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

Conventional methods of enriching exoelectrogens are cost-prohibitive or lack specificity. Here we report a low-cost and simple approach to enrich exoelectrogens from a mixed microbial inoculum. We subjected native microorganisms from a pilot-scale biological activated carbon (BAC) filter 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. After three transfers, 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.