1998 Progress Report: Norwalk Virus-Like Particles (VLPs) for Studying Natural Groundwater DisinfectionEPA Grant Number: R824775
Title: Norwalk Virus-Like Particles (VLPs) for Studying Natural Groundwater Disinfection
Investigators: Grant, Stanley B. , Estes, Mary K. , Olson, Terese M. , Ogunseiten, Oladele
Institution: University of California - Irvine , Baylor College of Medicine
Current Institution: University of California - Irvine , University of Michigan
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 1995 through August 1, 1996 (Extended to October 31, 1999)
Project Period Covered by this Report: September 1, 1997 through August 1, 1998
Project Amount: $230,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water
Objective:An increasing number of communities in the United States rely on recycled wastewater for a portion of their drinking water supply, so-called "potable reuse." One obvious concern associated with this practice is the possibility that microbial pathogens present in the wastewater may contaminate water supplies and cause outbreaks of gastrointestinal disease. Filtration is commonly employed in potable reuse as one of several barriers to the transmission of microbial contaminants. The goal of this study is to evaluate how well filtration works as a treatment method for removing an important waterborne pathogen, Norwalk virus, from water. From a scientific perspective, our goal is to determine how microscale surface and solution chemistry affects the removal efficiency.
Progress Summary:During the review period, one manuscript describing our work was published in the journal Water Research, bringing to two the total number of journal articles generated by this research project to date. These two journal articles described the influence of solution and surface chemistry on the filtration of recombinant Norwalk Virus (rNV) particles and a filamentous bacteriophage that was isolated from reclaimed wastewater. In both studies, we found that pore fluid chemistry strongly affects filtration efficiency, by modulating the electrostatic interaction force between virus and collector on close approach. In particular, the removal of the rNV particles and the filamentous bacteriophage could be increased by adjusting the solution pH to the isoelectric point of the viruses, or by increasing the pore fluid ionic strength. At the microscale, these adjustments to the solution chemistry act to reduce the repulsive electrostatic force between virus and collector, leading to diffusion-limited virus filtration.
All of our previous studies have been conducted using well-defined sources of water (distilled water and reagent grade chemicals). During this third year of the grant, we set out to examine how well our results would extrapolate to systems more representative of field conditions. To this end, we conducted a suite of packed bed filtration experiments involving three different viruses (the bacteriophage MS2 and PRD-1 and the rNV particles) and two different sources of water, including groundwater and highly treated wastewater. In addition, we developed and tested a technique that allows us, for the first time, to characterize the spatial distribution of viruses retained within the filter. This methodological breakthrough permits direct testing of the standard filtration theories that are used to predict virus removal. These new experiments have yielded a very rich data set that has far-reaching implications for water reuse, as itemized below.
- We discovered that virus filtration does not follow first-order kinetics as commonly assumed, but is better described by a "fractal model" that recognizes the intrinsic heterogeneity of both the viruses and the collectors in natural systems.
- The fractal model of filtration predicts a slow power-law decay in virus concentration with distance, instead of the fast exponential decay predicted by standard theory. The power-law nature of virus filtration is consistent with our experimental results. The practical import of this result is that the first-order kinetics utilized for designing potable reuse systems can vastly over-predict the removal of viruses by filtration. From a modeling perspective, our results suggest that there is no single rate constant that can be found to characterize virus filtration and hence, existing models for virus transport in the subsurface (e.g., VIRALT) may be fundamentally flawed.
- For the experiments conducted with treated wastewater, we found that natural organic matter (NOM) present in the wastewater significantly attenuated virus filtration, presumably by forming a steric and/or electrosteric barrier to virus deposition. Hence, virus removal efficiencies could be strongly affected by the NOM concentration in the wastewater being recycled.
These results will be written up as journal manuscripts during the final (no-cost extension) year of the project. These results also will be summarized in the Ph.D. dissertation by the graduate student that was funded under this project, Mr. Jeremy Redman. Mr. Redman plans to defend his Ph.D. on July 1, 2000.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 15 publications||2 publications in selected types||All 2 journal articles|
||Redman JA, Grant SB, Olson TM, Adkins JM, Jackson JL, Castillo MS, Yanko WA. Physicochemical mechanisms responsible for the filtration and mobilization of a filamentous bacteriophage in quartz sand. Water Research, January 1999;33(1):43-52.||
R824770 shared with R824775 (Final)