UV irradiation as a microbial safety barrier

This was the PhD research project of Kristjan Pullerits. Kristjan was an industrial PhD student working for Sweden Water Research, Sydvatten and Lund University.

A glass of drinking water contains millions of microorganisms which most of the time are safe for humans to consume. Also in the drinking water distribution system, bacteria grow on the pipe walls, a biofilm. Research have shown that the global warming affects the raw water which is used for drinking water production by increasing the nutrient levels which in term can stimulate microbial growth. To prevent outbreaks of pathogenic organisms in the drinking water there are various microbiological safety barriers at water treatment plans that inactivate or remove the harmful organisms.

About the project

This project has looked more closely at how the safety barrier UV irradiation affects the microbiology in drinking water. UV irradiation has been used to inactivate microbes since the beginning of the 20th century. The principle with UV irradiation in drinking water is that the irradiation alters the microorganisms DNA and prevents the reproduction of microbes and more specifically pathogens.

A lot of studies have been done in lab environments with lab cultivated microbes which have shown that UV irradiation is effective against these lab strains. However, bacteria in the environment are more resilient than lab strains, how is UV irradiation affecting these more robust organisms out in the environment in reality?

The project investigated how UV irradiation affects the whole community of microorganisms in drinking water. Can some types of microbes be more resistant to UV irradiation? Can the UV damage be repaired? What is happening in the distribution system if more resilient organisms survive?