Normalization of Viral Loads in Wastewater-Based Epidemiology Using Routine Parameters: One Year Monitoring of Sars-Cov-2 in Urban and Tourist Sewersheds

In wastewater-based epidemiology normalization of experimental data is a critical aspects as emerged in the recent surveillance of COVID-19. Normalisation facilitates the comparison between different areas or periods and to evaluate the differences due to the fluctuation of the population for work or tourism. Analysis of biomarkers in wastewater (i.e. drugs, beverage and food compounds, microorganisms such as PMMoV or crAssphage, etc.) is complex to use and is not routinely monitored. This work compares the results of alternative normalization approaches applied to SARS-CoV-2 loads in wastewater using population size calculated with conventional hydraulic and/or chemical parameters (i.e. total suspended solids, chemical oxygen demand, nitrogen forms, etc.), commonly used in routine monitoring of water quality. A total of 12 wastewater treatment plants were monitored and 1,068 samples of influent wastewater were collected in urban areas and in highly tourist areas (summer and/or winter). The results indicated that both census and population estimated with ammonium are effective and reliable parameters to normalize SARS-CoV-2 loads in wastewater from urban sewersheds with negligible fluctuating people. However, this study reveals that in the case of tourist locations, the population calculated using NH4-N loads can provide a better normalization of the specific viral load per inhabitant.