University of Eastern Finland Researchers Found High Power UV LEDs About as Effective as Combination of Low Power UV and Chlorine for Killing Viruses in Water

Researchers from University of Eastern Finland found in a new study that a combined water disinfection treatment using both chlorine and UV radiation can be highly effective. The study isolated various coliphages from treated municipal wastewater. Coliphages are viruses that infect E.coli bacteria, and they can be used to model human enteric viruses in studies of disinfection. Almost half of the isolated coliphages were found to be highly resistant to chlorine or UV radiation. So, neither chlorine nor low power UV radiation alone were shown to be effective against all coliphages.

“This highlights the importance of a combined treatment,” said Doctoral Student Alyaa Zyara, MSc, from the University of Eastern Finland, who presented the results in her doctoral dissertation.

The researchers first exposed the coliphages to a low chlorine concentration (0.1 or 0.5 mg Cl/L) for 10 minutes. Then they exposed the coliphages to low UV radiation (only 22 mWs/cm2). After both treatments in that order, more than 99.9% of all of the isolated coliphages became inactivated. However, when they reversed the order of the treatments with the UV exposure first and chlorine second, they found the disinfection was much less effective.

The study also looked at the use of UV-LED technology alone for disinfecting drinking water from UV and chlorine resistant viruses. The study tested 270nm UV-LEDs with a 120 mW irradiation capacity. UV LEDs with this power and wavelength haven’t been used in disinfection studies previously.

They found that as little as 2 minutes of exposure to this UV-LED treatment, reduced the coliphage population 90-99.9% in a 5.2-litre reactor. And an irradiation time of 10 minutes in the same reactor increased the coliphage population reductions to 99.99 – 99.999%.

The researchers showed that 120 mW power UV-LEDs at 270 nm are effective for inactivating most DNA and RNA viruses tested. They noted however, that it is difficult to compare the efficiency of different UV LED wavelengths to disinfect coliphages because of the difference in water volumes, the reactor configurations, and types of water are often different from one UV-LED study to the next. So, they recommended that the efficiency of different wavelengths and wavelength combinations should be further studied.


Zyara, A.M.; Heinonen-Tanski, H.; Veijalainen, A.-M.; Torvinen, E. UV-LEDs Efficiently Inactivate DNA and RNA Coliphages. Water 2017, 9, 46. DOI: 10.3390/w9010046

Zyara, A.M. (2018). Removal of viruses from drinking water by chlorine and UV disinfections (Doctoral Disertation). Retreived from:


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