Unveiling the Viral Escape: Quantification of Microfloc-bound Viruses in Precoagulation and Membrane Filtration

Abstract The implementation of precoagulation prior to the physical removal process is expected to attain a high virus removal rate. However, a risk exists for viruses to form small flocs and subsequently escape into the effluent of physical removal processes. This study evaluated how the virus in the microflocs could be quantified by conventional virus quantification methods (Plaque assay and quantitative PCR (qPCR) assay). In this study, the microflocs dissolution phenomenon in a phosphate buffer solution was employed as a floc dissolving test and virus concentrations before and after floc dissolving were quantified. The findings revealed an increase in virus concentrations by > 1.0 − >3.9 log pfu/ml by the Plaque assay and by 1.7 − >4.0 log copies/ml by the qPCR assay, following the dissolution of microflocs prepared in the humic acid test water. In the case of treated wastewater, the concentration increases were confirmed in all samples by the Plaque assay and in 7 out of 8 samples by the qPCR assay. Fewer viruses were detected in the microflocs that remained undissolved by either Plaque assay or qPCR assay.