Carbon dots coupled bioelectrocatalysis for enhanced methane productivity in anaerobic co-digestion of sewage sludge and food waste: Focusing on enhancement mechanisms and microbial community succession

The limited electron transfer efficiency and poor stability of microorganisms are challenges in traditional bioelectrocatalytic food waste treatment. Herein, carbon dots (CDs) possess excellent biocompatibility and electrochemical properties. When combined with bioelectrocatalysis, CDs can regulate microbial community structure and enhance electron exchange capacity. The results demonstrated that compared with the control group (28.1 mL/g-VS/d), the CDs at a dosage of 0.50 g/g VS could increase CH4 production by a factor of 7.8. CDs not only increase CH4 production but also improve the digestate's stability, making it suitable for use as bio-fertilizer. Moreover, a significantly high Methanobacterium richness (11.6%) signified an intensified utilization of hydrogen and formic acid pathways in CH4 production. Particularly, the biocompatible CDs could be absorbed by microorganisms, forming an environmental network that was more conducive to electron transfer with unabsorbed CDs and accelerating interspecies electron transfer. This work provides mechanistic insights into boosting CH4 production in AD.