Monitoring of bacterial biofilm formation and permeability reduction in sands using complex electrical conductivity

Abstract

Geophysical monitoring of bacterial activities in subsurface has drawn significant interest in various civil engineering, hydrocarbon recovery, and soil remediation practices. This study explored the feasibility of use of complex electrical responses to monitor bacterial biofilm formation in soils. A column experiment was conducted, in which the model bacteria Shewanella oneidensis MR-1 were cultured in a sand-pack and stimulated to form biofilms. During the bacterial growth and biofilm formation, the variations in complex electrical conductivity were monitored at a frequency range of 0.1 - 1000 Hz while measuring the permeability reduction. As a result of the bacterial growth and biofilm formation, it was observed that the imaginary conductivity significantly increased by more than 1000% and the real conductivity was reduced by more than 10% over 10 days of the experimental run. At the same time, the permeability was reduced by 70%. However, these variations diminished along the sand column as the distance became farther from the nutrient injection port. It appeared that the imaginary conductivity effectively captured biofilm formation in porous media, while the real conductivity was heavily affected by porosity reduction as well as pore fluid conductivity. In addition, imaginary conductivity detected different responses for bacterial growth and bioclogging in frequency domain, while real conductivity had no variation with frequency. As a result, the imaginary conductivity had power law with permeability of soil at certain frequency. The obtained results suggest that complex conductivity can be effectively used to capture the bacterial biofilm formation and the resulting permeability reduction in soils.