Driving factors for bioclogging of pores and porous media

Understanding the interplay between hydrodynamics and biogeochemical processes is of growing importance in environmental applications and studies, especially in the fields of bioremediation and ecology. The majority of the microbial communities living in soil have a surface-attached lifestyle, allowing them to form biofilms. The biofilm growth influences pore geometries by clogging them and thus redirecting the flow, which in return affects biofilm development and local mass transport. After initially clogging single pores, the biofilm structure expands to larger clusters before eventually clogging the porous medium entirely. We study these processes with a soil-born microorganism, Bacillus subtilis, in microfluidic devices mimicking porous media to get a mechanistic understanding of the driving factors of bioclogging of porous media on different scales.

Carefully designed porous geometries were used for the experiments to study biofilm growth under different flow conditions. After being seeded with bacteria, devices were exposed to a continuous nutrient flow during several days. Continuously monitoring the pressure evaluation and imaging the biofilm growth using Brightfield microscopy allowed a high temporal resolution of biofilm growth processes.

An interplay of hydraulic parameters and geometric features of the porous medium as well as the mass flow rate of nutrients drive the speed of pore clogging. Besides the pore scale clogging, the initiation of biofilm formation as well as the speed of clogging of the entire medium are influenced by the before mentioned parameters. Furthermore, the size and number of the biofilm clusters formed seem to drive the medium scale clogging. This leads to inverting trends concerning the clogging rate in one pore when compared to the porous medium scale for different pore sizes. These results shed light on the pore-scale mechanism as well as driving parameters of biofilm formation and bioclogging and their transferability to the next larger scale, e.g. a porous medium.