Is cheaper than Ozone disinfection
· Effective against bacteria, moulds, spores and viruses
· Effective against chlorine resistant species such as cryptosporidium & giardia
How UV light is produced:
Nearly all commercial industrial and municipal Ultra Violet disinfection systems use mercury vapour lamps to produce Ultra Violet light for disinfection.
There are basically two types of UV lamps available either Low Pressure lamps producing monochromatic light at 254nm or Medium Pressure lamps producing polychromatic light between 200 and 300 nm.
UV light: the twin effect
In the context of water treatment UV light has two major effects. The first is a biological effect in which microorganisms are disabled, providing effective disinfection of water, and second a chemical effect in which unwanted chemicals are broken down for easy removal in later processes.
Biological effect – the mechanism of UV disinfection
Strong sunlight disinfects water by permanently de-activating bacteria, spores, moulds and viruses. Over a century ago, scientists identified the part of the electromagnetic spectrum responsible for this well-known effect; wavelengths between 200nm and 300nm, often called UV-C.
The mechanism of de-activation is well documented and unlike chemical disinfectants the organism is unable to develop any immune mechanisms. The mechanism involves the absorption of UV energy by the DNA in the organism, which fuses the DNA and prevents replication.
Chemical effect – Photolytic reduction
UV light of the right wavelength has the ability to break chemical bonds, and thereby help in the reduction of unwanted chemicals in water. This process is called Photolysis and has many industrial applications: