Epidemiological monitoring of sewage sludge and wastewater from an upflow anaerobic sludge blanket reactor using SARS-CoV-2 as a model

This study explores the potential of sludge-based monitoring from an upflow anaerobic sludge blanket reactor for epidemiological surveillance, using SARS-CoV-2 as a model. We monitored SARS-CoV-2 copy numbers and mutations, and compared concentrations in sludge to concentrations in wastewater samples taken on the same days. From January to August 2021, 32 sludge samples were analyzed; 30 (93%) were positive for SARS-CoV-2, and copy numbers varied from 0.147 to 2.314 copies ×10⁶/L. In wastewater samples collected on the same days, 31 (96%) were positive for SARS-CoV-2, and copy numbers ranged from 0.058 to 3.014 copies ×10⁶/L. The concentration of SARS-CoV-2 in the sludge rose along with confirmed hospitalization cases in March, while wastewater SARS-CoV-2 concentrations rose 2 weeks earlier along with numbers of new confirmed cases. Mutations of variants of concern, Gamma and Delta, were identified in sludge samples in the same months that they became dominant in the corresponding regions. Our results indicate that, although monitoring of sewage sludge was not effective in anticipating infection numbers, it is a promising way to gain insight into the epidemiological situation in a city or region.