A bit of theory
Bactericidal water treatment with ultraviolet irradiation is a crucial final stage in every water treatment process. Thanks to simplicity and disinfection efficiency, ultraviolet technology is largely used in daily lives and manufacturing – everywhere pure water is needed.
Water disinfection with ultraviolet (UV) rays is part of physical (reagents free) methods of water treatment. Major benefit of such method is the ability to preserve composition and properties of treated water. The disinfection effect of the UV irradiation primarily is a result of photochemical reactions in molecular structure of DNA and RNA occurring under UV influence. These molecular structures are the informational basis of the reproductive apparatus of any living organism, in particular, bacteria and viruses. Photochemical reaction results in irreversible damage of DNA and RNA, as well as in damage of membrane structure and cell walls of microorganisms, leading to their demise.
One of the positive factors is that during water purification, peroxide compounds do not accumulate and, under the influence of UV irradiation, some pyrogenic substances, caught in water, are deactivated.
Numerous studies proved that the bactericidal effect of UV irradiation is stronger than chlorination on both most common pathogenic vegetative bacteria and spore bacteria. In addition, UV irradiation has an inactivating effect on viruses, causing their death at an activation energy of 16–40 mJ/cm2, surpassing the ozonation method in this index. As a comparison, to achieve high virucidal effect, an ozone dose of 0.5–0.8 g/l and contact duration of up to 12 minutes are required, while during UV irradiation, viruses inactivation occurs in seconds.
It is known that some types of bacteria are able to form strains that are insensitive to the action of chlorine. To deactivate such microorganisms, UV irradiation methods are irreplaceable: bacteria do not develop resistance to UV bactericidal action. It is important to note that there is no limitation of the upper dose threshold for UV irradiation, therefore, by increasing the dose of UV radiation, the desired level of disinfection can always be achieved.