Microfiltration (MF) and Ultrafiltration (UF) for Sewage and Surface Water Concentration for SARS-CoV-2 and Other Enveloped Viruses' Detection in Wastewater-Based Epidemiology (WBE).
This study objective was to evaluate hollow fiber membranes for concentration of enveloped enteric viruses in sewage and surface water samples. Microfiltration (MF, 0.2 µm nominal pore size) and ultrafiltration (UF, 100 kDa molecular weight cut-off) hollow fiber membranes were compared for the concentration of the bovine respiratory syncytial virus, and the influence of initial sample volumes (1, 1.5, and 2 L), permeate recovery rates (60%, 70% and 80% of the initial volume collected as permeate, equivalent to volumetric concentration factors of 2.5, 3.3 and 5), and backwashing was assessed. Polyethylene glycol precipitation followed by centrifugation (PEG-C) was evaluated both as a stand-alone method and as a secondary step applied to the membrane concentrate. MF and UF membranes had a similar capacity to retain pollutants and to concentrate organic matter in most parameters and conditions (p > 0.05). In sewage, increasing the initial volume from 1 to 2 L raised recovery from 20.7 ± 0.1% to 30.0 ± 0.1% with MF and from 20.8 ± 0.1% to 25.3 ± 0.1% with UF (p < 0.05), whereas changes in the permeate recovery rate produced no significant differences (p > 0.05). In surface water recovery did not exceed 5.5%, and every increment in the permeate recovery rate produced a significant increase (p < 0.05). Backwashing had a stronger effect on RNA recovery than pore size or the remaining operational parameters, reaching 29.3 ± 9.3% with MF and 33.8 ± 13.7% with UF in sewage and nearly doubling recovery in surface water. In sewage, PEG-C alone (14.1%) was statistically similar to membrane filtration alone (12.1% to 12.3%, p > 0.05), while combining both techniques raised recovery to 23.0% to 25.5%. In surface water, membranes alone recovered 0.8% against 2.4% for PEG-C (p < 0.05), and the combination of UF with PEG-C reached 5.7%, making it a valid alternative, albeit more time consuming and requiring additional equipment. Recoveries are expressed as the ratio between the genome copy concentration in the concentrate and in the spiked sample; on a total genome copy basis they correspond to 4% to 9% in sewage and to about 1% in surface water.