The influence of electrostatic interactions and heterogeneity on the packed bed filtration of Norwalk virus and coliphage indicators

Norwalk virus is one of the leading causes of waterborne non-bacterial gastroenteritis. However, the environmental factors that influence its transport in porous media are poorly understood, in part because of difficulties in culturing this virus. These difficulties have been overcome by employing recombinant Norwalk virus particles that are morphologically and antigenically similar to native NV, but are noninfectious. For the first time, studies examining the influence solution chemistry has on the packed-bed filtration of Norwalk virus were conducted. These results are compared with similar experiments conducted with viruses that are often used as indicators of water quality.; With respect to physicochemical filtration, viruses are primarily stabilized by repulsive electrostatic interactions arising upon close approach to the quartz filter media. The degree of filtration is shown to be strongly influenced by the surface electrical properties of the virus, which can be modulated by adjusting the solution chemistry of the pore fluid. When the repulsive electrostatic forces are “turned off”, viruses are rapidly filtered. Contrary to extant theory, larger viruses are more effectively filtered than smaller viruses; indicating that small viruses—such as the male-specific coliphage MS2—may be useful as conservative indicators for human viruses.; A new model is derived for particle filtration that accounts for heterogeneity at two different spatial scales. Heterogeneity at the particle/collector scale (microscale heterogeneity) leads to a slow power-law decay of contaminant concentration with distance, instead of the fast exponential decay predicted by the standard model. Heterogeneity at the filter scale (macroscale heterogeneity) provides another level of complexity. Under “dirty bed” conditions, macroscale heterogeneity dominates virus removal rates. Model predictions are verified by experimental results utilizing the recombinant NV particles.