Iron-based materials maintain biofilm equilibrium and function as external capacitors to minimize electron loss under intermittent power supply in MEC-AD methane production

Microbial electrolysis cell-anaerobic digestion (MEC-AD) is a cost-effective approach for methane (CH₄) recovery from food waste, but its CH₄ conversion efficiency requires improvement. To address this, a MIL-100(Fe)-modified carbon cloth anode was developed to enhance anodic biofilm formation and CH₄ bioconversion efficiency. At an applied voltage of 0.8 V, the highest daily CH₄ yield reached 141.6 mL/g COD/d, a 61 % increase, and increased further to 227.5 mL/g COD/d under intermittent power supply. By facilitating extracellular electron transfer (EET) in electrogenic bacteria, MIL-100(Fe) regulated biofilm thickness and maintained dynamic biofilm equilibrium. Additionally, as an external capacitor, MIL-100(Fe) functioned as a “temporary storage site” for electrons under intermittent power supply, reducing bioelectron loss. Metagenomic analysis revealed that MIL-100(Fe) significantly enriched Bacteroidia and Methanosarcina, promoting carbohydrate metabolism and CH₄ production. Under intermittent power supply, MIL-100(Fe) further enriched Geobacter, enhancing electron transfer efficiency. This study demonstrates that iron-based anode modification effectively enhances CH₄ production from food waste by optimizing biofilm structure and metabolic pathways, providing a promising strategy for improving MEC-AD performance.