Role of hydrophobic and electrostatic interactions for initial enteric virus retention by MF membranes

Membranes are of increasing interest for the removal of human enteric virus es from wastewater, especially when the goal of treatment is reuse. Limited work has been undertaken on fundamental issues such as aggregation and the role of electrostatic and hydrophobic interactions, as opposed to the siev ing of viruses by membranes. One apparently critical factor would be the is o-electric point (pI) of a virus. As an example of a worst-case model virus , the retention of bacteriophage MS-2 was investigated using hydrophobic (G VHP) and hydrophilic (GVWP) 0.22 mum MF membranes at different pH levels an d with different salts. High retention levels were measured at the iso-elec tric point of MS-2, pH 3.9 (5 log retention) and pH 7 (4.3 log retention) i n the presence of salts and with a hydrophobic membrane. When retention was compared on a hydrophilic membrane, it was clear that hydrophobic interact ions dominated virus retention, and this was improved by salt, presumably c ausing reduction of the Gouy double-layer when MS-2 was charged (pH 7). Thi s paper shows that knowledge of the adsorption characteristics of viruses a nd the suspending conditions are important to predict removal of viruses by hydrophobic MF membranes, and discusses some of the practical implications of these important hydrophobic interactions. (C) 2001 Elsevier Science B.V . All rights reserved.