Metabolic steering of landfill–derived microbial consortia for selective production of organic acids and ethanol under anaerobic acidification

Transitioning from petrochemical–derived products to sustainable bioprocesses requires low–cost inocula and robust operational strategies. Yet, the undefined mixed inocula (UMI) tunability from landfill ecosystems for selective chemical production remains underexplored. Here, we investigated ethanol and organic acid (acetate, lactate, and propionate) production during anaerobic acidification of starch using landfill–derived microbial consortia (LF–MC) and LF–MC pre–incubated in MRS broth (ILF–MC). Batch fermentations at 39 ± 0.5 °C (72 h) with starch loadings of 10–25 g/L and a shock load (100 g/L) revealed that ethanol remained stable across inocula (∼20 mmol/L), underscoring process robustness, while product distribution varied markedly with inoculum type. LF–MC predominantly yielded acetate (102.9 mmol/L), supporting its application as a low–cost inoculum for acetate–oriented bioprocesses, whereas ILF–MC favored lactate accumulation (44.5 mmol/L), relevant for polylactic acid (PLA) bioplastic production. Shock–load conditions suppressed metabolite yields, emphasizing the need for substrate tolerance in process design. This study proves that landfill-derived consortia can be steered toward distinct product spectra, establishing a simple, tunable, and economically viable platform for sustainable waste–to–chemicals pathways in industrial biorefineries.