Feasibility of Covid-19 Virus Detection in Upstream Reaches of Sanitary Sewer Systems

Detecting Covid-19 and other viruses in sanitary wastewater systems has become common in recent years. However, the majority of monitoring efforts are conducted by collecting samples at a wastewater treatment plant over an extended period of time. This procedure loses memory of the nature of the unknown source further upstream in the collection system. This study was conducted to investigate the feasibility of detecting, in principle, individual sources of virus by monitoring within the upstream reaches of a sewer system. It has also been demonstrated that Covid-19 virus are more concentrated in fecal material that is primarily transported in solid phase in the sewer system. We performed experiments by adding surrogates (fluorescent dye and a deactivated bovine coronavirus, BCoV) for virus laden material by adding the source via a toilet flush at three locations within buildings at varying upstream distances from the monitoring station, generally on the order of 500-2000 m. Various sampling strategies were tested and the final configuration involved addition of the fluorescent dye followed two hours later by the addition of BCoV. The fluorescent dye was monitored continuously while BCoV was collected in 10-minute samples. The dye concentration profiles were analyzed to estimate the longitudinal dispersion coefficient and compared to formulas developed for idealized point source discharges. The BCoV profiles were represented by about ten ten-minute samples. They were found to exhibit a similar pattern to the fluorescent dye profile in some cases. In other cases, there was evidence that the solids were detained within to building lead to the collection sewer, suggesting that the longitudinal flow distribution, in particular low flows in the upper reaches of a collection system could have important effects on the travel time of the tracers, making it difficult to estimate locations of sources in such a system. Recommendations were developed for sampling frequency to ensure that a point source could be detected.