INVESTIGATE SPECTRAL INDUCED POLARIZATION SIGNATURES OF BACTERIAL GROWTH IN POROUS MEDIA

Abstract

Spectral induced polarization (SIP) technique is a promising geophysical technique for delineating variations in the subsurface properties due to biogeochemical processes in a minimally invasively manner. Previous geophysical researches have demonstrated the sensitivity of complex conductivity to microbial growth in porous media. The real component of complex conductivity is associated with electromigration of the charge carriers, and the imaginary conductivity represents the reversible energy storage of the charge carriers at certain polarization length scales. In this study, we developed a quantitative model to investigate the relationship between SIP responses and bacterial growth and decay in porous media. We focus on the direct contribution of bacteria to the complex conductivity in porous media in the absence of biomineralization. Surface conductivity and induced polarization of bacteria (α - polarization) are due to the Stern layer of counterions occurring in a brush of polymers coating the surface of bacteria, and can be related to the cation exchange capacity of bacteria. The modeling results show the mobility of counterions in Stern layer is very small which is in agreement with reported experimental observations. By coupling this new model with reactive transport modeling codes in which the evolution of bacterial populations is described by Monod kinetics, we show that the growth rate and endogenous decay coefficients of bacteria in sands can be inferred non-intrusively from SIP data. To further validate the model, a set of experimental data on Zymomonas mobilis growth in fine silica sands is compared with model results in order to quantitatively analyze the SIP responses associated with bacterial activity.