Effects of bacterial, chemical, physical and meteorological variables on virus removal by a wastewater treatment plant.

The purpose of wastewater treatment is to minimize chemical and microbial contamination of recipient waters. The present study evaluated the impacts of meteorological variables, such as temperature and rainfall, on the removal of human viruses and indicators by a wastewater treatment plant servicing Pisa, Italy. Data were obtained during four sampling campaigns from 2007 to 2010. Wastewater sewage samples were analyzed for human adenovirus (HAdV) and norovirus using quantitative molecular techniques. In parallel, Escherichia coli, enterococci and somatic coliphages were measured, and meteorological and chemical data were recorded. We detected a continuous presence of HAdV in both influent and effluent samples with an average removal rate of 2.01 log10 Genomic Copies/l. An association between meteorological parameters and viral removal rates was detected only for rainfall and HAdV removal during a specific sampling campaign. No correlation was found between viral data and microbial, chemical and physical ones. Viral removal rates were not strongly influenced by meteorological conditions and were unrelated to other process indicators routinely monitored. Our results suggest that HAdV is a suitable parameter to assess the viral removal efficiency of wastewater treatment plants, particularly in the case of heavy rainfall.