Nanoscale roughness controls reversible virus attachment and the setback distance to protect human health

Pathogenic viruses in groundwater pose a risk to human health when contaminated groundwater is used for drinking water and/or to irrigate fresh produce. A setback distance from a contaminated water source is commonly used to ensure adequate virus removal in aquifers to protect human health. A transport model was used to determine the sensitivity of factors that influence the setback distance to achieve a 12 log₁₀ reduction in virus concentrations. This analysis revealed that the reversibility of attached viruses strongly impacts the required setback distance, but available literature indicates large irreversibly attached fractions. Systematic studies were therefore conducted to better understand and quantify underlying factors that influence virus attachment, detachment, and the reversible fraction using interaction energy calculations, the Maxwellian kinetic energy model for diffusion, and/or energy and torque balances. Irreversible attachment is demonstrated to be controlled by charge heterogeneity (CH) parameters, with higher values occurring for larger probabilities of CH, larger sized CH, more positive CH, at higher ionic strength, and for smaller sized viruses. Virus detachment and reversible fractions occurred due to the combined influence of CH and nanoscale roughness (NR). Reversible attachment was greater for smaller roughness fractions on the virus, but similar behavior occurred for roughness on the solid or both the virus and solid. Solid phase inactivation played an important role in the setback distance when the reversible fraction was high but can be neglected when it is low. These results provide valuable insight to optimize conditions to remove viruses and minimize required setback distances to protect groundwater supplies and human health.