Electrochemical Techniques for Real Time, in-Situ Monitoring of Biogeochemistry

Abstract

Microorganisms exert an enormous influence on the biogeochemical cycling of minerals and on the detoxification of subsurface contaminants. The capacity of microbes to transfer electrons extracellularly provides them with tremendous opportunities to alter the geochemistry. These microbial electrochemical processes also provide technical opportunities to study phenomena related to biogeochemical change, especially environmental clean-up of inorganic contaminants in the subsurface. By regarding bacteria as small electronic circuits we could monitor changes in their physiological status through electrochemical techniques. A flat patterned electrode positioned in-situ provided a versatile design that accommodated numerous electrochemical techniques including electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Changes in phase shift, relative real permittivity and imaginary conductivity were monitored and provided valuable real time, in-situ information regarding microbial dynamics. Microbial redox interactions were also followed by monitoring low frequency phase shifts in the subsurface environment. These techniques correlated impedance parameters to specific biogeochemical and physiological processes that allowed us to evaluate biogeochemical activity, especially related to the growth dynamics of microorganisms. Our approach of incorporating electrochemical techniques, especially EIS and CV has enormous potential to provide valuable information about changes in subsurface microbial activity and contaminant behavior in-situ. Figure 1 shows examples of cellobiose conversion to acetate and voltammograms of C. phytofermentans during growth. This information can be used to direct subsurface sampling activities and be used in conjuction with data from conventional sampling to provide information about subsurface activity and dynamics. Figure 1