Reduction of Norwalk virus, poliovirus 1 and coliphage MS2 by monochloramine disinfection of water Available to Purchase

The reduction of Norwalk virus (NV) by a 2 mg/L dose of pre-formed monochloramine was determined at pH 8 and 5°C in bench-scale, batch disinfection experiments using quantitative RT-PCR for NV assays. Two other enteric viruses, poliovirus 1 (PV1) and coliphage MS2, were included for comparison and assayed by infectivity as well as RT-PCR. After 3h, reductions of PV1 and MS2 by infectivity assays were about 1 log₁₀ but there were no reductions of these viruses by RT-PCR assays. Hence, RT-PCR underestimated virus inactivation by monochloramine. However, NV reduction by monochloramine was about 1 log₁₀ by RT-PCR assay, suggesting that it is more susceptible to monochloramine than the other two viruses tested. Based on RT-PCR titre reduction, the CT₉₉ value for NV was about 775 mg-min/L. If the reduction of NV infectivity by monochloramine is ever greater than the reduction of RT-PCR signals, the CT₉₉ value would be smaller. However, the results of this study indicate that NV and the other enteric viruses tested are not rapidly and extensively reduced by disinfection with pre-formed monochloramine.