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Transport of Cryptosporidium parvum oocysts in a silicon micromodel
Yuanyuan Liu1, Changyong Zhang, Markus Hilpert
1Department of Civil and Environmental Engineering, the Center of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
Abstract:
Effective removal of Cryptosporidium parvum oocysts by granular filtration requires the knowledge of oocyst transport and deposition mechanisms, which can be obtained based on real time microscopic observation of oocyst transport in porous media. Attachment of oocysts to silica surface in a radial stagnation point flow cell and in a micromodel, which has 2-dimensional (2-D) microscopic pore structures consisting of an array of cylindrical collectors, was studied and compared. Real time transport of oocysts in the micromodel was recorded to determine the attached oocyst distributions in transversal and longitudinal directions. In the micromodel, oocysts attached to the forward portion of clean collectors, where the flow velocity was lowest. After initial attachment, oocysts attached onto already attached oocysts. As a result, the collectors ripened and the region available for flow was reduced. Results of attachment and detachment experiments suggest that surface charge heterogeneity allowed for oocyst attachment. In addition to experiments, Lattice-Boltzmann simulations helped understanding the slightly nonuniform flow field and explained differences in the removal efficiency in the transversal direction. However, the hydrodynamic modeling could not explain differences in attachment in the longitudinal direction.
Insights
Understanding Cryptosporidium parvum oocyst transport in granular filters is key for effective removal. Real-time microscopic observation revealed oocyst attachment mechanisms and deposition patterns in porous media.
Area of Science:
- Environmental Science
- Microbiology
- Fluid Dynamics
Background:
- Effective removal of Cryptosporidium parvum oocysts is crucial for water safety.
- Understanding oocyst transport and deposition mechanisms in granular media is essential for optimizing filtration processes.
Purpose of the Study:
- To investigate oocyst transport and attachment mechanisms in porous media using real-time microscopic observation.
- To compare oocyst deposition in a radial stagnation point flow cell and a 2-D micromodel.
Main Methods:
- Real-time microscopic observation of oocyst transport in a micromodel with cylindrical collectors.
- Attachment and detachment experiments.
- Lattice-Boltzmann simulations to analyze flow fields.
Main Results:
- Oocysts preferentially attached to the forward portion of collectors where flow velocity was lowest.
- Oocysts formed aggregates on collectors, reducing available flow regions.
- Surface charge heterogeneity was identified as a factor in oocyst attachment.
- Lattice-Boltzmann simulations explained transversal removal efficiency differences but not longitudinal ones.
Conclusions:
- Real-time observation and simulations provide insights into oocyst deposition in granular media.
- Surface properties and flow dynamics significantly influence oocyst removal efficiency.
- Further research is needed to fully understand longitudinal attachment differences.
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