Virus Inactivation by Sequential Ultraviolet-Chlorine Disinfection: Synergistic Effect and Mechanism

The outbreak of COVID-19 has aroused intensive concern regarding whether the disinfection process in water treatment plants can effectively prevent the spread of viruses. Ultraviolet (UV) and chlorine multi-barrier disinfection processes are commonly used in water treatment plants; however, their effects on virus removal is still unclear. In this study, the efficacy of different disinfection processes (i.e., UV, free chlorine and their combinations) on waterborne viruses using bacteriophage surrogates (i.e., MS2 and PR772) as alternative indicators was analyzed. The results showed that the inactivation rates of PR772 by single UV and free chlorine disinfection were both higher than those of MS2. PR772 was approximately 1.5 and 8.4 times more sensitive to UV and chlorine disinfection than MS2, respectively. Sequential UV-chlorine disinfection had a synergistic effect on virus inactivation, which was enhanced by an increase in the UV dose. Compared with single free chlorine disinfection, UV irradiation at 20 mJ cm−2 enhanced the MS2 and PR772 inactivation with a 1.5-fold and a 1.1-fold increase in the inactivation rate constants of subsequent chlorination, respectively. Virus inactivation was remarkably promoted under the previous UV irradiation at 40 mJ cm−2, which presented a 2.7-fold increase and a 1.7-fold increase in the inactivation rate constants of MS2 and PR772, respectively, in the subsequent chlorination. The mechanism of the synergistic effect of sequential UV-chlorine disinfection was also determined through sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using MS2 as an indicator. The results showed that the synergistic effect was due to damage to MS2 surface proteins caused by previous UV disinfection, which enhanced the sensitivity of MS2 to chlorination. This study provides a feasible approach for the efficient killing of viruses in water supply and drainage.