Pre-fermentation enhances lipid recovery from food waste: mechanistic insights and full-scale validation

Lipids in food waste (FW) are promising biofuel precursors, but their recovery from slurry-type FW is limited by entrapment within carbohydrate-protein-solid matrices and emulsion-like structures. This study developed a short-term pre-fermentation pretreatment strengthened by a mixed acidifying inoculum to improve intrinsic lipid recovery before thermal centrifugation. In laboratory tests, inoculated pre-fermentation increased lipid yield by 36.3% relative to the initial slurry and recovered 97.8% of the Soxhlet-determined total solvent-extractable lipid content after 24  h. Particle refinement, viscosity reduction, total organic carbon release, lactate accumulation, pH decline, and Lactobacillus dominance indicated that hydrolysis-assisted acidification disintegrated the slurry matrix and improved lipid accessibility. Recovered lipids also showed moderate compositional shifts, including increased saturation, slight C8-C16 enrichment, and minor branched-chain fatty acids, suggesting limited microbial effects on the recovered lipid profile. Full-scale validation at a 600 tonnes/day FW treatment facility achieved a 13.9% lipid-yield increase under an 8  h retention time and lower inoculum dosage, demonstrating practical applicability in an operating wet-thermal recovery line. An incremental cost-benefit estimate indicated a positive annual net benefit under conservative assumptions. Overall, inoculation-strengthened pre-fermentation provides a low-retrofit and process-compatible strategy for enhancing FW lipid recovery within existing treatment chains.