Impact of coagulation on SARS-CoV-2 and PMMoV viral signal in wastewater solids

Wastewater surveillance (WWS) has received interest from researchers, scientists, and public health units for its application in monitoring active COVID-19 cases and detecting outbreaks. While WWS of SARS-CoV-2 has been widely applied worldwide, a knowledge gap exists concerning the effects of enhanced primary clarification, the application of coagulant to primary clarifiers, on SARS-CoV-2 and PMMoV quantification for reliable wastewater-based epidemiology. Ferric-based chemical coagulants are extensively used in enhanced clarification, particularly for phosphorus removal, in North America, and Europe. This study examines the effects of coagulation with ferric sulfate on the measurement of SARS-CoV-2 and PMMoV viral measurements in wastewater primary sludge and hence also settled solids. The addition of Fe 3+ to wastewater solids ranging from 0 to 60 mg/L caused no change in N1 and N2 gene region measurements in wastewater solids, where Fe 3+ concentrations in primary clarified sludge represent the conventional minimum and maximum concentrations of applied ferric-based coagulant. However, elevated Fe 3+ concentrations were shown to be associated with a statistically significant increase in PMMoV viral measurements in wastewater solids, which consequently resulted in the underestimation of PMMoV normalized SARS-CoV-2 viral signal measurements (N1 and N2 copies/copies of PMMoV). pH reduction from coagulant addition did not contribute to the increase in PMMoV measurements. Thus, this phenomenon is likely attributed to the partitioning of PMMoV particles to the solids of wastewater from the bulk liquid phase of wastewater.