Reduction of norwalk virus, poliovirus 1 and coliphage MS2 by monochloramine disinfection of water

The reduction of Norwalk virus (NV) by a 2 mg/L dose of pre-formed monochlo ramine was determined at pH 8 and 5 degrees C in bench-scale, batch disinfe ction experiments using quantitative RT-PCR for NV assays. Two other enteri c viruses, poliovirus 1 (PV1) and coliphage MS2, were Included for comparis on and assayed by infectivity as well as RT-PCR. After 3 h, reductions of P V1 and MS2 by infectivity assays were about 1 log(10) but there were no red uctions of these viruses by RT-PCR assays. Hence, RT-PCR underestimated vir us inactivation by monochloramine. However, NV reduction by monochloramine was about 1 log(10) 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 R T-PCR signals, the CT99 value would be smaller. However, the results of thi s study indicate that NV and the other enteric viruses tested are not rapid ly and extensively reduced by disinfection with pre formed monochloramine. (C) 1998 Published by Elsevier Science Ltd on behalf of the IAWQ. All right s reserved.