Influence of virus analytical methods on the estimation of virus reductions by ultrafiltration

This study evaluated the influence of analytical methods on the quantitative estimation of viruses in recycled waters and their reductions by an ultrafiltration (UF) engineering-scale system. Adenoviruses, crAssphage, Pepper mild mottle virus (PMMoV), culturable male-specific and somatic coliphages selected through a comparative quantitative analysis were evaluated in UF feed and UF permeate using a combination of analytical methods for virus concentration and absolute quantification of virus genomes and infectious coliphages by digital PCR and plaque assays, respectively. Both methods of virus concentration, centrifugal ultrafiltration and the InnovaPrep CP Select™ Concentrating Pipette (CP), demonstrated similar performance for the recovery of viruses from UF feed and UF permeate, however the CP approach allowed more rapid sample filtration than centrifugal ultrafiltration. Procedures commonly applied for the detection of viruses in water generated different quantitative outcomes that were influenced by the type of virus and other natural sources of variation associated with UF feed and UF permeate water. These quantitative outcomes in virus measurements led to highly variable estimations of virus reductions ranging from no apparent reduction to a maximum of 2-log₁₀. These results indicate that more accurate estimations of virus levels and reductions in water purification processes require adjustments in analytical procedures under the wide variety of water characteristics associated with each stage of treatment. A thorough understanding of the interactions between structural features of natural occurring viruses in recycled waters and water quality characteristics is crucial for improving virus recoveries and for the assessment of membrane-based treatment systems as barriers against microbial targets of environmental and public health concern.