Virus detection in influent, activated sludge, and effluent from municipal wastewater treatment plants using composite and grab samples in Finland

Wastewater-based surveillance has been commonly used as a monitoring tool for public health. Also, viruses present in wastewater can pose a health risk. In this study, we screened enterovirus, rhinovirus, norovirus GI and GII, pan-adenovirus, and gastroenteritis-causing adenovirus F40/41 in different wastewater sample types using reverse transcription quantitative polymerase chain reaction and quantitative polymerase chain reaction. We analyzed composite influent samples (N = 22), grab influent samples (N = 20), composite effluent samples (N = 78), grab effluent samples (N = 21), and activated sludge samples (N = 34) collected from six municipal wastewater treatment plants in the Pirkanmaa region of Finland. We detected the viruses in the influent to discover if they had the potential to be monitored using wastewater-based surveillance. In addition, we studied viruses in effluent and activated sludge to detect viruses that persisted in treatment processes. Furthermore, all sample types were compared to discover differences in the viral contents of different wastewater sample types. We detected all the studied viruses in influent, while in activated sludge, we detected enterovirus, pan-adenovirus, and adenovirus F40/41, and in effluent enterovirus, norovirus GI and GII, pan-adenovirus, and adenovirus F40/41 were identified. In addition, the relative amount of all the viruses was the highest in the influent. Our study also showed that composite sampling was a more representative and sensitive method for virus monitoring in wastewater than grab sampling, as the relative amount of the viruses present in composite samples was higher than in grab samples. Since we found abundant viruses in effluent, further studies are required to assess their infectivity and potential health risks as environmental pollutants.