Monitoring microbial sulfate reduction in porous media using multipurpose electrodes

Abstract

[1] There is growing interest in the application of electrode-based measurements for monitoring microbial processes in the Earth using biogeophysical methods. In this study, reactive electrode measurements were combined to electrical geophysical measurements during microbial sulfate reduction occurring in a column of silica beads saturated with natural river water. Electrodic potential (EP), self potential (SP) and complex conductivity signals were recorded using a dual electrode design (Ag/AgCl metal as sensing/EP electrode, Ag/AgCl metal in KCl gel as reference/SP electrode). Open-circuit potentials, representing the tendency for electrochemical reactions to occur on the electrode surfaces, were recorded between sensing/EP electrode and reference/SP electrode and showed significant spatiotemporal variability associated with microbial activity. The dual electrode design isolates the microbial driven sulfide reactions to the sensing electrode and permits removal of any SP signal from the EP measurement. Based on the known sensitivity of a Ag electrode to dissolved sulfide, we interpret EP signals exceeding 550 mV recorded in this experiment in terms of bisulfide (HS − ) concentration near multiple sensing electrodes. Complex conductivity measurements capture an imaginary conductivity (s″) signal interpreted as the response of microbial growth and biomass formation in the column. Our results suggest that the implementation of multipurpose electrodes, combining reactive measurements with electrical geophysical measurements, could improve efforts to monitor microbial processes in the Earth using electrodes.

Geophysical Properties of the Near Surface Earth: Electrical Properties

“…Data from Knight and Nur (1987a,b) and B € orner and Sch € on (1991) are sandstones, data from Slater and Glaser (2003) are alluvial unconsolidated sediments, and data from Slater et al (2006) are artificial kaolinite-sand mixtures. Table 5 Relative dielectric permittivity of various common minerals (after a compilation by Sch € on (2004) of data from Dortman (1976), Keller (1989), Olhoeft (1981), and Parkhomenko (1965) compounds and the biomediated precipitation of metal sulfides (Placencia-Gó mez et al, 2013;Zhang et al, 2013) and calcite can produce electrical dispersions with characteristic frequencies often in the low-frequency range (Personna et al, 2008;Zhang et al, 2010Zhang et al, , 2012. The linear regression is s 00 ¼S por 0.8 (R 2 ¼ 0.82).…”

“…Zhang et al (2010) made measurements of complex conductivity, electrode potential, and self-potential on a column of sand saturated with river water in which microbial activity was altering the sulfide chemistry of the water. Zhang et al (2010) made measurements of complex conductivity, electrode potential, and self-potential on a column of sand saturated with river water in which microbial activity was altering the sulfide chemistry of the water.…”

“…Zhang et al (2010) made measurements of complex conductivity, electrode potential, and self-potential on a column of sand saturated with river water in which microbial activity was altering the sulfide chemistry of the water. Zhang et al (2010) inverted their measurements to estimate the biogenic production of bisulfide at each point in their sand column during the whole experiment. Potential changes started about 6 days after the experiment began and continued until its end, about 22 days later.…”

Quadrature conductivity: A quantitative indicator of bacterial abundance in porous media

“…In the last decade, the remote detection of processes associated with bacterial activity in porous media has been demonstrated using various active and passive geophysical methods including electric and seismic techniques (e.g., Naudet and Revil, 2005;Ntarlagiannis et al, 2005b;Williams et al, 2005;Davis et al, 2006;Linde and Revil, 2007;Personna et al, 2008;Zhang et al, 2010). Under some circumstances, bacterial activity can also be detected passively using the self-potential method (Naudet et al, 2003(Naudet et al, , 2004Revil et al, 2010;Risgaard-Petersen et al, 2012.…”

Microbial ecology and geoelectric responses across a groundwater plume

“…Standard practice was followed in collecting and identifying drift relative to the reference electrode (Naudet et al 2004). Data were acquired using miniature non polarizing Ag/AgCl electrodes (Petiau 2000) made in house, modified from a design by (Zhang et al 2010) with a METRA HIT 22S high impedance voltmeter (20MΩ) with a rugged single core wire. The electrodes were tested for variation in the lab before and after use in the field by measuring the voltage between the electrodes, electrodes indicating a variation of over 2mV were discarded and any results obtained were not used.…”