Pyrogenic carbonaceous materials (PCMs), such as biochar and activated carbon, are used in many water and wastewater treatment facilities, at remediation sites, and make up as much as half of the total organic carbon in soils. Until recently, PCMs were thought to be only passive, functioning to adsorb chemical and biological constituents. New research shows that PCMs can also react with contaminants. A key challenge for PCM-mediated reductions of contaminants, such as halogenated solvents, is the need to replenish reserves of electrons in PCMs. Chemical reductants, such as dithionite and borohydride, or electrochemical methods are commonly used to deliver electrons into PCMs. These approaches are not feasible in large-scale systems where PCMs are amended. Some naturally occurring microorganisms can replenish electrons when they transfer electrons from a suitable electron donor (e.g., acetate) into PCMs via respiration. Our knowledge of the presence of these unique microorganisms in real systems and the ability to enhance their ability to regenerate PCM electron storage remains unclear. To help answer this question, we subjected microbial communities from a biological activated carbon (BAC) system to incubations with acetate 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)−1. After three culture transfers, acetate oxidation rates increased 4.3-fold, and microbial morphologies and GAC surface coverage became homogenous. Although present at &lt;0.01% in the inoculum, Geobacter species were significantly enriched in the incubations (up to 96% relative abundance), suggesting they were responsible for reducing the GAC. The ability to quickly and effectively develop an exoelectrogenic microbial community using PCMs may help initiate and/or maintain environmental systems where PCM-mediated reductions of contaminants are employed.

Replenishing the electron storage capacity of pyrogenic carbonaceous materials using microbial communities

ACS Fall 2021

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