Using synchrotron-based X-Ray microtomography and functional contrast agents in environmental applications

Despite very rapid development in commercial X-ray tomography technology, synchrotron-based tomography facilities still have a number of advantages over conventional systems. The high photon flux inherent of synchrotron radiation sources allows for (i) high resolution to micro- or nanometer scales depending on the individual beamline, (ii) rapid acquisition times that allow for collection of sufficient data for statistically significant results in a short amount of time as well as prevention of temporal changes that would take place during longer scan times, and (iii) optimal implementation of contrast agents that allow us to resolve features that would not be decipherable in scans obtained with a polychromatic radiation source. This chapter highlights recent advances in capabilities at synchrotron sources, as well as implementation of synchrotron-based computed microtomography (CMT) to two topics of interest to researchers in the soil science, hydrology, and environmental engineering fields, namely multiphase flow in porous media and characterization of biofilm architecture in porous media. In both examples, we make use of contrast agents and photoelectric edge-specic scanning (single- or dual-energy type), in combination with advanced image processing techniques

Visualization and characterization of biofilm spatial distribution in porous media using x-ray computed microtomography

This work focuses primarily the development of methods for imaging microbial biofilms in opaque porous media using x-ray computed microtomography (CT). Two methods for evaluating biofilms in porous media are presented. The first focuses on the addition of silver-coated, hollow glass microspheres to a biofilm-containing micro-model. The silver-coated microspheres affix to the surface of biofilm present in the hydraulically available pore space providing a surface coating at the biofilm-aqueous phase interface which is detectable using synchrotron-based CT scanning. Through image processing, the silver microspheres were able to be isolated and a triangulated mesh representing the biofilm surface was able to be reconstructed and quantified. The second method focuses on the addition of a pore-filling barium sulfate contrast agent to biofilm column growth reactors. Methods for analyzing and quantifying data sets collected using both polychromatic and monochromatic (synchrotron-based) CT are presented. Finally, the barium sulfate method for imaging biofilm using synchrotron-based x-ray CT is applied to a biofilm growth experiment evaluating growth of Shewanella oneidensis under hydraulic loading rates corresponding to Reynolds numbers of 0.1, 1.0 and 10. Results from this study show good agreement between laboratory measured changes in hydraulic conductivity and hydraulic conductivity estimates generated using the segmented CT data sets and the Kozeny-Carman model for estimating hydraulic conductivity using porosity measures