Effect of lactic acid on short-chain fatty acids and hydrogen production during anaerobic fermentation of acidified food waste

This study investigated the effect of lactic acid (LA) on the anaerobic fermentation of acidified food waste with methanogen activity inhibition. LA significantly increased hydrogen production during the anaerobic fermentation. Particularly, the experimental group containing 3 g/L of LA achieved the highest cumulative hydrogen production of 57.02 ± 2.10 mL/(g VSS), representing a 487.84% increase compared with the control group. However, at a concentration of 15 g/L, LA completely inhibited hydrogen production owing to the significant negative effects of its high concentration on microorganisms. The 10 g/L LA-containing reactor exhibited a short-chain fatty acids (SCFAs) concentration of 14,150.17 ± 232.15 mg COD/L, which significantly exceeded the 5,804.59 ± 118.39 mg COD/L in the control group. Notably, butyric acid was identified as the dominant SCFAs in the acidified food waste. Enzyme activity prediction analysis revealed an increased abundance of gene associated with butyryl-CoA dehydrogenase in the LA-containing food waste reactor, which facilitated the conversion of LA to butyric acid. Furthermore, microbial community analysis indicated that LA altered the structure of the bacterial community, leading to a significant reduction in its diversity and uniformity. LA promoted the conversion of organic matter to long-chain acids, particularly n-butyric acid. These findings indicate the significance of inhibiting the methanogenic pathway to enhance hydrogen and acid production from acidified food waste. This study provides a promising strategy for enhancing anaerobic fermentation efficiency and optimizing solid waste utilization. © 2025 Elsevier Ltd