Grantee Research Project Results
Final 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 Amount: $536,316
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
The objectives of this research project were to: (1) evaluate the merits of bank filtration for removing/controlling pathogens; (2) establish the merits of using the removal of particles and other parameters as surrogates for pathogen removal; and (3) explore the mechanisms of pathogen transport during riverbank filtration (RBF) and important system variables.
Summary/Accomplishments (Outputs/Outcomes):
RBF is a process by which river water is subjected to ground passage prior to its extraction and use as a drinking water source. Research was conducted to evaluate the benefits of RBF in regard to control of microorganisms at three Midwest United States drinking water utilities that currently use RBF (the Indiana-American Water facilities at Jeffersonville and Terre Haute, IN, and the Missouri-American Water facility at Parkville, MO) and to explore the transport of microorganisms, particles, and potential surrogate parameters through laboratory-scale riverbank sediment columns under different physical/chemical conditions. In addition, the molecular analysis of viral nucleic acid by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was compared to viral infectivity assays to elucidate the public health risks posed by viral transport through sediments.
Key findings and implications of this research are presented in the following two sections, which focus on the two major phases of this research project: (1) field monitoring; and (2) bench-scale riverbank sediment column experiments.
Field Monitoring Study
Two wells at each site were chosen for the field study. At the Indiana-American Water study site, located along the Ohio River in Jeffersonville, IN, Well #9 (580 feet [177 m] from the river) and Well #2 (100 feet [30 m] from the river) were sampled for this study. At the Indiana-American Water study site, along the Wabash River in Terre Haute, IN, the Collector Well (located 90 feet [27 m] from the Wabash River, with horizontal arms extending out from the center at a depth of approximately 80 feet [24 m] below the river bottom) and Well #3 (400 feet [122 m] from the river) were sampled for this study. Finally, at the Missouri-American Water facility, located along the Missouri River in Parkville, MO, Well #4 and Well #5 (both wells located approximately 120 feet [37 m] from the river) were sampled for this study.
Average concentrations and log reductions of the protozoan pathogens Cryptosporidium and Giardia upon RBF at the three study sites could not be accurately determined because of the low and variable concentrations in the river waters and the lack of detectible concentrations in the well waters, demonstrating the importance of potential surrogate and indicator parameters for measuring RBF effectiveness. Average concentrations of aerobic and anaerobic spore-forming bacteria, which have both been proposed as potential surrogates for the protozoans, were reduced at the three facilities by 0.8 to more than 3.1 logs and 0.4 to more than 4.9 logs, respectively. Average concentrations of male-specific and somatic bacteriophage were reduced by more than 2.1 logs and greater than or equal to 3.2 logs, respectively. Total coliforms were rarely detected in the well waters, with 5.5 and 6.1 log reductions in average concentrations at the two wells at one of the sites relative to the river water. Average turbidity reductions upon RBF at the three sites were between 2.2 and 3.3 logs.
Riverbank Sediment Column Study
The results of the column experiments with riverbank sediment demonstrated the importance of the aquifer and source water characteristics (including size distribution and pore water chemistry) on the efficiency of the RBF process for controlling microorganism concentrations. Transport of Escherichia coli CN13, Clostridium perfringens spores, Cryptosporidium oocysts, and 4.5-mm latex microspheres was very sensitive to the physical (e.g., size distribution) and chemical characteristics (e.g., pH, organic carbon content, iron content) of the sediment. There was little breakthrough observed in sediment with a d10 of 0.045 mm, pH of 4.6, 0.36 percent organic carbon, and 0.16 percent iron (extractable by sodium pyrophosphate), whereas nearly complete breakthrough was observed in sediment with a d10 of 0.10, pH of 4.8, 0.20 percent organic carbon, and 0.10 percent iron, and in sediment with a d10 of 0.13 and pH of 4.8. Transport of the viruses (particularly bacteriophage MS2 and poliovirus) was less dependent on the sediment characteristics.
