ULTRAVIOLET DISINFECTION

The effect of UV light on bacteria, viruses, spores and moulds has been known to science for many years.  The shortwave ultraviolet energy is lethal to micro-organisms as the UV rays penetrate the cell membranes and destroy the DNA inside the cell, effectively destroying the organism and it’s ability to reproduce. Ultraviolet disinfection is extremely fast, it requires no chemicals or additives and cannot be overdosed. No chemical residuals are left in the treated water. The UV intensity (dose) is measured in mJ/cm2. For domestic situations UV systems should give at least 30 mJ/cm2 and for larger industrial systems 40 mJ/cm2. The dose required to inactivate bacteria depends on the bacteria.  The higher the dose of UV the more of each bacteria are killed. Typical dose to inactivate 99% (log 2) of bacteria are listed below: Crytosporidium parvum                    4.9 mJ/cm2 Clostridium perfingens                     8.4 mJ/cm2 Giardia lambia                                    <5 mJ/cm2 Vibro cholerae (cholera)                   1.4 mJ/cm2 Shingela dysenteriae                        1.2 mJ/cm2 Escherichia coli (E Coli)                     2.8 mJ/cm2 Salmonella typhi                                4.8 mJ/cm2 Legionella pneumophila                  5 mJ/cm2 Poliovirus typ 1                                  14 mJ/cm2 Campylobacter jejuni                        3.4 mJ/cm2