Resilient performance indicator virus for membrane filtration considering surface charge, hydrophobicity, and morphology

Highly abundant viruses in environmental waters/wastewaters-for example, Pepper Mild Mottle Virus (PMMoV), Aichi virus (AiV), and F-specific RNA coliphages-have been monitored as performance indicator viruses to evaluate the virus removal capacity of full-scale drinking and wastewater treatment systems. These viruses have also been employed in bench-scale challenge tests as performance indicators in place of pathogenic viruses. However, due to the difficulty of directly evaluating pathogenic virus behavior, the selection of appropriate indicators to ensure the safety of treatment processes remains under debate. Our study aims to identify a more resilient performance indicator virus for membrane filtration processes by examining the influence of surface charge, hydrophobicity, and morphology on removal efficiency. We measured the zeta potentials and contact angles of bacteriophage MS2, PMMoV, and AiV, and evaluated their adsorption to membrane surfaces, and removal efficiency by membrane filtration. PMMoV has a rod-shaped structure, whereas the others have a sphere-shaped structure. Although these viruses showed similar zeta potentials, their contact angles varied, indicating hydrophobicity strength in the order of MS2 < PMMoV < AiV. In filtration experiments, PMMoV showed the highest removal efficiency despite its intermediate hydrophobicity among the three viruses. AiV, the most hydrophobic virus, showed removal performance similar to that of MS2, the least hydrophobic virus. Our results indicate that the rod-shaped structure of PMMoV enhanced its removal by membrane filtration, and that the spherical viruses, such as MS2 and AiV, may serve as more resilient performance indicators. IMPORTANCE: This study combines physicochemical evaluations with discussions to propose a resilient performance indicator virus for membrane filtration processes. The charge characteristics and hydrophobicity of MS2, PMMoV, and AiV were experimentally evaluated. Although all three viruses exhibited similar surface charges, their hydrophobicity differed. However, these differences did not significantly influence virus removal by membranes. Instead, our findings highlight the critical role of viral morphology in governing removal behavior during membrane filtration. These results provide new insights into the selection of appropriate performance indicator viruses for both bench-scale and full-scale virus removal evaluations.