Reinforcement of Microbial Electrolytic Cells by Redox Mediators Modified Carbon Felt Electrodes: Electrochemistry and Microbial Dynamics.

Redox mediators (RMs) have been widely employed in bioelectrochemical systems to enhance electron transfer efficiency. However, systematic comparisons of RM-driven microbial selectivity and its direct correlation with methane production in microbial electrolysis cells (MECs) remain unexplored. This study investigates methane production in MECs using carbon felt (CF) electrodes modified with four RMs, i.e., neutral red (NR), anthraquinone-2,6-disulfonic acid disodium salt (AQDS), humic acid (HA), methyl viologen (MV), and the conductive polymer polyaniline (PANI). Cyclic voltammetry and electrochemical impedance spectroscopy revealed superior electrochemical activity for NR- and HA-modified electrodes (CF-NR, CF-HA) among the tests. CF-NR and CF-PANI demonstrated the highest biocompatibility, supporting 25% and 15% greater biofilm biomass than unmodified CF, respectively. Modified electrodes exhibited lower alpha diversity than CF, indicating enhanced selectivity in microbial enrichment. Overall, CF-HA achieved the highest methane yield (304.1 mL CH₄/g COD), ~20% higher than the CF control. This study demonstrates that modification-specific microbial enrichment critically governs MEC performance, whereas the quantity of biomass adhesion to the electrode is not the determining factor.