UV radiation for water disinfection more effective after chlorination, finds study

March 08, 2018 // By Julien Happich
Researchers from the University of Eastern Finland have shown that a two-pronged approach to water disinfection combining chlorine with UV radiation, was the most effective when UV exposure was carried out last.

The study isolated different coliphages from treated municipal wastewater. While nearly half of the isolated coliphages were revealed to be highly resistant to chlorine or UV radiation, a combination of both treatments became up to 99.9% effective.

The researchers found that when coliphages were first exposed to a low chlorine concentration (0.1 or 0.5 mg Cl/L) for 10 minutes followed by low UV radiation (only 22 mWs/cm 2), more than 99.9% of all of the coliphages studied became inactivated. But combining the two treatments in a reverse order (UV first, chlorine second) made the disinfection much less effective.

In their study, the researchers also tested UV-LEDs for disinfecting drinking water, showing that a 270nm UV-LED with an optical power output of 120mW was enough to cause a 90-99.9% reduction in the coliphages tested in a 5.2-litre reactor, within 2 minutes. Extending the irradiation time to 10mn in the same reactor increased the reductions to between 99.99 and 99.999%. This is to be compared with the same disinfection treatment performed with a traditional mercury UV lamp at a 254nm wavelength, yielding similar coliphages reductions but in a water volume orders of magnitude smaller (10 millilitres).

The results were part of the doctoral dissertation of Alyaa Zyara, "Removal of viruses from drinking water by chlorine and UV disinfections", whose findings were originally reported in Journal of Water and Health, and Water.

University of Eastern Finland - www.uef.fi