Developing microbial communities containing a high abundance of exoelectrogenic microorganisms using activated carbon granules.

Microorganisms that can transfer electrons outside their cells are useful in a range of wastewater treatment and remediation technologies. Conventional methods of enriching exoelectrogens are cost-prohibitive (e.g., controlled-potential electrodes) or lack specificity (e.g., soluble electron acceptors). In this study a low-cost and simple approach to enrich exoelectrogens from a mixed microbial inoculum was investigated. After the method was validated using the exoelectrogen Geobacter sulfurreducens, microorganisms from a pilot-scale biological activated carbon (BAC) filter were subjected to incubations in which acetate was provided as the electron donor and granular activated carbon (GAC) as the electron acceptor. The BAC-derived community oxidized acetate and reduced GAC at a capacity of 1.0 mmol e (g GAC). After three transfers to new bottles, acetate oxidation rates increased 4.3-fold, and microbial morphologies and GAC surface coverage became homogenous. Although present at <0.01% in the inoculum, Geobacter species were significantly enriched in the incubations (up to 96% abundance), suggesting they were responsible for reducing the GAC. The ability to quickly and effectively develop an exoelectrogenic microbial community using GAC may help initiate and/or maintain environmental systems that benefit from the unique metabolic capabilities of these microorganisms.