Electric stimulation coupled with activated carbon enhances lactic acid production from food waste

High-value recycling of food waste (FW) can be accomplished through the production of lactic acid (LA). In this work, LA was produced via electro-fermentation (EF) on FW as a single substrate in non-sterile, non-inoculated environment. Electric stimulation (ES) coupled with granular activated carbon (GAC) was used to increase LA production. The findings demonstrated that the addition of 10 g/L of GAC to the system at a voltage of -1 V for 144 h of fermentation resulted in an increase in the LA concentration and maximum production rate of 33.6% and 12.2%, respectively, when compared to the Blank group. The experimental group coupled with ES and GAC also exhibited the highest intracellular NADH/NAD⁺ ratio, a notable increase in the abundance of Actinobacteriota and Proteobacteria, and prominent redox peaks. In terms of the synergistic regulatory effect of key enzymes, the activity of α -glucosidase was enhanced. Besides, the abundance of related enzymes such as lactate dehydrogenase increased, significantly strengthening the glycolytic pathway for LA production and inhibiting the heterolactic fermentation process. The results of this study provide an effective way to recycle FW and provide theoretical support for the analysis of the synergistic mechanism of electron transfer and metabolic regulation in the EF system.