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Log Reduction Explained

So what does Log Reduction mean?

Log Reduction (as in Logarithmic Reduction) refers to a predictable percentage that a given pathogen will be inactivated by a disinfection method.  A 1 log reduction will see the pathogen of interest reduced by 90% from the influent level. A 2 log reduction will see a 99% reduction, 3 log by 99.9%, and so on.

Does it take the same amount of UV light to achieve the same log reduction for different pathogens?

No. The UV Dose requirements to achieve a certain log reduction are different for all pathogens. For example as you can see in the video above, to achieve a 4 log reduction for E. Coli you would need a UV dose of 12.8 mJ/cm2 whereas for Salmonella you would need a UV dose of 7 mJ/cm2.

Does it take the same marginal increase in UV Dose to get to a higher log reduction level of inactivation?

No. The curve that reflects a given pathogens response to a UV dose is rarely linear. So it will take a higher amount of energy to increase from one log reduction level to another. One common mistake that is made is take to the UV dose for 1 log activation and multiply it to calculate the higher level.

Most importantly, why does this matter?

When installing and designing a UV system its extremely important to know the target pathogens as well as the needed level of inactivation for a given process. Knowing these two elements will help to ensure that the UV system is delivering the proper UV dose.

Looking for more information on how UV Disinfection for your process? One of the members of our sales team would be happy to talk you through any questions you have. Click here to get in touch with our team and we will reach out to you as soon as possible to answer your questions.