SARS-CoV-2 RNA is enriched by orders of magnitude in primary settled solids relative to liquid wastewater at publicly owned treatment works

• Published in: Environmental science water research & technology 2022-03, Vol.8 (4), p.757-770
• Main Authors: Kim, Sooyeol, Kennedy, Lauren C, Wolfe, Marlene K, Criddle, Craig S, Duong, Dorothea H, Topol, Aaron, White, Bradley J, Kantor, Rose S, Nelson, Kara L, Steele, Joshua A, Langlois, Kylie, Griffith, John F, Zimmer-Faust, Amity G, McLellan, Sandra L, Schussman, Melissa K, Ammerman, Michelle, Wigginton, Krista R, Bakker, Kevin M, Boehm, Alexandria B
• Format: Article
• Language: English
• Subjects: Chemistry; Clarifiers; COVID-19; Detection; Empirical analysis; Epidemiology; Health services; Influents; Laboratories; N gene; Nucleic acids; Production methods; Raw wastewater; Ribonucleic acid; RNA; Sensitivity; Severe acute respiratory syndrome; Severe acute respiratory syndrome coronavirus 2; Solids; Wastewater; Wastewater treatment
• ISSN: 2053-1400; 2053-1419
• DOI: 10.1039/d1ew00826a

Wastewater-based epidemiology has gained attention throughout the world for detection of SARS-CoV-2 RNA in wastewater to supplement clinical testing. Raw wastewater consists of small particles, or solids, suspended in liquid. Methods have been developed to measure SARS-CoV-2 RNA in the liquid and the solid fraction of wastewater, with some studies reporting higher concentrations in the solid fraction. To investigate this relationship further, six laboratories collaborated to conduct a study across five publicly owned treatment works (POTWs) where both primary settled solids obtained from primary clarifiers and raw wastewater influent samples were collected and quantified for SARS-CoV-2 RNA. Settled solids and influent samples were processed by participating laboratories using their respective methods and retrospectively paired based on date of collection. SARS-CoV-2 RNA concentrations, on a mass equivalent basis, were higher in settled solids than in influent by approximately three orders of magnitude. Concentrations in matched settled solids and influent were positively and significantly correlated at all five POTWs. RNA concentrations in both settled solids and influent were correlated to COVID-19 incidence rates in the sewersheds and thus representative of disease occurrence; the settled solids methods appeared to produce a comparable relationship between SARS-CoV-2 RNA concentration measurements and incidence rates across all POTWs. Settled solids and influent methods showed comparable sensitivity, N gene detection frequency, and calculated empirical incidence rate lower limits. Analysis of settled solids for SARS-CoV-2 RNA has the advantage of using less sample volume to achieve similar sensitivity to influent methods.