Mesoscale and microscale observations of biological growth in a silicon pore imaging element

Better physical understanding is needed of the processes affecting biological growth in aquifers, filtration beds, and recharge basins. Toward this end, a two-dimensional random width network pore model etched in a silicon wafer was developed to simulate microbial growth in porous media representative of fine sand. This Silicon Pore Imaging Element (SPIE) was seeded with a mixed culture and fed with 0.34 mM acetate under aerobic conditions and at fixed flow rate. Twelve filamentous colonies grew in a dense manner in the upgradient and lateral directions and at low density in the downgradient direction. Heterogeneous colonization led to empty zones. Particle tracking suggested rerouting of flow due to biomass growth. Microscale time-lapse measured filamentous growth rates (0.5 to 1.6 mu m/min) were in good agreement with measured mesoscale colony expansion rates. Rather than the microscale concept of biomass developing at the surface of soil grains, filamentous growth may be better represented as mesoscale colonies spanning over several pores and separated from each other by open flow channels. Biological clogging might he prevented if such flow channels could be kept open in some manner.