O estudo isolou diferentes colifagos de águas residuais municipais tratadas. Os colifagos são vírus que infectam a bactéria E.coli, e podem ser usados como modelos para vírus entéricos humanos em estudos de desinfecção. Quase metade dos colifagos isolados eram altamente resistentes ao cloro ou à radiação UV, e é por isso que nem o cloro nem a radiação UV sozinhos foram eficazes contra todos os colifagos.
"This highlights the importance of a combined treatment," says Doctoral Student Alyaa Zyara, MSc, from the University of Eastern Finland, who presented the results in her doctoral dissertation.
Quando os colifagos foram expostos pela primeira vez a uma baixa concentração de cloro ({{0}},1 ou 0,5 mg Cl/L) por 10 minutos seguido por baixa radiação UV (apenas 22 mWs/cm2), mais de 99,9 por cento dos todos os colifagos estudados ficaram inativados. No entanto, quando a ordem do tratamento foi invertida (UV primeiro, cloro em segundo), a desinfecção foi muito menos eficaz.
"It is more effective to first use a low dosage of chlorine followed by a low dosage of UV radiation than to use high chlorine or UV dosages alone. The order of treatment is also important: using UV radiation first and chlorine second was less effective. In other words, the combination treatment using chlorine first and UV second can be recommended as a disinfection method for viruses."
The study also tested novel UV-LED technology, as UV-LEDs are a new method for disinfecting drinking water. The study used UV-LEDs operating at a wavelength of 270 nm and with a 120 mW irradiation capacity, which haven't been used in disinfection studies before. As little as 2 minutes of this UV-LED treatment was enough to cause a 90-99.9 percent reduction in the coliphages tested in a 5.2-litre reactor. Irradiation time of 10 minutes in the same reactor increased the reductions to 99.99 -- 99.999 percent . A traditional mercury UV lamp at a 254 nm wavelength caused similar or slightly higher reductions in 2 or 10 minutes, but the water volume was only 10 millilitres.
"UV-LEDs are a promising method for disinfecting water, since they consume less energy than traditional mercury UV lamps. Furthermore, as UV-LEDs do not contain any mercury, they are safer for the environment."
The findings were originally reported in Journal of Water and Health, and Water.
