Time-resolved X-ray micro-tomography of a bio-degraded residual oil phase in porous media.
A. E. Larue, L. Bernard, Y. Davit, M. Quintard, M. Marcoux
In the context of bio-remediation of residual hydrocarbon in soils, we seek to understand the kinematics of bacterial degradation amongst the different phases of a polluted soil in the saturated zone namely the aqueous, oily and biofilm phases. In this work, we image a bioreactor consisting of a centimetric, water-saturated sand column within which a residual oil saturation of n-C16 has been established. An indigenous P. Fluorescens strain from a polluted site is used for biodegradation. The system is placed in a continuous liquid flow and under controlled bio-mechanical conditions (differential pressure, O 2 consumption and NPK values) as we follow the temporal evolution of the residual oil saturation using X-ray micro-tomography imaging (pixel size 19 μm). This powerful tool is well-known for investigating porous media systems 1 and, through the use of selected contrast agents, 3D images of the different phases can be obtained. We used the Python library Image Processing Software Development Kit ® (IPSDK) created by Reactiv’IP which is specially adapted for the processing of large tomographic images. Several metrics concerning the residual oil phase are acquired such as the spatial distribution of the oil blobs, their individual volume, size and available surface area for mass exchange. Due to the large size of the highly resolved images, High Performance Computing resources of CALMIP supercomputing centre under the allocation 2016-[p12166] was used. Tracking of the temporal evolution of individual blobs both at the Darcy and pore scales is thus achieved, unlocking important information on the kinematics of mass exchange such as rate of degradation to the ratio of available surface area along with preferential flow zones. We also determined a Representative Elementary Volume (REV), for both porosity and oil saturations, to thereafter carry out pore scale simulations for comparison with experimental data.
