Enhancing biogas and electricity recovery using an iron-manganese oxide catalyzed bioanode in an integrated submersible microbial fuel cell-anaerobic digester

Submersible microbial fuel cell-anaerobic digestion (SMFC-AD) systems offer biogas up-gradation along with electricity generation but require improved anodic kinetics for better performance. In this study, iron-manganese oxide (FeMnO₃) nanoparticles were synthesized by chemical precipitation method and used as an anodic catalyst in SMFC-AD to improve the redox chemistry at anode thereby enhancing the overall reactor performance. Moreover, the performance of integrated SMFC-AD with and without the catalyst was evaluated under different external resistance (R_ext) viz 10 Ω, 100 Ω, and 1000 Ω. SMFC-AD with the catalyst demonstrated a maximum methane yield of 0.436 ± 0.007 L-CH₄/gCOD at a R_ext of 1000 Ω, followed by a methane yield of 0.406 ± 0.008 L-CH₄/gCOD and 0.384 ± 0.003 L-CH₄/gCOD at 10 Ω and 100 Ω, respectively. However, SMFC-AD at 100 Ω exhibited the maximum current and power generations of 2.11 mA and 0.46 W/m², respectively, which were significantly higher than the values obtained for 10 Ω (0.22 mA, 0.21 W/m²) and 1000 Ω (0.38 mA, 0.19 W/m²). Microbial community analyses revealed the enrichment of exoelectrogenic and methanogenic microbial consortia (Geobacter and Methanobacteria) in the anodic biofilm increasing the interspecies electron transfer reactions.