Adapting microbial communities to low anode potentials improves performance of MECs at negative potentials

Influence of two polarization potentials on a bioanode microbial community isolated from a hypersaline coastal lagoon of the Yucatan peninsula, in México

In recent years, halotolerant biofilms have become a subject of interest for its application in Bioelectrochemical systems for wastewater treatment. To determine if the polarization potential affects the microbial community of a halotolerant bioanode, four bioanodes were poised at potentials of +0.34 V/SHE and - 0.16 V/SHE and the 16S rRNA gene was analyzed through a MiSeq (Ilumina) system. Oceanospirillum, Halomonas and Marinobacterium were the most predominant genus; no previous studies have reported the presence of Oceanospirillum in anodic biofilms. The fitness with the dataset for +0.34 V/SHE with a modified Butler Volmer Monod model, gives a value of K₁ was 0.0002 (2.64 A m^-2 and 38% coulombic efficiency), indicating the fastest electrochemical reaction. Whereas that -0.16 V/SHE case, the high value of K₁ (12.2 with 1.82 A m^-2 and 10% coulombic efficiency) indicated that the electron transfer was far from being reversible (Nernstian).

Evaluation of Electrode and Solution Area-Based Resistances Enables Quantitative Comparisons of Factors Impacting Microbial Fuel Cell Performance

Direct comparisons of microbial fuel cells based on maximum power densities are hindered by different reactor and electrode sizes, solution conductivities, and materials. We propose an alternative method here, the electrode potential slope (EPS) analysis, to enable quantitative comparisons based on anode and cathode area-based resistances and operating potentials. Using EPS analysis, the brush anode resistance ( R_An = 10.6 ± 0.5 mΩ m²) was shown to be 28% lower than the resistance of a 70% porosity diffusion layer (70% DL) cathode ( R_Cat = 14.8 ± 0.9 mΩ m²) and 24% lower than the solution resistance ( R_Ω = 14 mΩ m²) (acetate in a 50 mM phosphate buffer solution). Using a less porous cathode (30% DL) did not impact the cathode resistance but did reduce the cathode performance due to a lower operating potential. With low-conductivity domestic wastewater ( R_Ω = 87 mΩ m²), both electrodes had higher resistances [ R_An = 75 ± 9 mΩ m², and R_Cat = 54 ± 7 mΩ m² (70% DL)]. Our analysis of the literature using EPS analysis shows how electrode resistances can easily be quantified to compare system performance when the electrode distances are changed or the sizes of the electrodes are different.