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

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 (≤50 mA/m 2 ) 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 (≤0.2 mA/m 2 ). 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.

Suitability of granular carbon as an anode material for sediment microbial fuel cells

“…However, taking also the use of plants and possible agricultural practices into account, this study has shown that granular materials can provide a good alternative. MFC-technology has been proposed as a means of alternative or enhanced soil or sediment remediation (Yuan et al 2010;Zhang et al 2010;Williams et al 2010). The idea behind this concept is to provide an extra electron donor or acceptor in the form of an electrode.…”

Bioremediation in Water Environment: Controlled Electro-Stimulation of Organic Matter Self-Purification in Aquatic Environments

“…In the field, the electrode spacing seems not so crucial. Results from a sensing probe (graphite anode embedded within a sand pack) for monitoring in situ microbial activity in an aquifer undergoing bioremediation, shows that MFC can produce detectable currents despite long range separation (6 m) between anode and cathode [148]. To overcome spacing issue, several setups are proposed as: tubular setup where the electrodes are separated only by a low-cost cloth and so the cathode catalytic surface (conductive paint + catalyst) inside the tube is directly exposed to air to allow efficient oxygen reduction; or 3D setup with multilayer or honeycomb anode structure.…”

Bioreactor technology in marine microbiology: From design to future application

“…An oxygen reduction reaction is not a solution as this will be counterproductive towards mitigation of the eutrophication. However a long distance cathode (Williams et al, 2010) can be used when it is placed on the water surface where there is a lot of photosynthetic oxygen production. Another possibility is to make use of a nitrate reducing biocathode reaction .…”