Magnetite-driven food waste conversion toward high-value medium-chain fatty acids production through promoted...

Achieving high-value valorization of food waste (FW) into medium-chain fatty acids (MCFAs) is vital for alleviating environmental pressure and advancing carbon neutrality. However, the inherent electron transfer and metabolic bottlenecks in FW bioconversion process restrains the conversion efficiency of MCFAs. Herein, the performance and comprehensive mechanisms of Fe₃O₄-enhanced MCFA production were comprehensively studied through integrated batch fermentation tests, bio-electrochemical characterizations, and metagenomic analysis. Results revealed that the optimal dosage of 8 g/L Fe₃O₄ enhanced caproate production to 3409.32 mg COD/L (a 3.7-fold increase over the control group). Notably, this dosage drove the further elongation of carbon chains, yielding high-energy-density heptanoate (C7) and caprylate (C8), thereby elevating MCFA selectivity from 5.5 % to 38.6 %. Further analysis indicated that Fe₃O₄ promoted all biological processes (solubilization, hydrolysis, acidogenesis, and chain elongation). Mechanically, Fe₃O₄ optimized the electrochemical microenvironment, enhancing conductivity and electron transport system (ETS) activity by 32.5 % and 69.1 %, respectively. The correlation-based network analysis confirmed a strong correlation (r > 0.4) between product distribution, iron cycling (Fe²⁺ concentration), and conductivity. Metagenomic analysis elucidated that by enriching core functional genera like Clostridium and Sphaerochaeta and associated functional microbial genes, Fe₃O₄ synergistically promoted the efficient bioconversion of FW into MCFAs. This study offers new mechanistic insights into enhancing MCFA production via magnetite-regulated electron transfer, providing a robust strategy for efficient resource recovery from complex organic wastes.