Inactivation of Viruses by Combination Processes of UV and Chlorine

Adenoviruses, the most UV resistant microorganism currently known, are posing concerns in UV treated drinking water. To reduce the risk from adenovirus infection, combination processes of UV and chlorination are attractive. Bacteriophage MS2 and adenovirus 5 (AdV5) were used in this study, and inactivated by low-pressure UV (LPUV) lamp, chlorination, sequential processes (UV-Cl2 and Cl2-UV) and a simultaneous process (UV/Cl2). MS2 was more resistant against chlorine than AdV5, and CT values for 2 log reduction of MS2 and AdV5 were 0.77 and 0.033 mg-min/L, respectively. However, AdV5 was more resistant to UV than MS2 and required a 101 mJ/cm of fluence for 2 log reduction. Compared to the application of UV or chlorine separately, an increasing trend of MS2 inactivation rate was found in the sequential processes, which was statistically significant (p < 0.05, ANCOVA). The simultaneous process of UV/Cl2 for MS2 provided about 2.3 times higher inactivation rate than a summation of inactivation rates by the separate application of either chlorine or UV, even at the same UV fluence rate and the same initial chlorine concentration. The combination processes of UV and chlorine, either sequential or simultaneous application, seemed to be more effective than a standalone process in viral inactivation.