Humans can survive several days without food but only a few days without water. Thus, drinking water is the most important source of nourishment, and there is plenty of water available on the Earth; in fact, if you took all of the water resources available on the earth and shaped them into a cube, the cube would have an edge length of 1180 kilometers [1]. Only a few thousandths of these resources are available as fresh water and can thus be used as potential drinking water.
Drinking water is processed fresh water and has a high degree of purity. It is safe for consumption, does not contain contaminants or pathogenic microorganisms, and ideally contains minerals.
Preparation of Drinking Water via Disinfection
Drinking water is not available everywhere in sufficient quantities: In some regions, fresh water is only available from precipitation and is thus contaminated. Polluted water can lead to diseases, and even death. To be fit for consumption, it is necessary to treat and sterilize this water.
Different methods are used to sterilize water; one such method is sterilization via UV radiation. This process is particularly advantageous because it is neutral in taste and economical.
Sterilization via UVC Radiation
Radiation in the wavelength range between 100 nm and 280 nm is referred to as UVC radiation. This very short-wave radiation is absorbed by the Earth’s atmosphere; thus, it does not reach the Earth’s surface. If this radiation comes into contact with microorganisms, their DNA is damaged within a very short period of time, reproduction is no longer possible, and the viruses and pathogens are wiped out.
Studies performed by Prof. Dr. Hellmann from the University of Applied Sciences in Aschaffenburg have shown that sterilization was most effective when the bacteria under examination were illuminated with a wavelength of 280 nm. The following bacteria were tested: Escherichia coli, Enterobacter cloacae, and Kebsiella pneumoniae [2].
Light Sources
Mercury vapor lamps are primarily used as UVC light sources. They will soon be replaced by UV LEDs, which are now available commercially.
The Advantages of UV LEDs
Even though UV LEDs have a low efficiency, they will become the most promising sources of sterilization with UV light. They are much smaller than mercury vapor lamps, and the greatest advantage is their particularly undemanding power supply: UV LEDs can be operated with a direct current and thus directly connected to solar cells. They can, therefore, be used anywhere – even in areas without a reliable electricity supply.
A Look at the Future
UVC LEDs possess great market potential. These products are not yet superior in terms of efficiency and lifetime but still well suited for use in mobile water sterilization. In the future, they will surely be used in critical environments, such as, for example, hospitals to avoid further use of the hazardous material mercury.
Did you know that UVC radiation is also used in air disinfection?
Sources:
[1] lexikon.wasser.de/index.pl?begriff=Wasservorkommen&job=te,
[2] elektor Special Project: LEDs 2, S.40 ff,
www.h-ab.de/uploads/media/WasserentkeimungUV.pdf
