UV disinfection - How to eliminate viruses I bacteria I wastewater

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Natural and manmade water sources such as rivers, lakes, dams, streams, and stormwater tanks may contain living microorganisms (bacteria, fungi) or nonliving structures like viruses which can be harmful for human health. Therefore, water and wastewater treatment plants in developed countries test and treat water before it is used for drinking, bathing, filling swimming pools, food preparation or cooking. At the same time however, 60% of all infant mortality worldwide is linked to infectious and parasitic diseases, most of them related to inadequate water disinfection in undeveloped countries.
Chemical disinfection approaches like chlorine dosing damage the cell membrane of microorganisms and then enter the cell to disrupt cell respiration and DNA activity. Chlorine also kills most viruses, but it requires retention times of up to 30min or more.

In comparison UV light provides rapid, effective inactivation of microorganisms through a physical process. When bacteria, viruses and protozoa are exposed to the germicidal wavelengths of UV light, they are rendered incapable of reproducing and infecting.

Ultraviolet (UV) light is emitted by our sun however its invisible for the human eye. On the electromagnetic spectrum its positioned between X-rays and visible light with wavelengths between 100 and 400 nanometers. This spectrum is categorized as germicidal meaning it damages DNA and sterilizes surfaces with which it comes into contact. For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of skin cancer.

When microorganisms or viruses are exposed to UV light their nucleic acids are damaged in a way that they are rendered incapable of reproducing and infecting. Bacteria absorb light for growth processes therefore high energy UV light is absorbed as well and enters cellular RNA and DNA. This absorption of UV energy forms new bonds between adjacent nucleotides, creating double bonds or dimers. The longer the exposure to UV light, the more thymine dimers are formed in the DNA and the greater the risk of an incorrect repair or a "missed" dimer. If cellular processes are disrupted because of an incorrect repair or remaining damage, the cell cannot reproduce or infect anymore.

It has been proven that UV light treatment is a rapid and effective way to inactivate a wide list of pathogenic bacteria and viruses. Unlike chemical disinfection like chlorine dosing, UV light also eliminates protozoan parasites which cause for example Malaria. However, UV disinfection is usually a single pass treatment and if used insufficiently, bacteria strains could regrow during transportation from treatment facilities to private households.

Видео UV disinfection - How to eliminate viruses I bacteria I wastewater канала Karl-Uwe Schmitz