Maintenance of Geobacter-dominated biofilms in microbial fuel cells treating synthetic wastewater

• Biofilms adapted well to synthetic wastewater as COD removal approached 0.8 g·L− 1.
• Biofilms retained 80% of their initial community structures in synthetic wastewater.
• Community structure was least stable in biofilms with initially high diversity.
• Higher power densities (100 ± 19 mW·m− 2) are delivered by the new biofilms.

Geobacter-dominated biofilms can be selected under stringent conditions that limit the growth of competing bacteria. However, in many practical applications, such stringent conditions cannot be maintained and the efficacy and stability of these artificial biofilms may be challenged. In this work, biofilms were selected on low-potential anodes (− 0.36 V vs Ag/AgCl, i.e. − 0.08 V vs SHE) in minimal acetate or ethanol media. Selection conditions were then relaxed by transferring the biofilms to synthetic wastewater supplemented with soil as a source of competing bacteria. We tracked community succession and functional changes in these biofilms. The Geobacter-dominated biofilms showed stability in their community composition and electrochemical properties, with Geobacter sp. being still electrically active after six weeks in synthetic wastewater with power densities of 100 ± 19 mW·m− 2 (against 74 ± 14 mW·m− 2 at week 0) for all treatments. After six weeks, the ethanol-selected biofilms, despite their high taxon richness and their efficiency at removing the chemical oxygen demand (0.8 g·L− 1 removed against the initial 1.3 g·L− 1 injected), were the least stable in terms of community structure. These findings have important implications for environmental microbial fuel cells based on Geobacter-dominated biofilms and suggest that they could be stable in challenging environments.