Investigation of Biofilm Growth within a Monodisperse Porous Medium under Fluctuating Water Level Assessed by Means of MRI

Microorganisms settle in diverse partially saturated porous media in the form of biofilms. The alteration of hydraulic properties and diffusive transport processes occurs simultaneously with biofilm growth in porous media. Imaging methods offer the ability to directly visualize and quantify alterations on the pore scale. However, imaging methods have mainly observed biofilm growth in completely saturated porous media. The current study used magnetic resonance imaging (MRI) to dynamically visualize biofilm growth within a porous medium under alternating drainage and flushing events. Prior to the MRI experiments, the sample was cultivated for 6 days within a porous medium consisting of 2 mm glass spheres. Starting from day 6, growth was monitored using MRI over a period of 7 days. The approach allowed for a visualization of all fractions (biofilm, water, air, and porous material) after drainage as well as flushing events. Biofilm was found to preferentially grow within permanently wetted areas situated next to pore throats. Furthermore, an increase in the water retention and connectivity of the liquid phase was found. The largest liquid cluster covered 11% (day 6) and 91% (day 12) of the total retained water, suggesting that biofilm growth might improve diffusive transport processes within partially saturated porous media.