2002 Progress Report: Microbial Pathogen Removal During Bank FiltrationEPA Grant Number: R829010
Title: Microbial Pathogen Removal During Bank Filtration
Investigators: Ryan, Joseph N. , Harvey, Ronald W. , Elimelech, Menachem
Institution: University of Colorado at Boulder , United States Geological Survey , Yale University
EPA Project Officer: Page, Angela
Project Period: September 1, 2001 through August 31, 2004 (Extended to August 30, 2005)
Project Period Covered by this Report: September 1, 2001 through August 31, 2002
Project Amount: $506,006
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
The overall objective of this research project is to develop a model of oocyst transport in porous media that can accommodate the physical and geochemical heterogeneity present in alluvial valley aquifers used for riverbank filtration. The specific objectives of this research project are to determine the effect of: (1) microbe size on transport; (2) physical heterogeneity of the porous media on transport; (3) geochemical heterogeneity of the porous media on transport; (4) microbe release from unfavorable attachment sites; and (5) high pumping rates on microbe release. Our incomplete understanding of processes and properties affecting pathogenic microbe transport during riverbank filtration is currently limiting our ability to predict the effectiveness of this water treatment option. We propose a series of fundamental experiments designed to better understand the effects of microbe size, physical and geochemical heterogeneity of the porous media, and high pumping rates on the transport of Cryptosporidium parvum oocysts in alluvial valley aquifers used for riverbank filtration.
A study of the zeta potential of C. parvum oocysts from three different suppliers and two different inactivation treatments (heat, formalin) was conducted. Based on this study, a supplier was selected and an inactivation treatment was chosen. No significant difference was observed between the zeta potential of live, heat-treated, and formalin-treated oocysts.
A laboratory flow-through column experiment was set up and tested to explore the effect of physical and geochemical heterogeneity on the transport of C. parvum oocysts. Experiments were conducted to measure the transport properties of oocysts through sands of five different grain sizes and seven different amounts of ferric oxyhydroxide coatings. The results were used to plan and interpret the intermediate-scale tank experiment.
The intermediate-scale aquifer tank experiment was planned. Sands from different suppliers were evaluated for purity and grain size. Sands of five different grain sizes (from 0.12 to 0.86 mm median grain size) were selected for the experiments and obtained in large quantities. The hydraulic conductivities of the sands were measured. Portions of the sands were coated with ferric oxyhydroxides to create a total of 13 different sands to generate a physically and geochemically heterogeneous porous medium in the aquifer tank. A length of 5 m and a height of about 1 m were selected for the tank based on preliminary modeling. A random-packing plan was created, and the tank was packed with the sands in 5 by 20 cm units. Flow was tested using a sodium nitrate tracer. The tracer transport was modeled using a two-dimensional transport model.
A laboratory flow-through column and a stagnation point flow apparatus were set up to explore the mechanisms governing the attachment and detachment of C. parvum oocysts from model surfaces (quartz, glass). A set of experiments was conducted on the effect of ionic strength on oocyst transport. The experiments suggested that secondary minimum attachment is important for oocysts.
Over the next 2 years, our work will focus on laboratory column, aquifer tank, and stagnation point flow experiments. The laboratory column experiments will explore: (1) the effect of microbe size; (2) the effect of physical and geochemical heterogeneity on microbe transport; and (3) the effect of flow rate on oocyst release. These experiments will utilize porous media of higher purity than those obtained in bulk for the aquifer tank experiment. The aquifer tank experiment examining the transport of oocysts in the random physically and geochemically heterogeneous porous medium will be conducted and modeled. The stagnation point-flow experiments will explore the effects of solution composition, pH, and ionic strength on the mechanisms of oocyst attachment and detachment.