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Drinking water may sometimes smell bad, making people worry about chemicals. Water-treatment facilities currently use chlorine (which produces small amounts of potentially carcinogenic by-products) to keep tap water clean, but it leaves a telltale taste. Tel Aviv University scientists have determined that ultraviolet (UV) light might be a better solution.
Dr. Hadas Mamane of TAU’s Porter School of Environmental Science and Faculty of Engineering Prof. Eliora Ron of the Wise Faculty of Life Sciences and their doctoral student Anat Lakretz recently determined the optimal UV wavelength for keeping water free of microorganisms. Their approach could be used by water-treatment plants as well as large-scale desalination facilities.
“UV light irradiation is being increasingly applied as a primary process for disinfecting water,” says Lakretz. “In our recent study, we’ve shown how this treatment can be optimized to kill free-swimming bacteria – the kinds that also stick inside water-distribution pipes and clog filters.”
This undesired “stickiness” of bacteria is called bio-fouling and is costing taxpayers billions of dollars each year. “No one should be drinking microorganisms. In addition, when they get stuck in the pores of filters, they create serious problems,” adds Lakretz.
Irradiation, currently used to sterilize various foods, could be a pre-treatment to inactivate suspended microorganisms, with the secondary goal of preventing bio-fouling. In their study, reported in the journal Bio-fouling
, the researchers looked at targeted UV wavelengths on the bacteria Pseudomonas
aeruginosa, commonly found in drinking water.
The TAU researchers investigated UV wavelengths between the 220 to 280 nanometer (nm) scale and found that any wavelength between 254 and 270 nm effectively cleans water. Those in the same range were also best for keeping membranes clear of bacterial build-up in desalination plants. Special lamps that emit a multi-wavelength UV spectrum – more advanced than the single-wavelength UV lamps found in home water systems – were used.
The UV “zap” also prevented bacterial re-growth after UV inactivation. “The best way to kill these microorganisms was to damage their DNA,” says Lakretz. “The damage that the UV light causes has no known negative effect on the water,” she adds. In addition, the prevention of biofilm formation was dependent on the dose of UV. The researchers reported less bio-fouling when a bigger dose of UV light was applied to the water around the film.
The approach is even more helpful against parasites that aren’t affected by chlorine treatment, such as Giarrdia
, two harmful types that cause severe diarrhea and even death. Children, the elderly and those in developing nations are particularly vulnerable. “Sewage leakage into water supplies poses a big problem in terms of bacterial contamination, and is something UV light could correct,” says Lakretz.
Small amounts of chlorine or other oxidants will still be necessary to make sure residual bacteria don’t enter the water further along the distribution pipeline. But Lakretz says this new approach can also reduce the amount of carcinogenic by-products that chlorine produces.
The TAU team is part of the MAGNET consortium, an Israeli research-oriented project aimed at commercializing “clean” technologies.AMPHIBIAN WARNING FOR QUAKES?
Keep your eyes on the toads. British scientists say they’ve discovered
that common toads can detect impending earthquakes several days in
advance. Researchers from the Open University in London, who published
their findings recently in the Journal of Zoology
, were quoted by UPI
as saying they found 96 percent of male toads (Bufonidae
) in a
population abandoned their breeding site five days before an earthquake
struck L'Aquila in Italy last year. The breeding site was located 65
kilometers from the earthquake’s epicenter.
The scientists said the number of paired toads at the site also dropped to zero three days before the earthquake.
The researchers did not explain where the females went and whether the
male toads’ sudden departure could have been circumstantial and not due
to the earthquake (for example, maybe the Italian males were going out
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