Grantee Research Project Results
2004 Progress Report: Study of Particle and Pathogen Removal During Bank Filtration of River Waters
EPA Grant Number: R829011Title: Study of Particle and Pathogen Removal During Bank Filtration of River Waters
Investigators: Bouwer, Edward J. , Schwab, Kellogg J. , O'Melia, Charles R. , LeChevallier, Mark W. , Aboytes, Ramon
Institution: The Johns Hopkins University
EPA Project Officer: Page, Angela
Project Period: August 24, 2001 through August 23, 2004 (Extended to August 23, 2005)
Project Period Covered by this Report: August 24, 2003 through August 23, 2004
Project Amount: $536,316
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
Riverbank filtration (RBF) is a process that subjects river water to ground passage prior to its use as a drinking water source. Experience with RBF in Europe and more recently in the United States has demonstrated significant improvements in raw water quality, including removal of natural organic matter, biodegradable compounds, pesticides, microbes, and other contaminants. Little is known, however, about the extent to which RBF may reliably remove Giardia, Cryptosporidium, and other pathogens (e.g., bacteria and viruses) from the river water. The objectives of this research project are to: (1) evaluate the merits of RBF for removing/controlling pathogens in drinking water supplies; and (2) establish the merits of using removal of particles and other potential water quality indicator parameters as surrogates for pathogen removal.
Progress Summary:
This research project consists of: (1) field studies to document actual changes in pathogen and particle concentrations from rivers of similar source quality in the context of variations in subsurface travel distances, pumping rates, season, porous medium properties, and residence times; and (2) parallel laboratory column studies with aquifer media to evaluate relationships among the transport of pathogens and potential surrogate parameters (including particle counts, bacterial spores, and bacteriophage). Column experiments with different media characteristics (grain size, pH) and feed solution conditions (flow rate, ionic strength, and temperature) were performed to evaluate the sensitivity of the microorganism, particle, and surrogate behavior to the aquifer sediment and source water characteristics.
The results of the field monitoring phase of this research project illustrate the need for a better understanding of the mobility of pathogens of interest (particularly Giardia and Cryptosporidium) in comparison to the mobility of potential surrogate and indicator parameters in RBF systems. The potential surrogate/indicator parameters measured here were present in the river waters in significantly higher concentrations and occurred more frequently during the monthly sampling campaign than the protozoan pathogens, providing a better characterization of the input concentrations to the system. The parameters measured, however, also exhibited a large range of reductions in the well waters relative to the river waters (removals of less than 1 log to greater than 6 logs). A better understanding of how such parameters behave during RBF relative to the pathogens is essential as the industry moves toward a protocol to assign treatment credits for using RBF to control microorganisms.
The current results of the column study phase of this research project demonstrate the importance of the sediment grain size distribution on the transport of the pathogens and potential surrogates. All microbes and surrogates broke through nearly completely in columns with effective grain sizes of 0.10 and 0.13 mm. Mixtures fed through columns with 0.045 mm effective grain diameter showed no measurable breakthrough after 14 pore volumes. The large difference in breakthrough behavior suggests that the transport of the microorganisms and particles through the aquifer sediment is very sensitive to the size distribution of the sediments. Column experiments demonstrated higher die-off rates of viruses (by comparing plaque assay and molecular assay results) at a pH of 5.5 relative to a neutral pH and lower die-off rates at 4°C compared to room temperature.
Particle counts in six size ranges (2-3 μm, 3-5 μm, 5-7 μm, 7-10 μm, 10-15 μm, and > 15 μm) were taken during several column experiments to evaluate whether they tracked the breakthrough of the microorganisms. The results indicate that a significant number of particles in the effluent were borne in the column itself, as flow through the sediment mobilized sediment particles. These data demonstrate that the presence of sediment-borne particles in bank-filtered river waters will likely limit the usefulness of particle counts as a surrogate for pathogen transport through the aquifer.
Future Activities:
We will complete the column study phase of this research project, and the results will be analyzed and summarized. The importance of physical and chemical characteristics (e.g., pH, ionic strength, sediment size distribution) on the transport behavior of the microorganisms and particles will be evaluated, particularly in regard to the relationship between the pathogens and the potential surrogate parameters.
Effluent samples assayed for viable MS2 bacteriophage and polioviruses using classical cell culture methods also were analyzed for total virus loads utilizing quantitative reverse transcription-polymerase chain reaction (qRT-PCR). qRT-PCR quantifiably detects nucleic acid from infectious virions and noninfectious (i.e., inactivated) viruses present in analyzed samples, potentially providing a more accurate estimate of total viral breakthrough during RBF. Statistical analysis on samples collected and tested by both infectivity assays and qRT-PCR will be conducted during the no-cost extension period to provide an understanding regarding the total virus removal efficiency during RBF.
The results of the field and column studies will be integrated and summarized in the context of their implications for the future use and regulation of riverbank filtration as well as for future research needs. A final report on the results of this project will be prepared and submitted.
Journal Articles:
No journal articles submitted with this report: View all 13 publications for this projectSupplemental Keywords:
pumping, wells, treatment, regulations, water quality, microorganisms, Giardia, Cryptosporidium, pathogens, aquifer,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Water, Environmental Chemistry, Health Risk Assessment, Risk Assessments, Environmental Microbiology, Environmental Monitoring, Physical Processes, Drinking Water, clostridium, groundwater disinfection, microbial contamination, pathogens, river water , monitoring, ecological risk assessment, disinfection byproducts, aquifer characteristics, microbiological organisms, water quality parameters, waterborne disease, exposure and effects, disinfection byproducts (DPBs), exposure, cryptosporidium , drinking water distribution system, particle counts, treatment, microbial risk management, human exposure, water quality, drinking water contaminants, drinking water treatment, Giardia, water treatment, riverbank filtrationProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.