Virus rejection by the reverse osmosis-ultrafiltration processes

Rejection of viruses by commercial grade asymmetrical cellulose acetate membranes commonly used in the ultrafiltration and reverse osmosis processes was evaluated. Various concentrations of coliphage T2 and poliovirus were innoculated in the feed water of a bench scale ultrafiltration-reverse osmosis unit and virus concentrations in the produce were determined. The insoluble polyelectrolyte technique for concentrating extremely low levels of virus was modified and standardized for use in the study. Membrane penetration studies indicated that limited numbers of virus passed the membranes. The penetration of viruses may be attributable to the presence of random areas of imperfect crosslinkage of the cellulose acetate in the dense layer of the membrane. Despite limited virus penetration, all of the cellulose acetate membranes used in this study rejected an extremely high percentage of the viruses and provided a product water of excellent quality.