Micro-aeration enhances lactic acid production in food waste fermentation

Micro-aeration is a promising strategy to enhance hydrolysis and acidogenesis in anaerobic fermentation systems, but its role in lactic acid (LA) fermentation of food waste (FW) remains unclear. Here, four 1.5-L semi-continuous reactors (35 °C, HRT = 3 d) were run at dissolved oxygen < 0.5 mg/L with aeration loads of 0, 109, 327 and 872 mL air/(gVS·L). Moderate aeration (327 mL air/(gVS·L)) increased steady-state LA to 17.68 ± 1.14 g/L (0.40 g/gVS), 35.5 % higher than strict anaerobiosis, with LA contributing > 85 % of product COD and maximum hydrolysis and acidification efficiencies. In contrast, excessive aeration (872 mL air/(gVS·L)) decreased LA yield. Amplicon and metatranscriptomic analyses showed that micro-aeration enriched homofermentative Lactobacillus amylolyticus and activated pyruvate oxidase-acetyl phosphate-acetate and NADH peroxidase pathways, enhancing redox balancing and starch hydrolysis. Overall, controlled micro-aeration steered metabolism toward energy-efficient homofermentative LAB, improving LA yield and process stability.