Studi ini mengisolasi coliphages yang berbeda dari air limbah kota yang diolah. Coliphages adalah virus yang menginfeksi bakteri E.coli, dan mereka dapat digunakan sebagai model untuk virus enterik manusia dalam studi desinfeksi. Hampir setengah dari kolifag yang diisolasi sangat resisten terhadap klorin atau radiasi UV, dan inilah mengapa klorin maupun radiasi UV saja tidak efektif melawan semua kolifag.
"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.
Ketika kolifag pertama kali terpapar pada konsentrasi klorin rendah ({{0}}.1 atau 0,5 mg Cl/L) selama 10 menit diikuti dengan radiasi UV rendah (hanya 22 mWs/cm2), lebih dari 99,9 persen semua coliphages dipelajari menjadi tidak aktif. Namun, ketika urutan perawatan dibalik (UV pertama, klorin kedua), disinfeksi jauh kurang efektif.
"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.
