Virus removal by microfiltration: Effects of electrostatic and hydrophobic interactions

Virus removal by membrane filtration is challenging due to the small size of these microorganisms. For microfiltration (MF) membranes, which have pore sizes above 100 nm (i.e., larger than most viruses), surface interactions are of critical importance in determining virus removal. The present study aims to evaluate the impact of surface interactions on virus removal by MF membranes wherein predictions by extended DLVO (XDLVO) modeling are compared with experimental data on virus clearance. The study employed four viruses (MS2, Qβ, phiX174, phi6), two MF cartridge membranes (nylon and PTFE), and several solution chemistry conditions to cover a range of virus-membrane surface interaction scenarios. For the hydrophilic nylon membrane, the highest log removal values (LRVs) were observed at the pH when the filter carried a slightly positive charge. For the hydrophobic PTFE membrane, higher LRVs were attained for high ionic strength solutions, wherein the electric double layer was compressed, even at pH values where the filter was negatively charged. We conclude that the electrostatic interaction determines whether viruses can approach the membrane and hydrophobic interactions are a critical factor in retaining viruses near the membrane surface, preventing viral leakage into the filtrate. The surface interactions have to be considered in virus membrane filtration.