Article

Electrode-Based Approach for Monitoring In Situ Microbial Activity During Subsurface Bioremediation

Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Environmental Science and Technology (Impact Factor: 5.48). 11/2009; 44(1):47-54. DOI: 10.1021/es9017464
Source: PubMed

ABSTRACT Current production by microorganisms colonizing subsurface electrodes and its relationship to substrate availability and microbial activity was evaluated in an aquifer undergoing bioremediation. Borehole graphite anodes were installed downgradient from a region of acetate injection designed to stimulate bioreduction of U(VI); cathodes consisted of graphite electrodes embedded at the ground surface. Significant increases in current density (< or =50 mA/m2) tracked delivery of acetate to the electrodes, dropping rapidly when acetate inputs were discontinued. An upgradient control electrode not exposed to acetate produced low, steady currents (< or =0.2 mA/m2). Elevated current was strongly correlated with uranium removal but minimal correlation existed with elevated Fe(II). Confocal laser scanning microscopy of electrodes revealed firmly attached biofilms, and analysis of 16S rRNA gene sequences indicated the electrode surfaces were dominated (67-80%) by Geobacter species. This is the first demonstration that electrodes can produce readily detectable currents despite long-range (6 m) separation of anode and cathode, and these results suggest that oxidation of acetate coupled to electron transfer to electrodes by Geobacter species was the primary source of current. Thus it is expected that current production may serve as an effective proxy for monitoring in situ microbial activity in a variety of subsurface anoxic environments.

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    • "Microbial activity monitoring has also been proposed as another application of an MFC-based sensor (Patchett et al., 1988; Tront et al., 2008a,b; Williams et al., 2010b). The idea is based on the response of current generation to different substrate (BOD) concentrations based on the activity of the biofilm colonized on the anode. "
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    • "In order to scale-up this strategy for successful in situ application, extensive testings based on subsurface characteristics and site-specific design needs to be studied. Williams and colleagues (2010) for the first time demonstrated the in situ applicability of graphite electrodes in the subsurface serving as electron acceptors for microbial stimulation during uranium bioremediation at Rifle site in Colorado. A similar approach may be employed for the remediation of chlorinated solvents. "
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    • "While it is known that attached populations constitute the majority of cells in the subsurface and there are physiological differences between attached and suspended microbial communities, few studies have examined differences between these two fractions [14,15]. One such difference associated with a specific group involves the iron-reducing bacteria, which are usually associated with a solid substrate [16] and therefore are expected to be underrepresented in the bulk groundwater. "
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