In situ microbial degradation or transformation of subsurface contaminants is typically limited by the availability of terminal electron acceptors (TEAs) (for contaminant oxidation) or electron donors (for contaminant reduction). The availability of TEAs and electron donors is itself limited by the physical permeability of the subsurface matrix, groundwater flow velocity, and cost.  To overcome these limitations, solid TEAs in the form of electrodes have recently been utilized as an intermediate and alternative electron acceptor to enhance microbial degradation of groundwater contaminants such as petroleum hydrocarbons.  The interactions between the microbes and the electrodes in the bioelectrochemical systems (BESs) promote extracellular transfer of electrons beyond the immediate area surrounding the anode, thus, enhancing the oxidation of contaminants in the matrix.  For example, BES electrodes were installed within the saturated matrix at a leaking underground storage tank site, where benzene was the primary contaminant of concern.  After 2 years of operation, 74% and 96% decreases in benzene concentration (3.06 to 0.79 mg/L and 2.14 to 0.09 mg/L, respectively) were observed for the overall site and within the source area, respectively, which exceeded the performance of other remedies.  Another use of electrodes is the formation of a low-intensity electric field in the groundwater matrix, where soil particles in the subsurface form “microelectrodes”.  These microelectrodes promote redox reactions at and near their surfaces, resulting in the degradation of contaminants, mainly through reductive pathway.  For example, such low-intensity electric field was applied within the saturated zone at a site where tetrachloroethene (PCE) was the primary contaminant of concern.  The PCE concentration decreased by 33% (from 103 to 69 μg/L) after less than 4 months of operation.  This presentation will discuss possible mechanisms of contaminant degradation from interactions of microbes and electrodes, as well as present field and laboratory case studies demonstrating applications of these interactions.

Enhanced groundwater contaminants degradation by microbes, electrodes, and “microelectrodes”

2019 Spring National Meeting

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