Removal of pepper mild mottle virus by full-scale microfiltration and slow sand filtration plants

It is important to evaluate the removal of enteric viruses by drinking water treatment processes so that viral infection risk can be assessed and managed. However, evaluating the removal of enteric viruses by full-scale treatment processes can be challenging due to the low numbers of viruses and the presence of substances in the water samples that inhibit detection. In this study, we evaluated the removal of pepper mild mottle virus (PMMoV) by microfiltration (MF) and slow sand filtration (SSF) at two full-scale drinking water treatment plants in Japan, quantifying virus concentrations with real-time polymerase chain reaction (qPCR). The removal of PMMoV by MF ranged from 0.0 to >0.9 log(10), although concentrations were below the detection limit for half of the treated water samples. SSF removed PMMoV by up to 2.8 log(10); however, the removal efficiency decreased to 0.0-1.0 log(10 )under cold water temperatures. Process control showed that nucleic acid extraction and qPCR efficiency were inhibited in nearly 40% of water samples. Dilution, DAX-8, and ferrihydrite treatments for purification were effective in mitigating these inhibitory effects.