The threshold of aeration intensity in micro-oxygen lactic acid fermentation and the underlying microbial mechanisms

The unique contribution of this study lies in the systematic quantification of clear aeration intensity thresholds and their underlying microbial mechanisms for maximizing lactic acid (LA) production from completely untreated mixed agricultural wastes. Micro-oxygen aeration could improve LA yield from low cost agricultural wastes, yet its effectiveness is strongly dose-dependent. This study employed swine manure and apple waste as feedstocks to produce LA through micro-oxygen co-fermentation, systematically investigating the impacts of aeration intensity (0-2000 mL/L/d) on LA synthesis efficiency and microbial community structure. Results showed that aeration intensity greatly affected LA production and carbon source metabolic pathways. The optimal micro-oxygen aeration intensity-defined as the level yielding the highest peak LA concentration (23.1 g/L), was determined to be 1000 mL/L/d. Moderate micro-oxygen aeration promoted Lactobacillus dominance (52%), while excessive aeration shifted the community toward hydrolytic bacteria (e.g., Clostridium_sensu_stricto_1, Terrisporobacter), associated with increased carbon competition and potential respiratory dissipation, ultimately diminishing LA production. These findings identify an optimal aeration window for maximizing LA production from agricultural wastes and provide insights into microbial regulatory mechanisms, offering a theoretical basis for precise control of microbial consortia dynamics in high-value waste valorization-advancing sustainable bio-processes for environmental management and carbon-neutral organic acid production.