Leverage of medium-chain fatty acids production: Unravel effect of lipid to anaerobic electro-fermentation

Lipids, prevalent in food waste, are typically considered inhibitors of anaerobic fermentation. To enhance fatty acid yield, researchers have attempted electro-fermentation. However, the influence of lipids on the generation of medium chain fatty acids (MCFAs) in anaerobic electro-fermentation remains unclear. This study challenges this notion by demonstrating that an optimal lipid content (6 g/100 g) under 0.9 V applied voltage significantly enhances medium-chain fatty acid (MCFA) production and selectivity in anaerobic electro-fermentation, yielding 2.99 g COD/L (20 % of total fatty acids). Kinetic and metatranscriptomic analyses revealed a dual-pathway mechanism: lipids directly contributed to MCFA synthesis via β-oxidation, and simultaneously promoted the chain elongation of butyrate. This was driven by a microbial community shift that enriched chain-elongating bacteria (e.g., Aneurinibacillus) and significantly upregulated carboxylesterase (CE1) activity. Our findings propose a practical strategy of refluxing lipid from three-phase separation to upgrade food waste into valuable chemicals.