Analysis of Hydroxyl Radicals and Inactivation Mechanisms of Bacteriophage MS2 in Response to a Simultaneous Application of UV and Chlorine.

The simultaneous application of UV and chlorine (expressed as UV/Cl2) as a water treatment method may be a good disinfection option for UV-resistant microorganisms, such as human adenoviruses (HAdVs). In this study, we developed two approaches using UV/Cl2: one to quantitate the OH• radicals based on the degradation of the probe compound para-chlorobenzoic acid (pCBA) and the other to use bacteriophage MS2 to understand the virus inactivation mechanisms in response to UV, chlorine and UV/Cl2 disinfection using reverse-transcription quantitative polymerase chain reaction (RT-qPCR), attachment and genome penetration assays. The results revealed that OH• radicals were produced at a concentration of 2.70 × 10-14 M in the UV/Cl2 treatment with a practical chlorine dose of 1 mg/L and with a minimum UV254 fluence of approximately 10 mJ/cm2, whereas UV or chlorine alone did not produce OH• radicals. In the UV/Cl2 treatment, synergistic effects on viral genome damage were observed, but were not directly due to OH• radicals. The ability of MS2 to penetrate the genome of the host bacteria was impaired, but its ability to attach to the host was not affected by the treatment. We concluded that the major cause of virus inactivation in response to UV/Cl2 was the damage to the viral genome caused by combination actions of chlorine species and OH• radicals.