Particle counts were found to be a poor quantitative surrogate for the transport of latex microspheres through aquifer sediments because of the presence of sediment-borne particles in the effluent. Particle counts, however, may still be useful as an indicator of a change in microbial removal efficiency. Transport of bacteriophage MS2 was conservative relative to that of poliovirus under the conditions tested, indicating its potential value as a conservative surrogate for the human virus. Quantitative RT-PCR detected viruses in the columns with high sensitivity. The differences in the virus concentrations detected by qRT-PCR and by plaque assay increased over time, reflecting the higher level of inactivated viruses in the samples over time. This difference indicates that qRT-PCR may overestimate the health risk of the samples because it detects both infective and inactivated viruses.
Conclusions:
The Long Term 2 Enhanced Drinking Water Treatment Rule (LT2ESWTR) provides utilities using RBF up to 1-log removal credit for Cryptosporidium. The results of this research demonstrated the ability of the RBF process to provide substantial reductions in microorganism concentrations relative to the raw river water. Low and variable concentrations of Cryptosporidium oocysts and Giardia cysts in the river waters prevented an accurate determination of removal efficiency during RBF, and despite the absence of significant concentrations in well waters, the data do not preclude the possibility of breakthrough of the protozoan pathogens if conditions became more favorable for transport through the aquifer (e.g., a sharp increase in protozoan concentrations in the river or loss of fine-grained sediment at the river/aquifer interface resulting from increased river flow).
Because of the uncertainty inherent in monitoring low and variable pathogen concentrations, evaluation of RBF efficiency must rely on surrogate or indicator parameters. Aerobic and anaerobic spore-forming bacteria, which have been proposed as surrogates for the protozoans, demonstrated 0.4- to more than 4.9-log removals upon RBF at the three study sites. If these bacteria are assumed to behave similarly to the protozoans, these data support the Cryptosporidium credits assigned to RBF by the LT2ESWTR (0.5- and 1.0-log reduction credits for wells located 25 feet and 50 feet from the river, respectively), and further demonstrate the potential for the removal of several log units higher than the current credits provide. There have been few studies, however, comparing pathogen and potential surrogate transport in RBF systems. Similarly, reductions of more than 2 logs of bacteriophage upon RBF at the three study sites demonstrate the potential for RBF to control virus concentrations, but little is known about the validity of using bacteriophage as surrogates for human viruses in RBF systems.
The column studies demonstrated a clear dependence of microorganism transport behavior in aquifer sediments on the specific characteristics of the system. The physical and chemical characteristics of the pore water (pH, ionic strength) and the sediment (size distribution, pH, organic matter content) have a significant impact on the removal efficiency of the RBF process. Additional variables such as flow rate, aquifer heterogeneity, and local climate are likely to impact microorganism transport in RBF systems.
Although the conservative approach of the LT2ESWTR is meant to provide adequate protection against waterborne disease, there should be a mechanism by which utilities using RBF can document and obtain additional credit for pathogen removal. Because of the site-specific nature of the RBF process, such a protocol should include careful characterization of the system, including the physical and chemical properties of the aquifer sediments and the surface and ground waters. The likely effects of system variables (e.g., river hydrology, water chemistry) on microorganism transport should be well studied. Furthermore, utilities using RBF and regulatory agencies have relied heavily on the use of surrogate and indicator parameters to evaluate removal of the pathogens. To this end, a better understanding of the relationship between transport of pathogens and more easily measured indicator/surrogate parameters would be greatly beneficial to the development of a uniform protocol to document RBF effectiveness.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 13 publications | 1 publications in selected types | All 1 journal articles |
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Type | Citation | ||
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Weiss WJ, Bouwer EJ, Aboytes R, LeChevallier MW, O’Melia CR, Le BT, Schwab KJ. Riverbank filtration for control of micoorganisms: results from field monitoring. Water Research 2005;39(10):1990-2001. |
R829011 (Final) |
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Supplemental Keywords:
river, bank, filtration, pathogens, Cryptosporidium, wells, groundwater, drinking water, public health, virus detection,, RFA, Scientific Discipline, PHYSICAL ASPECTS, Health, Water, Environmental Chemistry, Health Risk Assessment, Environmental Microbiology, Risk Assessments, 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.