Concentration of Virus Particles from Environmental Water and Wastewater Samples Using Skimmed Milk Flocculation and Ultrafiltration.

Water and wastewater-based epidemiology have emerged as alternative methods to monitor and predict the course of outbreaks in communities. The recovery of microbial fractions, including viruses, bacteria, and microeukaryotes from wastewater and environmental water samples is one of the challenging steps in these approaches. In this study, we focused on the recovery efficiency of sequential ultrafiltration and skimmed milk flocculation (SMF) methods using Armored RNA as a test virus, which is also used as a control by some other studies. Prefiltration with 0.45 µm and 0.2 µm membrane disc filters were applied to eliminate solid particles before ultrafiltration to prevent the clogging of ultrafiltration devices. Test samples, processed with the sequential ultrafiltration method, were centrifuged at two different speeds. An increased speed resulted in lower recovery and positivity rates of Armored RNA. On the other hand, SMF resulted in relatively consistent recovery and positivity rates of Armored RNA. Additional tests conducted with environmental water samples demonstrated the utility of SMF to concentrate other microbial fractions. The partitioning of viruses into solid particles might have an impact on the overall recovery rates, considering the prefiltration step applied before the ultrafiltration of wastewater samples. SMF with prefiltration performed better when applied to environmental water samples due to lower solid concentrations in the samples and thus lower partitioning rates to solids. In the present study, the idea of using a sequential ultrafiltration method arose from the necessity to decrease the final volume of the viral concentrates during the COVID-19 pandemic, when the supply of the commonly used ultrafiltration devices was limited, and there was a need for the development of alternative viral concentration methods.